In both my evolution class and general talks for laypeople, I use the evolution of whales as a great example of predicted and then discovered transitional forms. Those creationists who claim that “there is microevolution but not macroevolution” are simply unable to deal with this wonderful series of fossils, documenting the transition between a terrestrial “even-toed” animal (artiodactyl), and modern marine whales, showing all gradations of the transition. And most of the change took place over only about 10 million years, a remarkably short time for such a pronounced change in body form and lifestyle. Remember that our divergence from chimps took place about 6 million years ago, and we’re much more similar to chimps than are whales to their terrestrial ancestors! (The closest living relative to whales, by the way, is the hippo, which can serve as an example of how a “half-terrestrial/half aquatic” animal can be perfectly adapted to its environment—something creationists claim is impossible argues against natural selection producing whales.
I’ve put below the diagram of whale evolution I use in my talks (I was kindly given permission to use it by Ken Miller, and the sources are shown on the slide). Note that not only do we see all sorts of intermediate stages, but independent dating of those fossils shows them to occur in the precise temporal order expected if they were transitional forms. (The tree below shows the time when each form diverged from its ancestor.) The rear legs get smaller, the nostrils move atop the head to form the blowhole, the earholes and hair disappear, a new auditory apparatus forms, the pelvis separates from the spine, and so on. It’s all described in Why Evolution is True.
But it’s described even better in a new article in National Geographic, “Valley of the whales,” by Tom Mueller (free online!). I often recommend articles for my readers, but I demand that you read this one. It’s a wonderful combination of travelogue and scientific exposition of one of our best transitional series, and it’s extremely well written. It describes my colleague Phil Gingerich and his team’s work in the Wadi Hitan, a desolate section of the Egyptian desert only 100 miles from the Pyramids of Giza. There (and also in Pakistan) lies a rich treasure of early whale fossils. Mueller describes the scene, the finds, and what scientists now know about the evolution of whales from artiodactyls. The writing is concise and clear, and that’s why I’d like you to read it. Here’s a specimen:
The common ancestor of whales and of all other land animals was a flatheaded, salamander-shaped tetrapod that hauled itself out of the sea onto some muddy bank about 360 million years ago. Its descendants gradually improved the function of their primitive lungs, morphed their lobe fins into legs, and jury-rigged their jaw joints to hear in the air instead of water. Mammals turned out to be among the most successful of these land lovers; by 60 million years ago they dominated the Earth. Whales were among a tiny handful of mammals to make an evolutionary U-turn, retrofitting their terrestrial body plan to sense, eat, move, and mate underwater.
That is what I call good popular science writing: lively and not dumbed down.
Around 45 million years ago, as the advantages of a water environment drew whales farther out to sea, their necks compressed and stiffened to push more efficiently through the water, behind faces lengthening and sharpening like a ship’s prow. Hind legs thickened into pistons; toes stretched and grew webbing, so they resembled enormous ducks’ feet tipped with tiny hooves inherited from their ungulate ancestors. Swimming methods improved: Some whales developed thick, powerful tails, bulleting ahead with vigorous up-and-down undulations of their lower bodies. Selection pressure for this efficient style of locomotion favored longer and more flexible spinal columns. Nostrils slid back up the snout toward the crown of the head, becoming blowholes. Over time, as the animals dived deeper, their eyes began to migrate from the top toward the sides of the head, the better to see laterally in the water. And whale ears grew ever more sensitive to underwater sound, aided by pads of fat that ran in channels the length of their jaws, gathering vibrations like underwater antennae and funneling them to the middle ear.
Though finely tuned to water, these 45-million-year-old whales still had to hitch themselves ashore on webbed fingers and toes, in search of fresh water to drink, a mate, or a safe place to bear their young. But within a few million years whales had passed the point of no return: Basilosaurus, Dorudon, and their relatives never set foot on land, swimming confidently on the high seas and even crossing the Atlantic to reach the shores of what is now Peru and the southern United States.
Mueller’s piece is accompanied by a lovely photo gallery with pictures by Richard Barnes. Here’s a few that I’ve chosen.
