DK THE ECOLOGY BOOK

GMEOSNELLEEFSCIUSALHREES SOLAR ENERGY IS BOTH
WITHOUT LIMIT AND

WITHOUT COST

THE TIME HAS
COME FOR SCIENCE
TO BUSY ITSELF WITH
THE EARTH ITSELF
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ON A DIFFERENT

TIMESCALE

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WWEITAEHNRVETIHPRELOANNYAMIETNUNGRTDAICLE IF YOU DO NOT KNOW THE NAMES OF
THINGS, THE KNOWLEDGE OF THEM

IS LOST

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FOREWORD BY

TONY JUNIPER

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CONTRIBUTORS

JULIA SCHROEDER, CONSULTANT DEREK HARVEY

Julia Schroeder received her Ph.D. in Animal Ecology from the A naturalist and teacher with a particular interest in evolutionary
University of Groningen in the Netherlands. From 2012 to 2017, biology, Derek Harvey graduated in Zoology from Liverpool University
she headed a research group at the Max Planck Institute for in the UK. He has taught a generation of biologists and led student
Ornithology in Germany, studying social behavioral ecology. Julia expeditions to Costa Rica, Madagascar, and Australasia. Derek now
currently researches and teaches evolutionary biology at Imperial concentrates on writing and consulting for science and natural
College London. history books.

CELIA COYNE TOM JACKSON

Celia Coyne is a freelance writer and editor living in Christchurch, A writer for 25 years, Tom Jackson is the author of about 200 nonfiction
New Zealand. She is the author of Earth’s Riches and The Power of books for adults and children and has contributed to many more. Tom
Plants and writes and edits articles on science and natural history studied zoology at Bristol University, UK, and worked in zoos and as a
for magazines, newspapers, journals, websites, and books in the UK, conservationist before turning to writing about natural history and all
Australia, and New Zealand. Her aim is to make scientific subjects things scientific.
accessible to lay readers.
ALISON SINGER
JOHN FARNDON
Alison Singer is a Ph.D. candidate in Community Sustainability at
The author of hundreds of books on science and nature for both Michigan State University, US, where she studies storytelling and
children and adults, John Farndon studied geography at Cambridge science communication. She has a broad educational background in
University. He has written extensively on earth sciences and the writing, ecology, and the social sciences. Alison has worked as an
environment, focusing in particular on conservation and ecology. educator for environmental charities, and for the US Environmental
His books include The Oceans Atlas, The Wildlife Atlas, How the Earth Protection Agency.
Works, and The Practical Encyclopedia of Rocks and Minerals.

TIM HARRIS

After studying Norwegian glaciers in college, Tim Harris traveled the
world in search of unusual wildlife and extraordinary landscapes. He
has explored the dunes of the Namib Desert, climbed Popocatépetl in
central Mexico, camped in the Sumatran rain forest, and searched
the frozen Sea of Okhotsk in Russia. He is a former Deputy Editor of
Birdwatch magazine in the UK and has written books about nature for
adults and children.

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CONTENTS

12 INTRODUCTION 34 We’ve discovered 66 The fitness of a foraging
the secret of life animal depends on
THE STORY The role of DNA its efficiency
OF EVOLUTION Optimal foraging theory
38 Genes are selfish
20 Time is insignificant molecules 68 Parasites and pathogens
and never a difficulty The selfish gene control populations
for nature like predators
Early theories of evolution ECOLOGICAL Ecological epidemiology
PROCESSES
22 A world previous to ours, 72 Why don’t penguins’
destroyed by catastrophe 44 Lessons from feet freeze?
Extinction and change mathematical theory Ecophysiology
on the struggle
23 No vestige of a beginning for life 74 All life is chemical
—no prospect of an end Predator–prey equations Ecological stoichiometry
Uniformitarianism
76 Fear itself is powerful
24 The struggle for existence 50 Existence is determined Nonconsumptive effects
Evolution by natural selection by a slender thread of predators on their prey
of circumstances
32 Human beings are Ecological niches ORDERING THE
ultimately nothing NATURAL WORLD
but carriers for genes 52 Complete competitors
The rules of heredity cannot coexist 82 In all things of nature
Competitive exclusion there is something of
principle the marvelous
Classification of living things
54 Poor field experiments
can be worse than
useless
Field experiments

56 More nectar means
more ants and more
ants mean more nectar
Mutualisms

60 Whelks are like
little wolves in
slow motion
Keystone species

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84 By the help of 138 Life is supported by a vast
microscopes nothing network of processes
escapes our inquiry Energy flow through
The microbiological ecosystems
environment
140 The world is green
86 If you do not know Trophic cascades
the names of things, the
knowledge of them is lost 144 Islands are ecological
A system for identifying all systems
nature’s organisms Island biogeography

88 “Reproductively isolated” 114 Birds lay the number 150 It is the constancy of
are the key words of eggs that produce numbers that matters
Biological species concept the optimum number Ecological resilience
of offspring
90 Organisms clearly Clutch control 152 Populations are subjected
cluster into several to unpredictable forces
primary kingdoms 116 The bond with a true dog The neutral theory of
A modern view of diversity is as lasting as the ties of biodiversity
this earth can ever be
92 Save the biosphere and Animal behavior 153 Only a community
you may save the world of researchers has a
Human activity 118 Redefine “tool”, redefine chance of revealing
and biodiversity “man”, or accept the complex whole
chimpanzees as humans Big ecology
96 We are in the opening Using animal models to
phase of a mass understand human behavior 154 The best strategy
extinction depends on what
Biodiversity hotspots others are doing
Evolutionarily stable state
126 All bodily activity
THE VARIETY depends on temperature
OF LIFE Thermoregulation in insects

102 It is the microbes that ECOSYSTEMS
will have the last word
Microbiology 132 Every distinct part of
nature’s works is
104 Certain tree species necessary for the
have a symbiosis support of the rest
with fungi The food chain
The ubiquity of mycorrhizae
134 All organisms are
106 Food is the potential sources of food
burning question for other organisms
Animal ecology The ecosystem

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156 Species maintain the 170 I have great faith THE LIVING EARTH
functioning and stability in a seed
of ecosystems Ecological succession 198 The glacier was God’s
Biodiversity and ecosystem great plow
function 172 The community Ancient ice ages
arises, grows,
ORGANISMS IN matures, and dies 200 There is nothing
A CHANGING Climax community on the map to mark
ENVIRONMENT the boundary line
174 An association Biogeography
162 The philosophical study is not an organism
of nature connects the but a coincidence 202 Global warming isn’t a
present with the past Open community theory prediction. It is happening
The distribution of species Global warming
over space and time 176 A group of species
that exploit their 204 Living matter is the most
164 The virtual increase of the environment in powerful geological force
population is limited by a similar way The biosphere
the fertility of the country The ecological guild
The Verhulst equation 206 The system of nature
178 The citizen Biomes
166 The first requisite is network depends
a thorough knowledge on volunteers 210 We take nature’s services
of the natural order Citizen science for granted because we
Organisms and their don’t pay for them
environment 184 Population dynamics A holistic view of Earth
become chaotic
167 Plants live on a different when the rate of 212 Plate tectonics is not all
timescale reproduction soars havoc and destruction
The foundations of Chaotic population change Moving continents
plant ecology and evolution
185 To visualize the big
168 The causes of differences picture, take a 214 Life changes Earth
among plants distant view to its own purposes
Climate and vegetation Macroecology The Gaia hypothesis

186 A population
of populations
Metapopulations

188 Organisms change
and construct the
world in which
they live
Niche construction

190 Local communities that
exchange colonists
Metacommunities

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218 65 million years ago 270 The introduction
something killed half of a few rabbits could
of all the life on do little harm
the Earth Invasive species
Mass extinctions
274 As temperatures increase,
224 Burning all fuel the delicately balanced
reserves will initiate system falls into disarray
the runaway greenhouse Spring creep
Environmental
feedback loops 242 The chemical barrage 280 One of the main threats
has been hurled against to biodiversity is
THE HUMAN the fabric of life infectious diseases
FACTOR The legacy of pesticides Amphibian viruses

230 Environmental pollution 248 A long journey 281 Imagine trying to build
is an incurable disease from discovery a house while someone
Pollution to political action keeps stealing your bricks
Acid rain Ocean acidification
236 God cannot save these
trees from fools 250 A finite world can support 282 The environmental
Endangered habitats only a finite population damage of urban sprawl
Overpopulation cannot be ignored
240 We are seeing the Urban sprawl
beginnings of a rapidly 252 Dark skies are now
changing planet blotted out 284 Our oceans are turning
The Keeling Curve Light pollution into a plastic soup
A plastic wasteland
254 I am fighting
for humanity 286 Water is a public trust
Deforestation and a human right
The water crisis

260 The hole in the ozone
layer is a kind of
skywriting
Ozone depletion

262 We needed a mandate
for change
Depletion of natural resources

266 Bigger and bigger boats
chasing smaller and
fewer fish
Overfishing

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306 The time has come for 324 We are playing dice with
science to busy itself the natural environment
with the Earth itself The economic impact of
Environmental ethics climate change

308 Think globally, 326 Monocultures and
act locally monopolies are destroying
The Green Movement the harvest of seed
Seed diversity
310 The consequences of
today’s actions on 328 Natural ecosystems and
tomorrow’s world their species help sustain
Man and the Biosphere and fulfill human life
Programme Ecosystem services

ENVIRONMENTALISM 312 Predicting a population’s 330 We are living on this
AND CONSERVATION size and its chances planet as though we have
of extinction another one to go to
296 The dominion of man Population viability analysis Waste disposal
over nature rests only
on knowledge 316 Climate change is 332 DIRECTORY
Humankind’s dominance happening here. It 340 GLOSSARY
over nature is happening now 344 INDEX
Halting climate change 351 QUOTE ATTRIBUTIONS
352 ACKNOWLEDGMENTS
322 The capacity to sustain
the world’s population
Sustainable biosphere
initiative

