Even before I started school, I had an information resource. I mean, besides my mom. I can still vividly recall the Golden Book Encyclopedia for children arranged on a shelf in my parents’ Victorian farmhouse. I learned to count by going over the slim, colourful, numbered volumes. At one point, I came upon the word “race.” I don’t remember what let me to that topic.
Anyway, the brightly illustrated pages informed me in scholarly tones that humans were divided into three races. People who looked like me belonged to the Caucasoid race. People who looked Asian, including the indigenous people of North America, were part of the Mongoloid race. People with the features typical of sub-Saharan Africans belonged to the Negroid race.
Of course, we now know that this was all bunk. Having discovered DNA and decoded the human genome, scientists agree that there is no such thing as race. All humans, African, Asian, European or Native American, are very closely related to each other. I might look different from the friends I have in Nigeria or Hong Kong, but genetically we are all cousins.
Birthplace of all modern humans
We are far more closely related than all chimps are, for example, even though there are many more humans than chimpanzees in the world. The other thing we now know for sure, based on our genes, is that we are all Africans. Our species, Homo Sapiens, emerged there and then gradually migrated out to every corner of the planet.
This week, a team of researchers concluded that they had located the birthplace of all modern humans in the Kalahari in Botswana. They make a case for humans arriving on the scene about 200,000 years ago and living in the region they identify for about 70,000 years. Climate change then gradually led them to migrate out to other parts of Africa and eventually beyond.
The study was a collaboration by experts in the fields of genetics, geology and climatology. Scientists took blood samples from 200 living people from cultures where we don’t know much about their DNA. These people live as foragers and hunter-gatherers in Namibia and South Africa.
Experts in the fields of genetics, geology and climatology
They speak Khoisan languages. They’re the ones with the characteristic click consonants. Readers may have noticed this language type in the popular African film The Gods Must Be Crazy, for example.
The study looked at their mitochondrial DNA, which we all get from our mothers. It then compared it to over 1,000 other Africans, mostly from southern Africa. These comparisons let them put together a kind of family tree.
As study lead professor Vanessa Hayes put it, “It has been clear for some time that anatomically modern humans appeared in Africa roughly 200,000 years ago. What has been long debated is the exact location of this emergence and subsequent dispersal of our earliest ancestors.”
“one of the most productive ecosystems for sustaining life”
She added, “Mitochondrial DNA acts like a time capsule of our ancestral mothers, accumulating changes slowly over generations. Comparing the complete DNA code, or mitogenome, from different individuals provides information on how closely they are related.”
The location the researchers identified used to contain the most extensive lake system in the history of Africa. Geologist Dr. Andy Moore explains, “Prior to modern human emergence, the lake had begun to drain due to shifts in underlying tectonic plates. This would have created a vast wetland, which is known to be one of the most productive ecosystems for sustaining life.”
According to Professor Hayes, “”The first migrants ventured northeast, followed by a second wave of migrants who travelled southwest. A third population remained in the homeland until today.” The team was able to draw this conclusion because, as she puts it, “”We observed significant genetic divergence in the modern humans’ earliest maternal sub-lineages, that indicates our ancestors migrated out of the homeland between 130 and 110 thousand years ago.”
Shifts in climate allowed our ancestors to migrate for the first time
Climate scientist, Professor Axel Timmermann used computer models to study how the summer solar radiation in the southern hemisphere varies. He found that the variation is based on the way the earth’s axis slowly wobbles. This changes the climate.
In his words, “These shifts in climate would have opened green, vegetated corridors, first 130 thousand years ago to the northeast, and then around 110 thousand years ago to the southwest, allowing our earliest ancestors to migrate away from the homeland for the first time.”
Even so, not everybody left home. Many early humans stayed behind as others wandered off to other climes. We can still spot their descendants. As Professor Hayes explains, “”Eventually adapting to the drying lands, maternal descendants of the homeland population can be found in the greater Kalahari region today.”
”It would be astonishing if our all ancestry arose in one small homeland.”
Almost immediately, these findings, which are published in the journal Nature, ran into controversy. Other scientists are skeptical that DNA analysis alone can prove the exact location where humans first arose. Population geneticist Alwyn Scally of Cambridge argues, “I’m persuaded that southern Africa was an important area for human evolution.” But, he continues, ”It would be astonishing if all our genetic ancestry at this time arose in one small homeland.”
Other geneticists, like Sarah Tishkoff of the University of Pennsylvania, don’t think that science can reliably trace someone’s lineage based only on their maternal ancestry. We also don’t know for sure that the distant ancestors of the women who speak Khoisan languages lived in the same region as their modern descendants. How do we know that they didn’t migrate there at some other point?
When experts DISAGREE, no opinion IS certain
Bertrand Russell famously said, “The skepticism that I advocate amounts only to this. That, when the experts are not agreed, no opinion can be regarded as certain by a non-expert.” My only expertise in genetics comes from the write-up I got when I mailed in one of those home DNA kits.
All I learned from that is that I “Likely have at least a little bit of a unibrow.” They’re right, but it doesn’t qualify me to weigh in on this difference of opinion.
We will never truly understand ourselves until we know where we came from. We are zeroing in on the answer to that question. Even so, science still has some work to do before we can define our place or origin with precision. Here’s hoping that more study can resolve this disagreement.
We always have more to learn if we dare to know.
Garvan Institute of Medical Research
Human Origins in a southern African palaeo-wetland and first migrations
Science Magazine (AAAS)