My brother Ben is now a respectable consultant for the Oxford English Dictionary, but when he was a kid, he was a puzzle freak, pure and simple. In fourth grade he’d spend hours paging through a big unabridged Webster’s, looking for obscure words that he could use to create a fiendish rebus. Little did I know that one day one of his favorite puzzles–the doublet–would become useful to me in thinking about evolution.
The challenge of a doublet is to turn one word into another. You are allowed to change one letter at a time, but each change must produce a real word. Here’s a doublet that suits a post on evolution: Change APE to MAN.
Now imagine that having solved the APE-to-MAN puzzle, you tell a friend about your triumph.
Your friend scoffs. "That’s ridiculous," he says. "I don’t believe you’ve found a missing link between APE and MAN. It doesn’t exist."
You furrow your brow. "Wait," you say. "No, I think maybe you didn’t hear how the puzzle works–"
"I mean, what comes in between?"
"Well, there’s APT, and then–."
"APT? Please! That’s nothing like MAN. They don’t have a single letter in common. It’s just a completely separate word on its own."
"But then there’s OPT–"
"OPT? Are you kidding me? That’s just as irrelevant. You can’t just go from APE to MAN through OPT."
"But what about MAT? That’s a lot like MAN."
"Sure," your friend says, rolling his eyes. "But what on Earth does it have to do with APE?"
Is he really not getting it, you might ask yourself, or is he just pretending not to understand what I’m saying? That’s how I felt when someone sent me an email to tip me off about an attack at the creationist web site Answers in Genesis. It is based on either a misunderstanding or a misrepresentation of what evolution is all about. And doublets help to explain why.
The attack concerns an interview I gave recently to an Australian radio talk show. The Aussies called me up to talk about President Bush’s endorsement of discussing Intelligent Design in schools. Along the way, I explained why creationism has failed to win support in the scientific community. For one thing, creationists often base their arguments on supposed gaps in evolution, such as "missing links" in the fossil record. I talked about how creationists used to talk about the absence of intermediate fossils that would show how whales had evolved from land mammals. But once paleontologists began to find walking whales, the creationists no longer made that argument, moving on to some other gap.
I guess the creationists in Australia were listening to me that day, because now Mark Looiy of Answers in Genesis is here to tell you that in fact "creationists have been devoting many a printed (and web) pageand public lecturesto assertively debate the evolutionary whale claim."
Let’s set aside the fact that scientific debates take place at conferences of scientific societies or in the pages of peer-reviewed biology journals. What exactly are the creationists offering in these pages and lectures? They claim that the fossils of early whales don’t support the argument that whales evolved from land mammals, but their claims are unfounded for a number of reasons.
For one thing, Looiy’s article (and a book by Jonathan Sarfati that he links to as evidence that creationists are still on the whale evolution case) are simply riddled with factual errors. To choose just one example, Sarfati claims that the fossil of Ambulocetus, an alligator-like whale with big feet, is "(conveniently) missing" the pelvis and other parts that are supposedly crucial to establishing the transition from land to sea. I imagine here a paleontologist gasping at the sight of a pelvis that disprove evolution and smashing it with his rock hammer. In fact, Hans Thewissen, the paleontologist who discovered Ambulocetus in Pakistan, has gone back year after year and has now found its pelvis and almost every other bone in this creature. And the complete skeleton supports his initial conclusion that this whale used its legs to kick through the water like an otter.
But there’s a more fundamental problem with Looiy and Sarfati’s take on whales. They look at individual fossils of whales and declare that each one tells us nothing about how whales evolved into marine mammals. The oldest whale, the goat-like Pakicetus, had fully terrestrial legs, so it tells us nothing. Much later, the fully aquatic whale Basiolosaurus retained tiny legs complete with ankles, but since it was completely marine, it also tells us nothing.
What they either don’t know or don’t want to explain is that scientists reconstruct evolutionary history by looking not at one species, but as many species as they can. They draw evolutionary trees by analyzing fossils or DNA, and they look at the traits that are shared by species on different branches of the tree. Pakicetus does look to have been very terrestrial, but it also had peculiar structures in its skull that are only found in whales. Over time, whale legs appear to have changed as whales adapted to the water–first becoming otter-like in the case of Ambulocetus, and then more seal-like in the case of Rodhocetus. Basilosaurus was much further along in this evolution, with much reduced legs that offered no help in swimming at all. And today, whales carry vestiges of hips.
No one species bridged the entire transition from land mammal to marine whale, just as no word bridges the transition from APE to MAN. What’s more, many of these early whale fossils–while related to living whales–did not give rise to them directly. They’re more like aunts and uncles to today’s living whales. In some cases, such as a group called remingtonocetids, walking whales branched off in weird directions of their own, in some cases evolving bizarre heron-shaped heads. A couple years ago Thewissen summarized all the information available on fossil and living whales with this tree–a tree that continues to support the evolution of whales from terrestrial ancestors. It may not be the full solution to the doublet LAND MAMMAL to MARINE WHALE, but it’s a very good start.