A. Humans: A Recent Branch on the Tree of Life

This second episode sets out to answer some big questions: "Who are we? Where do we come from? How did we get here? Why do we look the way we do?"

"The story of human evolution," we are told, "is really just a small chapter in a much larger story--the story of all living things." As University of Chicago paleontologist Neil H. Shubin puts it: "Evolution shows us that we're much more connected to the rest of the world, the rest of animal life--than we could ever have imagined."

Accompanied by beautiful photography of wild animals, and shots of scientists chipping away at rocks or peering through microscopes, the narrator continues: "The deeper we dig, the farther back we go, the more we see that everything alive has evolved from a single starting-point. The tree of life has been branching for four billion years, and we can now follow the branches back to their roots."

As the camera focuses on the fossilized fin of an ancient fish lying next to the bones of a human arm, Shubin says: "When we look back over time, we find certain signposts, certain key events--the great transformations, the big evolutionary steps." Then, as a whale rises majestically out of the water, the narrator explains: "Fifty million years ago, land mammals were transformed into sea creatures. Long before that, fish colonized land. At the dawn of animal life itself, the very first bodies appeared. These are just some of the chapters in life's story--our story."

After learning that all of human existence is only a brief moment at the end of a very long history of life, we are told that even though we are latecomers "we have been shaped by the same forces that have shaped all living things. To understand how we fit in, we need to look back to long before our own origins, and see how evolution has shaped other living things."

B. Whale Evolution

The scene shifts to whales gliding effortlessly beneath the waves, and the narrator tells us that their origin "was a mystery." According to University of Michigan paleontologist Philip D. Gingerich, "whales are so different from every other kind of mammal that we can't easily relate them to anything else, and so they're off by themselves as a branch of mammal evolution."

As air-breathers, mammals live mostly on land; but whales and dolphins are mammals that live in water. "But we know that mammals evolved on land," Shubin says, "so it's a real puzzle how whales originally evolved. By understanding how that happens, we'll begin to understand how these big jumps--these big transformations--happen generally."

Gingerich explains how he discovered--and identified--the fossilized bones of a whale-like creature in Pakistan. His search for what scientists call "transitional forms" between land animals and whales later took him to the Sahara Desert, which used to be covered by water. There he discovered numerous fossils of a previously discovered extinct whale, Basilosaurus. But Gingerich, unlike those who had gone before him, found tiny leg bones with the fossils--thereby showing that Basilosaurus was a whale with legs.

The narrator explains that the land-dwelling ancestors of modern whales might have found food and safety in the water of an ancient sea: "Over millions of years, front legs became fins, rear legs disappeared, bodies lost fur and took on their familiar streamlined shape." The list of transitional forms between ancient land animals and modern whales, we are told, has grown, proving that "the evidence for evolution is all around us, if we choose to look for it."

Ignoring the fact that the transitional series isn't as neat as it is portrayed here, there are at least two problems with interpreting these fossils as evidence for Darwinian evolution. First, it is impossible to determine whether one fossilized species is ancestral to another. According to Henry Gee, chief science writer for Nature, "the intervals of time that separate fossils are so huge that we cannot say anything definite about their possible connection through ancestry and descent." The fossils examined in this episode are separated by millions of years and thousands of generations. But it's hard enough to determine who our own great-great-great grandparents are, even though they are of the same species, the time span is measured in hundreds of years, and we have written records to help us. We can only assume that these intermediate fossil forms were connected by a chain of ancestry and descent.

Second, mere similarity does not demonstrate an ancestor-descendant relationship. Many of the striking similarities we see today among various organisms were well know to Darwin's predecessors, who attributed them to a common designer. Ford automobiles show a series of transitional forms between the Model T and current models, but all of them were designed and created by intelligent agents. It would make no sense to say that Ford automobiles evolved in a Darwinian fashion unless we could show that a natural mechanism produced them, without any help from human designers. Similarly, before we can call transitional forms between ancient land mammals and modern whales evidence for Darwinian evolution, we must show that a natural mechanism produced them--or at least was capable of producing them.See . Not surprisingly, the actual story of whale-like fossils is not as neat as the one told here. There are long-standing disputes over the identity of the land ancestor, the geological position of various fossils, and whether these were the ancestors of modern whales. Modern molecular studies have added to the controversy. For a short survey of some of the disputes, see Ashby L. Camp, "The Overselling of Whale Evolution," available at:

And that mechanism has to be demonstrated with more plausibility--not to mention evidence--than we see here. To claim merely that "front legs became fins, rear legs disappeared, bodies lost fur and took on their familiar streamlined shape" is not good enough. We have no evidence from modern animals that front legs can become fins, or that a body can assume a radically different shape--much less that a land animal can make the numerous physiological changes it would need for life in the water. Fossils of extinct animals do not necessarily show us descent from a common ancestor, nor do they show us that the change was due to Darwinian natural selection acting on random variations.

The scene changes to an aquarium, where we are told that "bones aren't the only evidence for whale evolution. Their ancestry is also visible in the way they move." The fact that marine mammals propel themselves through the water with up-and-down movements instead of the side-to-side movements characteristic of fish is supposed to indicate their descent from land mammals. But perhaps this is just a common feature of mammals, like air breathing or bearing live young. How does the fact that marine mammals move like other mammals provide evidence for Darwinian evolution?

