For a long time now it has been increasingly recognised that the human (aka anatomically modern human, AMH, Homo sapien etc…) evolutionary line is not like the simple ape-to-man illustration we stereotypically see. Our earliest and messy ancestry is branches, clusters and accumulations of different species either dying out, or meeting and mating. This ancestry spans millions of years, and unfortunately there are still so many gaps in our understanding of how we humans developed to become what we are today. Fortunately, 2017 was a massive year for human evolution discoveries and updates! Here is a look back at last year’s biggest evolutionary revolutions…
A BIT OF BACKGROUND…
The earliest modern humans were previously estimated to have emerged in East Africa around 200, 000 years ago, using the fossils found at Omo Kibish in Ethiopia, and growing numbers of genetic analyses on both modern and ancient DNA from the past three decades.
The genetics not only suggested that all of us humans alive today descended from a single group of Homo sapiens from East Africa, but that they gradually, and in waves, dispersed out of Africa between the 60 and 70 thousand (years ago) marker, with the pioneers of these travellers reaching the Middle East around 50-60 thousand years ago, and Europe another 10 millennia, or so, later.
These migrating humans joined the decreasing numbers of Neanderthals that already inhabited this area of the globe. Neanderthals are also considered a Homo species (their formal name is Homo neanderthalensis), as are the lesser-known Denisovans (Homo sp. altai or Homo sapiens spp. denisova), sharing the characteristic big brains and subsequent advanced tool use. Both of these Homo species are still (mostly) believed to not be an ancestor of Homo sapiens, but to have arisen from some common ancestor which reached Eurasia earlier. Similarly, most scholars also believe that these three Homo species mixed at some point in time, which explains why all non-African populations today present a small percentage of Neanderthal DNA in their systems. Even in light of more recent research this bit still stands, if only a bit earlier than we thought!
WE’RE HOW OLD?!
But now, just when we thought our earliest anatomically modern ancestors were emerging in East Africa, they were in fact already wandering around quite happily in North Africa and the Middle East! Interestingly, we have had earlier suggestions of this from the century-old Qafzeh and Skhul (Israel) skulls, but these were disregarded (…bad dating, the bones were not found in their original place – there can be a number of explanations). Jump ahead another 100 years, and in 2010 we discovered the ‘impossibly’ old teeth from Qesem, near Tel Aviv. These teeth quite obviously presented both modern human and Neanderthal characteristics. What was more bewildering was that when they were directly dated, the age of around 300, 000 years ago was produced – a time when modern humans were not supposed to exist, and especially not in the Middle East. Interestingly, the lithics, or stone tool technology, from the site corroborated this earlier human out-of-Africa idea. Yet again though, this idea was batted away, and the fossils put away for later consideration. That time for later consideration is now… well, 2017!
These ‘impossibly’ early human remains can no longer be put to the back of our minds and labelled anomalies. Genetic and dating technology continues to advance, and examples of earlier humans keep on cropping up across the world.
Skeletal remains from Jebel Irhoud (Morocco) were initially excavated in the 1960s, dated to approximately 40 thousand years ago, and controversially deemed Neanderthal. Further excavation at Jebel Irhoud, and re-analysis of these skulls last year actually indicated that they were 100, 000 years old, if not more! So, were our early human ancestors heading north and out of Africa long before we previously thought? Were they developing in the north as well as, or instead of, the east?
A skull showing remarkable parallels to these Moroccan examples, and their unusually modern human features, was also re-analysed in 2017. The Dali skull, known for its source location in the Dali Region of China, is considered part of the Homo erectus (archaic and not modern human) species and dates to around 260, 000 years ago! So, were the earliest Homo sapiens not as isolated as we thought? Although some have denounced this idea, the similarities between these remains cannot be ignored. Gene flow is starting to look more multi-directional, rather than a one-way system out of Africa.
MORE INTER-SPECIES SEX THAN EXPECTED
Considering this supposed earlier movement of humans out of Africa, more inter-species intermingling makes sense. Another 2017 discovery, although from a Neanderthal bone, was very enlightening for our human ancestry. The (femur) bone, found in the Neanderthal-heavy region of Germany, was dated to 120, 000 years ago, but was genetically proven, using mitochondrial DNA (or mtDNA, which is passed on solely from the mother as explained in the video below) to be significantly more similar to modern humans than to any early Neanderthal. Weird, considering that these two species’ common ancestor supposedly lived around 700, 000 years ago and since then they lived separately until around 60 thousand years ago. It’s like a hidden and mysterious inter-species romance which we are only just discovering! The genetic (mtDNA) analysis of this bone shows that between about 220 and 460, 000 years ago an African, modern, population mixed with at least some Neanderthals (enough to be recognised in the lineage). Although this is remains a wide time-span estimation, the whole period pre-dates when any modern humans were supposed to be beyond Africa and getting it on with their sister-species (not as dodgy as it sounds).
Could this be our direct ancestors romancing their more northern counterparts, or was it a parallel lineage of modern humans which eventually became extinct like all other Homos? The most likely scenario, with the data we have so far, is that Homo sapiens and Neanderthals have been coexisting and intermixing in the Middle East and Israel for longer than we already recognise. Our relationship with Neanderthals was not short-lived, and these earlier groups may not all have gone extinct. For instance, a recent study has found traces of early human migration in the genomes of at least some modern populations today.
Although we shouldn’t get carried away, and start changing the overarching course of human evolution in our school books and university lectures, we have to remember we are talking about not just hundreds or thousands of years, but hundreds of thousands – it’s kind of expected to have gaps, missing links and areas of the completely unknown! We currently have a lot of years to play with in between this sparse selection of early human remains where anything could have been going on! It will be nothing but exciting to see what we discover in the future! We shouldn’t be inclined to strictly categorise and pigeonhole new (and old) discoveries, but be open to an array of interpretations and ancestral complexities.
IN 2018 WE SHOULD LOOK FORWARD TO…
We can always hope for new, fantastic finds! New evidence found in 2018 and beyond will add to the global population of ancient individuals we’ve uncovered, hopefully pointing us (slightly more) in the right direction. Whether this direction is just out of Africa, or more of a multiregional population repeatedly connected by pioneering migration and gene flow, we’ll just have to wait and see.
Again, it is the genetics which we will now turn to, to see whether they line up with all of these revolutionary finds! Genetics are now able to estimate when a species arose using a ‘molecular clock’ (geneticists cleverly use the rate at which DNA mutates to estimate how far back that particular species branched off from its original ancestral line). These molecular clocks remain just that though, estimates – as there has not yet been a definite consensus on the rate of these mutations. Attempts to find and define a rate, if there is one, would be invaluable in determining how old we are, and how much we got about before we already thought we did!
Did you enjoy reading about our changing understanding of evolution? Do you want to learn more? Why not check out another great blog dedicated to just that, Anthropology.net!
Do you have any ideas or opinions on our ancestry? If so, let us know – you could even write about it (or anything else you fancy)!