Read why darwin matters epub format

Authors: Michael Shermer

why darwin matters

Advertising Download Read Online

Also by Michael Shermer

 

Science Friction: Where the Known Meets the Unknown

 

The Science of Good and Evil

 

In Darwin’s Shadow: The Life and Science of Alfred Russel Wallace

 

The Skeptic Encyclopedia of Pseudoscience
(general editor)

 

The Borderlands of Science: Where Sense Meets Nonsense

 

Denying History

 

How We Believe: Science, Skepticism, and the Search for God

 

Why People Believe Weird Things

 

WHY DARWIN MATTERS

 

MICHAEL SHERMER

 

WHY DARWIN
MATTERS

 

Times Books
Henry Holt and Company, LLC
Publishers since 1866
175 Fifth Avenue
New York, New York 10010
www.henryholt.com

 

Henry Holt
®
is a registered trademark of
Henry Holt and Company, LLC.

 

Copyright © 2006 by Michael Shermer
All rights reserved.
Distributed in Canada by H. B. Fenn and Company Ltd.

 

For further information on the Skeptics Society and
Skeptic
magazine,
contact P.O. Box 338, Altadena, CA 91001, 626-794-3119;
fax: 626-794-1301; e-mail: [email protected]
www.skeptic.com

 

Library of Congress Cataloging-in-Publication Data

 

Shermer, Michael.
   Why Darwin matters: the case against intelligent design / Michael Shermer.—1st ed.
       p. cm.
   ISBN-13: 978-0-8050-8121-3
   ISBN-10: 0-8050-8121-6
       1. Evolution (Biology) 2. Intelligent design (Teleology) I. Title.

   QH366.2.S54 2006                                                                      2006041243
   576.8—dc22

Henry Holt books are available for special promotions
and premiums. For details contact: Director, Special Markets.
First Edition 2006
Designed by Victoria Hartman
Printed in the United States of America
1   3   5   7   9   10   8   6   4   2

 

To Frank J. Sulloway

 

“There ain’t naught a man can’t bear if he’ll only be dogged.
It’s dogged as does it.”

 

In Darwin’s footsteps in all ways

 

There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved
.

 

—Charles Darwin,
On the Origin of Species
, 1859

 
CONTENTS

 

 

 

Prologue:
Why Evolution Matters

 

1. The Facts of Evolution

 

2. Why People Do Not Accept Evolution

 

3. In Search of the Designer

 

4. Debating Intelligent Design

 

5. Science under Attack

 

6. The Real Agenda

 

7. Why Science Cannot Contradict Religion

 

8. Why Christians and Conservatives Should Accept Evolution

 

9. The Real Unsolved Problems in Evolution

 

Epilogue:
Why Science Matters

 

Coda:
Genesis Revisited

 

Appendix:
Equal Time for Whom?

 

Notes

 

Selected Bibliography

 

Acknowledgments

 

Index

 
PROLOGUE

 
Why Evolution Matters
 

Hence both in space and time, we seem to be brought somewhat near to that great fact—that mystery of mysteries—the first appearance of new beings on this earth.

—Charles Darwin,
Journal of Researches
, 1845

 

In June 2004, the science historian Frank Sulloway and I began a month-long expedition to retrace Charles Darwin’s footsteps in the Galápagos Islands. It turned out to be one of the most physically grueling experiences of my life, and as I have raced a bicycle across America five times, that is saying something special about what the young British naturalist was able to accomplish in 1835. Charles Darwin was not only one sagacious scientist; he was also one tenacious explorer.
1

I fully appreciated Darwin’s doggedness when we hit the stark and barren lava fields on the island of San Cristóbal, the first place Darwin explored in the archipelago. With a sweltering equatorial sun and almost no fresh water, it is not long before water-loaded seventy-pound packs begin to buckle your knees and strain your back. Add hours of daily bushwhacking through dense, scratchy vegetation, and the romance of fieldwork quickly fades. At the end of one three-day excursion my water supply was so dangerously low that Frank and I collected the dew that had accumulated on the tents the night before. One day I sliced my left shin on a chunk of a’a lava. Another day I was stung by a wasp and one side
of my face nearly doubled in size. At the end of one particularly grueling climb through a moonscapelike area Darwin called the “craterized district,” we collapsed in utter exhaustion, muscles quivering and sweat pouring off our hands and faces, after which we read from Darwin’s diary, in which the naturalist described a similar excursion as “a long walk.”

