If humans give birth in space, babies would have giant, alien-shaped heads.

If humans give birth in space, it would be very different from giving birth on Earth. First, we'd be impacted by the zero gravity environment.

  Scientists have studied a lot of pregnant animals in space, including salamanders, fish, and rats, but not humans. Over 60 women have traveled to space, yet none were pregnant during the trip, let alone gave birth while floating in zero gravity.

But with talk of future space colonies and cities on Mars, there's a good chance that one day humans will give birth somewhere beyond Earth, and that brings up some interesting questions. What will it be like? How will space babies look? And ultimately, how will giving birth in space be different?

The most obvious difference is the low-gravity environment, and without the aid of Earth's gravitational pull, it might make it more difficult for the mother when it comes time to push the baby out. Plus, if one day women lived in space permanently, some of the risks of pregnancy would be much greater than on Earth.

For one, without the stress of Earth's gravity, her bones lose density. Studies show that astronauts, for instance, lose 1% to 2% of their bone density for every month spent in space, and that would be especially concerning for giving birth because the pelvis could fracture in the process. In fact, doctors recommend that women with brittle bones avoid a natural birth altogether, which could mean births in space would be left to other methods.

Scott Solomon: That could lead to an increased reliance on C-sections for childbirth for people living in space.

Narrator: That's Scott Solomon, an evolutionary biologist and professor at Rice University. He walked us through what space might do to generations of humans born in low-gravity environments. We already know that the way we give birth influences our anatomy. For example, the size of our heads is restricted by the size of our mothers' birth canals.

Solomon: With more C-sections, that could lead to larger heads in our descendants because they wouldn't be constrained by the size of the birth canal.

Narrator: And down the road, larger heads wouldn't be the only major change. We may also change color, says Solomon. That's because in space we have less protection against harmful space radiation like cosmic rays, so to counteract that, we may evolve ...

Solomon: new types of skin pigments, like the melanin that protects our skin from ultraviolet sunlight on Earth. That could mean that future generations living beyond Earth will evolve to have different skin colors.

Narrator: The more melanin you have, the darker your skin. So Solomon predicts that people living in space may develop darker skin over time. But he says these changes might take centuries or millennia for enough time for many generations of women to give birth in space.

Solomon: Eventually, people living in space could evolve to be different enough from people on Earth that we would consider them to be different species.

Narrator: But for now, we just need one very brave woman to pave the path.