Evolution? 'It's not only a theory. It is a historical
fact, evident and provable.' (2 of 2)
(Top Posts - Science - 021609)

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Charles Darwin 
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David Attenborough on Darwin
(Sir David Attenborough discusses
how Darwin helped shape his career

Sir David Attenborough's View
on Science and Religion

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February 5, 2009 

Evolution: The Never-Ending Story 
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Why evolution is for real 

You may have noticed that some people reject evolution, 
a natural-science explanation for the breadth of living 
creatures, in favor of creationism, a religious-supernatural 
belief that God created all the living creatures. 

What evidence supports evolution through natural selection? 

1. Evolution is written in the leftovers. Why do ostriches 
have wings if they cannot fly? A gifted designer would have 
jettisoned the wings, but evolution's "use-it-if-you-didn't- 
lose-it" approach has instead repurposed them to be used 
in threat displays and balancing the bird as it sprints. 

2. Evolution is written in development. During their 
early stages, animals often mimic the embryonic stages 
of common ancestors. In a dolphin fetus, buds for rear 
limbs develop and then disappear, showing that dolphins 
(like whales) descended from four-legged animals. (Illus- 
trating the previous point, the bones in the dolphin's front 
flippers reveal their evolutionary origin as front legs.) 

The study of evolution through development, called "evo- 
devo," reflects the fact that the genetic controls on devel- 
opment resist change. Thus evolution, instead of deleting 
structures, may change the purpose and/or alter the struc0 
ture in a way that promotes survival and reproduction. 

3. Evolution is inscribed in the rocks. Younger rocks 
overlie older ones, so fossils of younger descendants 
always appear above fossils of older ancestors, and liv- 
ing creatures resemble younger fossils more than older 
ones. While Darwin had little fossil evidence and relied 
largely on studies of living organisms to examine change 
through time, in the 150 years since "The Origin of Spe- 
cies," millions of fossil discoveries have proven him cor- 

4. Evolution is written in the genes. As organisms 
divide into new species, they retain almost all of their 
genes, even as occasional changes help establish a new 
species. Because humans and chimps had a common 
ancestor about 7 million years ago, our genes are about 
98.5 percent alike. 

Our last common ancestor with the fungi appeared more 
than 500 million years ago, yet about half of our genes 
are also found in fungi. 


Because once nature solves a problem, it hoards the 
genes for that solution. Although our ancestors devel- 
oped heads and limbs, they still needed -- and retained -- 
genes to solve many of the same basic biochemical prob- 
lems that confront fungi. 

Convergent evolution 

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Old World euphorbs 
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The Old World euphorbs (above) and the New World 
cacti (below) evolved water-retentive flesh and spines to 
cope with a desert environment. The groups may look 
alike, but genetically they are not closely related. 

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New World cacti 
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5. The march of the look-alikes. The deserts of the 
new world contain spiny cacti, while those of the old 
world contain euphorbs. 

Both groups comprise tough, leafless plants with low 
surface area and a succulent tissue that holds water, 
but cacti contain a clear fluid, and euphorbs contain 
a milky, bitter fluid. 

This is convergent evolution: Similar environmental 
forces have shaped ancestors that lacked a close gen- 
etic relationship into modern organisms with a strong 
external resemblance. 

6. Island idyll. Barren volcanic islands that rise from 
the ocean offer empty ecological niches to the first 
arriving organisms, which can then diversify through 
"adaptive radiation" into numerous, closely related 

In the Galapagos Islands, which played a key role in 
spurring the theory of evolution, Darwin saw that one 
species of finch had arrived and then branched out to 
form a group of related species which could take 
advantage of the local seeds, nuts and fruit. 

"Darwin's" finches are unique to the Galapagos, be- 
cause they evolved after they reached the islands. 

7. Island influence. Remote, oceanic islands are 
often missing big groups of organisms; Hawaii, for 
example, has abundant native plants, insects and 
birds but no native mammals, freshwater fish or rep- 


Because plants, insects and birds could survive long 
journeys across or above the ocean, the other groups 
could not. 

Making book on evolution 

We condensed the above examples from "Why Evolu- 
tion Is True," a new book that explains exactly what 
its title claims ... 

