On Wednesday 22 December 2021 at 18:53:07 UTC, Paul Crowley wrote:
IF homo had been an active predator on these massive animals
1.5 ma to 0.5 ma then the genus would have been a part of
the ecology and left roughly the same number of fossils as any
other major predator (such as, say, Homotherium -- the sabre-
tooth tiger). Homo fossils are almost totally absent from the
landscape -- present at most as one for every 10,000 homo-
theriums, probably closer to somewhere between one in
100,000 and one in a million.
Yet the only likely cause of this pattern -- the fall in size over
1.5 Myr of dominant herbivores -- can only be the result of
homo behaviour.
What was it?
It's a difficult question, and impossible to answer if you're
trying to work with a crazy (or semi-crazy) theory of human
evolution, such as "running on the savanna" or living in
swamps, or "living in forests carrying dome-shields around".
I believe that small numbers of hominins, working over
thousands of generations, eliminated local carnivores
and omnivores that they regarded dangerous. They never
(or very rarely) did this by direct confrontation. Instead,
they poisoned them. Exactly how doesn't really matter,
and they probably changed their methods whenever the
wildlife appeared to be getting wise to their current
techniques. They placed poisoned bait around their
settlements, which acted as 'sinks' for those species. Each
new generation of predator coming into the locality would
notice the abundance of food in the form of prey species,
and the absence of local predators. They'd fill their bellies;
(few instances of starving predators will be found in the
vicinity of hominin settlements). But soon they'd fall
victim to the baited traps.
As the number of predators declined, the prey species --
predominantly herbivores -- would rapidly expand their
numbers and begin to roam freely. Within a century or
so, they'd destroy the habitat of the region. The hominin
population would have to move on, and repeat the cycle.
In a few thousand years, they'd have done enough to the
continent-wide ecology to institute an ice-age.
An ice-age has worldwide effects: everything gets cold,
the atmosphere becomes cold, dry and dusty; sea-levels
fall, forests become smaller, often turning into grasslands,
savannas become deserts.
Up to ~1 ma, the ice-ages were less severe and widespread
and were shorter than those after ~1 ma, lasting around
40 Kyr, on average. The wildlife refugia between 2.6 ma and
1.0 ma, especially in Asia, were larger and more common,
enabling faster rebounds.
Why did larger species suffer more than smaller ones (from
the recurring ice-ages)?
I suggest that it is simply that populations of larger species
were smaller, more widely dispersed, and with slower
maturation. Often they were more specialised. All these
factors meant that they found it more difficult to cope with
the radical changes brought about by the ice-age/interglacial
cycles. They could prosper, and compete with smaller species,
when times were good and food supplies were relatively
predictable. But when times became extremely hard, none
would survive. Members of smaller species would also suffer,
and populations would disappear, but a few groups or
individuals would manage to get through, and enable the
species to survive.
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