297 Nature is a
great economist
The peaceful coexistence
of humankind and nature

298 In wildness is the
preservation of the world
Romanticism, conservation,
and ecology

299 Man everywhere is
a disturbing agent
Human devastation
of Earth

300 Solar energy is
both without limit
and without cost
Renewable energy

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FOREWORD

As a small child, I was fascinated by nature—birds, I am delighted that Dorling Kindersley decided to produce
butterflies, plants, reptiles, fossils, rivers, weather, and much The Ecology Book, setting out the key concepts that have
else. My youthful passions set me on the path to being a helped shape our understanding of how Earth’s incredible
life-long naturalist, and to working as an environmentalist, natural systems function. In the pages that follow readers
studying the natural world and promoting action for its will also discover something about the history of ecological
conservation. I have worked as a field ornithologist, writer, concepts, the leading thinkers, and the different perspectives
campaigner, policy advocate, and environmental advisor. All from which they approached the questions they sought
of these diverse interests and activities have, however, been to answer.
linked by a single theme: ecology.
One thing that sets this book apart is the manner
Ecology is a vast subject, embracing the many disciplines in which the rich, memorable, and attractive content
needed to understand the relationships that exist between is presented. A huge body of information and insight is
different living things, and the physical worlds of air, water, effectively conveyed by clear layout, graphics, illustrations,
and rock within which they are embedded. From the study and quotes, enabling readers to quickly achieve an
of soil microorganisms to the role of pollinators, and from understanding of many important ecological ideas and
research into the water cycle to investigating Earth’s climate the people behind them: James Lovelock’s Gaia Hypothesis,
system, ecology involves many specialist areas. It also Norman Myers’s warnings about impending mass extinction,
unites many strands of science, including zoology, botany, and Rachel Carson’s work to expose the effects of toxic
mathematics, chemistry, and physics, as well as some pesticides among them.
aspects of social science—especially economics—while
at the same time raising profound philosophical and The diverse body of information found in the pages that
ethical questions. follow could not be more important. For while the headlines
and popular debate suggest it is politics, technology, and
Because of the fundamental ways in which the human economics that are the vital forces shaping our common
world depends on healthy natural systems, some of the most future, it is in the end ecology that is the most important
important political issues of our age are ecological ones. They context determining societies’ prospects, and indeed the
include climate change, the effects of ecosystem damage, future of civilization itself.
the disappearance of wildlife, and the depletion of resources,
including fish stocks, freshwater, and soils. All these I hope you find The Ecology Book to be an enlightening
ecological changes have implications for people and are overview of what is not only the most important subject, but
increasingly pressing. also the most interesting.

Considering the huge importance of ecology for our Tony Juniper CBE
modern world, and the many threads of thought and ideas Environmentalist
that must be woven to gain an understanding of the subject,

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INTRODU

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CTION

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14 INTRODUCTION

For the earliest humans, Swedish botanist Carl Linnaeus organisms change over time, and
a rudimentary knowledge developed a classification system, even become extinct. The
of ecology—how organisms Systema Naturae, the first scientific Frenchman Jean-Baptiste Lamarck
relate to one another—was a matter attempt to name species and proposed the first cohesive theory
of life and death. Without having group them according to of evolution—the transmutation
a basic understanding of why relatedness. Throughout this of species by the inheritance of
animals grazed in a certain place time, essentialism—the idea that acquired characteristics—in 1809.
and fruit-bearing plants grew in each species had unalterable However, some 50 years later it was
another, our ancestors would not characteristics—continued to Charles Darwin—influenced by his
have survived and evolved. dominate Western thought. experiences on the epic expedition
of HMS Beagle—and Alfred Russel
How living animals and plants Great breakthroughs Wallace, who developed the concept
interact with each other, and Geological discoveries in the late of evolution by means of natural
with the nonliving environment 17th and early 18th centuries began selection, the theory that organisms
interested the ancient Greeks. to challenge the idea of essentialism. evolve over the course of generations
In the 4th century BCE, Aristotle Geologists noted that some fossil to adapt better to their environment.
and his student Theophrastus species suddenly disappeared Darwin and Wallace did not
developed theories of animal from the geological record and were understand the mechanism by
metabolism and heat regulation, replaced by others, suggesting that which this happened, but Gregor
dissected birds’ eggs to discover Mendel’s experiments on peas
how they grew, and described There are some 4 million pointed at the role of hereditary
an 11-level “ladder of life,” the first different kinds of animals and factors later known as genes,
attempt at classifying organisms. representing another giant leap in
Aristotle also explained how some plants in the world. Four evolutionary theory.
animals consume others—the first million different solutions to
description of a food chain. the problems of staying alive. Making connections
The relationships between
In the Middle Ages (476–1500), David Attenborough organisms and their environment,
the Catholic Church discouraged and between species, dominated
new scientific thought, and human ecological study in the early
understanding of ecology advanced 20th century. The concepts of
very slowly. By the 16th century, food chains and food webs (who
however, maritime exploration, eats what in a particular habitat)
coupled with great technological and ecological niches (the role an
advances, such as the invention organism has in its environment)
of the microscope, led to the developed, and in 1935, Arthur
discovery of amazing life forms and
a thirst for knowledge about them.

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INTRODUCTION 15

Tansley introduced the concept New concerns botany, and their microdisciplines,
of the ecosystem—the interactive Early ecology was driven by a it relies on geology, geomorphology,
relationship between living desire for knowledge. Later, it was climatology, chemistry, physics,
organisms and the environment used to find better ways to exploit genetics, sociology, and more.
in which they live. Later ecologists the natural world for human needs. Ecology influences local and
developed mathematical models to As time went on, the consequences national government decisions
forecast population dynamics within of this exploitation became about urbanization, transportation,
ecosystems. Evolutionary theories increasingly evident. Deforestation industry, and economic growth.
also advanced with the discovery was highlighted as a problem as The challenges posed by climate
of the structure of DNA, and the early as the 18th century, and the change, rising sea levels, habitat
evolutionary “vehicle” provided problems of air and water pollution destruction, the extinction of
by mutation as DNA is replicated. became obvious in industrialized species, plastic and other forms of
nations in the 19th century. In 1962, pollution, and a looming water crisis
New frontiers Rachel Carson’s book Silent Spring pose serious threats to human
Improved technology opened up alerted the world to the dangers of civilization. They demand radical
new possibilities for ecology. An pesticides, and six years later Gene policy responses based on sound
electron microscope can now Likens demonstrated the link science. Ecology will provide the
make images to half the width of a between power station emissions, answers. It is up to governments
hydrogen atom, and computer acid rain, and fish deaths. to apply them. ■
programs can analyze the sounds
made by bats and whales, which are In 1985, a team of Antarctic Even in the vast and
higher or lower than can be heard scientists discovered the dramatic mysterious reaches of the sea
by the human ear. Camera traps and depletion of atmospheric ozone
infrared detectors photograph and over Antarctica. The link between we are brought back to the
film nocturnal creatures, and tiny greenhouse gases and a warming fundamental truth that
satellite devices fitted to birds can of Earth’s lower atmosphere had nothing lives to itself.
track their movements. been made as early as 1947 by Rachel Carson
G. Evelyn Hutchinson, but it was
In the laboratory, analysis of decades before there was a scientific
the DNA of feces, fur, or feathers consensus on the man-made causes
indicates which species an animal of climate change.
belongs to, and throws light on
the relationship between different The future
organisms. It is now easier than Modern ecology has come a long
ever for ecologists to collect data, way since the science was first
helped by a growing army of recognized. It now draws on many
citizen scientists. disciplines. In addition to zoology,

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OTHFEEVSOTOL

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URYTION

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18 INTRODUCTION In his Essay on the Theory HMS Beagle sets sail on a
of the Earth, Georges Cuvier circumnavigation of the world, with
James Hutton presents suggests that fossils are the
his theory that Earth is remains of extinct creatures Charles Darwin serving as the
much older than was voyage’s naturalist. The trip provides
previously believed, and wiped out by periodic
“catastrophic” events. Darwin with the information that
that Earth’s crust is inspired his theory of evolution
continuously changing.
by natural selection.

1785 1813 1831
1809 1823

Jean-Baptiste Lamarck Amateur fossil
publishes Philosophie Zoologique, hunter Mary Anning
where he argues that animals acquire uncovers the first intact
characteristics as a consequence of plesiosaurus skeleton.
use or nonuse of different body parts,
triggering mutations over generations.

Ancient myths, religions, and was the driving force behind this these processes take place slowly,
philosophies all reflect an change. He speculated that Earth’s history had to be much
enduring fascination with characteristics acquired by animals longer than was previously thought.
how the world began and man’s during their lifetime were inherited
place in the story of life on Earth. In by the next generation: giraffes, for Natural selection
the West, Christianity held that all example, became slightly longer- In 1858, Charles Darwin and Alfred
animals and plants were the result necked by stretching up to reach Russel Wallace delivered a paper
of a perfect creation. On the chain higher leaves, and passed this trait that would change biology forever.
or ladder of being, no species could to their offspring; over many Darwin’s observations on the epic
ever move from one position to generations, giraffes grew longer voyage of the Beagle (1831–36),
another. Species were immutable, and longer necks. his correspondence with other
an idea called essentialism. naturalists, and the influence
Fossil evidence of extinct life of Thomas Malthus’s writings
The 18th-century Age of forms with features that resembled inspired Darwin’s insight that
Enlightenment began to challenge modern descendants, found by evolution came about by what he
orthodox Christian beliefs. French pioneering geologists such as called natural selection. He spent
zoologist Jean-Baptiste Lamarck Georges Cuvier, also suggested 20 years gathering supporting data,
rejected the prevailing Bible-based Earth had more ancient origins. but when Wallace wrote to him
notion of Earth being only a few Meanwhile James Hutton and with the same idea, Darwin
thousand years old. He argued that Charles Lyell argued that geological realized it was time to go public.
organisms must have changed from features could be accounted for by His subsequent book, On the
simple life forms to more complex the constant, ongoing processes Origin of Species by Means of
ones over millions of years, and that of erosion, and deposition—a view Natural Selection, provoked outrage.
the “transmutation” of species called uniformitarianism. Because

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THE STORY OF EVOLUTION

Gregor Mendel’s paper The Selfish Gene by
“Experiments with Plant Hybrids” evolutionary biologist Richard

outlines findings from his pea Dawkins offers a new
plant experiments, laying perspective on evolution,
the foundations for the looking at the gene, as opposed
field of genetics.
to the species or group.

