There was a time, when most of our knowledge about the early Homo sapiens came from material which they left behind: their bones, the tools which they made (artifacts), the bones of the animals which they hunted, and archaeological features (remains of houses and campsites, cave paintings). Then, in the 1950s, everything began to change with a new tool for looking at the human past. It began in 1953 in the Eagle, a pub often frequented by researchers from the nearby Cavendish Laboratory at Cambridge University. Francis Crick announced to those in attendance: “We have found the secret of life.” The secret, discovered by Francis Crick and James D. Watson, was DNA.
The next step came when researchers in California began to use DNA as a way of unraveling the mysteries of the past. In his book The Neandertal Enigma: Solving the Mystery of Modern Human Origins, James Shreeve reports it this way:
“Then Allan Wilson and another Berkeley scientist named Vincent Sarich got it into their heads to look for clues to the human past not out on the African savanna but among the proteins of living people and primates.”
Human DNA is not only our biological blueprint, but it also contains the records of our genetic ancestors stretching back for hundreds of thousands of years. Geneticist Bryan Sykes, in his book The Seven Daughters of Eve, has pointed out:
“Within the DNA is written not only our histories as individuals but the whole history of the human race.”
He goes on to say:
“Our DNA does not fade like ancient parchment; it does not rust in the ground like the sword of a warrior long dead. It is not eroded by wind or rain, nor reduced to ruin by fire and earthquake. It is the traveller from an antique land who lives within us all.”
In his book Humans: From the Beginning, Christopher Seddon puts it this way:
“Encoded in DNA within the genome of each human alive today is the story of every migration involving that individual’s forbears going back to the emergence of Homo sapiens; and before that an evolutionary history of our species that stretches back through its hominin, primate and mammal ancestry, to the very origins of life on this planet.”
Genes, by the way, are not the same as DNA. Sam Kean, in his book The Violinist’s Thumb and Other Lost Tales of Love, War, and Genius as Written by Our Genetic Code, explains:
“They’re not identical and never have been. DNA is a thing—a chemical that sticks to your fingers. Genes have a physical nature, too; in fact, they’re made of long stretches of DNA. But in some ways genes are better viewed as conceptual, not material. A gene is really information—more like a story, with DNA as the language the story is written in.”
Mitochondrial DNA
In understanding our human past, geneticists and biological anthropologists often look at mitochondrial DNA or mtDNA (also written as mDNA). This type of DNA is passed from a woman to her children. In other words, all of us have mtDNA which we inherited from our mothers. Females will pass this mtDNA on to their children, while males will not pass it on. Analysis of this mtDNA provides us with female lineages that stretch back to the very beginnings of Homo sapiens in Africa about 200,000 years ago. Back in the nineteenth century, many of the early evolutionists, such as Charles Darwin, had guessed that modern human had first evolved in Africa, but they had no way of actually proving it. The analysis of mtDNA makes it quite clear that the hearth for Homo sapiens is in Africa and from this African homeland, our species has populated the entire planet.
Looking at anatomically modern humans (often abbreviated as AMH), Robin Dunbar, in his recent book Human Evolution, reports:
“Using mitochondrial DNA (mtDNA), the genetic evidence suggests that the origins of AMH lay in a relatively small population of about 5,000 breeding females who lived around 200,000 years ago. This doesn’t mean that the entire population at the time consisted of only 5,000 females, but rather that only these 5,000 females have contributed to the genetic make-up of all humans alive today.”
In copying DNA from one generation to the next, mistakes—which we can call mutations—are made. In mtDNA mutations occur at about ten times the mutation rate for nuclear DNA and this provides us with a more reliable indicator of change through time. Mutations in mtDNA occur at about one mutation every 3,500 years and this provides geneticists with a kind of molecular clock. Christopher Seddon explains:
“When two populations become separated, each begins to pick up its own distinct set of mutations. By determining the difference between equivalent genetic sequences in two populations, it is possible to estimate the time since they diverged from one another. The molecular clock principle can be applied to long-separated human groups (for example Aboriginal Australians and Native Americans), or to species (for example modern humans and chimpanzees).”
Since mtDNA traces matrilineal descent, this has enabled geneticists to group data into distinct genetic lineages known as haplogroups. Geneticists have creatively designated these haplogroups with letters and numbers. The oldest haplogroup is L0 which is the predominate haplogroup among the Khoisan-speaking people of Africa, such as the !Kung and the San.
Y-Chromosome DNA
A second type of DNA which can be used to provide insights into our past is the Y-chromosome DNA. This type of DNA is passed through the male line and thus provides insights into male lineages. There is often a link between the Y-chromosome DNA and patrilineal surnames.
One of the interesting cases where Y-Chromosome DNA was used to resolve an ancient mystery involves the Lemba tribe in Africa. The Lemba have a tribal tradition about their Jewish roots. Sam Kean explains:
“…ages and ages ago, a man named Buba led them out of Israel to southern Africa, where they continue today to spurn pork, circumcise boys, wear yarmulke-like hats, and decorate their homes with emblems of elephants surrounded by six-sided Stars of David.”
In Judaism, the Cohanim have special ceremonial rites: they are a priestly family with responsibilities for the Temple service and blessing of the people. The Cohanim, a male patrilineal lineage (i.e. all are descended from the same male), are descendants of Aaron, the brother of Moses. According to tradition, the Cohanim lineage has passed from father to son without interruption for more than 100 generations. Geneticists have found a specific set of markers for the Cohanim. Among the Lemba, Y-Chromosome DNA analysis has shown that 10% of the Lemba men have the signature Cohanim Y-Chromosome, thus providing proof of traditional Jewish roots.