Death permeates these islands. Animal carcasses are scattered everywhere. The vegetation is coarse and scrappy. Dried and shriveled cactus trunks dot the bleak landscape. The lava terrain is so broken with razor-sharp edges that progress across it is glacially slow. Many people have died there, from stranded sailors of centuries past to wanderlust-driven tourists in recent years. Within days I had a deep sense of isolation and fragility. Without the protective blanket of civilization none of us are far from death. With precious little water and even less edible foliage, organisms eke out a precarious living, their adaptations to this harsh environment selected over millions of years. A lifelong observer of and participant in the evolution-creation controversy, I was struck by how clear it is in these islands: Creation by intelligent design is absurd. So how then did Darwin depart the Galápagos a creationist?

This is the question that Frank Sulloway went there to answer. Sulloway has spent a lifetime reconstructing how Darwin pieced together the theory of evolution. The iconic myth is that Darwin became an evolutionist in the Galápagos, discovering natural selection as he itemized finch beaks and tortoise carapaces, as he observed how each species had uniquely adapted to the available food and the island ecology. The legend endures, Sulloway notes, because it fits elegantly into a Joseph Campbell–like tripartite myth of the hero who (1) leaves home on a great adventure, (2) endures immeasurable hardship in the quest for noble truths, and (3) returns to deliver a deep message—in Darwin’s case, evolution.
The myth is ubiquitous, appearing in everything from biology textbooks to travel brochures, the latter of which inveigle potential customers to see what Darwin saw.

The Darwin Galápagos legend is emblematic of a broader myth that science proceeds by select eureka discoveries followed by sudden revolutionary revelations, as old theories fall before new facts. Not quite. Theories power perceptions. Nine months after departing the Galápagos, Darwin made the following entry in his ornithological catalogue about his mockingbird collection: “When I see these Islands in sight of each other, & possessed of but a scanty stock of animals, tenanted by these birds, but slightly differing in structure & filling the same place in Nature, I must suspect they are only varieties.” He was seeing similar
varieties
of fixed kinds, not an
evolution
of separate species. Darwin did not even bother to record the island locations of the few finches he collected (and in some cases mislabeled), and these now-famous birds were never specifically mentioned in the
Origin of Species
. Darwin was still a creationist.
2

Through careful analysis of Darwin’s notes and journals, Sulloway dates Darwin’s acceptance of evolution to the second week of March, 1837, after a meeting Darwin had with the eminent ornithologist John Gould, who had been studying Darwin’s Galápagos bird specimens. With access to museum ornithological collections from areas of South America that Darwin had not visited, Gould corrected a number of taxonomic errors Darwin had made (such as labeling two finch species a “Wren” and an “Icterus”), and pointed out to him that although the land birds in the Galápagos were endemic to the islands, they were notably South American in character.

Darwin left the meeting with Gould, Sulloway concludes, convinced “beyond a doubt that transmutation must be responsible for the presence of similar but distinct species on the different islands of the Galápagos group.” In Darwin’s mind, the allegedly immutable
“species barrier” had been shattered. That July, 1837, Darwin began his first notebook on
Transmutation of Species
. By 1844 he was confident enough to write in a letter to his botanist friend and colleague Joseph Hooker, “I was so struck with distribution of Galapagos organisms &c &c, & with the character of the American fossil mammifers &c &c, that I determined to collect blindly every sort of fact which cd bear any way on what are species.” Five years at sea and nine years at home poring through “heaps” of books led Darwin to admit that, for him, “at last gleams of light have come, & I am almost convinced, (quite contrary to opinion I started with) that species are not (it is like confessing a murder) immutable.”
3