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Why Evolution Is True 
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"Its ignorant opponents like to say that the process of 
evolution by natural selection is 'only a theory'. (That's 
how they prove their ignorance.) Jerry Coyne shows 
with elegance and rigor that it is a hypothesis that meets 
and withstands all tests, and strengthens itself as a theory 
thereby. One could almost say that it had the distinct 
merit of being true. 
-Christopher Hitchens, author of God is not Great 

"For anyone who wishes a clear, well-written explana- 
tion of evolution by one of the foremost scientists work- 
ing on the subject, Why Evolution is True should be 
your choice." 
-Edward O. Wilson, author of Consilience, On Human 
Nature, and Sociobiology 

"Evolution is the foundation of modern biology, and in 
Why Evolution Is True, Jerry Coyne masterfully ex- 
plains why. From the vast trove of evidence of evolu- 
tion scientists have gathered, Coyne has carefully sel- 
ected some of the most striking examples and explained 
them with equal parts grace and authority." 
-Carl Zimmer, author of Microcosm: E. coli and the 
New Science of Life 

"Jerry Coyne has long been one of the world's most 
skillful defenders of evolutionary science in the face of 
religious obscurantism. In Why Evolution is True, he 
has produced an indispensable book: the single, acces- 
sible volume that makes the case for evolution. 

But Coyne has delivered much more than the latest vol- 
ley in our "culture war"; he has given us an utterly fascin- 
ating, lucid, and beautifully written account of our place 
in the natural world. If you want to better understand 
your kinship with the rest of life, this book is the place 
to start." 
-Sam Harris, author of The End of Faith and Letter 
to a Christian Nation and founder of the Reason Project 

"I once wrote that anybody who didn't believe in evolu- 
tion must be stupid, insane or ignorant, and I was then 
careful to add that ignorance is no crime. I should now 
update my statement. Anybody who doesn't believe in 
evolution is stupid, insane, or hasn't read Jerry Coyne. 
I defy any reasonable person to read this marvellous 
book and still take seriously the 'breathtaking inanity' 
that is intelligent design 'theory' or its country cousin, 
young earth creationism." 
-Richard Dawkins, author of The God Delusion and 
many other books 

"Why Evolution is True is the book I was hoping 
would be written someday: an engaging and accessible 
account of one of the most important ideas ever con- 
ceived by mankind. The book is a stunning achievement, 
written by one of the world's leading evolutionary biolo- 

Coyne has produced a classic -- whether you are an 
expert or novice in science, a friend or foe of evolu- 
tionary biology, reading Why Evolution is True is 
bound to be an enlightening experience. 
- Neil Shubin 

"Scientists don't use the word 'true' lightly, but in this 
lively and engrossing book, Jerry Coyne shows why 
biologists are happy to use it when it comes to evolution. 

Evolution is 'true' not because the experts say it is, nor 
because some world view demands it, but because the 
evidence overwhelmingly supports it. There are many 
superb books on evolution, but this one is superb in a 
new way -- it explains out the latest evidence for evolu- 
tion lucidly, thoroughly, and with devastating effective- 
-Steven Pinker, Harvard University, and author of The 
Stuff of Thought: Language as a Window into Human 


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Praise Darwin 
Evolve Beyond Belief 
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Secularist group posts 'Praise Darwin' billboards 
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Living World / Evolution 

Discover Interview

DNA Agrees With All the Other Science: Darwin
Was Right 

Molecular biologist Sean Carroll shows how 
evolution happens, one snippet of DNA at a time 

by Pamela Weintraub 
published online February 19, 2009 
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Click here to see DISCOVER's special package 
on Darwin in honor of his 200th birthday and the 
150th anniversary of The Origin of Species. 

When Sean Carroll was a graduate student at Tufts 
School of Medicine in Boston, he found himself 
seduced by spectacular new studies of the humble 
fruit fly. That work, which eventually won a Nobel 
Prize for its principals, showed that modifying a 
single gene during a fly's embryonic development 
could transform the insect's body plan: 

     Instead of becoming an antenna, a body 
     extension could develop into a leg. 

Carroll continued to study these genes and, some 
years later, found that they were not restricted to 
fruit flies; they turned out to be part of a master 
tool kit that sculpts the body structures of all ani- 
mals, ranging from humans to nematode worms. 

The discovery of this small set of universal body- 
building genes gave Carroll and others a fresh way 
to explore the inner workings of evolution. 

