From “Mystery of Disappearing Bird Digit Solved?” (ScienceDaily, Sep. 4, 2011), we learn the answer to one of life’s little mysteries: How does the three-toed bird foot map onto the five-toed mammal foot:
Evolution adds and subtracts, and nowhere is this math more evident than in vertebrates, which are programmed to have five digits on each limb. But many species do not. Snakes, of course, have no digits, and birds have three.
Yale scientists now have a good handle on how these developmental changes are orchestrated in the embryo. But there is still one outstanding debate on birds: Which digits are they? A thumb with index and middle fingers, or the index, middle and ring fingers?
As it turns out, a Yale genomic analysis shows that on a three-toed foot, the first digit starts where the index finger on a hand would be.
Can evolution easily add functional digits to vertebrates? Subtraction, it seems, has always been easier. There’s a message in that about how evolution really works – for those who care.