Will humans evolve into a different species?

Chris Smith put this question to astrobiologist Lewis Dartnell...

Lewis - This links into the question that Xander had earlier. I think what's going on when your body is adapting to microgravity is actually your body's doing something really clever. It's doing its best to adapt to a new environment and actually by doing things like decreasing your bone density and reducing your muscle mass, it's doing a very good job of adapting to that new microgravity environment. And it only becomes a problem when you come back down to earth and suddenly there's this gravity tugging away at you. But if you were consigned to spend the rest of your life in microgravity, maybe you become some kind of shuttle pilot between Earth and Mars and back again, you maybe don't mind that much that your body's now adapted to this microgravity environment because it suits your workplace. It suits the lifestyle you've got now. But if we're looking over a much longer time scale, over the time scale over which evolution happens, it's not really so much how far away from earth and across the galaxy you would have to be before evolution would start kicking in. How long would you need to wait? And so when we do have Martians, boys and girls who are born on Mars from parents who've gone there as astronauts, they won't so much as evolve, but their bodies will have permanently adapted to this new environment. They're likely to be quite tall and spindly because their entire skeleton body has developed and grown in one third Earth gravity. They would probably end up being banished gravitationally. They would never then be able to go visit their home world of earth because their body is simply not capable of standing up to gravity.

Chris - That's pause for thought, isn't it?