When we meet a stranger one of the first things we typically do is silently assign them an age – “oh, he’s maybe in his late 30s.” Placing people on an age continuum is a basic way we organize (and sometimes shortchange) humans in our world.
That age-dating strategy is even more useful when it comes to understanding our distant ancestors, especially when approximate dates may be the only information we have.
In recent decades the conventional view of the Homo sapiens timeline has gone something like this: five to seven million years ago hominids and chimpanzees diverged from a common ancestor in Africa. These branches continued to evolve and divide in Africa until around 200,000 years ago when a primitive form of Homo sapiens emerged. Another 100,000 years later a version of anatomically modern humans appeared. Groups of them – our direct ancestors – ventured north into Europe and Asia some 50,000 years ago, gradually making their way to Mumbai, Beijing, New York and all points between.
Three other Homo species preceded us in migrating out of Africa into Europe and Asia. H. erectus, H. antecessor and H. heidelbergensis are estimated to have made those journeys between 800,000 and 600,000 years ago.
This loose timeline continues to be refined as more fossils are discovered and we improve our ability to extract DNA from fossils. A report by Gemma Tarlach in the January, 2018 issue of Discover magazine surveyed papers published in scientific journals in 2017 that refute, modify and advance our knowledge. These findings shift our origins further back.
In some cases, way way back. Paleoanthropologist Jean-Jaques Hublin and colleagues reported in the journal Nature that in Morocco they found the partial remains of at least five humans, plus tools and other artifacts. Their big wow was dating Homo sapiens material as 300,000 years old, which is a stunning 100,000 years older than what had been thought. Hublin said, “We are not claiming that Morocco become the cradle of modern humankind. We think early forms of humans were present all over Africa.” In September a separate team proposed in the journal Science an even earlier start date for our species. When that team sequenced the DNA from the fossils of seven individuals found in southern Africa, they concluded that modern Homo sapiens emerged 350,000 years ago. Pushing back the birth date of our direct ancestors by a hundred or more millennia is kind of a big deal.
In recent years DNA evidence has established that our species was broad-minded about sexual partners. 100,000 years ago our forebears were interbreeding with Neanderthals and Denisovans, who were our relatives but not what you would call our same species. New evidence published this year in Nature Communications indicates that the hanky-panky started a lot sooner than was thought. This evidence came from maternally inherited mitochondrial DNA (mtDNA) extracted from a Neanderthal bone found in a German cave in the 1930s. The mtDNA was from a Homo sapiens female who evolved in Africa – our homeland – and mated with a European-evolved Neanderthal at least 220,000 years ago.
Turning our attention to Down Under, the accepted timeline for our species’s arrival in Australia was 47,000 years ago. This year, however, a team reported in Nature that 65,000 years ago is the appearance date now suggested by thousands of artifacts from a northern Australia site. Another team reported in Nature that teeth found in an Indonesian cave are from anatomically modern humans who occupied the site 63,000 to 73,000 years ago.
I’ve thrown a lot of dates at you at the end of one tumultuous year in our species’s history. (Has there ever not been a tumultuous year?) The cumulative effect of these findings is to make our species older. My intent was to arouse some curiosity about our distant past, and perhaps offer some reassurance as we stumble into 2018. It can be salutary to reflect for how many millennia we humans have been trying to get this “life thing” right. Much of the time we’re still flailing. Happy New Year!
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