Neil Shubin returns to conclude the story of whale evolution. "In one sense, evolution didn't invent anything new with whales," he says, "it was just tinkering with land mammals. It's using the old to make the new, and we call that tinkering."

Sort of like what people do with automobiles?

C. Moving onto the Land

Land animals came before whales, but fish came before land animals. So the great transformation that produced land animals preceded the one that produced whales. "It was the moment when fish crawled out of the water."

"The first creatures to leave the water really started something," the narrator explains. "Their ancestors eventually evolved into today's reptiles, birds, and mammals. And these creatures' common origins are still visible in their bodies. Just like us, they all have bodies with four limbs--they're all tetrapods."

Neil Shubin jumps in again: "What that means is that all these different creatures are descended from a common ancestor which had something very similar, or akin, to limbs."

"Just what was that common ancestor," the narrator asks, "and how did it leave the water 370 million years ago?" Shubin and his colleagues find fossils in Pennsylvania suggesting that early tetrapods lived in streams, while Cambridge University paleontologist Jenny Clack finds fossils in Greenland suggesting that fish evolved limbs before they left the water.See . For the standard story, see:

Shubin points to the fossil fish fin and human arm skeleton that we saw at the beginning of the episode, and he notes the similarity in the arrangements of their bones. According to the narrator: "With the basic pattern in place, the fin-to-limb transition was merely a series of small changes occurring over millions of years." And a cartoon animation shows us how easy this might have been. But a cartoon animation, no matter how plausible, does not show how real animals in real time could have been transformed from fish into land animals.

Shubin continues: "There's really no goal to evolution. Evolution wasn't trying to make limbs; it wasn't trying to push our distant ancestors out of the water. What was happening was a series of experiments." And the narrator concludes: "Fish experimented with all sorts of survival strategies. . . . The first tetrapods possibly found another way to survive"--by getting out of the water.

So fish "experimented" with survival "strategies" that included growing legs. But clever human biologists have been experimenting with fish for years, and they have not come up with a strategy to make fish grow even the beginnings of legs. What sense does it make to say that fish "experimented" with growing legs?

The truth is that scientists don't know how the first legs--or the first tetrapods, or the first air-breathers, or the first whales--originated. The fossils tell us that aquatic animals preceded land animals, and that land animals preceded whales. On the question of what caused these great transformations, however, the fossils are silent.

But without knowing what caused these great transformations, how can Shubin say with such confidence that evolution had no goal? How does he know?

D. The Cambrian Explosion

As the camera pans over the fossilized remains of ancient animals, the narrator says: "The water-to-land transformation wasn't the first time evolution had experimented with radical new forms of life. An even earlier explosion--perhaps the most significant of all--occurred just over half a billion years ago. This was the one that led to animal life itself."

Shubin elaborates: "Evolution tinkered with fish to make limbs, but fish carry the baggage of their own past. Think of a fish. It has a head, it has a tail, and a bunch of fins in between. That's a body plan--the way the body's put together. But that's just one of many ways of putting animals together." We're shown pictures of jellyfish, a millipede, a beetle, and a crab. "The question is: What sort of tinkering led to these body plans? I mean really what we're dealing with here is the origin of animals."

"According to the fossil record," the narrator says, "animals burst upon the earth rather suddenly," hundreds of millions of years ago. "Scientists call this crucial transformation the Cambrian explosion." Cambridge University paleontologist Simon Conway Morris explains: "The Cambrian explosion was effectively one of the greatest breakthroughs in the history of life. About half a billion years ago, suddenly things change, we have this extraordinary explosion of diversity. And this sudden appearance of the fossils led to this term, the Cambrian explosion. Darwin, as ever, was extremely candid--he said, Look, this is a problem for my theory. How is it that suddenly animals seem to come out of nowhere? And to a certain extent that is still something of a mystery."

It certainly is. In Darwin's theory, all animals are descended from a common ancestor. If the theory were true, we would expect the history of animal life to begin with one form; as time passes, this form would give rise to two or three that are only slightly different from each other; and with more time, these would give rise to other forms, even more different from each other. Finally, after millions of generations, we would see the major differences that now separate clams from starfish and insects from vertebrates.

In the fossil record, however, these major differences appear first . In other words, the fossil pattern is exactly the opposite of what we would expect from Darwin's theory. Darwin himself was aware of the problem (as Simon Conway Morris points out); but he hoped that it would be remedied as more fossil discoveries showed the expected long history of gradual divergence before the Cambrian. A century and a half of additional fossil collecting, however, have shown that Darwin was wrong, and the Cambrian explosion was real.See . Darwin wrote in The Origin of Species that "if the theory be true, it is indisputable that before the lowest Cambrian stratum was deposited long periods elapsed . . . [in which] the world swarmed with living creatures." Yet he acknowledged that "several of the main divisions of the animal kingdom suddenly appear in the lowest known fossiliferous rocks." Darwin called this a "serious" problem which "at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained." (Chapter X; page numbers will vary depending on the edition.)

