Humans are clearly still evolving. Even though the criteria for passing on our genes is just managing to survive until we reproduce, natural selection keeps on working behind the scenes. But just what changes have occurred in our species over the last 2,000 years? It's a very short span, evolutionarily speaking, but new techniques have made it possible to see how we have evolved in the past two millennia.
In a recently published paper from Stanford University, researchers show just how they managed to tease the results of evolution from the changes in human DNA in recent times, as well as listing some of those changes.
The trick is to look at alleles, which are multiple and different instances of the same gene in a stretch of DNA. The differences are caused by mutations. When a mutant allele gets reproduced, it also takes the genes surrounding it along for the ride. Jerry Coyne, University of Chicago professor and author of Why Evolution Is True, explains in a blog post how this works:
Now, however, we can, by DNA sequencing, look at DNA directly, and with some fancy statistical footwork, get an idea of which genes have changed in frequency so fast that they must have been due to positive natural selection.
The result is that we can see which traits have changed in the past 2,000 to 3,000 years. They are hair color, height, lactose tolerance and insulin levels, infant head circumference and birth weight, and decreased BMI in males. One big set of changes are based around reproduction. Female hip size has increased, as has the lower age limit for the beginning of menstruation and therefore fertility. Also, the menopause occurs later.
Taken alone, these shifts may not seem huge. We haven't grown bigger thumbs to better use our smartphones, for instance. But the fact that significant changes are measurable over a relatively short time shows that we can track the changes in our genome almost as they happen, and that's pretty exciting stuff.