1866 1976
1859 1953 2003

Darwin elaborates on his In The Eagle pub in The Human Genome
theories of evolution in On the Cambridge, UK, Crick and Project produces the first
Origin of Species by Means
of Natural Selection, which Watson announce that genetic blueprint of
they have discovered Homo sapiens.
is an instant sellout.
the structure of DNA.

Although the idea of evolution of thought were complementary, that genetic information is “written”
became widely accepted, the rather than contradictory. In 1942, on DNA molecules. The errors that
mechanism that made natural Julian Huxley articulated the occur when DNA copies itself create
selection possible was not yet synthesis between Mendel’s mutations—the raw materials for
known. In 1866, an Austrian monk genetics and Darwin’s theory evolution. By the 1980s it was
called Gregor Mendel made a huge of natural selection in his book possible to map and manipulate the
contribution to genetics when he Evolution: The Modern Synthesis. genes of individuals and species. In
published his findings on heredity the 1990s, the mapping the human
in pea plants. Mendel described The double helix genome paved the way for medical
how dominant and recessive traits Advances in technology such as research into gene therapy.
pass from one generation to the X-ray crystallography led to more
next, by means of invisible “factors” discoveries in the 1940s and ’50s, Ecologists also want to establish
that we now call genes. and the foundation of the new whether genes influence behavior.
discipline of molecular biology. Back in 1964, William D. Hamilton
The rediscovery of Mendel’s In 1944, chemist Oswald Avery popularized the concept of genetic
work in 1900 initially sparked sharp identified deoxyribonucleic acid relatedness (“kin selection”) to
debate between his supporters and (DNA) as the agent for heredity. explain altruistic behavior in
many Darwinians. At the time, Rosalind Franklin and Raymond animals. In The Selfish Gene (1976),
evolution was believed to be based Gosling photographed strands of the Richard Dawkins further advanced
on the selection of small, blending DNA molecule in 1952, and James the gene-centered approach. It is
variations, but Mendel’s variations Watson and Francis Crick confirmed clear that aspects of evolutionary
clearly did not blend. Three decades its double helix structure the biology will still spark debate as
later, geneticist Ronald Fisher and following year. Crick then showed long as ecologists continue to
others argued that the two schools develop Darwin’s theory. ■

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20

FTAOINMRDENNIAESTVIUENRRSEIAGDNIIFFFICICAUNLTT, Y

EARLY THEORIES OF EVOLUTION

IN CONTEXT Before the 18th century, most material, struck off the Sun by a
people believed that plant comet, that had taken 70,000 years
KEY FIGURES and animal species stayed to cool (a huge underestimate, in
The Comte de Buffon unchanged throughout time—a view fact). As Earth cooled, species had
(1707–88), Jean-Baptiste now known as essentialism. This appeared, died off, and were finally
Lamarck (1744–1829) idea came under challenge as a replaced by ancestors of those
result of two developments: the known today. Noting similarities
BEFORE intellectual movement known as the among animals such as lions,
1735 Swedish botanist Carl Enlightenment (c. 1715–1800), and tigers, and cats, Buffon deduced
Linnaeus publishes Systema the Industrial Revolution (1760–1840). that 200 species of quadrupeds had
Naturae, a system of biological evolved from just 38 ancestors. He
classification that later helped The Enlightenment was marked also believed that changes in body
to determine species’ ancestry. by scientific progress and increased shape and size in related species
questioning of religious orthodoxy, had occurred in response to living
1751 In “Système de la nature” such as the claim that God created in different environments.
French philosopher Pierre Earth and all living things in seven
Louis Moreau de Maupertuis days. Then, as the Industrial In 1800, French naturalist Jean-
introduces the idea that Revolution gathered pace, canals, Baptiste Lamarck went further. In a
features can be inherited. railroads, mines, and quarries lecture at the Museum of Natural
cut through rock strata and revealed
AFTER thousands of fossils, mostly of Nature is the system of laws
1831 Etienne Geoffroy Saint- animal and plant species that no established by the Creator for
Hilaire writes that sudden longer existed and had never been the existence of things and
environmental change can seen before. These suggested that for the succession of creatures.
cause a new species to develop life began long before the widely
from an existing organism. accepted creation date of 4400 bce, The Comte de Buffon
deduced from biblical sources.
1844 In Vestiges of the Natural
History of Creation, Scottish Animal adaptation
geologist Robert Chambers In the late 1700s, French scientist
argues—anonymously—that Georges-Louis Leclerc, Comte de
simple creatures have evolved Buffon, upset church authorities
into more complex species. by asserting that Earth was much
older than the Bible suggested. He
believed it was formed from molten

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THE STORY OF EVOLUTION

See also: Extinction and change 22 ■ Uniformitarianism 23 ■ Evolution by
natural selection 24–31 ■ The rules of heredity 32–33

History in Paris, he argued that …continuous use of Jean-Baptiste
traits acquired by a creature during any organ gradually Lamarck
its lifetime could be inherited by strengthens, develops
its offspring—and that a buildup and enlarges that organ. Born in 1744, Jean-Baptiste
of such changes over many Jean-Baptiste Lamarck Lamarck attended a Jesuit
generations could radically alter college before joining the
an animal’s anatomy. develop from simple to more French army. Forced by an
complex forms in a “ladder” of injury to resign, he studied
Lamarck wrote several books progress. The other, via the medicine and then pursued
in which he developed this idea inheritance of acquired traits, his passion for plants, working
of transmutation. He argued, for helped them adapt better to their at the Jardin du Roi (Royal
instance, that the use or nonuse of environment. When Charles Darwin Garden) in Paris. Supported
body parts eventually resulted in developed his theory of evolution by the Comte de Buffon,
such features becoming stronger, by means of natural selection, he Lamarck was elected to the
weaker, bigger, or smaller in a would reject many of Lamarck’s Academy of Sciences in 1779.
species. For example, the ancestors ideas, but both men shared the When the Jardin’s main
of moles probably had good belief that complex life evolved building became the new
eyesight, but over generations over an immense period of time. ■ National Museum of Natural
this deteriorated because moles did History during the French
not require vision as they burrowed Fossil finds changed ideas about Revolution (1789–99), Lamarck
underground. Similarly, giraffes how life began. The first example of an was placed in charge of the
gradually developed longer necks articulated plesiosaur—Plesiosaurus study of insects, worms, and
to enable them to reach leaves dolichodeirus—was discovered in 1823 microscopic organisms. He
growing high up in trees. by Mary Anning in Dorset, England. coined the biological term
“invertebrate” and often used
Drivers of evolution the relatively simpler forms of
Larmarck’s ideas about inherited such species to illustrate his
acquired traits were part of a wider “ladder” of evolutionary
early theory of evolution. He also progress. However, Lamarck’s
believed that the earliest, simplest work was controversial and
forms of life had emerged directly he died in poverty in 1829.
from nonliving matter. Lamarck
identified two main“life forces” Key works
driving evolutionary change. One,
he believed, made organisms 1802 Research on the
Organization of Living Bodies
1809 Zoological Philosophy
1815–22 Natural History of
Invertebrate Animals

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22

BTAOYWCOOAURTRLASDS,TPDRREOSEPVTHIROEOUYSED

EXTINCTION AND CHANGE

IN CONTEXT I n the early days of studying believe that the evidence of fossil
fossils, many people denied remains supported a theory of
KEY FIGURE they could be extinct species. evolution. Nevertheless, Cuvier’s
Georges Cuvier (1769–1832) They failed to see why God would central views have continued to
create and destroy creatures before win support, and modern evidence
BEFORE humans ever appeared, arguing points to at least five catastrophic
Late 1400s Leonardo da Vinci that unfamiliar fossil species might mass extinction events in Earth’s
argues that fossils are the still be living somewhere on Earth. past, including the one that wiped
remains of living creatures, In the late 18th century, French out the dinosaurs. Unlike Cuvier,
not just shapes spontaneously zoologist Georges Cuvier looked however, today’s scientists know
formed in the earth. into this by exploring the anatomy that life is not recreated out of
of living and fossil elephants. He nothing after a catastrophe. Rather,
1660s English scientist Robert proved that fossil forms such as when a mass extinction event kills
Hooke suggests that fossils are mammoths and mastodons were off many species, those left will
extinct creatures, since no anatomically distinct from living evolve and multiply—sometimes
similar forms can be found elephants, so they must represent relatively quickly—to fill vacant
on Earth today. extinct species. (It was highly ecological niches, as the mammals
unlikely that they still lived on did after the age of the dinosaurs. ■
AFTER Earth without being noticed.)
1841 English anatomist
Richard Owen calls huge Cuvier believed that Earth had
reptile fossils “dinosaurs.” experienced a series of distinct
ages, each of which ended with a
1859 Charles Darwin’s On the “revolution” that destroyed existing
Origin of Species explains how flora and fauna. He did not, though,
evolution can occur through
“natural selection.” Cuvier coined the name “mastodon”
for its Greek meaning of “breast tooth,”
1980 US scientists Luis referring to the nipplelike patterns on
and Walter Alvarez present the creature’s teeth, which were unlike
evidence that an asteroid those of any living elephants.
hit Earth at the time of the See also: Evolution by natural selection 24–31 ■ Ecological niches 50–51
extinction of the dinosaurs. ■ An ancient ice age 198–199 ■ Mass extinctions 218–223

