The story of humanity is written in our genes, and thanks to modern science and technology, we are finally able to read it. In our latest cover story, J.M. Ledgard reports from where it—and we—all began
From INTELLIGENT LIFE Magazine, Summer 2009
An hour’s drive and a 600-metre drop in altitude from Nairobi is Olorgesailie, a Lower Palaeolithic archaeological site on the floor of the Rift Valley in Kenya. It is blisteringly hot. Nothing moves in the heat of the day except dust, gathering into twisters. There are puff adders in the grass, scorpions under the rocks. The lions are thin, the giraffes few, the elephants killed. It might be the closest we have to the Garden of Eden.
From the campsite it is possible to make out the outline of the prehistoric lake which once flooded the plain in soapy water. According to potassium-argon dating, hominids lived here for 900,000 years. They made handaxes which they used to butcher the hippos, zebras and baboons they hunted and scavenged. Olorgesailie stands for the gaping history of our species, a blurry, half-formed and dreamlike time from which archaeology can pull out only pieces. The Kenyan anthropologist Louis Leakey uncovered a Homo erectus skull here in the 1940s; the brain cavity was disappointingly small. There must have been grunts, gestures with stones, blood, the sky blotted with vultures, ape children kept back in the darkness. The sense of space here is immense. So too is the sense of known time, hominid time, known at first in the way a beast knows time, in light and darkness, but conscious all the same. The night sky is black lacquered. Satellites pass across it like trams. There are shooting stars. Sometimes there is the sound of hyenas.
“To the extent we are hardwired, it is probably as small bands of hunter-gatherers,” says Spencer Wells, the American geneticist who heads the Genographic Project. Its aim is to take 100,000 DNA samples from indigenous peoples around the world and write the songline of mankind’s journey out of Africa from a place like Olorgesailie, obliterating any literal interpretation of the Garden of Eden and replacing it with a new evidence-based creed.
2. THE GENOGRAPHIC CREED
The creed holds that every single non-African on the planet is descended from one or possibly two small bands of humans who made it on rafts and skins across the Red Sea at the narrows of the Bab el-Mandeb, or Gate of Tears, about 50,000 years ago. We are a more maritime species than we ever supposed, even if we keep close to the shore. These early humans, this Mayflower on foot, scavenged shellfish along the tideline and in the rock pools, increasing their range by a few kilometres a year. Within 5,000-10,000 years, without much need for adaptation, they had worked their way around India and across the land bridges that then linked Asia with a short sea crossing to Australia.
Some 99% of the human genome is shuffled from one birth to the next. The Genographic Project traces the 1% of the genome which is not shuffled—mitochondrial DNA (mtDNA) through the maternal line and the Y-chromosome through the paternal. These jokers in the pack allow geneticists to work back to our common ancestors. Our mtDNA appears to coalesce in a single woman, who lived on the African savannah 150,000 years ago. Our Y-chromosome survives from a single man, who lived in the Rift Valley of Kenya or Tanzania 59,000 years ago. So Adam and Eve did exist—90,000 years apart. The discrepancy is because, unlike the biblical Adam and Eve, this couple only represent the last common Ancestors we can trace genetically.
About 60,000 years ago, our species had crashed to 2,000 individuals, then recovered with the help of language and conceptual thinking. The speed of our spreading is alarming set against evolutionary time, as if we’re bacteria. The journey of each individual is arranged by haplogroup, a branch of migration marked by a genetic mutation. Since the 1848 revolutions, the spread of mechanised transport and the rise of “isms” culminating in globalism, couples have been shuffling their distinct genetic families, or haplogroups, some representing tiny indigenous peoples, others much of western Europe. In many respects the Genographic Project is a race against time. Indigenous peoples amount to just 350m of the 6.8 billion people on the planet. The number of languages has gone from 15,000 in 1492 to 5,900 today. The ancient bloodlines are almost gone. Soon only the vampires will be left.
The Genographic Project, which is underwritten by National Geographic, IBM and the Waitt Foundation, revolves around the dazzling countenance of Spencer Wells (pictured below). With his blond hair, blue eyes and Nebraska roots, he is the ideal high priest to explain to white Americans that they are blacks gone curdy. His biography carefully notes that he was a “child prodigy with a love for both history and science” who entered the University of Texas at 16. He took his PhD at Harvard under the noted evolutionary geneticist Richard Lewontin, then worked for the founding father of population genetics, Luca Cavalli-Sforza, at Stanford. After a stint running a lab in Oxford and a couple of television shows, he became an explorer-in-residence at National Geographic, which he regards as “the world’s coolest job”.
For publicity’s sake, the project will help solve popular history questions. Did the Vikings leave a genetic imprint on America? How far did the Incas spread? But at its core is the hard science of population genetics.
Cavalli-Sforza’s “The History and Geography of Human Genes”, written with Paolo Menozzi and Alberto Piazza (Princeton University Press, 1994), is still considered the best overview of genetic diversity in humans. Cavalli-Sforza demolished the idea of there being different species of human being. No more Homo afer, asiaticus, europaeus, americanus and monstrous. Race, says Cavalli-Sforza, has hardly any useful biological meaning at all. It is about adaptation. Grain-eaters between the Baltic and Black Sea got pale skin, pale eyes and pale hair because they were under selective pressure to process more Vitamin D from limited sunlight. Lewontin, Wells’s other mentor, posited that if a nuclear war struck and only the Kenyan Kikuyu survived, they would still have 85% of the genetic variation of mankind; with a similar history and conditions, they too would turn blond and blue-eyed under the northern sun.
Cavalli-Sforza was the first to propose a global sample of genetic diversity, but his Human Genome Diversity Project foundered on insensitivity to indigenous peoples and a murky position on whether the DNA samples could be sold. The Genographic Project has learned from those mistakes. Instead of covering its costs with industrial sponsorship, it sells kits to interested members of the public, which in turn support a small legacy fund for indigenous peoples that sweetens their participation. The project has so far gathered 50,000 DNA samples from indigenous peoples. It has sold 300,000 kits at $100 a pop to the public in 130 countries. The major findings will be made public in 2011. “The biggest challenges have been bureaucratic and financial,” says Wells. The few remaining ethnolinguistic hotspots are in remote bits of rainforest, marsh, desert and steppe: National Geographic country.