NEW YORK — People the world over are almost identical, yet still so different genetically that they can be easily sorted into five major groups based on ancestry, new research shows.
In the largest study so far of human genetic variation, an international research team separated people by the major migrations of ancient humankind, from Africa into Eurasia, East Asia, Oceania and the Americas, in a way that overturns conventional notions of race.
With growing assurance, scientists are overturning deep-seated prejudices over what makes human beings different -- skin color, facial features, physique -- even as they risk creating new prejudices founded in the molecular biology of human genetic variation.
Researchers investigating human variation effectively heighten the importance of genetic differences, even as they discount misconceptions about racial distinctions and emphasize the unity of all humans.
"The core question," said biomedical ethicist Mildred Cho at Stanford University, "is why is it we keep looking at genes and variations and organizing them into categories?"
Everyone has a reason.
Many researchers are eagerly sifting the raw ore of human genetic variation for DNA sequences that could lead to more effective medications or better treatments for disease. Others hope to use racial profiling as a diagnostic tool to identify those at greater risk of chronic diseases or adverse reactions to prescription drugs. Some just want to better understand human evolution.
On the whole, there is less genetic difference between human beings than between any two members of almost any other mammalian species, scientists said.
But advances in biotechnology have made those minor differences more important and more lucrative than ever. Last month, researchers launched a $100-million effort to map as many of those variations as possible.
The latest research, published today in Science, highlights a paradox of modern genetics, several scientists said.
"Everybody is the same; everybody is different," said Mary-Claire King, an expert in human genetics at the University of Washington in Seattle. "That is the paradox."
In the new study, researchers pored through the biochemical scrawl of the human genome like a travel diary that records the migrations, matings, illnesses, wars of conquest and mishaps shaping the human species.