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THE STORY OF EVOLUTION

PNBREOGOVISENPSNETICNIGTGE,ONOFOFAAN END

UNIFORMITARIANISM

IN CONTEXT U niformitarianism is the … from what has actually
theory that geological been, we have data for
KEY FIGURE processes, such as the concluding [what] is
James Hutton (1726–97) laying down of sediment, erosion, to happen thereafter.
and volcanic activity, occur at the James Hutton
BEFORE same rate now as they did in the
1778 The Comte de Buffon, a past. The idea emerged in the late that most geological processes
French naturalist, suggests 18th century, as mining, quarrying, happen so gradually that the
that Earth is at least 75,000 and increased travel brought ever features he was discovering must
years old—far older than most more geological features to light, be astronomically old.
people believed at the time. including unusual rock strata and
previously unknown fossils, whose Uniformitarianism was not
1787 German geologist origins were then widely debated. generally accepted at once, not
Abraham Werner proposes least because it challenged a literal
that Earth’s layers of rock The generally accepted view interpretation of the creation stories
formed from a great ocean that that Earth was only a few thousand of the Old Testament. However, a
once covered the entire planet. years old had been challenged by new generation of geologists, such
His followers became known the Comte de Buffon, and in 1785 as John Playfair and Charles Lyell,
as Neptunists. Scottish geologist James Hutton threw their intellectual weight
also argued for Earth’s far greater behind Hutton’s ideas, which also
AFTER antiquity. Hutton’s ideas were inspired a young Charles Darwin. ■
1802 James Hutton’s theory formed during expeditions around
of uniformitarianism reaches a Scotland to examine layers of rock.
wider audience when Scottish He believed that Earth’s crust was
geologist John Playfair constantly changing, albeit mostly
publishes Illustrations of the slowly, and could see no reason to
Huttonian Theory of the Earth. suggest that the complex geological
actions of layering, erosion, and
1830–33 Principles of Geology, uplifting took place faster in the
by Scottish geologist Charles distant past than they did in the
Lyell, supports and builds on present. Hutton also understood
the uniformitarian ideas of
James Hutton. See also: Early theories of evolution 20–21 ■ Evolution by natural selection 24–31
■ Moving continents and evolution 212–213 ■ Mass extinctions 218–223

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ETHXE ISSTRTUGEGNLECFOER

EVOLUTION BY NATURAL SELECTION

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26 EVOLUTION BY NATURAL SELECTION

IN CONTEXT N atural selection, a concept Natural selection is daily
developed by British and hourly scrutinizing,
KEY FIGURE naturalist Charles Darwin throughout the world,
Charles Darwin (1809–82) and set out in his book On the the slightest variations.
Origin of Species by Means of
BEFORE Natural Selection (1859), is the Charles Darwin
1788 In France, Georges-Louis key mechanism of evolution in
Leclerc, Comte de Buffon, organisms, resulting in different
completes his 36-volume survival rates and reproductive
Histoire Naturelle, outlining abilities. Those organisms that have
early ideas about evolution. higher breeding success pass on
their genes to more of the next
1809 Jean-Baptiste Lamarck generation, so individuals with
proposes that creatures evolve these characteristics become
by inheriting acquired traits. more common.

AFTER To the Galapagos thousands of years. As Darwin
1869 Friedrich Miescher, a The young Charles Darwin first looked at landscapes around the
Swiss doctor, discovers DNA, began to consider evolution during world that had been affected by
although its genetic role is not his pioneering scientific expedition processes of erosion, deposition, and
yet understood. around the world aboard HMS volcanism, he began to speculate
Beagle from 1831 to 1836. As a young about animal species changing over
1900 The laws of inheritance man, Darwin accepted the orthodox very long time periods, and the
based on the pea plant interpretation of the Bible, that Earth reasons for such changes. By
experiments of Austrian was only a few thousand years old. examining fossils and observing
scientist Gregor Mendel in the However, while he was on board living animals, Darwin identified
mid-1800s are rediscovered. the Beagle, Darwin read Scottish patterns; he noticed, for example,
geologist Charles Lyell’s recently that extinct species had often been
1942 British biologist Julian published Principles of Geology, in replaced by similar, but distinct,
Huxley coins the term “modern which Lyell demonstrated that rocks modern ones.
synthesis” for the mechanisms bore traces of tiny, gradual, and
thought to produce evolution. cumulative change over vast time Darwin’s field work on the
periods—millions, rather than islands of the Galapagos archipelago
off South America in the fall

Charles Darwin Born in Shropshire, UK, in 1809, instantly. Despite continuing
Darwin was fascinated by natural ill-health, Darwin fathered
history from a young age. While 10 children and never stopped
at Cambridge University, he studying and developing new
became friendly with several theories. He died in 1882.
influential naturalists, including
John Stevens Henslow. As a result, Key works
Darwin was invited to join the
HMS Beagle expedition around the 1839 Zoology of the Voyage
world. Henslow helped Darwin of HMS Beagle
catalog and publicize his finds. 1859 On the Origin of Species
by Means of Natural Selection
Darwin’s research brought him 1868 The Variation of Animals
fame and recognition—the Royal and Plants under Domestication
Society’s Royal Medal in 1853, 1872 The Expression of
nd fellowship of the Linnean Emotions in Man and Animals
Society in 1854. In 1859, his book
On the Origin of Species sold out

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THE STORY OF EVOLUTION 27

See also: Early theories of evolution 20–21 ■ The rules of heredity 32–33 ■ The role of DNA 34–37 ■ The selfish gene 38–39
■ The food chain 132–133 ■ Mass extinctions 218–223 ■ Population viability analysis 312–315

of 1835 provided especially strong Comparison of Galapagos finch
evidence for his later theory of bill structure
evolution by natural selection. Here,
he observed that the shape of the Geospiza magnirostris Geospiza fortis
carapaces (shells) of giant tortoises The short, sharp bill of the Large The bill of the Medium Ground Finch
varied slightly from island to island. Ground Finch, the biggest of Darwin’s is variable, evolving rapidly to adapt
Darwin was also intrigued to find finches, enables it to crack nuts. to whatever size seeds are available.
that there were four broadly similar,
yet clearly distinct, varieties of
mockingbirds, but that no single
island had more than one species
of the bird. He saw small birds,
too, that looked alike but had a
range of beak sizes and shapes.
Darwin deduced that each group
possessed a common ancestor but
had developed diverse traits in
different environments.

Darwin’s conclusions Geospiza parvula Certhidea olivacea
On Darwin’s return to England, the The stubby bill of the Small Tree Finch, The slender, probing bill of the Green
differing beaks of the small birds which forages in foliage, suits its diet
he had found on the Galapagos, Warbler-finch helps it catch small
usually called “finches” although of seeds, fruits, and insects. insects and spiders.
they are not in the true finch family,
set him thinking. He knew that populations had evolved in different Malthus predicted that population
a bird’s beak is its key tool for Galapagos habitats, each group growth would eventually outstrip
feeding, so its length and shape adapted for a more or less specialist food production. This idea matched
offer clues to its diet. Later research diet by a process that he would the evidence Darwin had observed
revealed that there are 14 different later call “natural selection.” Over of ongoing competition between
finch species on the Galapagos time, the finch populations had individual animals and species for
islands. The differences in their become distinct species. resources. This competitive aspect
beaks are marked and significant. formed the backbone of Darwin’s
For example, cactus finches have In the early 21st century, coalescing theory of evolution.
long, pointed beaks that are ideal researchers at Harvard University
for picking seeds out of cactus uncovered new evidence of how By 1839, Darwin had developed
fruits, while ground finches have this happens at a genetic level. an idea of evolution by natural
shorter, stouter beaks that are Their findings, published in 2006, selection. He was, though, reluctant
better suited for eating large seeds showed that a molecule called to publish because he understood
on the ground. Warbler finches have calmodulin regulates the genes that the theory would unleash a
slender, sharp beaks, which are involved in shaping birds’ beaks, storm of controversy from those
ideal for catching flying insects. and is found at higher levels in who would view it as an attack
longer-beaked cactus finches than on religion and the Church. When,
Darwin speculated that the in shorter-beaked ground finches. in 1857, he began receiving
finches were descended from a communications from fellow British
common ancestral finch that had Refining the theory naturalist Alfred Russel Wallace,
reached the archipelago from the Darwin was influenced by Thomas who had independently arrived at
mainland of South America. He Malthus’s An Essay on the Principle very similar conclusions, Darwin
concluded that a variety of finch of Population (1798), in which realized he had to publish his ❯❯

