evolution & useless parts

I haven’t been reading much recently because I’ve got this huge stack of magazines that somehow have managed to overbreed underneath the coffee table and I’ve been trying to get them under control. I was reading one of those magazines the other night, the June issue of Discover, and there was an article in there about useless body parts. These are parts of the human body that are left over from evolution (the tailbone, vestigial body hair) or due to sexual redundancy (nipples on men).

What I hadn’t realized is that in addition to these obvious extra body parts that I had already heard about, there are a whole lot of other extra parts that some of us just don’t have.

Take, for example, the palmaris longus muscle. This is a long muscle that runs from the wrist to the elbow and attaches at the base of the thumb. According to the Discover article, it may have been important at one time to our ancestors for hanging and climbing, but serves no useful purpose now. In fact, somewhere between 10 to 20% of the population doesn’t have it at all or only has it on one side. (You can see if you have it with this test; I needed to twist my hand a little to see it. I still have it on both sides).

There are a whole bunch of these things: missing muscles, extra bones. Some of us have them and some of us don’t. In short: we are still evolving. Eric, with a degree in biology, says “duh,” but this is not something that had ever occurred to me. I had assumed that evolution was so slow to affect change that you could determine differences over time after they had happened, but not be able to point to actual population changes as they were occurring. I didn’t think that I would be able to point to someone next to me and say “that person has evolved fewer muscles than me.”

My mind is blown.