No, this isn’t about Neil Shubin’s wonderful book about fossils, fishes, and evolutionary remnants, but a an article by Dr. Michael Mosley on, oddly, the BBC News “health” page. You must see it, if only to watch the 30-second time-lapse video (made from high-quality scans) of the development of the embryonic human face up to ten weeks. As Mosley explains (and the video shows), our fishy ancestry explains that curious groove between our nose and upper lip, the philtrum. Have you ever wondered why it’s there? It doesn’t have any obvious adaptive function. It’s an evolutionary remnant.
The video (which I’m unable to embed) shows this clearly, but Mosley explains:
The early human embryo looks very similar to the embryo of any other mammal, bird or amphibian – all of which have evolved from fish.
Your eyes start out on the sides of your head, but then move to the middle.
The top lip along with the jaw and palate started life as gill-like structures on your neck. Your nostrils and the middle part of your lip come down from the top of your head.
There is no trace of a scar; the plates of tissue and muscle fuse seamlessly. But there is, however, a little remnant of all this activity in the middle of your top lip – your philtrum.
This whole process, the bits coming together of the various elements to produce a recognisable human face, requires great precision.
To fuse correctly the three sections must grow and meet at precisely the right time in the womb.
If the timing is out, by as little as an hour, the baby may grow up with a cleft lip or cleft lip and palate, which can be extremely disfiguring. Around the world one in 700 babies are born with clefts.
Mosley also explains two other odd developmental features explained only as remnants of a distant ancestry: the descent of our gonads (sound like the title of a Darwin book) from the body cavity, and hiccups, a series of spasms that is uncomfortable for us but was adaptive in our amphibian ancestors.