Here’s Wadi Hitan; the path is there for visitors to inspect the whale fossils in situ:
Here’s Gingerich with a portion of fossil whale jaw protruding from the rock. Would that all paleontologists could have their fossils so easily accessible!
Mohamed Samah (left) is Wadi Hitan’s head ranger, and is shown putting together the skeleton of a Dorudon (fourth from the bottom in the first diagram above). The article notes that this area, because of its wealth of important fossils, has earned status as a UNESCO World Heritage Site.
A skeleton of Malacetus from Pakistan (47 mya, not shown in my diagram), assembled in the basement of the University of Michigan. The caption notes that it had webbed feet and walked awkwardly on land, much like a sea lion. Note the elongated skull and reduced rear limbs.
The two pictures I like best are below, for they present undeniable visual proof of evolution. This is Basilosaurus (see diagram above), a 37-million-year-old fossil from Wadi Hitan. This was a fully aquatic beast. And although it might not have been a direct descendant of Malacetus, it shows roughly the amount of morphological change that occurred in those 10 million years—a lot! Look at how the forelimbs have become paddles, the tail has become long and flexible, and, especially, how the rear limbs have almost disappeared (they’re the tiny bones flanking the mid-section of the tail). But they’re still recognizable: rock-hard evidence that whales evolved from land animals—something amply confirmed by DNA sequencing.
Below is one of the pair hind limbs of Basilosaurus: each is 18 inches long—on a 50-foot skeleton! The femur, tibia, fibula, and tarsals are clearly recognizable. Gingerich surmises that these tiny limbs may have been used as “stimulators or guides for coopulation,” but it’s also possible that they were completely without function: remnants on the way out or simply something that remained as a byproduct of other important aspects of development.
Creationists often deny that these vestigial limbs are evidence for evolution, noting that they could function in copulation. But that’s ridiculous, for we not only see their gradual shrinkage over time, but—more important—why would the Creator make a “copulation guide” that had every bone homologous to those of the fully-functioning hind limbs of their ancestors, and of modern tetrapods? To deny that this is evidence for evolution shows the intellectual dishonesty of creationists.
Remember, vestigial traits need not be nonfunctional to serve as evidence of evolution.
There is a weird bit at the end of Mueller’s piece—some accommodationist testimony that doesn’t seem to belong in the article.
Ironically, Gingerich himself grew up in a strictly principled Christian environment, in a family of Amish Mennonites in eastern Iowa. (His grandfather was a farmer and lay preacher.) Yet at the time, he felt no clash between faith and science. “My grandfather had an open mind about the age of the Earth,” he says, “and never mentioned evolution. Remember, these were people of great humility, who only expressed an opinion on something when they knew a lot about it.”
Gingerich is still baffled by the conflict that many people feel between religion and science. On my last night in Wadi Hitan, we walked a little distance from camp under a dome of brilliant stars. “I guess I’ve never been particularly devout,” he said. “But I consider my work to be very spiritual. Just imagining those whales swimming around here, how they lived and died, how the world has changed—all this puts you in touch with something much bigger than yourself, your community, or your everyday existence.” He spread his arms, taking in the dark horizon and the desert with its sandstone wind sculptures and its countless silent whales. “There’s room here for all the religion you could possibly want.”
I’m not sure why Phil is baffled by the conflict between science and religion: their methodologies and conclusions are totally at odds, and here he absolutely conflates “religion” with “awe at the wonder of the universe.” Finding fossil whales is not the same thing as finding Jesus. The whole interpolation is gratuitous and jarring. I suspect that National Geographic stuck it in to soothe those readers whose worldview has been jarred by such convincing evidence for evolution. (Many “liberal” religionists still are uncomfortable with evolution, though they profess to accept it.) This seems to be the magazine’s way of saying, “Look readers: you can still have your faith and fossil whales, too!”
But I’m not going to come down hard on Gingerich for this. He’s a terrific guy, a crack scientist who has made pathbreaking discoveries, and we’ve both worked not only against creationists, but as severe critics of Gould and Eldredge’s theory of punctuated equilibrium. So who says that I can’t join forces with accommodationists?!
Go read the piece!