 

Like confessing a murder
. Dramatic words for something as seemingly innocuous as a technical problem in biology: the immutability of species. But it doesn’t take a rocket scientist—or an English naturalist—to understand why the theory of the origin of species by means of natural selection would be so controversial: If new species are created naturally, what place, then, for God? No wonder Darwin waited twenty years before publishing his theory.
4

From the time of Plato and Aristotle in ancient Greece to the time of Darwin and his fellow naturalist Alfred Russel Wallace in the nineteenth century, nearly everyone believed that a species retained a fixed and immutable “essence.” A species, in fact, was defined by its very essence—the characteristics that made it like no other species. The theory of evolution by means of natural selection, then, is the theory of how kinds can become other kinds, and that upset not only the scientific cart, but the cultural horse pulling it. The great Harvard evolutionary biologist Ernst Mayr stressed just how radical was Darwin’s theory: “The fixed, essentialistic species was the fortress to be stormed and destroyed; once this had
been accomplished, evolutionary thinking rushed through the breach like a flood through a break in a dike.”
5

The dike, however, was slow to crumble. Darwin’s close friend, the geologist Charles Lyell, withheld his support for a full nine years, and even then hinted at a providential design behind the whole scheme. The astronomer John Herschel called natural selection the “law of higgledy-piggledy.” And Adam Sedgwick, a geologist and Anglican cleric, proclaimed that natural selection was a moral outrage, and penned this ripping harangue to Darwin:

There is a moral or metaphysical part of nature as well as a physical. A man who denies this is deep in the mire of folly. You have ignored this link; and, if I do not mistake your meaning, you have done your best in one or two cases to break it. Were it possible (which thank God it is not) to break it, humanity, in my mind, would suffer a damage that might brutalize it, and sink the human race into a lower grade of degradation than any into which it has fallen since its written records tell us of its history.

 

In a review in
Macmillan’s Magazine
, the political economist and social commentator Henry Fawcett wrote of the great divide surrounding the
Origin of Species:
“No scientific work that has been published within this century has excited so much general curiosity as the treatise of Mr. Darwin. It has for a time divided the scientific world with two great contending sections. A Darwinite and an anti-Darwinite are now the badges of opposed scientific parties.”
6

 

Darwinites and anti-Darwinites
. Although the scientific community is now united in agreement that evolution happened, a century and a half later the cultural world is still divided. According to a 2005 poll by the Pew Research Center, 42 percent of Americans hold strict creationist views that “living things have existed in their
present form since the beginning of time” compared to 48 percent who believe that humans “evolved over time.” Evolution has made news as the fight over teaching evolution has entered the courts and the school boards yet again. To that point, the Pew survey found that 64 percent said they were open to the idea of teaching creationism in addition to evolution in public schools, and more than half of those individuals said they think evolution should be
replaced
by creationism in biology classrooms.
7

The evolution-creationism controversy is a cultural tempest in a scientific teapot—the debate is entirely cultural, even as professional scientists go about their business without giving Intelligent Design a second thought. Consider the geographic and political differences in attitudes about evolution, starting with the fact that evolution is under debate only in America (there are a few small creationist pockets in Australia, New Zealand, and the United Kingdom). And within the states, geography matters: 51 percent of Southerners accept the strict creationist view that humans were created as we are now and only 19 percent believe that we evolved through natural selection, while 59 percent of Northerners accept evolution through natural selection, and only 32 percent are creationists.

Given these demographics of belief, it came as no surprise to either conservatives or liberals when, in August 2005, President George W. Bush seemingly endorsed the teaching of Intelligent Design (ID) in public school science classes. As the story unfolded over the next two weeks, however, it became clear that the creationists, as well as many in the media and pundits on both the right and the left, had greatly exaggerated Bush’s remarks. In an interview at the White House with a group of Texas newspaper reporters, Bush had said that when he was governor of Texas, “I felt like both sides ought to be properly taught.” When a reporter asked for his position as president, Bush equivocated, saying, “I think
that part of education is to expose people to different schools of thought. You’re asking me whether or not people ought to be exposed to different ideas, and the answer is yes.” Well, of course, but Bush answered a different question.

