A snake with a rare atavism was discovered (and clubbed to death) in a Chinese bedroom. It had a single foot.
As freaky as this is, an atavism - the occurrence of an ancestral trait otherwise lost in the extant species - is good evidence for evolution. Given the right mutation(s), an organism may develop a trait as it was in all the ancestors of the species. There are many examples of this, such as humans with tails.
So what caused this? Contrary to what the snake expert on the site said, an autopsy won't reveal the cause. For that the snake's genome has to be sequenced. Was it a mutation in the germ-line (either egg or sperm), or a somatic mutation during early development? The fact that the snake only had one leg suggest that it would be somatic, or it would most likely have had two. (My youngest son has two different eye-colors, and no doubt that is caused by a somatic mutation.) What kind of mutation (single nucleotide, or a larger scale event)? And note, that if it is a somatic mutation, offspring of this individual would not have had legs. Shame that. I'm sure lots of people would fancy havinga rare legged snake, for a pet or for dinner.
Other good hypotheses have surfaced. Ironically, PZ Myers is guessing that pleiotropy is to blame (the irony being that I should have thought of that), by way of some gene(s) that control limb development also have other functions, and that constraint then prevented the gene(s) from being destroyed. Instead it could be silenced specifically for limb development, and it is this repressor that PZ guesses has been suppressed during early development by an environmental factor, leading to activation of the genes that make the limb. Another hypothesis is that the whole thing is a photoshop hoax, and yet another that it is the leg of the snake's last meal protruding through the skin. I highly doubt this last idea, seeing that the limb and digits are very well defined, which seems unlikely if the skin belongs to the snake.
5 hours ago in The Phytophactor