To put it mildly, human evolution is “a little complex.” For feelings, first and foremost: love, for example. It makes us want to keep people alive, it pushes us forward, it makes us make mistakes, it makes us accomplish feats. Science and technology, then, give us many powers to push us forward, and in some cases they make us worse. It is sometimes complicated by politics, greed and profit. And it is complicated by our relatively stable environment, which does not push us to adapt for thousands of years.
Then maybe it changes abruptly, putting us in difficulty and finding us unprepared. It is happening now, fast for climate change, and very fast for pandemics. But what happens when the change is radical? What would happen to generations of humans who have left Earth to find new lives in the vast wonder of space? What will the humans of the future look like in space, those of the Homo Cosmicus species?
The environment out there, beyond the protective environment of our home planet, is very different from the one we evolved in for millions of years. It is quite conceivable that our species will become something completely different.
For decades, imagining this potential transformation of humanity has been fertile ground for fiction.
In movie “Titan” (2018) the earth of 2048 can no longer accommodate life. Pilot Rick Janssen is then chosen for a forced evolution experiment that will transform him into a superhuman capable of surviving on Titan, one of Saturn's natural satellites. Despite the success of the experiment, the side effects will put the lives of Janssen and his family in danger.
If we talk about evolution due to the environment, however, in some films or series we see humans evolving into taller and more fragile creatures. In others we see the opposite: bones thicken on massive extrasolar planets, to support a higher body mass. Longevity is also imagined to be greater. In Banks' novels, humans develop the ability to live for centuries. In Schismatrix of Bruce Sterling, humans have changed to the point of being practically a new species.
Beyond science fiction, human metamorphosis away from Earth is not that far-fetched. Rather. If you think about it, humans are still evolving already here on Earth. Second Scott Solomon, Rice University's evolutionary biologist, migrating away from Earth will change us.
For evolutionary changes to occur, you need genetic variation and you need natural selection. When you have those two things for a population that is facing a big change in the environment, evolution can happen quickly. If Homo Cosmicus moves to, say, Mars, all of these factors will be there.
Scott Solomon
Space “hurts”
Environmental pressures will be a huge part of our transition from an Earth-bound species to a space one. This is already evident. Even a temporary journey through space physically changes people. Astronauts, after a few months in space, can take years to restore bone density lost in microgravity. Other changes happen even faster.
“There are some things that happen in an extremely rapid timeline”Says Kira Bacal,scientist and physician at the University of Auckland in New Zealand. Kira knows what she's talking about: she spent several years working at NASA's Johnson Space Center in the field of aerospace medicine.
There is, for example, the reflection of the baroreceptor. It regulates our blood pressure, keeping it at a constant level in response to external changes. It's the reason you don't faint when you get up, as it prevents blood from building up in your feet from gravity. In microgravity, this reflex is immediately compromised because you don't need it.
I changes also occur in the vestibular system, which helps us maintain balance and control eye movements. “Suddenly you find yourself in a situation where if you drop something from your hand, it doesn't go anywhere,” explains Bacal. “So the whole expectation of what's going to happen, the processing of the sensory input that you're getting, the way it feels to move through the space, no pun intended, is very different.”
Other changes that occur over time in microgravity include loss of bone density; without the constant stress of gravity placed on bones, they lose density at about 10 times the rate of osteoporosis. There are also anatomical changes in the eye, microstructural changes in the brain, and even changes in the gut microbiome.
Although these physiological changes give us an idea of the environmental pressures that could shape the spatial evolution of future humans, they affect individuals only to varying degrees and appear to return to normal when the astronaut returns to Earth, although sometimes this takes time. What about permanent changes?
Between nature and culture
How quickly can we expect to see permanent evolutionary adaptations in Homo Cosmicus ? To understand this, let's consider what happens on earth. Two examples above all: the disease resistance andadaptation to low oxygen at high altitude.
In the tropics, where malaria is more common, there is also a higher incidence of sickle cell anemia. This is because this hereditary disease, involves a gene that protects against malaria. The people who are most likely to survive malaria are also those with sickle cells. And different populations of people living at high altitudes they developed different adaptations to deal with low oxygen levels .
Both of the evolutions described are relatively recent and have manifested over the past tens of thousands of years, practically a blink in evolutionary terms.
But it is not only the environment that shapes the path of our evolution. Culture, the way we live and the choices we make, also play a role and can speed things up quite substantially. We can see things that have happened even in just the last few hundred years. For example, some studies have found that the timing of reproduction is evolving in modern human populations, and it is evolving in ways that are often surprising to people.
The case of Île aux Coudres
In the case of the French Canadian population of Île aux Coudres, for example, detailed church records dating back to the 18th century showed a curious trend: the average age at which women gave birth to their first child fell from 26 to 22 years in a span of 140 years. This reproductive age appears to be heritable, and women who reproduce younger have more children who also reproduce younger, coming to dominate the population. This is natural selection.
But in other places, the age of first child is rising, as women choose to delay having children for various reasons, now that those regions have the means to do so readily available (even delaying the subsequent menopause). This is culture at work. Culture, to be clear, has not replaced natural selection, it has simply changed it.
Culture, technology and natural selection will also be important for the humans of the future, for the Homo Cosmicus species.
Will there be artificial gravity or not? It would be the first, gigantic change. Starting with pregnancy. Not only is the birthing process difficult, but the minerals to grow the baby are often taken from the mother's bones, resulting in reduced bone density. So women who are more likely to survive pregnancy and childbirth in space may have denser bones. Technology and natural selection could both play a role there.
Will there be protection from cosmic radiation? How strong will it be? Radiation can trigger mutations (and cancer), and exposure to it can produce some unexpected evolutionary pathways. But the darker skin is more resistant to dangerous radiation so this may also play a role.
Overall, of course, we can't really predict what our descendants will look like in space. Also because we don't know all the factors that will come into play.
These and other minor influences will eventually shape a different human being, Homo Cosmicus.
But first of all: will there really be a Homo Cosmicus?
We may never become a true space species. It is also possible that we will never leave the solar system, but we will probably not stay here on Earth forever. Space agencies are already planning at least one base standing on the moon . We have sent several robotic missions to Mars and Plans are underway for a manned mission . A colony permanent on Mars it is no longer a matter of science fiction.
These are difficult environments, literally alien, with low gravity and intense radiation. They are completely different from our home planet, where we have been evolving for millions of years. These places will inevitably have an impact on the human body. So will the technology we have at our disposal, the way we travel and the decisions we Earth humans make about who gets up there. But not all differences are visible to the eye.
Eventually the humans of the future, our space descendants, may not look as different from us as we might expect.