The coverage of the Cambrian explosion in this episode is better than one usually sees in treatments of evolution. Most biology textbooks (including one co-authored by Kenneth Miller, who played a prominent role in Episode One), completely ignore the Cambrian explosion and the challenge it poses to Darwin's theory. Evolution's producers deserve to be commended for including it, though they largely ignore Simon Conway Morris's comment that the Cambrian explosion "is still something of a mystery," and thus pass up a chance to acquaint viewers with the controversy surrounding one of evolution's most exciting unresolved challenges.

Spectacular views of the Canadian Rockies now follow--home of the famous Burgess Shale, which has provided us with much of the best evidence for the Cambrian explosion. After surveying some of the forms found in the Burgess Shale, the narrator says: "All the basic body plans found in nature today are here. Everything that has lived for the last half-billion years came from tinkering with these initial designs. We can even see our own ancestor here." Simon Conway Morris displays a photograph of a tiny worm, Pikaia, and tells us "this might be the precursor of the fish, and so also, I believe--after a long evolutionary story--ourselves."

Neil Shubin returns to summarize what we've seen so far: "So what do we learn by looking at 600 million years of animal history? Evolution's tinkering with mammalness to make whales; in the same way, it's tinkering with fishiness to make tetrapods; and it's tinkering with animalness to make all the different body plans that we see."

There's that "tinkering" again. We've seen that animals burst upon the scene rather suddenly, that land animals came later, and that whales came later still. Things are certainly not what they used to be. But where is the evidence that it all happened through "tinkering"?

Shubin continues: "All these different creatures are variations of the same theme, re-stated over and over again. The question was, What was evolution tinkering with? One of the remarkable discoveries of the last twenty years is that evolution's not tinkering with the bodies, it's tinkering with the recipe, the machinery that builds bodies. What is that recipe? What is that machinery? It's the genes, the genes that build them."

Finally, we are promised some hard evidence of how these great transformations took place. Let's take a look at it.

E. The Genetic Mechanism of Evolution

"Fossils record the changes in animals' bodies over time," the narrator says, "but just how bodies changed was unknown. The search for the genetic mechanism of evolution took most of the century. When scientists finally found it, they were astonished by just how simple it was."

In the nineteenth century, geneticist William Bateson had observed that embryos would occasionally develop body parts in the wrong places. Then biologists in the 1940s discovered that they could produce such effects in fruit flies by using radiation. Stanford University developmental biologist Matthew P. Scott explains that, like Bateson, these researchers would occasionally find flies with "one part of the body in the wrong place, or a copy of a normal part of the body in another place."

Watch closely as a fruit fly with an extra pair of wings fills the screen. (Fruit flies normally have two wings, but this one has four.) Note that the wing visible here behind the normal pair is stiff and motionless. That's because the second pair of wings has no muscles. The extra wings are thus useless, and the fly has difficulty flying and mating--though that fact goes unmentioned here. Next we see a mutant fly with no wings (which of course has even more difficulty flying!), then a fly with stubby legs instead of antennae growing out of its head. All three of these mutant flies are cripples, and cannot survive long outside the laboratory.

"The scientists had triggered the changes by damaging the fly's DNA," the narrator says. He continues with an overview of how scientists in the past quarter-century have unraveled some of the ways in which genes affect embryo development. It's a fascinating story about painstaking research, requiring considerable patience and perseverance, which finally ended in success. One of those successes involved deciphering the action of the Antennapedia gene, in which mutations can cause flies to sprout legs from their heads. The narrator concludes that the "implications were mind-boggling," because such genes seemed to be "acting like architects of the body."

Could this discovery be generalized to other animals? The scene switches to Switzerland, where University of Basel cell biologist Walter Gehring describes how he removed a gene from a fruit fly that is needed for normal eye development, and inserted a comparable gene from a mouse. Gehring found that the mouse gene did the work of the fly gene. "The fruit fly had grown normal fruit fly eyes," the narrator explains, "using a gene from a mouse. Not only did the two creatures use the same mechanism--they used the very same gene. This was the mechanism behind extra wings, legs sprouting from heads, and Bateson's deformed animals. The century-long search was complete. The genetic engine of evolution turned out to be a tiny handful of powerful genes."

As we watch some more beautiful wildlife photography, University of Wisconsin geneticist Sean B. Carroll interprets the significance of this: "So what this means is--in some ways, some sense--evolution is a simpler process than we first thought. When you think about all of the diversity of forms out there, we first believed that this would involve all sorts of novel creations, starting from scratch, again and again and again. We now understand that, no, that evolution works with packets of information, and uses them in new and different ways and new and different combinations without necessarily having to invent anything fundamentally new, but new combinations."

As a series of brightly-colored cartoons shows the supposedly similar body organization of various kinds of animals, the narrator explains: "Suddenly, the commonality of form among animals was understood. Animals resembled each other because they all used the same set of genes to build their bodies--a set of genes inherited from a common ancestor that lived long ago." Matthew Scott adds: "And what we see now among all the animals are just variations on a body plan that existed half a billion years ago."

"And there's only one inescapable conclusion you can draw from that," says Carroll, "which is: If all of these branches have these genes, then you have to go to the base of that, which is the last common ancestor of all animals, and you deduce it must have had these genes. So the whole radiation of animals, the whole spring of animal diversity has been fed by essentially the same set of genes."