By observing how the genes changed during the 
course of embryonic development, scientists 
could track the emergence of a novel physical 
trait, the first step toward the creation of a new 
species. For the first time, researchers had direct 
access to the machinery of evolution and could 
actually watch it in the act. 

A new science, known as evolutionary develop- 
mental biology, or evo devo, was born. 

One of the great triumphs of modern evolutionary 
science, evo devo addresses many of the key 
questions that were unanswerable when Charles 
Darwin published On the Origin of Species in 
1859, and Carroll has become a leader in this 
nascent field. 


It has been 150 years since Charles Darwin pro- 
posed his theory of evolution in On the Origin 
of Species, yet in some ways the concept of 
evolution seems more controversial than ever 
today. Why do you think that is? 

It is a cultural issue, not a scientific one. 

On the science side our confidence grows yearly 
because we see independent lines of evidence 

What we've learned from the fossil record is 
confirmed by the DNA record and confirmed 
again by embryology. 

But people have been raised to disbelieve evo- 
lution and to hold other ideas more precious 
than this knowledge. 

At the same time, we routinely rely on DNA to 
convict and exonerate criminals. We rely on 
DNA science for things like paternity. We 
rely on DNA science in the clinic to weigh 
our disease risks or maybe even to look at 
prognoses for things like cancer. 

DNA science surrounds us, but in this one 
realm we seem unwilling to accept its facts. 

Juries are willing to put people to death based 
upon the variations in DNA, but they're not 
willing to understand the mechanism that cre- 
ates that variation and shapes what makes 
humans different from other things. 

It's a blindness. I think this is a phase that 
we'll eventually get through. 


In your new book, Remarkable Creatures, you 
relate how Darwin arrived at his theory of evo- 
lution. Can you connect the dots? 

As a college student Darwin collected beetles. 
He was looking for more opportunities to col- 
lect when there came this opportunity to be a 
naturalist on the British ship the HMS Beagle. 

It was seductive. He could go to faraway places- 
visit the tropics, places of incredible richness of 
life relative to cold, damp, gray England. 


Two stops in this five-year journey were pivotal. 

The first came early in the voyage when he ar- 
rived on the coast of Argentina and unearthed 
fossils of many species, including some un- 
known to science-for instance, fossils of giant, 
extinct sloths that had been enormous com- 
pared with the living sloths he saw in the South 
American forests. So it planted the seed in his 
mind that life had changed. 

Then Darwin got to the Galápagos Islands. He 
went from island to island collecting birds-mock- 
ingbirds and then finches-and realized that even 
when the birds appeared to be similar, on each 
island they were slightly different. After he left 
the Galápagos, on his way home to England, 
the lightbulb went on. 

He realized that if these birds lived on such sim- 
ilar islands but were slightly different from one 
another, there could be just one explanation: 
They had started out as a single species, but 
over time and with separation they had drifted 
apart and changed. 

This insight was widely regarded as heresy, but 

The prevailing idea was called special creation: 
that every species was created by a supernatural 
power and put in place on the earth for a speci- 
fied role in a specified time by a completely 
mysterious process. It wasn't open to natural 

Instead, Darwin said no, species are changeable, 
and the introduction of new species is a com- 
pletely natural process that follows natural laws 
just the way physics does. 

A fundamental aspect of human existence has 
been to ask how we got here. Evolution is the 
big answer to that big question. 

Obviously there are alternative answers that 
have prevailed for a very long time, but evo- 
lution has replaced a supernatural explanation 
of human origins with a naturalistic one. 

Beneath diverse exteriors, all animals share a 
set of body-building genes. If I had five min- 
utes with Darwin, I would start right there. It 
would blow his mind. 


What piqued your own interest in evolution? 

As a kid, I was fascinated by zebras and gir- 
affes and leopards. I kept snakes, and I loved 
their color patterns. As I got older I asked 
deeper questions-mainly, how are pattern and 
form generated? 

One of the most spectacular pageants on earth 
involves a complex creature developing from 
a single fertilized egg. Anyone who's a parent 
is still amazed that it works. 

When I was a graduate student, we could watch 
this happen, but we didn't understand the me- 
chanics. What was going on inside that would 
put limbs in the right place, put eyes in the right 
place, carve the circulatory system and the back- 

It was an irresistible mystery, made even more 
irresistible with the realization that what makes 
a snake different from a lizard, what makes a 
zebra different from a giraffe, are changes within 
that developmental process. 