Indeed, Bush’s science adviser, John H. Marburger III, said in a subsequent telephone interview with
The New York Times
that “evolution is the cornerstone of modern biology” and “intelligent design is not a scientific concept.” He added that the president’s comments should be interpreted to mean that ID might be discussed—not as science but as part of the “social context” in science classes, and that it would be “over-interpreting” Bush’s remarks to conclude that the president believes that ID and evolution should be given equal treatment in public school science curricula.
8

Rather than closing the controversy, Marburger’s clarification helped stoke a renewed debate over whether evolution is “only a theory” and how it should be presented in the classroom. Indeed, in late 2005 the Kansas State Board of Education voted 6–4 to revise the state’s science standards to include criticisms of evolution and to redefine science in a way that allows for the introduction of Intelligent Design creationism into the public school science curriculum (by deleting “natural explanations” from the definition of science). Shortly after the Kansas decision, a Bush-appointed conservative judge in Dover, Pennsylvania, ruled against Intelligent Design in a highly publicized court case. In early 2006 an Ohio board of education ruled not to include language that implies the introduction of Intelligent Design theory in science curricula. And there are at least a dozen more hot-spots around the country that will be settled by political debate, democratic vote, or a judge’s decision.

But whatever happens in these politically charged skirmishes, truth in science is not determined by the
vox populi
. It does not matter whether 99 percent or just 1 percent of the public (or politicians)
accepts a scientific theory—the theory stands or falls on the evidence, and there are few theories in science that are more robust than the theory of evolution. It took me a long time to realize this fact, for I began my career as a creationist. Saying this today almost feels like confessing a murder.

 

Like confessing a murder
. That is precisely how I felt when I realized that my creationist beliefs were wrong and that evolution actually happened. I became a creationist shortly after I became a born-again evangelical Christian in high school in 1971 and argued the creationist case through graduate school in 1977.
9
The evangelical movement was gathering momentum in the 1970s, and one of the central dogmas I took from it was that the biblical story of creation was to be taken literally; ergo, the theory of evolution had to be wrong.

Knowing next to nothing about evolution other than what I gleaned from reading creationist literature, I absorbed the arguments against the theory and practiced them on my undergraduate science and philosophy teachers. At Glendale College, which I attended for the first two years for general education requirements, I honed my debating skills as my creationist arguments were met with firm evolutionist counterarguments. At Pepperdine University, a Church of Christ institution where I finished my undergraduate degree, evolution was a nonentity as I witnessed for Christ and studied the theological underpinnings of the Christian faith. When I arrived at Pepperdine, in fact, I considered theology as a profession, but when I discovered that a doctorate required proficiency in Hebrew, Greek, Latin, and Aramaic, and knowing that foreign languages were not my strong suit (I struggled through two years of high school Spanish), I switched to psychology and mastered one of the languages of science: statistics. By the time I matriculated at
California State University at Fullerton for graduate training in experimental psychology, I was ensconced in the methods of science.

In science, the solutions to problems are based on established parameters to determine whether a hypothesis is probably right or definitely wrong. Statistics allow researchers to identify an event as likely to happen 99.99 percent of the time (rejecting the null hypothesis) or as insignificant. Instead of the rhetoric and disputation of theology, there are the logic and probabilities of science. What a difference this shift in thinking makes. In graduate school, I took a bevy of courses in research methods and statistics, and for recreation I signed up for a Tuesday evening course in evolution, just to see firsthand what had us creationists up in arms. The course was taught by an eccentrically charismatic biologist named Bayard Brattstrom, who from 7 to 10
P.M.
regaled his class with breathtaking discoveries from the science of evolutionary biology, and who from 10
P.M.
to closing time at the 301 Club just down the street held forth on science and religion, Darwin and Genesis, and all manner of related topics, accompanied by appropriate libations.