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28 EVOLUTION BY NATURAL SELECTION

ideas. Papers by Darwin and I see no good reasons why Sex (1871). This theory was distinct
Wallace were jointly presented the views given in this from natural selection, as Darwin
at a meeting of the Linnean volume should shock the recognized that animals select
Society of London in July 1858, mates based on characteristics that
under the title “On the Tendency religious views of anyone. do not simply favor survival. For
of Species to form Varieties; and Charles Darwin example, when Darwin considered
on the Perpetuation of Varieties the spectacular but cumbersome
and Species by Natural Means helped an individual organism tails of male peafowl (peacocks), he
of Selection.. live longer and reproduce more could not imagine the tail playing
successfully would be passed on any role in helping the individual
The following year, Darwin to more offspring, while those that bird to survive. He concluded that
published the theory in On the made the organism less successful they were designed to boost an
Origin of Species by Means of would be lost. Darwin called this individual’s chance of reproductive
Natural Selection. It offended some “natural selection”—a process success. Peahens choose males
scientists because it differed from that, over generations, enabled with the brightest tails, so the
Lamarck’s ideas of transmutation, a population of any given species genetic material of these showy
and also upset creationists who to adapt better and thrive in its males is passed to the next
argued that it undermined a literal chosen habitat. generation. Bright tail feathers
interpretation of the Bible. Others indicate that the bird is healthy, so
felt that the theory did not account Sexual selection choosing a mate with a bright tail
for the huge range of characteristics Darwin also developed a theory is a good strategy for the peahen.
in species and called it “unguided” of sexual selection. First outlined in However, Darwin’s idea that
and “nonprogressive.” On the Origin of Species, this was females choose a mate came under
developed further in The Descent fire; 19th-century society could
Darwin was confident. He knew of Man, and Selection in Relation to accept that males competed to
that all individual organisms in a reproduce (intrasexual selection),
species show a degree of natural but intersexual selection, where
variation; some have longer one sex (usually the female) makes
whiskers, or shorter legs, or brighter the choice, was ridiculed.
colors, for instance. Because
members of all species compete for Reproductive success is clearly
limited resources, he deduced that essential for the future of a species.
those whose traits are best suited Natural selection is often described
to their environment are more likely as “survival of the fittest,” but
to survive and reproduce. He also longevity alone is not particularly
argued that characteristics that

Natural selection

There is variation There is differential reproduction. There is heredity. End result:
in traits. No environment can support unlimited The dark beetles have If darkness is the
For example, some population growth, so some individuals more dark offspring winning trait, producing
beetles are pale and lose out. Here, birds eat the pale because this trait has a more offspring, in time,
others dark. beetles, so fewer of them reproduce. genetic basis. all beetles will be dark.

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THE STORY OF EVOLUTION

Kin selection

The peacock with the most splendid description of the scientific process. The term “kin selection” was
tail will attract the most peahens. Its In 1930, British geneticist Ronald first used by British biologist
bright tail will be passed on to its male Fisher wrote The Genetical Theory John Maynard Smith in 1964.
offspring, which will find it similarly of Natural Selection, which It is the evolutionary strategy
easy to attract mates. combined Darwin’s theory of that favors the reproductive
natural selection with the ideas success of an organism’s
helpful. If individual A lives 10 of heredity that the19th-century relatives, prioritizing them
times as long as individual B, but Austrian scientist Gregor Mendel above the individual’s own
the latter produces twice as many had developed. In 1937, Ukrainian– survival and reproduction.
offspring that then also breed, B American geneticist Theodosius ❯❯ It occurs when an organism
will pass on more genes to the next engages in self-sacrificial
generation than the longer-lived A. behavior that benefits its
relatives. Charles Darwin was
the first to discuss the concept
when he wrote about the
apparent paradox represented
by altruistic nonbreeding
social insects, such as worker
honeybees, which leave
reproduction to their mothers.
British evolutionary biologist
William Donald Hamilton
proposed that bees, for
example, behave in an
altruistic manner—assisting
others in reproduction—when
the genetic closeness of the
two bees and the benefit to
the recipient outweigh the
cost of altruism to the giver.
This is called Hamilton’s Rule.

Building on the theory Why do some die and some In honeybee colonies, female
Many of Darwin’s and Wallace’s live?… the answer was worker bees look after the queen
ideas have proved remarkably bee. They build the honeycomb,
accurate, despite the fact that clearly, that on the whole the gather nectar and pollen, and feed
the workings of genetics were not best fitted live. larvae, but they do not breed.
understood at the time. Although
Darwin himself had used the Alfred Russel Wallace
term “genetic” as an adjective
to describe the as-yet-unknown
mechanism of inheritance, it was
British biologist William Bateson,
in the early 20th century, who first
used the term “genetics” in a

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30 EVOLUTION BY NATURAL SELECTION

Albinism, as in this albino leopard organism carrying it, whereas environment, they become more
gecko, is a mutation causing a lack another might affect all its offspring common over the course of
of pigment. This mutation hinders the and future generations. generations. Over time, they may
gecko’s chances of survival, making it produce large enough divergences
lighter colored and sensitive to light. Inherited mutations may or may from the parent population for a
not alter an individual’s phenotype – new species to evolve—a process
Dobzhansky put forward the idea its physical traits and behavior. If called speciation.
that regularly occurring genetic mutations do affect the phenotype,
mutations are sufficient toprovide they may be to its advantage or Mutation rates are usually very
the genetic diversity—and disadvantage, helping or hindering low, but the process is ever-present.
therefore different traits—that an organism’s ability to survive The changes may be beneficial,
makes natural selection possible. and reproduce successfully. If they neutral, or harmful. They do not
He wrote that evolution was a hinder, they are likely to disappear occur in response to an organism’s
change in the frequency of an from the population; if they help needs, and are, in that respect,
“allele” in the gene pool, an allele an organism adapt better to its random. However, some types of
being one of the alternative forms of mutations occur more frequently
a gene that arise by mutation. The vast majority of large than others. Scientists now know,
mutations are deleterious; for example, that evolution can take
A mutation is a permanent small mutations are both far place very rapidly in bacteria
alteration in the sequence of more frequent and more likely because of their frequent mutations.
deoxyribonucleic acid (DNA), the
molecule that makes up a gene to be useful. Different rates of evolution
in one individual, resulting in Ronald Fisher The ancestors of all life on Earth
a sequence that differs from that were very simple organisms.
of other members of the species. Recent scientific research suggest
Mutations may occur as the result that the earliest “biogenic” rocks—
of the miscopying of DNA during derived from early life forms—date
cell division, or they may be caused back nearly four billion years. In
by environmental factors, such as that time, highly complex life forms
damage resulting from the sun’s have evolved, and later fossils
ultraviolet radiation. One mutation of species that look more similar
might affect only the individual to those of today reveal what has

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THE STORY OF EVOLUTION

Evolution in real time

Seen in the light of evolution, Individuals within Richard Lenski, a professor
biology is, perhaps, a species have at Michigan State University,
intellectually the established the Long-term
most satisfying and a variety of forms Experimental Evolution
inspiring science. of a characteristic. project in 1988. For more than
25 years, he studied 59,000
Theodosius Dobzhansky generations of the E. coli
bacterium. During this time,
occurred. For example, a fossil The individuals with he observed that the species
record stretches back 60 million the characteristic best used the glucose solution
years for ancestors of the horse. suited to the environment it lived in more efficiently,
The earliest of these were dog- are more likely to survive increasing in size but also
sized forest-dwelling animals with growing faster. Also, a new
several toes on each foot. Evolution and breed. species had evolved that was
produced much larger horses with able to use a compound in the
just a single hoof on each foot, These solution called citrate, which
adapted for life on open grasslands characteristics the parent bacterium could
where they would often have had are passed on not. Evolving bacteria can
to outrun predators. pose a potential threat to
to the next humans. Increasing antibiotic
Peppered moths (biston generation. use destroys many disease-
betularia) reveal change over a causing bacteria, but not those
shorter period. The moth is usually Two peppered moths exhibit with mutations that make
pale, providing camouflage against evolution at work, the lower one an them resistant to the drugs.
the bark of birch trees, but a example of industrial melanism. The As the non-resistant bacteria
mutation produces some black dark variety began to appear in British are killed off, the resistant
moths. Before the 19th century, cities in the early 1800s. strains become more
most peppered moths were pale. dominant, multiplying and
During the Industrial Revolution passing on their mutations
(1760–1840), however, smoky air left to future generations. That
deposits of soot on trees and is natural selection at work.
buildings in British cities, and the
black form became much commoner. Escherichia (E.) coli bacteria
By 1895, 95 percent of peppered can cause serious gut and other
moths in Britain’s cities were black, infections that will be increasingly
as paler moths were eaten by birds difficult to treat as drug-resistant
because their coloring provided no strains of E. coli multiply.
camouflage. This phenomenon
continues to act as an example of
Darwin’s theory in action today, as
the pale moth becomes common
once more due to the declining soot
concentrations in Britain’s cities. ■

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32

NHCAUORAREMTHRAUIINLNETRGBISMEBIFAUNTOTGERSLGYENES

THE RULES OF HEREDITY

IN CONTEXT L ong before scientists was not the case when he was
cracked the genetic code, working in his monastery garden.
KEY ECOLOGIST in 1866 an Austrian monk When he crossed a plant that
Gregor Mendel (1822–84) named Gregor Mendel was the first always produced green peas with
to show how traits are transferred one that always produced yellow
BEFORE through the generations. By means peas, the result was not yellowish-
1802 French biologist Jean- of much painstaking research, green peas—instead, all the peas
Baptiste Lamarck suggests Mendel accurately predicted the were yellow.
that traits acquired during the basic laws of inheritance.
lifetime of an organism are Mendel’s labors
transmitted to its offspring. When Mendel began his During the course of his research
experiments, scientists believed (1856–63), Mendel grew nearly
1859 Charles Darwin proposes that the various traits seen in 30,000 pea plants over several
his theory of evolution and plants and animals were handed generations and carefully recorded
natural selection in his book down through a “blending” process. the results. He focused on traits
On the Origin of Species by However, Mendel noticed that this
Means of Natural Selection.
Mendel’s pea experiment
AFTER
1869 Swiss chemist Friedrich Mendel’s 1 green 1 yellow PARENT GENERATION
Miescher identifies DNA, experiment F1 GENERATION
which he terms “nuclein.” with growing peas all yellow
proved that the gene
1953 Molecular biologists— carrying the yellow
including Briton Francis coloration was
Crick and American James dominant while the
Watson—discover the gene for green was
structure of DNA. recessive.