Understanding development was a passport to 
two fundamental questions: How does a com- 
plex creature form from an egg, and how have 
different types of creatures evolved? 

These seem like two very disparate ideas: the 
embryonic development of a single specimen 
and the evolution of a whole species. How did 
they get connected? 

At first paleontologists were studying evolution 
on vast timescales through fossils. Then geneti- 
cists came on the scene, and they were studying 
small-scale differences within species based on 
mutations in genes. 

What has been called the modern synthesis of 
the two fields emerged in the 1940s with the 
idea that the sorts of genetic differences you 
could observe in populations, right out your 
window, when compounded and extrapolated 
over vast periods of time, could account for 
the large-scale changes we see in the fossil 

So the modern synthesis was a harmonization 
of those two scales. 

But the modern synthesis did not explain evo- 
ution in full. It was still just a theory. Where 
was the empirical evidence? 

Darwin's theory of descent was a black box. 
You could not see exactly what kinds of changes 
were taking place to account for the differences 
in forms. But the study of embryonic develop- 
ment has allowed us to peer into the machinery 
of making these creatures. 

We can study their DNA text and their develop- 
ing embryos and ask, where do the differences 

That gave us the empirical data for the theory. 

You can't necessarily see the change happening 
in the adult, but you can see that if you change 
that nucleic acid base right there in that gene, at 
that particular point in embryonic development, 
that animal is darker. 

If you change those three bases over there, that 
limb is longer. 

This is the fundamental basis of evolution: 
changes in DNA. 


You've said evolution is like compounding inter- 
est. How so? 

Just like a good money market account, evolu- 
tion works through incremental change. If vari- 
ants within a species provide an advantage, no 
matter how slight, then that form, that capacity, 
will be favored. 

If evolving spots on wings makes you more 
attractive to mates or more evasive to preda- 
tors, those patterns will dominate. Those vari- 
eties will have more offspring. Added up over 
centuries, millennia, and longer periods of time, 
natural selection-the competition that takes 
place in nature between variant forms-is power- 
ful enough to forge all the changes that we've 
seen on the face of the earth. 

It is hard for most people to wrap their brains 
around such vast stretches of time. 

A century ago, Teddy Roosevelt was president 
and cars were barely in use. 

That seems like an unimaginable amount of time 
ago, but biologically and geologically speaking, 
it was a split second. A million years is just a 
fraction of the time that upright hominids have 
had to evolve. 

It takes time for sea levels to rise, for rivers to 
cut their course. As temperatures change, as 
rain forests grow up or deserts emerge, the 
creatures that live in these regions are adapting 
and changing too. 

You call the combination of evolution and embry- 
onic development evo devo. 

What is that, exactly? 

It is just shorthand for "evolutionary develop- 
mental biology," a mini-syllabic description of 
this field that's concerned with the evolution 
of development. 

It's related probably to Devo, the new-wave 
band of the early 1980s-those were the guys 
who played with dog dishes on their heads. 
Before then you could describe evolution as 
change over time, but we did not have any 
grip on that process until the 1980s. 


You saw the fruit fly as a window into evolu- 
tion and development. How did you make the 

It was not an obvious call, because the expec- 
tation was that fruit flies didn't have anything 
to do with the development of furry creatures. 

... it became clear from our research and 
others' that these body-building genes were 
not restricted to fruit flies; they were shared 
throughout the animal kingdom. It was a real 

All of a sudden we could do deep experiments 
at the most fundamental level to understand 
how form actually evolved. 

So scientists were seeing the same master 
genes at work in many different species? 

Yes. One shocking discovery was the relation- 
ship between our eyes and bug eyes. You 
wouldn't think they had anything in common, 

Bug eyes, with 800 facets, work by different 
optical principles than human eyes. For almost 
a century and a half, biologists thought that 
they had evolved independently, from scratch, 
and that eyes had been invented many times 
in the animal kingdom by completely different 
means-different recipes in different groups of 

We have now discovered that these eyes are 
formed by what is recognizable as the same 
gene, even though those animals have been 
evolving separately for 500 million years. 

When we took the mouse version of this 
gene-the same gene we find in the human- 
and put it in the fly and tweaked it, we in- 
duced fly eye tissue. 

