March 2015 shall go down as “the month in which it turned out everything was slightly older than we thought.” Two of the most important moments in human evolution were redated – the origin of our genus and (maybe) the original migration out of Africa. The last day of the month doesn’t disappoint either, bringing us the discovery that the most important event in human evolution – the evolution of Homo sapiens – may have occurred earlier than we thought.
Yes, our evolution was the most important part. Because at the end of the day palaeoanthropology is just an excuse to sit around, look at people and talk about how great they are.
“Archaic modern” may seem like a counter-intuitive phrase, but it refers to a fairly key period of our evolution. Modern humans do have several unique characteristics – most notably our prominent chins and foreheads – but there is a lot of grey area associated with them. How prominent does a chin have to be to be human?
Yeah, bet you didn’t expect the chin to be what makes us special. How much of our success can be attributed to the chin? How much did Neanderthals’ lack of a chin contribute to their extinction? Probably a lot, I don’t know. What am I, some sort of scientist?
One practical upshot of all this chinwagging is that there a bunch of fossils that look kind of human, but maybe not quite fully human. Yet they don’t look unhuman either. As such, they get dropped into the “archaic Homo sapiens” bucked until we figure out what to do with them.
The transition from this into proper Homo sapiens is believed to have occurred some time between 160,000 – 195,000 years ago in Africa; based on the fossil evidence. Many of the “archaic” branches continued to survive for many more years after proper humans emerged though.
Redating the emergence of the moderns
New research – published just in time to be included in “the month in which it turned out everything was slightly older than we thought” (or TMIWITOEWSOTWT) – presents some genetic data that may push back the origin of modern humans. As you would expect for our ancestral homeland, Africa has a deep and rich genetic history. There lives the San hunter-gatherers, the first “branch” of our species to emerge a whopping ~150,000 years ago.
This new study examined almost 80 new mitochondrial genomes in an effort to shed light on this rich genetic history. They discovered something interesting about almost every branch they studied, but the one relevant to us is what they found about that first branch (or L0d, as it’s excitingly called). These new genomes revealed that L0d split off sometime 150,000 – 199,000 years ago (or 178,000 years ago, if you want to use more reasonable confidence intervals)!
In otherwords, this definitely human branch may have emerged 4,000 years before the earliest clear evidence we have of humans (195,000 years ago) and certainly well within the weird overlap period (160 – 195,000 years ago) with archaic humans.
Does all that mean anything?
In human evolution a minor date shift can have some pretty significant implications. Looking back earlier in TMIWITOEWSOTWT, there was a discovery that shifted the origin of Homo by a mere 400,000 years that could really change how we view human evolution. Is this (potential) shift of just 4,000 years in the origin of Homo sapiens also significant?
Well not really.
However, this study still has some pretty significant implications. For starters, the fact that it pushed the definite origin of our species into the modern/archaic grey area implies that either (a) there are some more definite modern fossils from this period we’re going to find or (b) the line between archaics and moderns is a lot more fluid than we thought. Either of which would drastically reframe how we view our species’ origin.
Further, it could help us find any of those potential extra fossils. The mtDNA used in this study came from regions of Central and South Africa that haven’t been investigated as thoroughly as other locales (Idaltu, for example, came from East Africa). Could this guide the investigations that ultimately lead to the discovery of the first Homo sapien?
In short, this research may lead to our origins being pushed back slightly; but that isn’t important. What is important is how this could help reveal how all the messy evolution in Africa is connected. And I hope it does because trying to learn it all is a pain.
Chan EKF, Hardie R-A, Petersen DC, Beeson K, Bornman RMS, et al. (2015) Revised Timeline and Distribution of the Earliest Diverged Human Maternal Lineages in Southern Africa. PLoS ONE 10(3): e0121223. doi:10.1371/journal.pone.0121223