鼹鼠额外的一根手指

Former major league pitcher Antonio Alfonseca  had six fingers on each hand. One of his coaches was once asked about the consequences of Alfonseca having six fingers and replied, “He can’t flip you off.” Think about it.

Well, neither can many moles. Because most individuals of the type called talpid moles also apparently have six fingers on each foot. Or at least it looks that way. Now a study shows that they really only have the regular old five true fingers. The real thumb looks like the other four fingers, and what appears to be the thumb is actually a much larger-than-normal version of the radial sesamoid bone of the wrist. The finding is in the Royal Society journal Biology Letters. [Christian Mitgutsch et al, Circumenting the polydactyly ‘constraint’: The mole’s ‘thumb’]

The fake thumb has no joints, a dead giveaway that it’s not a real finger. And molecular markers show that the five true fingers develop together in a mole embryo, with the outsized sesamoid cropping up later. The arrangement is probably an advantage for an animal that spends a lot of time digging. And doesn’t convey displeasure with hand signals.

—Steve Mirsky