Discovering human interconnection through the history of our genes

Mapping Human History: Discovering the Past Through Our Genes. By Steve Olson. Houghton Mifflin, New York. 2002, ISBN 0-618-09157-2. 292 pp. Hardcover, $25.

Everyone in the world today is most likely descended from Nefertiti (through the six daughters she had with Akhenaton), from Confucius (through the son and daughter he is said to have had), and from Julius Caesar (through his illegitimate children, not through Julia, who died in childbirth). One need go back only a couple of millennia to connect everyone alive today to a common pool of ancestors.

The above is just one of many intriguing revelations the reader will find in Steve Olson's book Mapping Human History. Olson has worked for the National Academy of Sciences, the White House Office of Science and Technology Policy, and the Institute for Genomic Research. He is a proponent of the single-origin theory of modern human evolution. This theory holds that modern Homo sapiens is a new species that arose more than 100,000 years ago in Africa and moved across the globe replacing indigenous archaic populations.

Olson carefully and authoritatively sheds strong skepticism on the concepts of race and ethnic grouping. He believes that human groups are much too closely related genetically to differ in but the most superficial way. In other words, we are all cousins and are descended from Nefertiti, Confucius, and Julius Caesar.

A key to this skepticism concerning race is what we know about DNA and mitochondria. Mitochondria are "hitchhikers," so to speak, inside every human cell. They are almost certainly descended from bacteria that began to live inside the cells more than a billion years ago. They are the cellular battery pack providing the cell with energy. The cell, in turn, provides them with a comfortable place to live.

But all humans receive their mitochondria from their mothers. Sperm cells do have a few mitochondria, but "they are tossed away like worn-out flowers in the process of fertilization." Since mitochondria are transmitted from the mother, Olson writes that all "human mitochondrial DNA sequences that exist in the world today are descended from the mitochondrial DNA of a single woman." A mitochondrial Eve, if you please.

Olson relates his initial skepticism when he also first heard of this "Eve." He pondered how all six billion people on Earth could have descended from a single woman. Yet, now, he writes, "this is one of those wonderful scientific conclusions that is not only true but has to be true." He then proffers both mathematic and genetic explanations for Eve. Mitochondrial Eve was not the only woman alive during her time, by the way; it is just that her line survived.

Olson also writes there was an Adam and all men are his descendants. But again, this man was not the only man alive during his time and he probably did nor know Eve.

If our mitochondria come from this Eve and all Y chromosomes come from the Adam, does all of our DNA? No, writes Olson. All human DNA comes from approximately 86,000 people who once lived on Earth. if this is so, then why is everyone's DNA not the same? That question, writes Olson, is the single most important question in all of human biology. The question evokes issues of how different appearances of human groups occurred, why genetic diseases happen, and what role our genetic heritage plays in determining who we are.

The answer is mutation. Olson describes the different types of mutation and how mutation could have caused one of Eve's daughters to produce a different mitochondrial sequence. A distinct mitochondrial sequence is called a haplotype, and a group of related haplotypes that descend from a single ancestral haplotype is termed a haplogroup.

The majority of Mapping Human History is centered around investigating and studying these haplogroups. Olson starts in Africa and discusses very early man and his migration outward. Next he travels to the Middle East and discusses Aaron, Moses's brother. Aaron's male lineage was decreed by the Jewish God to become the high priest, the Kohanim, of the Israelites. Surnames of Cohen, Cohn, and Kahn are derivatives of Kohan. A few years ago geneticists found about 50 percent of Jews who presently identify themselves as Kohanim as having a set of particular genetic markers. Today this is called the Cohen Modal Haplotype. Thus Aaron may have been a real person.

Olson then sets his sail for Asia and Australia. He devotes a chapter to "Genes and Languages" and how they may have sprung from a common source. Europe is next on his itinerary, and he relates how every present-day European has some DNA from a Middle Eastern farmer and a Stone Age hunter-gatherer.

The Americas are next and Olson relates that not all of the Native American ancestors may have come from just the Bering Strait pass. Some may have come by boat.

Olson finishes his travels and his book with a stop in Hawaii. He describes how the Hawaiian "genetic history" is occurring backwards. In the single-origin theory, human groups become differentiated in appearance as they move across the globe and undergo some measure of reproductive isolation. In Hawaii, the reverse is happening. Physical distinctions that took thousands of generations to create are being undone with a few generations of intermarriage.