What's wrong with this picture? The story we have just heard ignores two fundamental problems. The first is that (as we saw above) the genetic changes shown here are--without exception!--harmful to the organism. In the wild, all of these changes would be quickly eliminated by natural selection. Geneticists have learned a lot about how genes affect embryo development, but they have not yet found a single mutation that changes the shape of an animal's body in a way that might be useful for evolution outside the laboratory. (Useful mutations occur in some cases of antibiotic resistance, as we shall see in Episode Four; but that's a far cry from changing the shape of an animal's body.)

The second problem is that the "tiny handful of powerful genes" is nowhere near as powerful as we are led to believe. Note that the mouse eye gene inserted into the fruit fly produced a fruit fly eye, not a mouse eye. In other words, the gene was not the "architect" of the eye; it merely acted as a switch, enabling the animal to make an eye when and where it needed one. But the gene has nothing to do with the kind of eye the animal makes. It's more like an electrical switch that can turn on a light, a computer, a vacuum cleaner--or whatever else is plugged into it. If these genes are what animals use to "build their bodies," and if all animals have the same set of genes, how come the various kinds of animals are so different from each other? Why don't fruit flies give birth to finches?

In fact, the genes described here are not even turned on by the embryo until the basic body plan is already formed. A fly is a fly, and a mouse is a mouse, long before these genes perform their switching jobs to tell the fly where to grow its legs, or the mouse whether to grow an eye. Whatever it is that builds animal body plans, it is certainly not this "tiny handful of powerful genes."See . For a detailed discussion of the problems with using four-winged fruit flies as evidence for evolution, see Jonathan Wells, Icons of Evolution (Washington, DC: Regnery Publishing, 2000), Chapter 9.

Once again, we are left without the evidence we were hoping to see. Instead, we are simply assured that evolution is simpler than we thought, and given the same line that modern animals are simply variations of an ancestral body plan that existed long ago.

F. From Ape to Human

"What about us?" the narrator asks. "Our bodies are built from the same genes that build all other animals. Yet we are different. No other animal designs or creates like we do." The camera pans slowly over Michelangelo's Sistine Chapel painting of God touching Adam. The narrator continues: "We seem so special, it's hard not to think that we're somehow an exception to evolution. But of course we're not. The transformation that led to us was no different from the others." In a familiar scene (which is repeated again and again throughout the series), an ape clambers down a log to the ground. "The crucial turning-point seems to have occurred about seven million years ago, when our ancestors left the trees and began to walk on two legs."

According to Arizona State University paleoanthropologist Donald Johanson, this probably first happened in East Africa. He and the narrator explain how walking on two feet seems to have opened the door to the evolution of our brains, though little is known about how our ancestors became bipeds. University of Texas anthropologist Liza J. Shapiro tries to answer this question by studying lemurs, because "we have to know what it was we started from." The narrator explains: "Like lemurs, our early ancestors could move in all sorts of ways." So "they were already adapted to so many movement styles, they could serve as the starting-point for a variety of evolutionary experiments. And that's just what happened."

After being assured that we evolved from a lemur-like animal, and that the striking similarities between chimps and us show that we only recently evolved from a common ancestor, we are told that "the few physical differences that set us apart seem to have made a great difference." Johanson points out some of them on models of human and chimp skeletons, and concludes: "These are minor differences. These are the sorts of tinkering that evolution did to change us into a modern biped." So "what we see is that evolution has worked the same way with us as it has with every single organism on this planet. We're here through a series of chance coincidences, specific adaptations, chosen opportunities."

Words like "tinkering" and "chance" clearly mean something other than what Michelangelo painted on the ceiling of the Sistine Chapel. But--once again--where is the evidence? That we are "built from the same genes that build all other animals"? That lemurs can "move in all sorts of ways"? That there are both similarities and differences between humans and chimps?

The truth is that the evidence for human origins is even weaker than some of the other evidence we've seen. According to Henry Gee, chief science writer for Nature, all the evidence for human evolution "between about 10 and 5 million years ago--several thousand generations of living creatures--can be fitted into a small box." Thus the conventional picture of human evolution as lines of ancestry and descent is "a completely human invention created after the fact, shaped to accord with human prejudices." Putting it even more bluntly, Gee concludes: "To take a line of fossils and claim that they represent a lineage is not a scientific hypothesis that can be tested, but an assertion that carries the same validity as a bedtime story--amusing, perhaps even instructive, but not scientific."See . For the Gee quotations see: Henry Gee, In Search of Deep Time (New York: The Free Press, 1999), 23, 32, 113-117, 202.

So Episode Two, instead of showing us the "underlying evidence" for Darwin's theory, leaves us with a bedtime story.

Notes

1. . Not surprisingly, the actual story of whale-like fossils is not as neat as the one told here. There are long-standing disputes over the identity of the land ancestor, the geological position of various fossils, and whether these were the ancestors of modern whales. Modern molecular studies have added to the controversy. For a short survey of some of the disputes, see Ashby L. Camp, "The Overselling of Whale Evolution," available at:

A. Humans: A Recent Branch on the Tree of Life

This second episode sets out to answer some big questions: "Who are we? Where do we come from? How did we get here? Why do we look the way we do?"

