Cardiovascular deconditioning in free-fall is simply a matter of vascular muscles atrophying from lack of use because they don't have to work as hard to pump blood against gravity. There may be techniques developed to mitigate this as well (again, for strengthening cardiovascular systems even in one gravity, which would reduce the incidence of earthly coronaries, strokes and aneurysms). Bone de-densification is (partially) a consequence of lack of exercise and the shock of walking, which could be mitigated by molecular osteopathic repair, something that many aging women could use right now.
Even without such advanced technologies, of course, humans in new environments will evolve to them, as they have to new environments on Earth (e.g., squat body types among the Inuit to reduce the heat-radiation area of the body to maintain body temperature in the cold, or less melanin content in the skin at high latitudes to allow the absorption of more vitamin D from less available sunlight). Will someone raised in a zero-gravity environment, who after generations has only vestigial legs from lack of need, or perhaps more prehensile toes or even a tail as an extra appendage with which to grab on to holds, still be a human?
Coming from the other direction, what if we take the titanium and aluminum and silicon emissaries that we've been sending out to other worlds and upload our minds into them, if such a thing is possible? Would they be human?
All of this discussion, of course, raises the question what is human and what is a transhuman? And who will settle space?
Joel Garreau wrote a very good book on the coming age of machine intelligence and enhanced humans, called "Radical Evolution," in which he asks just such questions. If we can imbue machines with our own consciousness, are they human? Or do we need the hormones that continually wash through our bodies and brains and seem to mediate our emotions and feelings? Are people suffering diseases that may be caused when such processes get out of control, including schizophrenia and clinical depression, still human? And if so, if we come up with a cure and can calm the chemical storms roiling the synapses, have they become less so? And note, Homer, it doesn't require some monstrous return of the Nazis for this to happen just free individuals, making individual decisions to enhance their bodies, and (hopefully, anyway) their lives.
Garreau came up with something he called the Bard Test (analogous to the famous Turing Test to determine if an entity was intelligent and conscious). If you could take the person (or persons) who wrote Shakespeare's works, and show him the interactions of such creatures, would he recognize them as human? Think of it as kind of like the old saying about art, or pornography, "I can't define human, but I know it when I see it." He uses "Star Trek" as an example. Picard and Riker? Sure. Troi? Despite the empathic stuff, yup. Worf? Well, once you get past the bizarre ridges and facial features, pretty much, yeah. How about Data? Could be. Sure have to give him points for a good effort.
Life has been evolving on this planet for hundreds of millions of years. So far, the highest product of that evolutionary process (at least in terms of enabling life to expand beyond the planet on which it was born) is the human species. Humans put a little beeping sphere into orbit 50 years ago to get things rolling, and humans will lead the charge of life out into the cosmos. In the future, they may not be the fragile bags of meat and bone we know today, but I suspect that they will be creatures who fill the universe with life and love and laughter (and yes, all of the other, less desirable traits that go with being human), and they will be our children.
I've enjoyed this discussion too, Homer. I hope that we can do it again, perhaps on the 100th anniversary, in a bar in the shadow of the walls of Tycho, or with a long view of a lunar mare, perhaps overlooking the historic Apollo 11 site. And I hope (and am optimistic) that we'll still be young enough to enjoy it.
Rand Simberg is a recovering aerospace engineer and manager, and commenter on space policy. He is also the blogger behind the website Transterrestrial Musings.