Two Routes to the Same Destination

By Ann Gauger

We have had a flurry of postings about examples of homoplasy and convergent evolution at our Facebook page.

My personal favorite so far: olfaction in insects and mammals. Both have olfactory receptors that are membrane channels. Here’s the surprising thing. Even though they have no common origin and no sequence similarity, the channels look a lot alike…that is, until you look closely. One is front to back, with its N terminus outside the cell, the other back to front with its N terminus inside. Nonetheless, both are proteins that span the membrane seven times, and serve as regulated olfactory receptors.

Go here for a link with pictures.

Conway Morris, in his brief article on the subject, said, “ in terms of transduction, the system evidently has no alternative. The molecule must be a seven-helix transmembrane protein; this is the molecule of choice. Evolution meets design: Darwin and Plato embrace.”