The scales fell from my eyes! It turned out that the creationist literature I was reading presented a Darwinian cardboard cutout that a child could knock down. (For example, if humans come from apes, why are apes still around? Of course, we didn’t evolve from modern apes; apes and humans evolved from a common ancestor who lived nearly seven million years ago.) What I discovered was that the preponderance of evidence from numerous converging lines of scientific inquiry—geology, paleontology, zoology, botany, comparative anatomy, molecular biology, population genetics, biogeography, embryology, and others—all independently converge to the same conclusion: Evolution happened.
Why Darwin Matters
is about how we know evolution happened, in the context of the challenges to evolution mounted by twenty-first-century creationists and Intelligent Design theorists.

 

Why does evolution matter?
The influence of the theory of evolution on the general culture is so pervasive it can be summed up in a single observation:
We live in the age of Darwin
. Arguably the most culturally jarring theory in history, the theory of natural selection gave rise to the Darwinian revolution that changed both science and culture in ways immeasurable. On the scientific level, the static creationist model of species as fixed types was replaced with a fluid evolutionary model of species as ever-changing entities. The repercussions of this finding were, and are, astounding. The theory of top-down intelligent design of all life by or through a supernatural power was replaced with the theory of bottom-up natural design through natural forces. The anthropocentric view of humans as special creations placed by a divine hand above all others was replaced with the view of humans as just another animal species. The view of life and the cosmos as having direction and purpose from above was replaced with the view of the world as the product of the necessitating laws of nature and the contingent events of history. The view that human nature is infinitely malleable and primarily good was replaced with a view of human nature in which we are finitely restricted by our genes and are both good and evil.
10

Darwin matters not only because his theory changed the world and reconfigured our position in nature, but because he launched a new and profound understanding of biology and science that has served future generations. Of the three intellectual giants of that epoch—Darwin, Marx, and Freud—only Darwin is still relevant for the simple reason that his theory was right, and the scientific evidence continues to support and refine it. In the memorable observation by geneticist Theodosius Dobzhansky, “Nothing in biology makes sense except in the light of evolution.”
11

THE FACTS OF EVOLUTION
 

 

The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth. As buds give rise by growth to fresh buds, and these, if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications.

—Charles Darwin,
On the Origin of Species
, 1859

 

The theory of evolution has been under attack since Charles Darwin first published
On the Origin of Species
in 1859. From the start, its critics have seized on the
theory
of evolution to try to undermine its facts. But all great works of science are written in support of some particular view. In 1861, shortly after he published his new theory, Darwin wrote a letter to his colleague, Henry Fawcett, who had just attended a special meeting of the British Association for the Advancement of Science during which Darwin’s book was debated. One of the naturalists had argued that
On the Origin of Species
was too theoretical, that Darwin should have just “put his facts before us and let them rest.” In response, Darwin reflected that science, to be of any service, required more than list-making; it needed larger ideas that could make sense of piles of data.
Otherwise, Darwin said, a geologist “might as well go into a gravelpit and count the pebbles and describe the colours.”
1
Data without generalizations are useless; facts without explanatory principles are meaningless. A “theory” is not just someone’s opinion or a wild guess made by some scientist. A theory is a well-supported and well-tested generalization that explains a set of observations. Science without theory is useless.

The process of science is fueled by what I call
Darwin’s Dictum
, defined by Darwin himself in his letter to Fawcett: “all observation must be for or against some view if it is to be of any service.”

Darwin’s casual comment nearly a hundred and fifty years ago encapsulates a serious debate about the relative roles of data and theory, or observations and conclusions, in science.
2
In a science like evolution, in which inferences about the past must be made from scant data in the present, this debate has been exploded to encompass a fight between religion and science.