"The story of human evolution," we are told, "is really just a small chapter in a much larger story--the story of all living things." As University of Chicago paleontologist Neil H. Shubin puts it: "Evolution shows us that we're much more connected to the rest of the world, the rest of animal life--than we could ever have imagined."

Accompanied by beautiful photography of wild animals, and shots of scientists chipping away at rocks or peering through microscopes, the narrator continues: "The deeper we dig, the farther back we go, the more we see that everything alive has evolved from a single starting-point. The tree of life has been branching for four billion years, and we can now follow the branches back to their roots."

As the camera focuses on the fossilized fin of an ancient fish lying next to the bones of a human arm, Shubin says: "When we look back over time, we find certain signposts, certain key events--the great transformations, the big evolutionary steps." Then, as a whale rises majestically out of the water, the narrator explains: "Fifty million years ago, land mammals were transformed into sea creatures. Long before that, fish colonized land. At the dawn of animal life itself, the very first bodies appeared. These are just some of the chapters in life's story--our story."

After learning that all of human existence is only a brief moment at the end of a very long history of life, we are told that even though we are latecomers "we have been shaped by the same forces that have shaped all living things. To understand how we fit in, we need to look back to long before our own origins, and see how evolution has shaped other living things."

B. Whale Evolution

The scene shifts to whales gliding effortlessly beneath the waves, and the narrator tells us that their origin "was a mystery." According to University of Michigan paleontologist Philip D. Gingerich, "whales are so different from every other kind of mammal that we can't easily relate them to anything else, and so they're off by themselves as a branch of mammal evolution."

As air-breathers, mammals live mostly on land; but whales and dolphins are mammals that live in water. "But we know that mammals evolved on land," Shubin says, "so it's a real puzzle how whales originally evolved. By understanding how that happens, we'll begin to understand how these big jumps--these big transformations--happen generally."

Gingerich explains how he discovered--and identified--the fossilized bones of a whale-like creature in Pakistan. His search for what scientists call "transitional forms" between land animals and whales later took him to the Sahara Desert, which used to be covered by water. There he discovered numerous fossils of a previously discovered extinct whale, Basilosaurus. But Gingerich, unlike those who had gone before him, found tiny leg bones with the fossils--thereby showing that Basilosaurus was a whale with legs.

The narrator explains that the land-dwelling ancestors of modern whales might have found food and safety in the water of an ancient sea: "Over millions of years, front legs became fins, rear legs disappeared, bodies lost fur and took on their familiar streamlined shape." The list of transitional forms between ancient land animals and modern whales, we are told, has grown, proving that "the evidence for evolution is all around us, if we choose to look for it."

Ignoring the fact that the transitional series isn't as neat as it is portrayed here, there are at least two problems with interpreting these fossils as evidence for Darwinian evolution. First, it is impossible to determine whether one fossilized species is ancestral to another. According to Henry Gee, chief science writer for Nature, "the intervals of time that separate fossils are so huge that we cannot say anything definite about their possible connection through ancestry and descent." The fossils examined in this episode are separated by millions of years and thousands of generations. But it's hard enough to determine who our own great-great-great grandparents are, even though they are of the same species, the time span is measured in hundreds of years, and we have written records to help us. We can only assume that these intermediate fossil forms were connected by a chain of ancestry and descent.

Second, mere similarity does not demonstrate an ancestor-descendant relationship. Many of the striking similarities we see today among various organisms were well know to Darwin's predecessors, who attributed them to a common designer. Ford automobiles show a series of transitional forms between the Model T and current models, but all of them were designed and created by intelligent agents. It would make no sense to say that Ford automobiles evolved in a Darwinian fashion unless we could show that a natural mechanism produced them, without any help from human designers. Similarly, before we can call transitional forms between ancient land mammals and modern whales evidence for Darwinian evolution, we must show that a natural mechanism produced them--or at least was capable of producing them.See . Not surprisingly, the actual story of whale-like fossils is not as neat as the one told here. There are long-standing disputes over the identity of the land ancestor, the geological position of various fossils, and whether these were the ancestors of modern whales. Modern molecular studies have added to the controversy. For a short survey of some of the disputes, see Ashby L. Camp, "The Overselling of Whale Evolution," available at:

And that mechanism has to be demonstrated with more plausibility--not to mention evidence--than we see here. To claim merely that "front legs became fins, rear legs disappeared, bodies lost fur and took on their familiar streamlined shape" is not good enough. We have no evidence from modern animals that front legs can become fins, or that a body can assume a radically different shape--much less that a land animal can make the numerous physiological changes it would need for life in the water. Fossils of extinct animals do not necessarily show us descent from a common ancestor, nor do they show us that the change was due to Darwinian natural selection acting on random variations.

The scene changes to an aquarium, where we are told that "bones aren't the only evidence for whale evolution. Their ancestry is also visible in the way they move." The fact that marine mammals propel themselves through the water with up-and-down movements instead of the side-to-side movements characteristic of fish is supposed to indicate their descent from land mammals. But perhaps this is just a common feature of mammals, like air breathing or bearing live young. How does the fact that marine mammals move like other mammals provide evidence for Darwinian evolution?

