Habitat:

According to the model, the new hybrid species with 46 chromosomes Homo sapiens successfully colonise and displace Homo erectus (riversiders) from the Afar triangle. The highly competitive environment acts to perfect language acquisition and many of the characteristic human cultural features. It is also the phase when I propose that the menopause and grandmothering evolved as education and skill transfer became key survival benefits. 

Meanwhile in Europe Homo neanderthanlensis and elsewhere other Homo species continued to expand and extend their technologies. The model predicts significant amounts of interbreeding between all the non-human hominids. This is the explanation  for the confusion surrounding the many paleospecies - the so-called "muddle in the middle."  Homo heidelbergensis, Homo Antecessor, Homo Helmui are all seen simply as hybrid hominids and therefore essentially all part of Homo erectus taxa. 

My model predicts that Homo sapiens was different, however. Unlike the other hominids, still with 48 chromosomes, our ancestors only had 46. This was sufficient a genetic barrier to prevent any interbreeding between us and the rest.

According to my theory, a quarter of a million years ago humans were inhabiting a habitat that would seem like paradise to us today. A small, beautiful tropical forest supplied by copious amounts fresh water pouring down from two sides of a  huge triangle of the rift valley. The forest went right up to the sea, the Danakil gulf, still present since the flooding of 4 million years earlier. It would have been a great time to live. I imagine beach parties would have been a regular ritualistic part of the culture and the monthly low tides associated with the full moon would have provided a wonderful romantic scene for lovers to stroll along miles of wet sand. I suspect that menstrual synchronisation took place at this time to coincide with with these full-moon beach parties.

Then, about 200,000 years ago, another major geological event of disastrous proportions in the northern rift  almost wiped out the entire species. The entire triangular sub-plate under Afar buckled upwards, causing the gulf to be cut off from the Red Sea. A The result was a major population bottleneck. I am assuming that massive volcanic activity caused a localised volcanic winter, blocking out the sun for weeks. This, plus the lava flows probably destroyed the forestation and our ancestral habitat. Of course it is possible that such a period of darkness might have contributed to the selection pressures for language, but I think that the ability for speech had arisen long before this.

Postulated main causes of death:

1. Inter-tribal warfare before the disaster, then the disaster - only a few hundred surviving.

2. Drowning.

3. Diseases - a small isolated relatively over-crowded population would be susceptible to this.

Socio-ecology & culture:

According to my model, the constant, fierce inter-tribal warfare that would have occurred in Afar at this time would have led to monogamous pair-bonded societies with women co-operating greatly with each other and the role of grandmothers of paramount importance.

I suspect that already by this time humans had full grammatical language and the resulting intelligence that results from it. I suspect that they had already created deities which were probably linked to creation myths that involved links with the sea.

Technologies:

I expect that these early people had already designed a complex array of lethal weapons in their inter-tribal wars. I  expect by this time the people would have discovered fire and were able to make stone tools for specialist purposes.