Prediction and Observation
 

Most essentially,
evolution is a historical science
. Darwin valued above all else prediction and verification by subsequent observation. In an act of brilliant historical science, for example, Darwin correctly developed a theory of coral reef evolution years before he developed his theory of biological evolution. He had never seen a coral reef, but during the
Beagle
’s famous voyage to the Galápagos, he had studied the types of coral reefs Charles Lyell described in
Principles of Geology
. Darwin reasoned that the different examples of coral reefs did not represent different types, each of which needed a different causal explanation; rather, the different
examples represented different stages of development of coral reefs, for which only a single cause was needed. Darwin considered this a triumph of theory in driving scientific investigation: Theoretical prediction was followed by observational verification, whereby “I had therefore only to verify and extend my views by a careful examination of coral reefs.”
3
In this case, the theory came first, then the data.

The publication of the
Origin of Species
triggered a roaring debate about the relative roles of data and theory in science. Darwin’s “bulldog” defender, Thomas Henry Huxley, erupted in a paroxysm against those who pontificated on science but had never practiced it themselves: “There cannot be a doubt that the method of inquiry which Mr. Darwin has adopted is not only rigorously in accord with the canons of scientific logic, but that it is the only adequate method,” Huxley wrote. Those “critics exclusively trained in classics or in mathematics, who have never determined a scientific fact in their lives by induction from experiment or observation, prate learnedly about Mr. Darwin’s method,” he bellowed, “which is not inductive enough, not Baconian enough, forsooth for them.”
4

Darwin insisted that theory comes to and from the facts, not from political or philosophical beliefs, whether from God or the godfather of scientific empiricism. It is a point he voiced succinctly in his cautions to a young scientist. The facts speak for themselves, he said, advising “the advantage, at present, of being very sparing in introducing theory in your papers; let theory guide your observations, but till your reputation is well established, be sparing of publishing theory. It makes persons doubt your observations.”
5
Once Darwin’s reputation was well established, he published his book that so well demonstrated the power of theory. As he noted in his autobiography, “some of my critics have said, ‘Oh, he is a good
observer, but has no power of reasoning.’ I do not think that this can be true, for the
Origin of Species
is one long argument from the beginning to the end, and it has convinced not a few able men.”
6

Against Some View
 

Darwin’s “one long argument” was with the theologian William Paley and the theory Paley posited in his 1802 book,
Natural Theology: or, Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature
. Sound eerily familiar? The scholarly agenda of this first brand of Intelligent Design was to correlate the works of God (nature) with the words of God (the Bible). Natural theology kicked off with John Ray’s 1691
Wisdom of God Manifested in Works of the Creation
, which itself was inspired by Psalms 19:11: “The Heavens declare the Glory of the Lord and the Firmament sheweth his handy work.” John Ray, in what still stands as a playbook for creationism, explains the analogy between human and divine creations: If a “curious Edifice or machine” leads us to “infer the being and operation of some intelligent Architect or Engineer,” shouldn’t the same be said of “the Works of nature, that Grandeur and magnificence, that excellent contrivance for Beauty, Order, use, &c. which is observable in them, wherein they do as much transcend the Efforts of human Art and infinite Power and Wisdom exceeds finite” to make us “infer the existence and efficiency of an Omnipotent and All-wise Creator?”
7

Paley advanced Ray’s work through the accumulated knowledge of a century of scientific exploration. The opening passage of Paley’s
Natural Theology
has become annealed into our culture as the winningly accessible and thus appealing “watchmaker” argument:

In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there. I might possibly answer, that, for any thing I knew to the contrary, it had lain there forever. But suppose I had found a watch upon the ground, and it should be enquired how the watch happened to be in that place. The inference, we think, is inevitable; that the watch must have had a maker; that there must have existed, at some time and in some place or other, an artificer or artificers who formed it for the purpose which we find it actually to answer; who comprehended its construction, and designed its use.

 

But life is far more complex than a watch—so the design inference is even stronger!

There cannot be design without a designer; contrivance without a contriver. . . . The marks of design are too strong to be got over. Design must have had a designer. That designer must have been a person. That person is GOD.
8

 

For longer than we have had the theory of evolution, we have had theologians arguing for Intelligent Design.