Neil Shubin returns to conclude the story of whale evolution. "In one sense, evolution didn't invent anything new with whales," he says, "it was just tinkering with land mammals. It's using the old to make the new, and we call that tinkering."

Sort of like what people do with automobiles?

C. Moving onto the Land

Land animals came before whales, but fish came before land animals. So the great transformation that produced land animals preceded the one that produced whales. "It was the moment when fish crawled out of the water."

"The first creatures to leave the water really started something," the narrator explains. "Their ancestors eventually evolved into today's reptiles, birds, and mammals. And these creatures' common origins are still visible in their bodies. Just like us, they all have bodies with four limbs--they're all tetrapods."

Neil Shubin jumps in again: "What that means is that all these different creatures are descended from a common ancestor which had something very similar, or akin, to limbs."

"Just what was that common ancestor," the narrator asks, "and how did it leave the water 370 million years ago?" Shubin and his colleagues find fossils in Pennsylvania suggesting that early tetrapods lived in streams, while Cambridge University paleontologist Jenny Clack finds fossils in Greenland suggesting that fish evolved limbs before they left the water.See . For the standard story, see:

Shubin points to the fossil fish fin and human arm skeleton that we saw at the beginning of the episode, and he notes the similarity in the arrangements of their bones. According to the narrator: "With the basic pattern in place, the fin-to-limb transition was merely a series of small changes occurring over millions of years." And a cartoon animation shows us how easy this might have been. But a cartoon animation, no matter how plausible, does not show how real animals in real time could have been transformed from fish into land animals.

Shubin continues: "There's really no goal to evolution. Evolution wasn't trying to make limbs; it wasn't trying to push our distant ancestors out of the water. What was happening was a series of experiments." And the narrator concludes: "Fish experimented with all sorts of survival strategies. . . . The first tetrapods possibly found another way to survive"--by getting out of the water.

So fish "experimented" with survival "strategies" that included growing legs. But clever human biologists have been experimenting with fish for years, and they have not come up with a strategy to make fish grow even the beginnings of legs. What sense does it make to say that fish "experimented" with growing legs?

The truth is that scientists don't know how the first legs--or the first tetrapods, or the first air-breathers, or the first whales--originated. The fossils tell us that aquatic animals preceded land animals, and that land animals preceded whales. On the question of what caused these great transformations, however, the fossils are silent.

But without knowing what caused these great transformations, how can Shubin say with such confidence that evolution had no goal? How does he know?

D. The Cambrian Explosion

As the camera pans over the fossilized remains of ancient animals, the narrator says: "The water-to-land transformation wasn't the first time evolution had experimented with radical new forms of life. An even earlier explosion--perhaps the most significant of all--occurred just over half a billion years ago. This was the one that led to animal life itself."

Shubin elaborates: "Evolution tinkered with fish to make limbs, but fish carry the baggage of their own past. Think of a fish. It has a head, it has a tail, and a bunch of fins in between. That's a body plan--the way the body's put together. But that's just one of many ways of putting animals together." We're shown pictures of jellyfish, a millipede, a beetle, and a crab. "The question is: What sort of tinkering led to these body plans? I mean really what we're dealing with here is the origin of animals."

"According to the fossil record," the narrator says, "animals burst upon the earth rather suddenly," hundreds of millions of years ago. "Scientists call this crucial transformation the Cambrian explosion." Cambridge University paleontologist Simon Conway Morris explains: "The Cambrian explosion was effectively one of the greatest breakthroughs in the history of life. About half a billion years ago, suddenly things change, we have this extraordinary explosion of diversity. And this sudden appearance of the fossils led to this term, the Cambrian explosion. Darwin, as ever, was extremely candid--he said, Look, this is a problem for my theory. How is it that suddenly animals seem to come out of nowhere? And to a certain extent that is still something of a mystery."

It certainly is. In Darwin's theory, all animals are descended from a common ancestor. If the theory were true, we would expect the history of animal life to begin with one form; as time passes, this form would give rise to two or three that are only slightly different from each other; and with more time, these would give rise to other forms, even more different from each other. Finally, after millions of generations, we would see the major differences that now separate clams from starfish and insects from vertebrates.

In the fossil record, however, these major differences appear first . In other words, the fossil pattern is exactly the opposite of what we would expect from Darwin's theory. Darwin himself was aware of the problem (as Simon Conway Morris points out); but he hoped that it would be remedied as more fossil discoveries showed the expected long history of gradual divergence before the Cambrian. A century and a half of additional fossil collecting, however, have shown that Darwin was wrong, and the Cambrian explosion was real.See . Darwin wrote in The Origin of Species that "if the theory be true, it is indisputable that before the lowest Cambrian stratum was deposited long periods elapsed . . . [in which] the world swarmed with living creatures." Yet he acknowledged that "several of the main divisions of the animal kingdom suddenly appear in the lowest known fossiliferous rocks." Darwin called this a "serious" problem which "at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained." (Chapter X; page numbers will vary depending on the edition.)