Our team showed that the same common 
gene is critical to building limbs in humans 
and fruit flies. It turns out that this gene is 
critical to building virtually everything that 
sticks out of the body: antennae, legs, horns, 

These kinds of experiments shattered our 
preconceptions and forced people to think 

Beneath these extremely diverse exteriors 
was a deeply shared common genetic tool 

If I had five minutes with Charles Darwin, 
I'd start right there. It would blow his mind. 


Can we apply these discoveries to the human 

We now know that the human genome and 
the chimp genome differ by only about 1 per- 
cent. Yet our bodies and brains are so differ- 
ent. How can we be so different from other 
primates if our genes are so much the same? 

How did we get the dexterity in our hands? 

How do we walk upright? How are we able 
to hold this conversation? How did we get 
big brains? 

Once you identify the meaningful functional 
changes that have taken place between us 
and chimps, you realize that pretty big dif- 
ferences in anatomy and behavior can result 
from a small degree of genetic divergence. 

Evo devo has given us the tools to explore 
this mystery: The same genes are being regu- 
lated and then used in a different way. Some- 
thing is happening a little earlier or in another 
place or is staying on a little bit longer. These 
are the time and space dimensions of devel- 
opment. It's like choreography. You've got 
the same dancers, but the ballet is different 
based on different cues. 

In your book Endless Forms Most Beautiful, 
you refer to the Cambrian explosion, a time 
when a vast number of new life-forms ap- 
peared at nearly the same time. Evolutionary 
skeptics often point to this kind of abrupt 
shift-doesn't such rapid change contradict 
your description of a single master tool kit 
and slow evolution over long stretches of 

Prior to about 543 million years ago, you 
saw things like jellyfish and spongelike 
creatures, but you didn't see bilateral crea- 
tures: worms and trilobites and things like 

Then in the Cambrian explosion, large and 
complex animal forms erupted. 

These forms in the Cambrian represent a lot 
of the major divisions of the animal kingdom 
we see today. 

The Cambrian explosion looks abrupt in the 
fossil record, but the surprising message 
from evo devo is that all the genes for build- 
ing big, complex animal bodies long predated 
the appearance of those bodies. 

Most of what was needed to create this incred- 
ible complexity already existed. The genes 
were expressed prior to the Cambrian in those 
more modest, soft-bodied creatures, but they 
had fewer jobs to do. 

Complexity evolved by expanding the uses 
of these genes rather than inventing lots more 
of them. 

It makes you wonder what kind of potential 
is just waiting to burst out today. 

Dinosaurs were the dominant vertebrates right 
up until the end of the Cretaceous. 

Mammals existed, but they were smaller, carv- 
ing lifestyles out of the dinosaurs' way. 

Take out the dinosaurs and in 10 or 15 million 
years mammals had evolved into all sorts of 
large forms and dominated terrestrial ecosys- 

When genetic potential met ecological oppor- 
tunity, you got elephants and bison and giraffes. 

Think about ecology as corking the bottle; take 
the cork out and things explode. 


You've presented an avalanche of irrefutable 
evidence, yet opponents of evolution seem to 
refute it all. How do you respond? 

You can hear me almost chuckling, because 
it's not reasonable, it's not rational, and as the 
years click by, it's ever more preposterous, 
but people still stick to their guns. 

Is there anything we can do to help persuade 
the skeptical public to accept the evolutionary 
way of looking at life? 

Seriously, teach evolution as a core theme in 
science from the early grades. 

The universe changes, the earth changes, and 
life changes with the evolving earth. 

Where do you see evolutionary biology going 

Today we're in a second golden age. 

We're not collecting the menagerie of critters 
that Darwin did or hauling them back to a 
museum. Instead, we're collecting the genetic 
recipes of creatures across the planet and 
trying to figure out how they came to be. 

We're looking right into the text of evolution, 
and even into the text of extinct creatures like 
woolly mammoths and Neanderthals, and 
we're asking what made them similar to or 
different from elephants or from us. 

A third golden age will come when we under- 
stand life beyond earth. How many times has 
life evolved, and how many origins have there 
been? Has life movedfrom planet to planet? Is 
the chemistry of extraterrestrial life different 
from that of life on earth? 

This will be difficult work, but we have to look 
ahead. Finding life elsewhere in the universe 
would bring a scientific revolution as big as 
any we've ever had. 

Click here to see DISCOVER's special package 
on Darwin in honor of his 200th birthday and the 
150th anniversary of The Origin of Species. 

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