2000s Researchers in the F2 GENERATION
field of epigenetics describe
inheritance by mechanisms
other than through the DNA
sequence of genes.

1 green 3 yellows

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THE STORY OF EVOLUTION

See also: Early theories of evolution 20–21 ■ Evolution by natural selection 24–31
■ The role of DNA 34–37 ■ The selfish gene 38–39

Heredity provides dominant or recessive. When both Gregor Johann Mendel
for the modification inherited factors are dominant,
of its own machinery. the resulting plant will show the Born Johann Mendel in 1822
James Mark Baldwin dominant trait. With a pair of on a farm in Silesia—then part
recessive factors, the plant will of the Austrian Empire and
American psychologist show the recessive trait. However, now in the Czech Republic—
if one dominant and one recessive Mendel studied philosophy
(phenotypes) that had only two factor are present, the plant will and physics at the University
distinct forms—for example, white show the dominant trait. of Olomouc (1840–43). At this
or purple flowers. When examining time, he became interested
the trait of yellow or green peas, Pioneering geneticist in the work of Johann Karl
Mendel took green pea plants and Mendel published his paper in Nestler, who was researching
cross-pollinated them with yellow 1866, but no one took much notice hereditary traits in plants
pea plants. The peas produced from until 1900, when the botanists and animals. In 1847 Mendel
this parent generation were all yellow Hugo de Vries, Carl Erich Correns, entered a monastery, where
and Mendel named them the F1 and Erich Tschermak von he was given the name
generation. He then cross-pollinated Seysenegg discovered his work. Gregor. He then went on
pea plants from the F1 generation Scientists then began proving to study science further at
with each other to produce the F2 Mendel’s theories more widely. Vienna University (1851–53).
generation. He found that some
peas produced were yellow and Within just ten years, scientists When Mendel returned
some were green. The F1 generation named the pairs of factors “genes” to his monastery in 1853,
showed only one trait (yellow), which and showed that they are linked on the abbot Cyril Napp gave
Mendel called “dominant.” However, chromosomes. It is now known that him permission to use the
in the F2 generation 75 percent had inheritance is far more complex gardens for his research into
the dominant yellow trait and 25 than Mendel recognized, but his hybridization. Mendel himself
percent displayed the nondominant meticulous research continues to became an abbot in 1868 and
—or “recessive”—green trait. form the basis for modern studies. ■ no longer had time for his
experiments. Although he
Laws of inheritance never received credit for his
Mendel theorized that every pea discoveries during his lifetime,
plant has two factors controlling he is widely regarded as the
each trait. When plants are cross- founder of modern genetics.
pollinated, one factor is inherited
from each plant. A factor can be Key works

Pea plants provided the raw data 1866 “Experiments with Plant
that Mendel used to develop his Hybrids,” Verhandlungen des
theories explaining the transmission of naturforschenden Vereines
traits from one generation to the next. in Brünn

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34

DOWTHIFSEEL’CVISOFEEVECERREETD IN CONTEXT

THE ROLE OF DNA KEY FIGURES
Francis Crick (1916–2004),
Rosalind Franklin (1920–
58), James Watson (1928–),
Maurice Wilkins (1916–2004)

BEFORE
1910–29 US biochemist
Phoebus Levene describes the
chemical components of DNA.

1944 US researchers Oswald
Avery, Colin Macleod, and
Maclyn McCarty show that
DNA determines inheritance.

AFTER
1990 British researchers,
led by embryologist Ian
Wilmut, successfully clone
an adult mammal—a sheep
named Dolly.

2003 Scientists complete
the mapping of the entire
human genome.

T he discovery of the structure
of DNA (deoxyribonucleic
acid) in 1953 is one of
the most important scientific
breakthroughs to date. It offered
the key to understanding the very
building blocks of life and explained
how genetic information is stored
and transferred. Englishman Francis
Crick and American James Watson
famously celebrated their joint
discovery in a low-key fashion
at their local pub in Cambridge,
followed by a letter published in
the journal Nature. Their discovery
had enormous potential for scientific
advances and had an important
impact on many fields of research,
from medicine to forensic science,
taxonomy, and agriculture. The
ramifications of their work still
reverberate today, as methods of

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THE STORY OF EVOLUTION 35

See also: Early theories of evolution 20–21 ■ Evolution by natural selection 24–31 ■ The rules of heredity 32–33 ■ The
selfish gene 38–39 ■ A system for identifying all nature’s organisms 86–87 ■ Biological species concept 88–89

Molecular biologists James Watson College, London, Franklin and DNA is like a computer
(left) and Francis Crick (right), pictured Wilkins were developing methods of program but far, far more
in 1953 with their double helix model X-raying DNA to view its structure.
of DNA. Watson called DNA “the most Watson had seen examples of advanced than any
interesting molecule in all nature.” Franklin’s work that hinted at DNA’s software ever created.
helical shape shortly before he and
handling genetic material advance Crick announced their breakthrough. Bill Gates
and we learn more about how
individual genes operate. In 1962 Crick, Watson, and with T to form base pair AT, and
Wilkins were awarded the Nobel G always pairs with C to form
Crick and Watson’s breakthrough Prize for Physiology or Medicine. base pair GC.
was the culmination of decades Franklin, who died in 1958, never
of research by numerous scientists, received recognition for her part DNA is the blueprint for life.
including Rosalind Franklin and in the discovery during her lifetime, Sequences of bases along the
Maurice Wilkins. While Crick and although Crick and Watson openly DNA strand constitute the genes
Watson worked with 3-D models acknowledged that her work was that provide the information that
to figure out how the components essential to their success. determines the complete form and
of DNA fitted together, at King’s physiology of an organism. A triplet
Double helix structure of bases is known as a codon, and
DNA is a molecule featuring two each codon specifies the production
long, thin strands that coil around of one of 20 amino acids; the order
each other to resemble a twisted in which the amino acids join
ladder, in a shape known as a together in a chain determines ❯❯
double helix. Using the ladder
analogy, the sides of the ladder are
made up of deoxyribose (a sugar)
and phosphate, while the rungs
of the ladder consist of paired
nitrogenous bases, adenine (A),
guanine (G), cytosine (C), and
thymine (T). A always pairs up

Genetic engineering useful—have greatly simplified A scientist analyzes a sample
and accelerated the process. In of DNA. Genetic manipulation in
Understanding the structure theory, geneticists can now splice medicine is standard practice and
of DNA has enabled scientists any gene with any other. They DNA profiling is a vital forensic tool.
to change or “engineer” the have attempted some intriguing
genetic material in cells. It is combinations, such as the
possible to cut out a gene from insertion of the gene for producing
one organism (the donor) and spider silk into goat DNA so
place it into the DNA of another that goats produce milk rich in
organism. When this practice proteins. Other substances that
was first attempted in the 1970s can be produced by modifying
it was both difficult and time- genes are hormones and vaccines.
consuming, but technological
advances—such as Clustered In gene therapy, a genetically
Regularly Interspaced Short modified vector (often a virus) is
Palindromic Repeats, or CRISPR, used to carry a gene into the DNA
which has been particularly of an organism to replace a faulty
or unwanted gene.

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36 THE ROLE OF DNA

Genetically the type of protein they go on the ladder down the middle to
modified food to make. For example, the produce two single strands. These
combination GGA is the codon for act as templates for the production
In agriculture, crops may be glycine. Sixty-four possible triplets of a second complementary
engineered to enhance them can be made from the four base DNA strand on each of them by
in some way. A genetically pairs, and 61 of them code for a matching up the appropriate base
altered crop is known as a particular amino acid. The other pairs. The process results in two
genetically modified organism three act as signals such as “start” strands of whole DNA that are
(GMO). Companies that and ”stop,” which govern how exactly the same as the original.
operate in this sector may information is read by the cellular
modify a plant’s DNA so that machinery. DNA is also organized Since DNA remains in the
it produces more of a certain into separate chromosomes, of nucleus of the cell, a related molecule
nutrient or a toxin specific to which there are 23 pairs in the called messenger ribonucleic acid
a particular insect pest. The human cell. (mRNA) copies segments of DNA
DNA of a plant may also be coding sequence and carries the
altered to become resistant to Copying the code information to the regions of the
a particular herbicide, so that When cells divide, DNA needs to cell where new proteins are made.
use of the chemical kills only be copied. This is achieved by the RNA is chemically related to DNA,
the weeds and not the crop. splitting of base pairs, which cuts but the thymine base (T) is
replaced by the base uracil (U),
Some ecologists argue that The structure of DNA which is less stable but requires
there is a risk of genetically less energy to make. Stable living
unmodified plants becoming organisms benefit from having
contaminated by GMOs. They DNA genomes, but RNA makes up
also point out that the long- genomes of some viruses, where
term effects of eating such stability can be less advantageous.
foods are as yet not properly
understood. Another concern DNA is found in all living things
is that in the future large on Earth, from amoebae to insects,
agrochemical companies could to trees, tigers, and humans. Of
control the world’s food supply course, the sequence of base pairs
by patenting the GMOs that varies, and this difference allows
they produce, to the detriment geneticists to trace relationships
of poorer nations. between different species.