From Natural Theology to Natural Selection
 

After abandoning medical studies at Edinburgh University, Charles Darwin entered the University of Cambridge to study theology with the goal of becoming a Church of England cleric. Natural theology provided him with a socially acceptable excuse to study natural history, his true passion. It also educated Darwin in the arguments on design popularized by Paley and others.
9
His intimacy with their ideas was respectful, not combative. For example, in November 1859, the same month that the
Origin of Species
was
published, Darwin wrote his friend John Lubbock, “I do not think I hardly ever admired a book more than Paley’s ‘Natural Theology.’ I could almost formerly have said it by heart.”
10
Both Paley and Darwin addressed a problem in nature: the origin of the design of life. Paley’s answer was to posit a top-down designer—God. Darwin’s answer was to posit a bottom-up designer—natural selection. Natural theologians took this to mean that evolution was an attack on God, without giving much thought to what evolution is.

Ever since Darwin, much has been written about what, exactly, evolution is. Ernst Mayr, arguably the greatest evolutionary theorist since Darwin, offers a subtly technical definition: “evolution is change in the adaptation and in the diversity of populations of organisms.” He notes that evolution has a dual nature, a “ ‘vertical’ phenomenon of adaptive change,” which describes how a species responds to its environment over time, and a “ ‘horizontal’ phenomenon of populations, incipient species, and new species,” which describes adaptations that break through the genetic divide.
11
And I’ll never forget Mayr’s definition of a species, because I had to memorize it in my first course on evolutionary biology: “A species is a group of actually or potentially interbreeding natural populations reproductively isolated from other such populations.”
12

Mayr outlines five general tenets of evolutionary theory that have been discovered in the years since Darwin published his revolutionary book:

 

1.
Evolution:
Organisms change through time. Both the fossil record of life’s history and nature today document and reveal this change.

 

2.
Descent with modification:
Evolution proceeds through the branching of common descent. As every parent and child knows, offspring are similar to but not exact replicas of their
parents, producing the necessary variation that allows adaptation to the ever-changing environment.

 

3.
Gradualism:
All this change is slow, steady, and stately. Given enough time, small changes within a species can accumulate into large changes that create new species; that is, macroevolution is the cumulative effect of microevolution.

 

4.
Multiplication:
Evolution does not just produce new species; it produces an increasing number of new species.

 

And, of course,

 

5.
Natural selection:
Evolutionary change is not haphazard and random; it follows a selective process. Codiscovered by Darwin and the naturalist Alfred Russel Wallace, natural selection operates under five rules:

 

A. Populations tend to increase indefinitely in a geometric ratio: 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024 . . .

B. In a natural environment, however, population numbers must stabilize at a certain level. The population cannot increase to infinity—the earth is just not big enough.

C. Therefore, there must be a “struggle for existence.” Not all of the organisms produced can survive.

D. There is variation in every species.

E. Therefore, in the struggle for existence, those individuals with variations that are better adapted to the environment leave behind more offspring than individuals that are less well adapted. This is known as
differential reproductive success
.

As Darwin said, “as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either
one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life.”
13

The process of natural selection, when carried out over countless generations, gradually leads varieties of species to develop into new species. Darwin explained:

It may be said that natural selection is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, whenever and wherever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life. We see nothing of these slow changes in progress, until the hand of time has marked the long lapses of ages, and then so imperfect is our view into long past geological ages, that we only see that the forms of life are now different from what they formerly were.
14

 

The time frame is long and the changes from generation to generation are subtle. This may be one of the most important and difficult points to grasp about the theory of evolution. It is tempting to see species as they exist today as a living monument to evolution, to condense evolution into the incorrect but provocative shorthand that humans descended from chimpanzees—a shorthand that undercuts the facts of evolution.

Natural selection is the process of organisms struggling to survive and reproduce, with the result of propagating their genes into the next generation. As such, it operates primarily at the local level. The Oxford evolutionary biologist Richard Dawkins elegantly described the process as “random mutation plus non-random cumulative selection,”
15
emphasizing the non-random. Evolution is not the equivalent of a warehouse full of parts randomly assorting themselves into a jumbo jet, as the creationists like to argue. If evolution were truly random there would be no biological jumbo jets.
Genetic mutations and the mixing of parental genes in offspring may be random, but the selection of genes through the survival of their hosts is anything but random. Out of this process of self-organized directional selection emerge complexity and diversity.

