How to make a bat

One of the interesting things about bats is that they appear fully-formed early in the fossil record, perhaps giving comfort to creationists. But aside from the fact that small, soft-boned animals wouldn't fossilize well, there has been a suspicion among the evolution-minded to suspect that bats evolved rapidly.

Instead the picture is both more complex and more satisfying. The relations between genes (the genotype) and the resulting critter (the phenotype) have much to do with regulatory mechanisms and especially how these come into play during development of the embryo.

PZ Myers illustrates this in relation to one my favorite animals in How to make a bat.

... Organisms function as wholes, and changes in one property trivially induce concordant changes in other properties. Tug on one element, changing it's orientation or size, and during embryogenesis any adjacent elements make compensatory adjustments, so that the resultant form flows, fits, and looks organic.

I've always suffered from the tug a mistaken notion of the relation between genetics and the resulting organism. Like the idea that there is a gene for eye color, for example. This notion is popular and springs from a sort-of common-sense simplification. But it's wrong:

This isn't that surprising a feature of development, though, unless you have the mistaken idea that the genome encodes a blueprint of morphology. It doesn't; what it contains is a description of interacting agents that work together in a process to produce a complex result. Changes in genes and regulatory elements can essentially produce changes in rules of development, rather than crudely specifying blocks of morphology.

The article goes on to show how a change regulatory genes and the proteins they encode for can radically change the length of digits in the paw of a developing embryo. Much of the rest of the morphology follows along. Or how to make a bat.

Speaking of bat limbs. I once had the treat of watching a bat walk. They do so quite gracefully, I can tell you, especially when you consider that they are ambulating on feet and thumbs. Here's some video of one climbing:


YouTube Flash, about 30 seconds.

Link