adenine thymine Good and bad errors
cytosine guanine DNA is a highly stable molecule,
but sometimes mistakes, known
New kinds of rice are being A DNA molecule consists of a double as mutations, occur. These can be
developed through genetic helix formed by two strands, made up in the form of an error, duplication,
modification. This may improve of sugars and phosphates, linked by or omission in the order of the
the nutritional value of the crop paired base nucleotides: adenine and nucleotides A, C, G, and T. Mutation
or its resistance to disease. thymine or cytosine and guanine. can be spontaneous—the result
of errors that occur when the DNA
is copied—or may be induced
by external influences such as
exposure to radiation or cancer-
causing chemicals. Some mutations
have no effect, but others may
change what the gene produces
or inhibit the functioning of a
gene. This can lead to problems in
the organism as a whole. Examples

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THE STORY OF EVOLUTION

DNA barcoding

of disorders caused by gene Mutated blood cells occur in The idea of DNA barcoding
mutations include cystic fibrosis sickle-cell disease—a genetic disorder was first raised in 2003 when
and sickle-cell disease. passed on when both parents carry a team at the University of
the faulty gene. It can be painful and Guelph, Canada, suggested
Although many mutations are increases the risk of serious infections. that it would be possible to
harmful, occasionally a mutation identify species by analyzing
will confer an advantage on an parent. Additionally, with access a common section of their
individual, enabling it to survive in to such data it is possible to DNA. Led by Dr. Paul Hebert,
its environment better than others screen embryos for known genetic researchers chose a region in
of the same species. This type of disorders before implantation in the the gene known as cytochrome
mutation may end up being passed womb. By March 2018, the DNA of c oxidase 1 (“CO1”), made up
on through the process of natural around 15,000 organisms had been of 648 base pairs. This region
selection. Over many generations, sequenced. Such information can is quick to analyze, but the
mutation is a mechanism for help show how animals are related sequence is still long enough
diversification, survival of the in the evolutionary line and how to differentiate between and
fittest, and ultimately evolution. they have diversified. within animal species.
Different gene segments can
The human genome While the discovery of the be used for other forms of life.
On April 14, 2003, scientists composition and structure of DNA
completed the lengthy task of has revolutionized the science of The first part of the
mapping (sequencing) the entire heredity, it is worth noting that barcoding system involves
human genome. Geneticists worked the regions of DNA used for coding cataloguing samples of known
out the precise position of all the proteins account for just 2 percent species. The DNA is extracted
base pairs in a chain of some three of the entire human genome. and organized into a sequence
billion of the base nucleotides The nature of the other 98 percent of base pairs, a process known
comprising an estimated 30,000 is not yet fully understood by as “sequencing.” The sequence
individual genes. This has allowed geneticists, but it is believed that at is then stored in a computer
geneticists to identify new genes least some of these regions involve database, so that when a DNA
and the role they play in organisms. the regulation of the way genes are sample from an unknown
expressed, or activated. It seems species is sequenced and
Armed with this knowledge, that many more discoveries await entered into the database, the
an individual can find out if they future geneticists. ■ computer will match it with
have inherited a faulty gene from a existing records. The barcoding
technique has proved useful
for taxonomy, helping classify
animals and plants.

With genetic
engineering, we will
be able … to improve

the human race.
Stephen Hawking

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38

GENES ARE
MSEOLLFEICSUHLES

THE SELFISH GENE

IN CONTEXT T he concept of the “selfish for the bodily types and behaviors
gene” was popularized (phenotypic traits) that successfully
KEY FIGURE by British evolutionary promote their own propagation.
Richard Dawkins (1941–) biologist Richard Dawkins in his Supporters of the theory argue that
1976 book of that name. It states because heritable information is
BEFORE that evolution is fundamentally passed through the generations by
1963 British biologist William based upon the survival of different the genetic material of DNA, both
Donald Hamilton writes about forms of a particular gene at the natural selection and evolution
the “selfish interests” of the expense of others. The forms that are best considered from the
gene in The Evolution of survive are those that are responsible perspective of genes.
Altruistic Behaviur.
Natural selection works toward the survival
1966 American biologist of the gene, not the individual.
George C. Williams proposes
in his book Adaptation and Male black widow Animals that warn
Natural Selection that altruism spiders mate others of approaching
is a result of selection taking even though the
place at the level of the gene. predators sacrifice
females eat them themselves at the
AFTER immediately after.
1982 Richard Dawkins argues expense of the
in The Extended Phenotype wider group.
that the study of an organism
should include analysis of Nonbreeding bees in bee
how its genes affect the colonies serve to help the
surrounding environment.
community survive.
2002 Stephen Jay Gould
critiques Dawkins’ theory in
The Structure of Evolutionary
Theory, which revisits and
refines the ideas of classical
Darwinism.

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THE STORY OF EVOLUTION

See also: Evolution by natural selection 24–31 ■ The rules of heredity 32–33
■ The role of DNA 34–37 ■ Mutualisms 56–59

A male black widow spider gingerly circumstances in which the gene Richard Dawkins
approaches a huge female to mate. This can achieve its own selfish goals by
genetically driven act will reproduce fostering apparent altruism in the Richard Dawkins was born
his genes but will lead to his death. organism. One example is kin in Kenya to British parents.
selection, the evolutionary strategy After the family returned to
Dawkins was strongly influenced that favours the reproductive the UK, he developed a strong
by the work of William Donald success of an individual organism’s interest in the natural world
Hamilton on the nature of altruism relatives, even at the cost of the and studied zoology at Oxford
and closely examined the biology individual’s own reproduction University. While there, he
of selfishness and altruism in The or survival. was tutored by Nobel Prize-
Selfish Gene. He argued that winner Niko Tinbergen, who
organisms were simply vehicles An extreme example of was a pioneer of animal
that supported their genes, or genetically based altruism is behavior studies. After a
“replicators.” Genes that help an eusociality. Honey bees are a eusocial brief period at the University
organism survive and reproduce species. They live in colonies which of California at Berkeley,
tend also to improve those genes’ include breeding and non-breeding Dawkins returned to Oxford
own chances of being replicated. individuals. By helping the colony to lecture in zoology.
survive, the many thousands of
Successful genes often provide non-breeding worker bees ensure Richard Dawkins is best
a benefit to the host organism. For the reproduction of the genes they known for his book The Selfish
example, a gene that protects an have in common with the sole Gene, in which he argues
animal or plant against disease breeding individual, the queen. that the gene is the principle
thereby helps that particular gene unit of selection in evolution.
to spread. However, the interests of Critics of Dawkins’ theory argue His theory later triggered a
the replicator and the vehicle may that since individual genes do not series of fierce debates with
sometimes seem to be in conflict. control behaviour, they cannot be Stephen Jay Gould and other
Genes drive the male black widow said to be acting selfishly. Dawkins evolutionary biologists.
spider to mate despite the risk of has maintained that he never Dawkins is also known as a
being eaten by her. However, the meant to suggest that genes had strong advocate of atheism
male’s sacrifice nourishes the their own conscious will. He later and feminism.
female and improves the prospect wrote that “the immortal gene”
of his genes being passed on. might have been a better title for Key works
both his concept and the book. ■
1976 The Selfish Gene
The theory of evolution 1982 The Extended Phenotype
is about as much 1986 The Blind Watchmaker
2006 The God Delusion
open to doubt as the 2009 The Greatest Show
theory that the Earth on Earth: The Evidence
goes around the Sun. for Evolution
Richard Dawkins

Selfishness and altruism
Gene selfishness usually gives rise
to selfishness in the behavior of an
individual organism, but there are

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PERCOOCLEOSGSI

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ECSAL

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42 INTRODUCTION

Joseph Grinnell publishes Robert MacArthur’s Dan Janzen observes the
his research on the California research on North American interdependence of acacia
warblers shows how different trees and the ants that reside
Thrasher, establishing the species can avoid directly on them, and concludes that
basis for the theory of competing with each other
ecological niches. the species evolved in a
in order to coexist. mutualistic manner.

1917 1957 1965

1925–26 1961 1969

The Lotka-Volterra model uses Joseph Connell reveals that Robert Paine
a mathematical equation to different types of barnacle coins the term “keystone
thrive in different tidal species” to describe species
describe the interactions between zones, although they could, that play a crucial role in
predator and prey.
in theory, live in any of them. ecosystem functions.

In the 5th century BCE, the Greek beyond their own local area. As Alfred Lotka introduced one of the
historian Herodotus described technology improved and people first mathematical models ever
watching crocodiles open their began to travel the world, scientists applied to ecology. Now known
jaws for plovers to pick food from such as Robert Hooke, Antonie van as the Lotka-Volterra model, its
their teeth. He may have been the Leeuwenhoek, Carl Linnaeus, predator–prey equations help
first to write about an ecological Alexander von Humboldt, Alfred predict the population fluctuations
process—in this case a mutualistic Russel Wallace, Charles Darwin, of these two groups.
relationship between reptiles and and Johannes Warming became
birds. Aristotle and Theophrastus increasingly aware of ecological In the early years of the 20th
observed many more interactions processes and laid the foundations century, Joseph Grinnell conducted
between animals and their of the science of ecology, even if extensive research into animals’
environment in the 4th century BCE. they didn’t use that word. habitat needs in the western United
States. He observed that species
Over the next two millennia, Mathematical models had different “niches” within a
countless other observations of the It had long been understood that habitat—and that if two species
natural world were made, but a deep one of the most basic ecological have approximately the same food
understanding of how organisms processes is the struggle for requirements, one will “crowd out”
interacted with each other and the survival: for herbivores to find food, the other. Darwin had observed this
world around them was hampered predators to find prey, and prey to on his travels aboard HMS Beagle,
by the inability to observe very avoid being eaten. Predators do but Grinnell’s axiom developed the
small things, those that were active everything they can to hunt and idea further, as did subsequent
at night, or those living underwater. eat prey, and the latter do all they research. In 1934, Georgy Gause
Additionally, few people with an can to avoid being eaten. In 1910, demonstrated what he called the
interest in nature experienced much competitive exclusion principle in

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ECOLOGICAL PROCESSES

Roy Anderson and Robert Research published by Robert Sterner and James Elser
May demonstrate how Ronald Pulliam, Eric Charnov, pioneer the study of ecological
and Graham Pyke expands on stoichiometry—how ratios of
epidemics affect animal the optimal foraging theory that different chemicals within
population growth rates. living organisms change
animals try to gather resources with certain reactions.
while wasting as little
energy as possible.