Natural selection is a description of a process, not a force. No one is “selecting” organisms for survival or extinction, in the benign sense of dog breeders selecting for desirable traits in show breeds, or in the malignant sense of Nazis selecting prisoners at Auschwitz-Birkenau. Natural selection, and thus evolution, is unconscious and nonprescient—it cannot look forward to anticipate what changes are going to be needed for survival. The evolutionary watchmaker is blind, says Dawkins,
pace
Paley.

By way of example, once when my young daughter asked how evolution works, I used the polar bear as an example of a “transitional species” between land mammals and marine mammals, because although they are land mammals they spend so much time in the water that they have acquired many adaptations to an aquatic life. But this is not correct. It implies that polar bears are
on their way
(in transition) to becoming marine mammals. They aren’t. Polar bears are not “becoming” anything. Polar bears are well adapted for their lifestyle. That’s all. If global warming continues, perhaps polar bears will adapt to a full-time aquatic existence, or perhaps they will move south and become smaller brown bears, or perhaps they will go extinct. Who knows? No one.

Where Are All the Fossils?
 

Evolution is a historical science, and historical data—fossils—are often the evidence most cited for and against it. In the creationist textbook,
Of Pandas and People
—one of the bones of contention in
the 2005 Intelligent Design trial of
Kitzmiller et al. v. Dover Area School District
, in Dover, Pennsylvania—the authors state: “Design theories suggest that various forms of life began with their distinctive features already intact: fish with fins and scales, birds with feathers and wings, mammals with fur and mammary glands. . . . Might not gaps exist . . . not because large numbers of transitional forms mysteriously failed to fossilize, but because they never existed?”
16

Darwin himself commented on this lack of transitional fossils, asking, “Why then is not every geological formation and every stratum full of such intermediate links?” In contemplating the answer, he turned to the data and noted that “geology assuredly does not reveal any such finely graduated organic chain; and this, perhaps, is the gravest objection which can be urged against my theory.”
17
So where
are
all the fossils?

One answer to Darwin’s dilemma is the exceptionally low probability of any dead animal’s escaping the jaws and stomachs of predators, scavengers, and detritus feeders, reaching the stage of fossilization, and then somehow finding its way back to the surface through geological forces and unpredictable events to be discovered millions of years later by the handful of paleontologists looking for its traces. Given this reality, it is remarkable that we have as many fossils as we do.

There is another explanation for the missing fossils. Ernst Mayr outlines the most common way that a species gives rise to a new species: when a small group (the “founder” population) breaks away and becomes geographically—and thus reproductively—isolated from its ancestral group. As long as it remains small and detached, the founder group can experience fairly rapid genetic changes, especially relative to large populations, which tend to sustain their genetic homogeneity through diverse interbreeding.
Mayr’s theory, called
allopatric speciation
, helps to explain why so few fossils would exist for these animals.

The evolutionary theorists Niles Eldredge and Stephen Jay Gould took Mayr’s observations about how new species emerge and applied them to the fossil record, finding that gaps in the fossil record are not missing evidence of gradual changes; they are extant evidence of punctuated changes. They called this theory
punctuated equilibrium
.
18
Species are so static and enduring that they leave plenty of fossils in the strata while they are in their stable state (equilibrium). The change from one species to another, however, happens relatively quickly on a geological time scale, and in these smaller, geographically isolated population groups (punctuated). In fact, species change happens so rapidly that few “transitional” carcasses create fossils to record the change. Eldredge and Gould conclude that “breaks in the fossil record are real; they express the way in which evolution occurs, not the fragments of an imperfect record.”
19
Of course, the small group will also be reproducing, following the geometric increases that are observed in all species, and will eventually form a relatively large population of individuals that retain their phenotype for a considerable time—and leave behind many well-preserved fossils. Millions of years later this process results in a fossil record that records mostly the equilibrium. The punctuation is in the blanks.