Evolution

Assessing the Future of Human Evolution



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Evolution is unavoidable. Therefore human evolution is unavoidable.

There is evidence that humans are still evolving. For example some 700 relatively new genes have been discovered in the human genome just within the last 5000 to 15,000 years. (See http://www.nytimes.com/2006/03/07/science/07evolve.html.) Other studies show what would seem to be a predictable trend: increases in brain size in humans over the last few thousand years (Evans, Patrick D. et. al. 2005. Microcephalin, a gene regulating brain size, continues to evolve adaptively in humans. Science 309: 1717-1720.) There are numerous other examples of human evolution taking place that are available in the scientific literature.

It is not really a question of whether or not humans will continue to evolve.

They will.

Even the direction of evolution is difficult to predict. Evolution is based on random inputs - mutations. So not only must some genetic characteristic be favored by natural selection, it must also occur as one of the possible random inputs in the first place.

However there is one thing that we can comfortably predict about human evolution - it will take place at a much slower rate in the future than it has in the past.

There are three factors affecting this slow rate of evolution.

First, evolution takes place most rapidly in small, genetically isolated populations. In such populations a specific genetic characteristic can become a part of the entire population's genome in a relatively few generations. Humans evolved into different races in populations which were genetically isolated from each other.

The human population, however, is currently very large - and continuously growing larger - as well as far from genetically isolated. With few exceptions it is possible to get from any place on Earth to any other place on the planet in 24 hours or less. Therefore the number of human generations required to have a new genetic characteristic become common throughout the human genome is very large.

The second factor is modern medicine. Natural selection works to eliminate genetic characteristics that cause early death or an inability to reproduce efficiently. Humans have developed modern medical practices, medications and techniques that allow people to live longer and have children where they might not have been able to do so in the past. Those are undoubtedly good things. But those techniques and procedures decrease the ability of natural selection to control evolution.

The third factor slowing down the rate of human evolution are human technologies that allow them to adapt to changing environments without evolving new biological features. The majority of significant evolutionary change is due to environmental change. Once an organism becomes well-adapted to its environment nearly any genetic change will be negative. An extra thick coat of fur doesn't benefit an animal that already has a coat of fur that is ideal for its environment. But if an Ice Age has begun, then that extra fur will be quite welcome.

Humans have technologies that allow them to adapt to different environments without needing genetic changes. Modern humans are the only species that can live comfortably in both Antarctica as well as deep within a tropical rain forest. Global warming may very well be a fact that will result in the extinction of many species of organisms on Earth. But it seems very likely that humans, even if they are unchanged by evolution, will continue to be able to survive even as the Earth's temperature rises.

Because of those factors, it is very likely that humans will look very much like they do now a million years from now.

There is one possible - even quite probable - condition that will make this prediction fail, however. That is the fact that humans will likely develop the technology to be able to engineer their own genetic characteristics as well as the genetic characteristics of other organisms. While ethical issues abound in doing such things, particularly in humans, it seems likely that such a technology will be available within a century or less.

What happens then is largely limited only by our own imagination.

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