1970s 1977 2002
1972 1991

Knut Schmidt-Nielsen Earl Werner publishes
publishes How Animals his findings about
Work. The book hugely nonconsumptive
effects of predators
influences the field on prey.
of ecophysiology.

laboratory projects. As William E. to play, too—as Earl Werner New technology
Odum put it in 1959, “the ecological demonstrated 30 years later. His Technological advances—including
niche of an organism depends not work revealed the non-consumptive sophisticated chemical sampling
only on where it lives, but also on impact of predatory dragonfly larvae techniques, satellites with remote
what it does.” on the behavior and physical sensing equipment, and computers
development of their tadpole prey. capable of rapidly processing huge
From field to lab quantities of data—have opened
Laboratory experiments and field Since the mid-20th century, up new areas of study.
observations are the main methods many new ideas on ecological
of providing data for the study processes have emerged. Work by Ecological stoichiometry, for
of ecological processes, but field Robert MacArthur and others on example, studies the flow of energy
experiments—in which a local competition between species led to and chemical elements throughout
environment is manipulated to test the development of optimal foraging food webs and ecosystems, from the
a hypothesis—were not conducted theory, which seeks to explain why molecular level up. Like so many
with scientific rigor until Joe animals choose to eat some food ideas in ecology, its origins can be
Connell’s work with barnacles items and not others. Mutualistic traced back many years, but only
in Scotland. His experiments—the relationships became better took hold with Robert Sterner and
results of which were published understood through the research James Elser’s 2003 book Ecological
in 1961—were meticulously planned of biologists such as Daniel Janzen. stoichiometry: The biology of
and observed, and were repeatable. Robert Paine’s work with starfish elements from molecules to the
and mussels also highlighted the biosphere. New techniques such
Connell set the “gold standard” concept of keystone species— as this will undoubtedly continue
for fieldwork, but experiments in those that have a disproportionate to deepen our understanding of
laboratories still have a vital role influence on their ecosystems. processes in ecology. ■

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LESSONS FROM

FOR LIFEOMANTHTEHMEATSICTARLUTGHEGOLREY

PREDATOR–PREY EQUATIONS

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46 PREDATOR–PREY EQUATIONS

IN CONTEXT Populations of two species, T he predator–prey equations
one predator, the are an early example of the
KEY FIGURES other prey, interact. application of mathematics
Alfred J. Lotka (1880–1949), to biology. Formulated in the 1920s
Vito Volterra (1860–1940) The prey has access to by American mathematician Alfred
food and its population J. Lotka and Italian mathematician
BEFORE growth is exponential. and physicist Vito Volterra, the
1798 British economist When prey animals meet two equations—also known as
Thomas Malthus shows that the Lotka–Volterra equations—
the rate at which the population a predator, they describe the way in which the
changes increases as the size are eaten. population of a predator species
of the population grows. and that of its prey fluctuate in
Eating prey results relation to each other.
1871 In Lewis Carroll’s novel in more predators.
Through the Looking Glass, Lotka proposed the equations
the Red Queen tells Alice, More predators in 1910, as a way of understanding
“you have to run just to stay results in less the rates of autocatalytic chemical
in the same place.” prey, reducing the reactions—chemical processes
number of predators. that regulate themselves. In the
AFTER following decade, he applied
1973 American biologist Leigh the equations to the population
Van Valen proposes the Red dynamics of wild animals.
Queen effect, which describes
the constant “arms race” In 1926, Vito Volterra arrived
between predators and prey. at the same conclusions. He had
become interested in the subject
1989 The Arditi–Ginzburg after meeting Italian marine
equations offer another model biologist Umberto D’Ancona.
of predator–prey dynamics D’Ancona told Volterra how the
by including the impact of the percentage of predatory fish
ratio between predator and prey. caught in nets in the Adriatic
Sea had greatly increased during
World War I. This change was
clearly linked to the drastic
reduction in fishing during the

Vito Volterra Born in 1860 in Ancona, Italy, the Volterra refused to swear loyalty
son of a Jewish cloth merchant, to Italy’s fascist dictator Benito
Vito Volterra grew up in poverty. Mussolini and was dismissed
Despite this, in 1883, aged just 23, from the University of Rome.
he secured a position as professor Forced to work abroad, he only
of mechanics at the University returned to Italy for a short time
of Pisa and began a career as before his death in 1940.
a mathematician. Further
professorships at the universities Key works
of Turin and Rome followed. In
1900, Volterra married, fathering 1926 “Fluctuations in the
six children, although only four Abundance of a Species
survived to adulthood. He was Considered Mathematically,”
made a senator of the Kingdom Nature
of Italy in 1905 and worked on the 1935 Les associations
development of military airships biologiques au point de vue
during World War I. In 1931, mathématique

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ECOLOGICAL PROCESSES 47

See also: Evolution by natural selection 24–31 ■ The selfish gene 38–39 ■ Ecological niches 50–51 ■ Competitive exclusion
principle 52–53 ■ Mutualisms 56–59 ■ Keystone species 60–65 ■ Optimal foraging theory 66–67

A cheetah pursues a Thomson’s increases as the population grows. occurring factors. As a result, wild
gazelle. The predator–prey equations From this theory, Malthus predicted populations should in theory be
are able to model the way populations a catastrophic future for humanity. more or less static, fluctuating only
of both species will change in response The number of humans was around the carrying capacity,
to the activities of the other. growing much more quickly than assuming the random impacts of
the amount of food that could be catastrophic events are ignored.
war years, but D’Ancona could not produced by the world’s farmlands.
explain why less fishing did not Eventually, Malthus argued, a point However, this relative
produce more fish of all kinds in the would be reached when the human equilibrium did not always match
nets. Using the same equations as population would succumb to up with observations—as in ❯❯
Lotka, Volterra eventually explained global famine and decline.
the fluctuations in both the predator The food species
and the prey species. Malthus’s bleak vision did not cannot, therefore, be
happen, thanks to technological exterminated by the
Population principles advances in agriculture and the predatory species, under
At the time Lotka and Volterra development of artificial fertilizers, the conditions to which
made their calculations, the science but his population model became our equations refer.
of population dynamics was still applicable to species populations
in its infancy, having barely moved within ecosystems. Every habitat, Alfred J. Lotka
on since the population studies of and the niche occupied by a species
British economist Thomas Malthus within its community of organisms,
in the late 18th century. According has a carrying capacity—the
to Malthus’s theory, a population maximum population that can
grows or declines rapidly as long be supported by the resources
as the environmental factors for available, such as water, space,
survival are constant, and the rate food, and light. Any rise in
at which that population changes population above this level is
likely to be reduced by naturally

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48 PREDATOR–PREY EQUATIONS

Mathematics without no reproduction limits and the species and the predation rate.
natural history is sterile, but rate of change in a population For example, oscillations in the
is proportional to its size; second, size of an ant population and that
natural history without that the prey population—presumed of an anteater are barely noticeable
mathematics is muddled. to be a herbivore—is always able because they reproduce at such
John Maynard Smith to find enough food to survive. different rates. The oscillations
Next, they assumed that the prey in the populations of species that
British mathematician population is the predators’ only breed at similar rates, such as the
and evolutionist source of nourishment, and that Iberian lynx and rabbit, are much
the predators never become full more pronounced.
D’Ancona’s account of a sudden and never stop hunting. Finally,
increase in the population of they assumed that environmental Nature’s arms race
predatory sea fish. One theory conditions, such as weather or The predator–prey equations
to explain this discrepancy natural disasters, had no impact revealed that species are locked
started from the premise that the on the process. The effect of the together in a never-ending struggle,
population of predators is related genetic diversity of the predators swinging from near disaster and
to the size of the population of their and prey animals on their ability to extinction to times of abundance
food supply, such as prey species. survive was not taken into account. and fertility. In this biological “arms
The relationship suggests that race,” the evolutionary pressure
when a lot of food is available, there When plotted on a graph, the on the prey species is to escape
will be a large predator population. predator population trails the rise predation and survive, so as to have
The growing predator population and fall of the prey population, and more offspring. Meanwhile, the
should then begin to reduce the is still rising as the prey population predator is under pressure to have
amount of prey, which will in starts to decline. This explained a higher predation rate in order
turn lead to a drop in the number D’Ancona’s observation of the larger to provide food for more offspring.
of predators. The size of both proportion of predators after the However, neither species is
populations will rise and fall, but prey population had been allowed superior, responding instead
the ratio of predators to prey will to boom by a reduction in fishing. to the adaptations of the other. The
remain stable. predator–prey relationship between
The relative fluctuations of the even-toed hoofed mammals—such
Such a balanced theory was still populations depends on the relative
at odds with species observations. reproductive rates of the two
Through mathematical modeling,
Volterra was able to show that the Predator–prey population cycles
average sizes of predator and prey
populations do indeed oscillate but KEY The predator and prey
the rate at which each population Prey populations rise and fall
is growing or declining is always Predator over time in regular cycles.
changing and almost never Although the degree to
matches the changes experienced which they change varies,
by the other population. To the cycle follows a broadly
eliminate variables, Volterra made similar pattern.
a series of assumptions: first, that
the prey and predator species have POPULATION

TIME