Human evolution is complex, to say the least.
It is complicated by love, which makes us keep people alive. It is complicated by the science and technology that enable us to do this. And it is complicated by our environment, which is relatively stable, meaning we haven't needed many significant adaptations over thousands of years.
But what will happen to the population of people – generations of people – who left Earth to find new life in the vast space?
The environment outside the protective environment of our home planet is very different from the one in which we have evolved for millions of years. It is possible that our species will become something completely different.
The very concept – human evolution outside the Earth – is not so far-fetched. It may seem that this is not so, but in everyday life people are still developing.
Scott Solomon, an evolutionary biologist at Rice University, has written a book about ongoing human evolution and has spent a lot of time pondering how we might evolve in the future. According to him, migration away from Earth will definitely change us.
“For evolutionary change to occur, you need genetic variation and natural selection,” he told ScienceAlert.
“When you have these two things, a population that is facing very big environmental changes, evolution can happen quickly. We will start it if we move, say, to Mars. '
Space will hurt you.
The pressure on the environment will be the main reason for our transition from terrestrial to space. This is already obvious. However, even a temporary walk in space physically changes people. Astronauts, even after months in space, can take years to regain bone density lost in microgravity. Some changes are happening even faster.
Kyra Bakal is a scientist and medical practitioner at the University of Auckland in New Zealand. She spent several years working at NASA's Johnson Space Center doing aerospace medicine.
“There are some things that happen very quickly,” she told ScienceAlert.
There is, for example, a baroreceptor reflex. It regulates our blood pressure by keeping it constant in response to external changes. This is the reason why you don't faint when you stand up and your blood doesn't collect in your legs due to gravity. In microgravity, this reflex is immediately disrupted because you don't need it.
Changes also occur in the vestibular system – finely tuned mechanisms that help us maintain balance and control our eye and hand movements.
“All of a sudden, you find yourself in a situation where if you drop something from your hands, it will not go anywhere,” explained Bakal.
Other changes that occur over time in microgravity conditions include loss of bone density; without constant gravity on your bones, they lose density about 10 times faster than people with osteoporosis. There are also anatomical changes in the eye, microstructural changes in the brain, and even changes in the gut microbiome.
Between nature and nurture.
Culture, technology, and natural selection will also be important for space humans. Will there be artificial gravity or not? Science fiction suggests that lack of gravity will cause humans to become fragile, but Solomon believes otherwise – simply because of childbirth.
Not only is the birth process difficult, but the minerals for the baby's growth are often taken from the mother's bones, resulting in a decrease in bone density. Thus, women who are more likely to survive pregnancy and childbirth in space may have denser bones to begin with, allowing them to live in order to have children with denser bones. Technology and natural selection can play a role here.
Will there be radiation protection? How strong will it be? Radiation can lead to mutation (and cancer), and it can lead to unexpected evolutionary paths. But darker skin is more resistant to hazardous radiation, so that can play a role too.
All of these and other, smaller influences will have different effects to shape a person optimized for their space environment.
In general, we cannot predict what our space descendants will look like because we do not know all the factors that will come into play.
We may never become a real space species. We may never leave the solar system. But we are also unlikely to stay here on Earth forever.