The coverage of the Cambrian explosion in this episode is better than one usually sees in treatments of evolution. Most biology textbooks (including one co-authored by Kenneth Miller, who played a prominent role in Episode One), completely ignore the Cambrian explosion and the challenge it poses to Darwin's theory. Evolution's producers deserve to be commended for including it, though they largely ignore Simon Conway Morris's comment that the Cambrian explosion "is still something of a mystery," and thus pass up a chance to acquaint viewers with the controversy surrounding one of evolution's most exciting unresolved challenges.

Spectacular views of the Canadian Rockies now follow--home of the famous Burgess Shale, which has provided us with much of the best evidence for the Cambrian explosion. After surveying some of the forms found in the Burgess Shale, the narrator says: "All the basic body plans found in nature today are here. Everything that has lived for the last half-billion years came from tinkering with these initial designs. We can even see our own ancestor here." Simon Conway Morris displays a photograph of a tiny worm, Pikaia, and tells us "this might be the precursor of the fish, and so also, I believe--after a long evolutionary story--ourselves."

Neil Shubin returns to summarize what we've seen so far: "So what do we learn by looking at 600 million years of animal history? Evolution's tinkering with mammalness to make whales; in the same way, it's tinkering with fishiness to make tetrapods; and it's tinkering with animalness to make all the different body plans that we see."

There's that "tinkering" again. We've seen that animals burst upon the scene rather suddenly, that land animals came later, and that whales came later still. Things are certainly not what they used to be. But where is the evidence that it all happened through "tinkering"?

Shubin continues: "All these different creatures are variations of the same theme, re-stated over and over again. The question was, What was evolution tinkering with? One of the remarkable discoveries of the last twenty years is that evolution's not tinkering with the bodies, it's tinkering with the recipe, the machinery that builds bodies. What is that recipe? What is that machinery? It's the genes, the genes that build them."

Finally, we are promised some hard evidence of how these great transformations took place. Let's take a look at it.

E. The Genetic Mechanism of Evolution

"Fossils record the changes in animals' bodies over time," the narrator says, "but just how bodies changed was unknown. The search for the genetic mechanism of evolution took most of the century. When scientists finally found it, they were astonished by just how simple it was."

In the nineteenth century, geneticist William Bateson had observed that embryos would occasionally develop body parts in the wrong places. Then biologists in the 1940s discovered that they could produce such effects in fruit flies by using radiation. Stanford University developmental biologist Matthew P. Scott explains that, like Bateson, these researchers would occasionally find flies with "one part of the body in the wrong place, or a copy of a normal part of the body in another place."

Watch closely as a fruit fly with an extra pair of wings fills the screen. (Fruit flies normally have two wings, but this one has four.) Note that the wing visible here behind the normal pair is stiff and motionless. That's because the second pair of wings has no muscles. The extra wings are thus useless, and the fly has difficulty flying and mating--though that fact goes unmentioned here. Next we see a mutant fly with no wings (which of course has even more difficulty flying!), then a fly with stubby legs instead of antennae growing out of its head. All three of these mutant flies are cripples, and cannot survive long outside the laboratory.

"The scientists had triggered the changes by damaging the fly's DNA," the narrator says. He continues with an overview of how scientists in the past quarter-century have unraveled some of the ways in which genes affect embryo development. It's a fascinating story about painstaking research, requiring considerable patience and perseverance, which finally ended in success. One of those successes involved deciphering the action of the Antennapedia gene, in which mutations can cause flies to sprout legs from their heads. The narrator concludes that the "implications were mind-boggling," because such genes seemed to be "acting like architects of the body."

Could this discovery be generalized to other animals? The scene switches to Switzerland, where University of Basel cell biologist Walter Gehring describes how he removed a gene from a fruit fly that is needed for normal eye development, and inserted a comparable gene from a mouse. Gehring found that the mouse gene did the work of the fly gene. "The fruit fly had grown normal fruit fly eyes," the narrator explains, "using a gene from a mouse. Not only did the two creatures use the same mechanism--they used the very same gene. This was the mechanism behind extra wings, legs sprouting from heads, and Bateson's deformed animals. The century-long search was complete. The genetic engine of evolution turned out to be a tiny handful of powerful genes."

As we watch some more beautiful wildlife photography, University of Wisconsin geneticist Sean B. Carroll interprets the significance of this: "So what this means is--in some ways, some sense--evolution is a simpler process than we first thought. When you think about all of the diversity of forms out there, we first believed that this would involve all sorts of novel creations, starting from scratch, again and again and again. We now understand that, no, that evolution works with packets of information, and uses them in new and different ways and new and different combinations without necessarily having to invent anything fundamentally new, but new combinations."

As a series of brightly-colored cartoons shows the supposedly similar body organization of various kinds of animals, the narrator explains: "Suddenly, the commonality of form among animals was understood. Animals resembled each other because they all used the same set of genes to build their bodies--a set of genes inherited from a common ancestor that lived long ago." Matthew Scott adds: "And what we see now among all the animals are just variations on a body plan that existed half a billion years ago."

"And there's only one inescapable conclusion you can draw from that," says Carroll, "which is: If all of these branches have these genes, then you have to go to the base of that, which is the last common ancestor of all animals, and you deduce it must have had these genes. So the whole radiation of animals, the whole spring of animal diversity has been fed by essentially the same set of genes."

