This blog is about trying to put some (speculative) flesh on the bones of the preceding 6,000 generations which have led to me. I haven’t got very far because I’m still struggling with what should be the necessary (and sufficient) assumptions to make before starting on speculation. Initially I was focused on the period from 100,000 to 200,000 years ago when AMH came into being in Africa. I assumed a singular Out of Africa event sometime after that and a rapid expansion from a small population in Arabia. I assumed they reached Australia by about 45,000 years ago and the Americas across the Bering Strait around 15,000 years ago. All this before the end of the last glacial age and the population explosion that settled agriculture brought.
But even these simple assumptions are now morphing. Archaeological evidence suggests that AMH reached Arabia prior to 100,000 years ago. Moreover they may have been many forays out of Africa into Arabia. There may have been two waves (at least) of expansion out of Arabia; one pre-Toba and one post-Toba. The explosion of DNA analysis work now indicates that all non-African humans have some Neanderthal DNA. Some have in addition some Denisovan DNA. Neanderthals (and Denisovans) had originated from archaic humans who had also originated in Africa and had spread over Eurasia. They disappeared as separate sub-species, not by some cataclysmic event but as they were gradually overwhelmed and “subsumed” into the main-stream which was – for whatever reason – much more successful. The main-stream species (now modern AMH) was irrepressibly promiscuous. It seems they mated with all other homo sub-species available (Neanderthal, Denisovan and possibly one other). The recent articles (here, here and here) about current East Asians having about 20% more Neanderthal DNA than current Europeans suggest that the AMH – Neanderthal matings were not an isolated one-time incident, but occurred at least twice.
So I need to rebuild the framework of assumptions on which to construct my narrative and that means going back to the very foundations. It is not important to my narrative that any or all of these assumptions are proven – only that they are feasible. What is important though is that none of the assumptions be demonstrably false. My current set of “layman” assumptions – still being refined are:
- The primate line diverges from a common ancestor to give the predecessors of gorillas and of humans/chimps at least 10 million years ago – in Africa.
- Archaic humans and chimpanzees diverged from a common ancestor around 8 million years ago (and for my narrative it does not matter if it was 5 million or 10 million years ago but it would matter if it was only 1 million years ago).
- This primate-human divergence occurred only once and only in Africa. Gorillas and chimps and bonobos are native only to Africa. If this or similar divergences took place in other locations as well any resulting species did not survive.
- In due course the homo line gave rise to the bipedal homo erectus around 3 million years ago – again only in Africa.
- Homo erectus left Africa – probably many times whenever glacial periods allowed – and spread across Europe and Asia but did not make it to the Americas.
- Neanderthals (in Eurasia), Denisovans (in East Asia) and possibly another sub-species (in South Asia?) evolved as the main-line from these archaic humans. Probably starting in the period from 600,000 years ago to about 400,000 years ago.
- Some admixture may have taken place between these populations whose territories had some overlap.
- In the meantime in Africa, modern humans evolved and separated from the archaic humans who – in other places – had evolved into the contemporary Neanderthals and Denisovans.
- In due course around 300,000 years ago the ancestors of modern humans appeared and AMH had established themselves in Africa by around 200,000 years ago. Other streams of homo erectus had by then died out.
- Then around 100 – 120,000 years ago populations of AMH had found their way into Arabia. There may have been many such excursions but possibly only one or two survived for any length of time.
- Sometime before the Toba explosion 74,000 years ago, a wave of expansion eastwards had reached what is now SE Asia and had begun to penetrate north into Central Asia. Most of these settlers were extinguished by the Toba explosion but some few pockets may have survived. A small population in Arabia probably survived or were replenished by further migrations – when humid conditions allowed – from Africa.
- Soon after the Toba event came a population explosion in a green Arabia/Persian Gulf/South Central Asia and the great expansion.
- And the interactions with the Neanderthals and Denisovans would have come about during – and maybe due to – this expansion (70 – 30,000 years ago).
And the rest is history.