A stem-cell revolution
Using retroviruses to introduce DNA into human skin cells, researchers in Japan and the U.S. created stem cells without using human embryos. While the new stem-cell lines appear to have all the promise of embryo-derived cells—they can develop into any cell in the human body—they present none of the ethical problems associated with harvesting embryos. “This work represents a tremendous scientific milestone,” said stem-cell expert Dr. Robert Lanza—“the biological equivalent of the Wright Brothers’ first airplane.” The discovery provides a road map for creating genetically matched replacement cells that could be used to treat patients for a variety of common and deadly diseases.

One man’s genome on display
Renowned geneticist J. Craig Venter exposed his deepest biological secrets. By publishing his entire genome, Venter revealed that he had wet earwax and a predisposition for Alzheimer’s. More significantly, the code provided revelations applicable to the entire human race. It turns out, for instance, that we’re less alike than we thought, sharing only 99 percent of our genome with other humans. And if Venter’s code can be mapped, so can anyone’s—meaning that in the future, doctors might offer personal genealogical assessments along with traditional health care.

Better bionics
Scientists ratcheted up their work on bionic limbs, in response to the recent wave of amputee soldiers from the wars in Iraq and Afghanistan. Doctors can now fuse real nerves with machine sensors, allowing amputees to control their bionics with their brains’ own motor mechanisms.

No more periods
Women can now choose whether or not they’d like to have a monthly period. It has long been possible to eliminate one’s menstrual period—any 21-day contraceptive, taken continuously, will do it. But a drug called Lybrel was released onto the market, the first contraceptive specifically designed to eliminate periods altogether. Researchers this year also found no ill effects in women who decided to forgo menstruation.

Surgery that doesn’t show
Doctors introduced scar-free surgical procedures, developing techniques to enter the body through natural openings instead of making incisions. In Pittsburgh, surgeons removed a boy’s brain tumor through his nose, doctors in India performed appendectomies through the mouth, and surgeons in New York and France removed the gall bladders of two women through their vaginas. In the future, said Dr. David Rattner, bowel surgery will be “like going to the dentist and getting a root canal.”

Chimps like us
Some of the distinctions between humans and chimpanzees fell by the wayside this year. Senegalese chimps were observed hunting small mammals with sticks that they had sharpened with their teeth—the sort of behavior once thought uniquely human. And researchers in a West African rain-forest site found evidence that chimps engaged in human-like toolmaking thousands of years ago, when they smashed nuts with large stones. In one realm, chimps this year proved they’re actually smarter than us: Three 5-year-old chimps beat a dozen human college students on a test of short-term memory. “It’s back to the drawing board again in terms of trying to define how humans are special,” said researcher Jill Pruetz.