Sitting in his office at Trinity College, Hartford, Connecticut, James Hughes explains his vision of a family gathering a couple of hundred years from now: One family member is a cyborg, another is outfitted with gills for living underwater. Yet another has been modified to live in a vacuum.

"But they will consider themselves as descendants of humanity,'' he says.

At no point in the interview does Hughes peel off his face to reveal a set of wires and blinking lights. Nor does he roll up his sleeves to expose super-strong mechanical limbs. Bearded and bespectacled, he looks pretty much the way you might expect a professor of health policy to look.

But as executive director of the World Transhumanist Association, he's one of the leaders in a movement that sees, in the next 50 years, a world where flesh fuses with mechanics and brains with circuitry. He recently published Citizen Cyborg, a book that has made waves in academic circles and urges the need to prepare for this future.

Transhumanism, a theory that has been kicking around for a few decades, envisions a "post-human'' phase where technology will bring us beyond human capabilities. Intelligence-boosting brain chips, extended life spans and even immortality are all part of this vision.

The movement has split into a number of factions, some of which take on a quasi-religious tone. The World Transhumanist Association, based in Willington, Connecticut, is one of the largest organizations and offers what Hughes calls a ``more mature and academically respectable'' take on the philosophy. According to its Transhumanist Declaration, the organization seeks "personal growth beyond our current biological limitations.''

It's an idea covering a lot of ground. Walking canes and eyeglasses are a basic form of transhumanism. And then there's uploading one's mind and living as sheer consciousness on a computer.

The organization was founded in 1997 by Nick Bostrom while he was a philosophy professor at Yale. Hughes says it has more than 30 chapters worldwide, including recent additions in Somalia and Uganda.

While transhumanism was long relegated to the scientific fringe, it has edged closer to the mainstream.

``I believe part of it is that these technological possibilities, five or 10 years ago, seemed like science fiction,'' says Bostrom, now director of the Future of Humanity Institute at Oxford University. ``Just the general progress that we've made makes it easier for people to see it happening.''

It has gained enough prominence to attract the attention of some well-known critics. One of them, political scientist Francis Fukuyama recently nominated transhumanism as the ``world's most dangerous idea'' in Foreign Policy magazine. His fear is that enhanced versions of the human being will threaten the sense of equality that societies have been working toward for centuries.

Much of what the transhumanists talk about is timely, topics including genetic engineering, cloning and the use of steroids and other performance-enhancing technologies in sports. But they also talk about things such as civil rights for artificially intelligent beings and animals whose learning and speaking abilities have been artificially enhanced.

Much of which informs one of the main questions transhumanism tries to answer: What makes a person? Hughes says ``human'' no longer works as a definition. A person, as Hughes sees it, would be any being with a certain level of self-awareness and intelligence, including robots and talking animals. Then, we would need to determine what rights these enhanced creatures have in our society.

``What are we going to say: `I'm sorry, you're not human - you shouldn't have the right to go to school and get an advanced degree?' '' he says.

The image of gorillas sitting in a college classroom discussing the Bronte sisters might cause some people to dismiss transhumanists as science fiction fanatics whose imaginations have gotten the best of them. But take a look at what's happening now, Hughes says: Scientists at IBM plan to build a computer model of a human brain; chips are being implanted in the brains of paralyzed people; MRI can be used to read thoughts. How many people 50 years ago, Hughes says, thought any of this was possible?

``I don't know how anyone who pays attention can't see how quickly things change,'' he says.

As an example of how quickly things change, Hughes points to a recent road race where runners objected to competing against an amputee with a mechanical leg. The prosthetic leg, they said, gave him an unfair advantage.

``When the cyborg athlete can out-perform the non-disabled athletes, that's transhumanism,'' he says.

Hughes describes himself as a ``techno-optimist'' and believes that human enhancements can lead to better lives. Others aren't so sure. Objections range from overpopulation to the possibility of hacking into people's brains.

Wesley Smith, a senior fellow at the Discovery Institute, a think-tank best known for advocating ``intelligent design'' as the basis of evolution, worries about what a transhumanist future would mean for humanity. If you listen to Hughes and other transhumanists, he says, we are nothing but ``so much meat on the hoof.''

``They're saying that being human does not have intrinsic value, that we have to earn our moral value by having requisite capacities, generally cognitive capacities,'' he says. And if merely being human loses its value, he says, legal distinctions will be made as to who and who doesn't deserve certain rights.

Hughes calls Smith, Fukuyama and other critics ``bioLuddites'' - people who expect only the worst from science. You can't stop scientific advancement, he says. But you can make sure it is pursued responsibly. There have always been crime and suffering, he says, but as societies advance, the better they become at protecting their citizenry. He says a post-human future will follow this pattern and most likely increase personal freedom.

``The tendency in our world is for an increased respect for personal rights,'' he says. ``We will increasingly become masters of our own fate.''