Humans are more evolvable now than at any time in history
About 73 percent of all genetic variation in humans has occurred in the last 5,000 years. According to a study published in Nature on November 28 co-written by Joshua Akey of the University of Washington, “Most of the mutations that we found arose in the last 200 generations or so. There hasn’t been much time for random change or deterministic change through natural selection. We have a repository of all this new variation for humanity to use as a substrate. In a way, we’re more evolvable now than at any time in our history.” In most studies of genetic variation, researchers estimated the age of more than one million variants of out DNA code found across human populations and found the majority to be relatively young. This was caused by a period characterized by both narrow reproductive bottlenecks and sudden, enormous population growth. As a consequence for the rapid growth and accumulation in gene variants, Akey’s group found that 86% of varients that seem to be deleterious are less than 10,000 years old, and many of them only existed for the last millennium.
One of the reasons for these large percentiles is due to the rapid population growth. 10,000 years ago at the end of the last ice age, there were about 5 million humans on earth and now there are 7 billion. During reproduction, random variations emerge and if multiplied across humanity’s expanding numbers, than an enormous amount of variation is generated. Natural selection never stopped acting and new mutations with especially beneficial effects, such as lactose tolerance, still spread rapidly, while those with immediately harmful consequences likely vanished within a few generations of appearing. But most variation has small, subtle effects. “Population growth is happening so fast that selection is having a hard time keeping up with the new, deleterious alleles,” said Akey. One of the factors that complicate natural selection in current times is the fact that it is not longer as natural as it used to be. These theoretical models do not account for culture and technology, which are two strong forces with major influences. As of now, the use of reproductive technologies is being studied to see if they ease selection pressure or make them more intense.
It seems common sense to me that evolution is still occurring, especially with the rapid growth that the population has experienced within the last few thousand years. As an organism, we were built to adapt and survive in some way or another, but the fact that so many deleterious mutations have occurred is amazing. I am curious if this is true with other species that have yet to be studied, or if it is due to the fact of how we have changed our natural eating habits and sexual reproduction through technology. Whatever the true cause is, I have always wondered what humans would be like in another 1,000 or 2,000 years and if any changes would even be noticeable. I hope more studies like these can predict what will happen to the human population within the next millennium.