About Rationally Speaking
Rationally Speaking is a blog maintained by Prof. Massimo Pigliucci, a philosopher at the City University of New York. The blog reflects the Enlightenment figure Marquis de Condorcet's idea of what a public intellectual (yes, we know, that's such a bad word) ought to be: someone who devotes himself to "the tracking down of prejudices in the hiding places where priests, the schools, the government, and all long-established institutions had gathered and protected them." You're welcome. Please notice that the contents of this blog can be reprinted under the standard Creative Commons license.
Thursday, February 21, 2008
One more example of how science works
Darwin listed the problem as one of the great mysteries of evolution he was not able to address in “The Origin of Species”: how did bats originate from terrestrial ancestors? The modern version of the conundrum hinged, until last week, on whether flight or echolocation (the amazing ability of bats to generate a sonar-like pulse to orient themselves and locate preys) came first. For decades biologists have been arguing in favor of either the flight-first or the echolocation-first hypothesis. There were reasonable arguments on either side: we know of the existence of some modern shrews that have a rudimentary system of echolocation, lending credence to the possibility that echolocation came first, as a means to locate prey on the ground first, and perhaps in arboreal environments later.
On the other hand, in the 1980s, studies showed that terrestrial echolocation is extremely expensive metabolically, and that it can be sustained easily by the animal only in flight (because the same muscles used to power flight also generate the sound waves, at little additional energetic cost). Still, the problem remained unsolved because all fossil bats known (until last week) were clearly capable of echolocation (we can tell from the size of the cochlea inside their ears) and capable of powered flight (as judged by their skeletal structure).
But that is what’s truly amazing about science: you can literally wake up one morning and find that someone has figured out the answer to a question that has vexed people for decades, sometimes centuries. In this instance, work by N.B. Simmons and collaborators has unearthed two specimens of bats that are 52.5 million years old (as close as we’ve gotten so far to the time scientists think bats originated from terrestrial ancestors). The stupendous fossils clearly show that the animals were capable of flight, but their cochleae simply could not have allowed echolocation. Mystery solved: flight came first!
But, the sensible reader might say, how did bats start to fly in the dark without echolocation? Wouldn’t they be literally bumping into things in the night? The currently favored hypothesis is that bats began to fly as diurnal animals, and were eventually pushed into a nocturnal habit by increased competition from birds, after the dinosaurs’ demise 65 million years ago. This hypothesis makes a very specific prediction about the structure of the eye sockets of early bats, which are expected to be different between diurnal and nocturnal animals. Unfortunately, the two specimens studied by Simmons and colleagues have their upper skulls crushed, so that it isn’t possible to reconstruct the eye sockets.
Science solved a mystery, only to run immediately into a new one. But of course, next week, or next year, someone may find a new fossil that will settle this question too, and so on and so forth. Now, when was the last time a creationist discovered something that settled a scientific dispute? Didn’t think so.