The human imagination is prone to wild embellishments. Only a few decades ago science fiction writers were confidently predicting that we would be moving around in flying cars; others have confidently predicted that we will be colonising planets by the end of the 21st century. Many things depicted by such writers may well prove possible but it is important not to get carried away.
Evolution is not an inexorable force. People will not simply change because they are exposed to space. Space travel itself is unlikely to affect human evolution. This is simply because natural selection is unlikely to be at work. An individual space traveller’s physiology may change; their metabolism may slow down due the decreased demands of gravity, certain of their muscles may become weaker even as others may become stronger. But merely being in space is unlikely to affect their genes. An environment can only exert itself on race’s evolution if that race spends many tens of generations in said environment and there is a distinct survival advantage to certain traits over others.
Currently, space travel is limited to a few individuals who may spend a few years in space but this is hardly enough to affect human evolution. However, were humans ever to colonize other planets it is likely that humans living in different worlds may gradually evolve in different directions. A new planetary environment would mean that humans would have to adapt.
Stronger gravity might affect the health of weak or overweight individuals, meaning naturally strong and resilient people would be preferred as mates. More intense sunlight might increase the risk of cancer in those with paler skin, darkening the skin tone of a planet’s inhabitants over time. People tend to recognise those possessed of healthy survival qualities as innately attractive; depending on the environment that people found themselves in it is possible that certain qualities would prevail over others and humans on separate plants would start to evolve in different directions, perhaps even more extreme than the differences seen between Asians, Africans, Americans, Europeans and other ethnic groups today.
The environment of space itself, however, can only affect human evolution if people begin to breed in it. People first have to spend enough time in space to recognise positive survival traits; there then has to be enough of a population and enough generations for those positive survival traits to breed into a group via natural selection. This can only happen if people begin to live in space rather than just travelling through it; such an eventually would require a fully self-supporting biome in orbit around a planet or sun. If such technology was available it would likely be put to use on planets such as Mars or the Moon first – each of which would prevent entirely different evolutionary challenges.
