The Attack Of The Divergers

Organisms must evolve and adapt to habitats on Earth if they are going to survive to reproduce and pass on their DNA. The human species is the result of evolution, we are descended from simpler life forms whose variations allowed them to survive in changing environments. Yet it can be argued that humans are no longer exposed to our environment. We have machines, clothing, and drugs that minimize our exposure to temperature, weather, and predators. But there is one thing from which we cannot isolate ourselves, and that is gravity (or the lack thereof).

Currently, most of the people who leave Earth’s gravity well are astronauts, who suffer a significant loss of bone and muscle mass, as well as a reduction in bone density, because of long-term exposure to zero gravity. This occurs because in zero gravity there is a shift in body fluids, resulting in decreased blood flow, which in turn makes it harder for the cardiovascular system to get nutrients to the bone. Exercise is known to counteract these effects, but the astronauts must spend large amounts of time doing the exercises. This leaves them much less time to perform the duties for which they went into space in the first place. For this reason, long-term habitats for humans in space would have to include artificial gravity, which would probably be simulated “by using a long-spin arm and a slow rotation." This implies a rotating space station with higher simulated gravity at the outer edges and zero gravity at the center of spin (like the space station in Babylon 5).

If the humans in space are going to diverge, they must be isolated from Earth and never (or almost never) spend significant amounts of time in our gravity well. They would be living and working in space and/or on moons and planets with lower gravity. It’s tempting to predict that these Space Humans would be smaller than us, with smaller, less dense bones. But that assumption is more in line with Lamarck’s Theory of Acquired Characteristics: the first generation of people who colonize space lose bone and muscle mass because they’re living in lower gravities, so their children are born smaller. According to modern evolutionary theory, it’s not their parents’ loss of muscle mass the children would inherit, it’s their DNA and (specifically) their cardiovascular system. Therefore the Space Humans who are most likely to pass their characteristics on to their children will be the ones with a cardiovascular system that can deliver nutrients to their bones (not to mention certain other body parts necessary for reproduction) in lower gravities.

Variability is the most important factor in the survival of any species, and those who can adapt to rapid change are the ones most likely to survive. Size and bone density are physical characteristics that can change even within the lifetime of an individual organism, depending on the amount of nutrients that organism receives and the outer forces (like gravity) acting upon that organism. People who live in space may very well be smaller than people who live on Earth, but any actual divergence will spring from differences that evolve in their cardiovascular systems. Since this system delivers oxygen and nutrients to the entire body, these changes could cause their organs to be different -- including their brains.

When that happens we may begin to see the emergence of a new species, one that can no longer (or no longer wants to) reproduce with us.