(RNS) Humanity is on its way out. Post-humanity -- technologically enhanced and perhaps even immortal -- is coming. The stuff of science fiction? No, it's creed to transhumanists, a diverse group of technological optimists who advocate the transformation of homo sapiens into a new species, one "better than human." Transhumanists see our era of rapid technological advance as the transitional phase between our human past and post-human future. Cochlear implants, artificial joints, genetic engineering, mood-altering and memory-enhancing drugs -- all are preludes to an era when people will routinely enhance their brains, improve their bodies and perhaps live forever. Critics, however, think this could be the worst calamity to befall us, both as individuals and as a species. And they argue we should be taking steps to prevent it now. Transhumanists come in a wide variety, said James J. Hughes, executive director of the World Transhumanist Association based in Willington, Conn. Some are interested in life extension. Some want to be immortal. Some think nanotechnology -- the emerging science of molecular machines -- will some day repair our bodies from the inside out. Others are convinced they'll someday extend their memories with computer implants or upload their consciousness into a smarter-than-human artificial intelligence. What all share is the desire "to ethically use technology to become more than human," said Hughes, whose organization has 3,000 members in 24 chapters across 98 countries. If transhumanism has a poster child, it's Steve Mann. A professor at the University of Toronto, Mann is arguably a cyborg -- a bionic human. For more than 20 years, he has invented and worn electronic equipment through which he experiences the world. Strolling the street, Mann can browse the Web or monitor his heart rate, pulse and brain waves through sensors implanted in his body. He can simultaneously videotape everything he sees. Glasses correct his vision electronically -- the prescription can be changed through software -- and help his memory by giving people virtual name tags. Mann next hopes to implant the entire system, to give people a full-time "visual memory prosthesis," he said. Not everyone is thrilled at the prospect of a post-human future populated by cyborgs, designer children, conscious computers, immortals and disembodied minds roaming the Internet. Some think we could engineer ourselves out of meaningful lives. "There is the thinking that we will get the `real us,' the better, higher us, from technology," said William B. Hurlbut, a Stanford biologist who serves on the President's Council on Bioethics. But Hurlbut argues that what makes us human depends on being in bodies that aren't always perfect and that can fail. "Our bodies are not just pieces of biochemical equipment," he said. "Our bodies are ourselves." Some transhumanists don't see what's so special about being human. Marvin Minsky, a Massachusetts Institute of Technology professor and pioneer in the field of artificial intelligence, calls humans "meat machines" possessed of limited, frail minds and mortal bodies. Like other leading computer scientists, Minsky celebrates a future when humans will be able to "upload" the contents of their brains into computers or robot brains. Ray Kurzweil, inventor of the first computer systems that could read aloud to the blind, is a prominent transhumanist thinker. He has long predicted the merging of humans and computers, and recently called for replacing the body's often imperfect molecular blueprint, DNA, with software, which unlike DNA wouldn't suffer mutations. These visions of man-machine fusion have parallels in religion, said Anne Foerst, professor of theology and computer science at St. Bonaventure University in New York. For one, they offer adherents the hope of an everlasting, perfect existence that brings "solace to those struggling with the injustices of daily life," Foerst said. One must also take on faith, in the case of brain downloads, that the mind works like a computer and that consciousness can simply be siphoned off like so much software, she said. Then there's immortality. "Transhumanists want to use technology to enhance and fulfill human potential," said the World Transhumanist Association's Hughes. "That's very hard to do if you die after only 70 years." "Most of my friends would have no problem with living 500 years or longer; there's so much to learn," said Ralph Merkle, a computer science professor at Georgia Institute of Technology and vice president of technology assessment for the Foresight Institute, an advocacy group for nanotechnology development based in Palo Alto, Calif. But living forever could rob life of its meaning, said Bill McKibben, author of "Enough: Staying Human in an Engineered Age." In the book he argues that without death, humans have no opportunity to sacrifice for their children, no reason to pour out a life's work under the literal deadline of mortality. "Human meaning is more vulnerable than they imagine," McKibben said. Samantha Atkins, an avowed transhumanist employed as a software engineer in San Jose, Calif., thinks we have little choice: Improving on humanity, in her view, is the only way to save the species.

"A lot of us don't believe that the current model of humans is adequate for solving the problems we face," Atkins said. "Holding onto the norm, the `way nature made us,' may condemn us."