According to genetic evidence to be published Friday, modern humanity may be much younger than expected, no more than 270,000 years old. And in terms of their Y chromosomes at least, all men are brothers.
They descended from a small group of male ancestors - Adams, if you will - whose sex-determining genes have been passed on relatively intact. In fact, male humans may be much more closely related genetically than are bands of other primates, such as chimpanzees or gorillas.
The finding adds to the mountain of evidence that all human beings share the same basic genetic blueprint, and that population differences and racial characteristics, though they appear large, are really superficial variations.
“The differences between us - as socially striking as we may wish to make them - are largely irrelevant from a biologist’s standpoint,” said Dr. Robert L. Dorit, Yale assistant professor of biology, who conducted the research with Hiroshi Akashi of the University of Chicago and Nobel Laureate Walter Gilbert of Harvard University.
In efforts to probe the human genome for biological clocks that reveal our past, the researchers performed molecular analysis on a specific portion of the male sex determining Y chromosomes of 38 men from around the world.
Genetic mutations occur at fairly predictable rates over time, but the scientists found no differences in the worldwide sample, indicating that the men all were related to progenitors who trod the earth about 270,000 years ago.
The mutation rate in the Y chromosome was established by comparing human DNA with that of related apes - chimpanzees, gorillas and orangutans. Humans are believed to have shared a common ancestor with chimps and gorillas about 5 million years ago, and with orangutans about 14 million years ago.
Mutations were found as expected in the other primates, but none in humans. “This probably means we are a very young species,” Dorit said.
Previous estimates for the origin of modern man (Homo sapiens) range from 100,000 to a million years ago.
The Adam theory, which appears in this week’s edition of the journal Science, roughly corroborates the timeline of the controversial “Eve” hypothesis of the 1980s, which holds that all humans are descended from female ancestors who lived in Africa about 200,000 years ago.
Although an animal species may start off with a broad mixture of different genes, scientists believe it is relatively easy for genes from a related group of individuals to become dominant in that species over time.
Evolutionists agree that hominids (early human ancestors) originally arose in Africa about four million years ago and spread from there into the rest of the world.
But no one knows where, when, or how often the hominids evolved into early humans. Now DNA evidence is yielding clues.