What's wrong with this picture? The story we have just heard ignores two fundamental problems. The first is that (as we saw above) the genetic changes shown here are--without exception!--harmful to the organism. In the wild, all of these changes would be quickly eliminated by natural selection. Geneticists have learned a lot about how genes affect embryo development, but they have not yet found a single mutation that changes the shape of an animal's body in a way that might be useful for evolution outside the laboratory. (Useful mutations occur in some cases of antibiotic resistance, as we shall see in Episode Four; but that's a far cry from changing the shape of an animal's body.)

The second problem is that the "tiny handful of powerful genes" is nowhere near as powerful as we are led to believe. Note that the mouse eye gene inserted into the fruit fly produced a fruit fly eye, not a mouse eye. In other words, the gene was not the "architect" of the eye; it merely acted as a switch, enabling the animal to make an eye when and where it needed one. But the gene has nothing to do with the kind of eye the animal makes. It's more like an electrical switch that can turn on a light, a computer, a vacuum cleaner--or whatever else is plugged into it. If these genes are what animals use to "build their bodies," and if all animals have the same set of genes, how come the various kinds of animals are so different from each other? Why don't fruit flies give birth to finches?

In fact, the genes described here are not even turned on by the embryo until the basic body plan is already formed. A fly is a fly, and a mouse is a mouse, long before these genes perform their switching jobs to tell the fly where to grow its legs, or the mouse whether to grow an eye. Whatever it is that builds animal body plans, it is certainly not this "tiny handful of powerful genes."See . For a detailed discussion of the problems with using four-winged fruit flies as evidence for evolution, see Jonathan Wells, Icons of Evolution (Washington, DC: Regnery Publishing, 2000), Chapter 9.

Once again, we are left without the evidence we were hoping to see. Instead, we are simply assured that evolution is simpler than we thought, and given the same line that modern animals are simply variations of an ancestral body plan that existed long ago.

F. From Ape to Human

"What about us?" the narrator asks. "Our bodies are built from the same genes that build all other animals. Yet we are different. No other animal designs or creates like we do." The camera pans slowly over Michelangelo's Sistine Chapel painting of God touching Adam. The narrator continues: "We seem so special, it's hard not to think that we're somehow an exception to evolution. But of course we're not. The transformation that led to us was no different from the others." In a familiar scene (which is repeated again and again throughout the series), an ape clambers down a log to the ground. "The crucial turning-point seems to have occurred about seven million years ago, when our ancestors left the trees and began to walk on two legs."

According to Arizona State University paleoanthropologist Donald Johanson, this probably first happened in East Africa. He and the narrator explain how walking on two feet seems to have opened the door to the evolution of our brains, though little is known about how our ancestors became bipeds. University of Texas anthropologist Liza J. Shapiro tries to answer this question by studying lemurs, because "we have to know what it was we started from." The narrator explains: "Like lemurs, our early ancestors could move in all sorts of ways." So "they were already adapted to so many movement styles, they could serve as the starting-point for a variety of evolutionary experiments. And that's just what happened."

After being assured that we evolved from a lemur-like animal, and that the striking similarities between chimps and us show that we only recently evolved from a common ancestor, we are told that "the few physical differences that set us apart seem to have made a great difference." Johanson points out some of them on models of human and chimp skeletons, and concludes: "These are minor differences. These are the sorts of tinkering that evolution did to change us into a modern biped." So "what we see is that evolution has worked the same way with us as it has with every single organism on this planet. We're here through a series of chance coincidences, specific adaptations, chosen opportunities."

Words like "tinkering" and "chance" clearly mean something other than what Michelangelo painted on the ceiling of the Sistine Chapel. But--once again--where is the evidence? That we are "built from the same genes that build all other animals"? That lemurs can "move in all sorts of ways"? That there are both similarities and differences between humans and chimps?

The truth is that the evidence for human origins is even weaker than some of the other evidence we've seen. According to Henry Gee, chief science writer for Nature, all the evidence for human evolution "between about 10 and 5 million years ago--several thousand generations of living creatures--can be fitted into a small box." Thus the conventional picture of human evolution as lines of ancestry and descent is "a completely human invention created after the fact, shaped to accord with human prejudices." Putting it even more bluntly, Gee concludes: "To take a line of fossils and claim that they represent a lineage is not a scientific hypothesis that can be tested, but an assertion that carries the same validity as a bedtime story--amusing, perhaps even instructive, but not scientific."See . For the Gee quotations see: Henry Gee, In Search of Deep Time (New York: The Free Press, 1999), 23, 32, 113-117, 202.

So Episode Two, instead of showing us the "underlying evidence" for Darwin's theory, leaves us with a bedtime story.

Notes

1. . Not surprisingly, the actual story of whale-like fossils is not as neat as the one told here. There are long-standing disputes over the identity of the land ancestor, the geological position of various fossils, and whether these were the ancestors of modern whales. Modern molecular studies have added to the controversy. For a short survey of some of the disputes, see Ashby L. Camp, "The Overselling of Whale Evolution," available at: