As previously stated, bats are the only mammals truly capable of flight. But why is this? Of all the species of mammals, why is it that only the Order Chiroptera can achieve flight? And how did such an extraordinary adaptation come to be? Well…the answer is…we really are not sure. But there is evidence that may lead to the answer.
In order for bats to be able to fly, their forelimbs had to undergo huge changes. The problem is that between the beginning and end of the evolution of the bat’s wing, how did the intermediary species survive when the evolutionary adaptation would not prove to be an advantage until evolution was complete? This question was in fact an argument brought up against Darwin’s theory of natural selection by St. George Mivart. Mivart argued, “What good is 2% of a wing?” The theory of relativity presented a problem, as the bats’ ancestors would not be “fit” to survive with only a partially evolved wing. Fossil records suggest that while birds slowly evolved the ability to fly, the current yet incomplete fossil record for bats suggests that they may have rapidly evolved wings.
Scientists looked to test this theory, by isolating an mRNA sequence prx1, which is fond in bats and mice and regulates forelimb size. The scientists have found that this gene is present in elevated levels in bats, and in more moderate levels in mice. Sure enough, when mice embryos were given additional prx1, their limbs were slightly, but still significantly longer than the average mouse. When prx1 was removed, though, there were no visible changes. This test supports the thory that bats’ evolution may have been rapid, as it seems that it takes very few genetic changes to elongate the limbs.