Growing up as I did in the northeast, I always assumed that the really weird life forms lived somewhere else–the Amazonian rain forest, maybe, or the deep sea. But we’ve got at least one truly bizarre creature we can boast about: the star-nosed mole. Its star is actually 22 fleshy tendrils that extend from its snout. For a long time, it wasn’t entirely clear what the moles used the star for. The moles were so quick at finding food–larvae, worms, and other creatures that turn up in their tunnels–that some scientists suggested that the star could detect the electric fields of animals.
That idea hasn’t panned out, but the truth has turned out to be just as exotic. As I write in tomorrow’s issue of the New York Times, the star is the most sensitive touch organ known to science. It is studded with 25,000 touch-sensitive nerve organs, which channel their sensations into 100,000 large nerve fibers (more than in your entire hand). These nerves then carry the signals to the brain, much of which is dedicated to interpreting what the star feels. As Ken Catania of Vanderbilt University reports in a paper appearing in the current issue of Nature, this heavy-duty wiring produces record-setting speed. As soon as the star-nosed mole comes into contact with food, it needs a fifth of a second to gobble it down. (The article includes a sequence, of frames from one of these filmed feasts.)
As some readers of the Times may notice, this mole article appears in the science section a day after an op-ed column appeared in the editorial section promoting Intelligent Design. Michael Behe, a Lehigh University biologist, claims that evolutionary biologists have not offered hypotheses for how complex things evolve in nature. Given this supposed lack of explanations, and given the supposedly obvious signs of design in biology, Behe concludes that life must be the product of an Intelligent Designer.
Behe is incorrect. In fact, evolutionary biologists have put together hypotheses for many complex systems, which they have published in leading peer-reviewed biology journals. The immune system is one example, which I blogged about in December. The star of the star-nosed moles is another. Ken Catania’s hypothesis for its origin starts with the observation that the star is not quite as unique as it may seem at first sight. The touch-sensitive organs it uses (called Eimer organs) are found on the noses of other moles, albeit it in far lower densities. What’s more, coast moles, close relatives of star-nosed moles, have small, pipe-shaped swellings at the very tip of its nose, which resemble the star on a star-nosed mole when it is still an embryo.
The star, Catania argues, evolved on a coast-mole-like ancestor. The swellings became larger, the nerves became denser, and the brain dedicated more space to processing the star’s signals. Natural selection favored this trend, according to Catania, because the star-nosed moles moved from dry habitats to wetlands, which are loaded with small insect larvae. In addition to big insects, such as earthworms or crickets, star-nosed moles added these small prey to their diet. The star provided benefits to the mole long before it had taken the full-blown form it has today. The more time the star-nosed moles shaved off their performance, the more calories they could take in each second.
Catania’s hypothesis takes into account all of the evidence he and others have gathered about star-nosed moles–their behavior, the microscopic structure of their star, the architecture of their brains, their ecology, and the same evidence in closely related moles. It builds on what scientists already know about variation, inheritance, and natural selection. As a hypothesis, it’s open to testing, based on further observations of star-nosed moles and their relatives. And that’s what Catania is doing.
As for corresponding published papers that use Intelligent Design to interpret the star-nosed mole, they do not exist. The closest I can find are some comments from Answers in Genesis. On their web site, they claim that Catania’s hypothesis cannot be right because it is based on "the discredited idea of Embryonic Recapitulation." This claim is based on the fact that the nineteenth century biologist Ernst Haeckel doctored some pictures of embryos in order to fit his own notion about how evolution progressed in certain directions. Nevertheless, the scientific consensus today–based on over a century of research since Haeckel’s day–holds that changes in the way embryos develop can lead to dramatic evolutionary change (Here’s a good account of the current undertanding.).
The Answers in Genesis site then asks, "Why would a primitive mammal suddenly start to develop such a specialized appendage? If it was already successfully hunting food without the star, what was the evolutionary trigger for the stars development?" Catania has already laid out this part of his hypothesis: the ancestors of star-nosed moles moved into wetlands, where variations that helped them feed on insect larvae could get them more food and boost their odds of reproducing. Other mole species, living in dry soil, didn’t have this incentive. What’s more, the delicate star would be damaged scraping against the hard tunnels dug by other moles.
These are some of the reasons why Catania and other scientists that I interview are not swayed by the sorts of claims made by Answers in Genesis or Michael Behe (as evidenced by the lack of peer-reviewed papers that they have inspired). Instead, what excites these scientists are the common themes that arise when they study the origins of different complex traits. Consider, for example, the adaptive immune system. I won’t go into detail here about the latest thinking about how it evolved (I already have here). But I will point out that it seems to have followed the same trajectory as the star-nosed mole. It did not come out of nowhere. Parts of the system–including organs, cells, and receptors, were already in place millions of years earlier, often serving different functions than they do today. These parts were then modified, connected together in new ways, and gradually took on the form they have today. The same goes for the star-nosed mole and many other case studies in complexity–even including artificial life.
In the interest of full disclosure, I cannot end this post before confessing that the evolution of complexity was not the only thing I found fascinating in working on this article. Searching for a point of comparison for the speed of star-nosed moles, I wound up at the web site for the International Federation of Competitive Eating. Did you know someone holds the record for eating cheesecake? Eleven pounds in nine minutes. Now that’s bizarre.