MAPPING HUMAN HISTORY

The take-home message of this five-continent trek by science writer Olson (Biotechnology, not reviewed) is that races don’t exist: genetically, we are all sisters and brothers under the skin.

That message has been promulgated in the press and professional literature lately as geneticists track the DNA in the human genome as well as in a cell’s mitochondria. These are the power factories that lie outside the cell nucleus, and we inherit them from our mothers. But Olson raises the level of discourse to a new high, assembling powerful evidence to support the no-races hypothesis. It all begins with “mitochondrial Eve,” member of a band living in east Africa over 100,000 years ago. Her descendants were the modern humans who migrated into Eurasia and, some 7,500 generations later, peopled all parts of the planet. Similarly, humans are descended from a male who passed on his Y chromosome to sons. Opponents arguing for a multiregional origin of mankind posit that different continental groups gave rise to racially distinct humans. Not likely, Olson and his sources counter, citing archaeological, fossil, and particularly biological evidence. Basically, scientists search global DNA samples looking for patterns of mutations that enable the reconstruction of genetic history. Example: A woman who gives birth to two daughters, one with the mother’s intact mitochondrial DNA and one with a single mutation, is the ancestor of two groups of females—one with the intact sequence, the other with the mutated form. These “haplotypes” create “haplogroups,” enabling scientists to trace who went where when. Y chromosome and other gene mutations allow similar analyses—all pointing to diversity, but also to biological identity. There are problems. Why no Neanderthal genes? What to do when researchers who want to study isolated groups or rare remains are accused of “stealing their DNA”? Even armed with the facts, can people ever overcome the cultural hierarchies that impose prejudice, stigma, slavery, genocide?

Olson takes a major step in the right direction, but it will be a long journey.