Scientists have been making amazing advances in bionic technology in recent years: robotic exoskeletons that help people walk, artificial eyes that help blind people see. Some of these technologies are meant as medical aids to help people regain function. But some of this research — by, say, the military — is meant to help give people superhuman capabilities.

And that raises all sorts of thorny ethical questions. Is there any point at which human augmentation is just wrong? Or are these just tools like any other — and part of our inevitable future?

To explore these questions further, I called up Jonathan Moreno, an ethicist at UPenn who's written extensively on these issues, including in his book Mind Wars: Brain Science and the Military in the 21st Century. Some highlights from our interview are below.

Artificial limbs may become so advanced, we'll prefer them to normal limbs

"People may end up liking them better," says Moreno. "But my guess is that they'll like them better for certain things, and under some circumstances they won't want to use them. A prosthetic arm might be a great idea if you're trying to play a sport. But if you're trying to make a sexual conquest, it may not be so good, unless we've evolved to the point where it's socially acceptable to put on your bionic arm."

But humans are unlikely to become full cyborgs

When many of us think of human augmentation, we think of cyborgs — people who are half human, half machine. Moreno is skeptical that this is what the future will look like. "That's the way we've sort of been conditioned to think of it," he says. "And then we know, of course, about the exoskeletons that DARPA is developing and so forth. We tend to think of it that way, but I'm not sure that's right."

"Could there be a world in which we're all bionic, the old science fiction stuff, all bionic bodies? I kind of doubt it."

Instead, the future will probably be a bit more biological — using human cells to create new organs or encourage the body to regenerate limbs, for example. "I think it's going to take a long time for this to work out, but what's going on right now in the tissue engineering labs, in the stem cell labs, ultimately I think that's where we're going and that these other sort of static-material technologies, these non-biological technologies, are a bridge — but they're not the final answer."

"There are certainly people who think that there's no reason that we can't somehow remember what our bodies have lost in evolutionary time, which is how to regrow a limb. Because there are obviously animals that do that, reptiles do that."

Steroids are nothing compared to what's coming

The military could possibly use the tissue-engineering approach to someday develop strong supersoldiers. "It would be figuring out a way to get our normal ability to grow muscle cells and tissues to be even better. So you would introduce stem cells that would help the muscles grow."

This may, however, be a ways off. "I won't be around to see it," Moreno says. "But I think in 30, 40, 50 years there will be some of that. And the junk that our athletes take now to grow muscle mass and so forth, that's going to be prehistoric. I really think that tissues will be the way to go."

"That's going to start mostly with tissues for therapeutic purposes, not for enhancement. You've got the tissue engineers and the people working with these new induced pluripotent stem cells and things like that, are trying to find alternatives to organ transplants. And eventually I have no doubt that people will find that there are some ways of using programs like that to build muscle."

There might be limits to how far we can augment humans

Moreno thinks there are likely natural boundaries of how far we can push the human body. Many advances might help restore human function — helping blind people see, helping people walk again. But superhuman soldiers could be more difficult. "If the cognitive-enhancement area has taught us anything, it's that it's hard to get the body, including the brain, to function at a continuously, reliably higher level than some physiological norm. It's much easier, it seems, to get somebody up to some physiological norm than it is to make them a lot better than that."

What's really at stake: our humanity

I asked Moreno what the creepiest thing about human augmentation was. "The creepiest thing is that we become more than human. Much of the history of ideas in the last 150 years, I think, is a response to Nietzsche, who said human beings, basically, that this is as far as we're going to get. And to solve all these problems we have we're going to have to develop an Overman or Superman, something that's more than human. And this whole business about transhumanism, the platform is really Nietzsche."

"For people like you and me, will we be able to redesign ourselves so that we really are transhuman and we live a lot longer and we live a lot healthier and we're a lot stronger and smarter and faster?"

"What that adds up to is a debate among social conservatives: Is there something we're giving up when we're no longer essentially what destiny decided we would be or what we were fated to be? At some point are we really giving up what it means to be human?"

"So part of that is the genetic lottery. And the other part of that is to be human you're supposed to strive. You're supposed to work really hard."

"The whole embryonic stem cell debate — that was all about this. That was all about feeling that the life sciences, biology, was taking us in a scary direction where we really were going to lose what it is to be truly human."

We might not ever be comfortable with some body modifications

In one sense, humans are already cyborgs — we're connected, via our smartphones, to an enormous body of information. We outsource much of our knowledge and memory to the internet. But people tend to freak out if you start talking about implanting an RFID chip into people, or a wire or electrodes. Interfering with the human body seems to be something we're uncomfortable with.

"It does seem to be," Moreno says. "But if it's cultural, then we can get habituated and become inured to it. It's an open question. And maybe people will not be freaked out by the wiring after a number of people have had it for a while. I don't know. These things that we do to our bodies, we do tend to become habituated. And artificial stuff, I think, is less tendentious as we go on with it."

"It's true there may be psychological limitations. No one really knows. I think if it's aesthetically acceptable, if it doesn't interrupt the contours of the human body, then I think it's more likely to be accepted — if it's invisible to us or if it fits a certain matrix we have in our head about what the human body's supposed to look like. So I think internal implants will be much more acceptable. But if it's grossly external it could be a problem."

"I think it's because we do have these deep — I would say even evolutionarily conserved — ideas about the human body that are really hard to change."

This interview has been edited for length and clarity.