hate to tell you, but 74,000 years ago isn't actually the same as 12,900 years ago. There are enough years in between for a human tribe to
get busy. Especially since they were only working fifteen hours a week and so had more time for nookie than a modern Japanese Sarariman. That is, after all, the period of time where humanity expanded from "Only one village survived" to "Human tribes on every continent except Antarctica." 'Course they had to eat a lot in order to multiply so much...
When humans reached North America 13,000 years ago, 78 species that weighed over a ton vanished in the terminal Pleistocene megafauna extinction. After scrutinizing the fossil record, a team of...
wildlife.org
I agree with your overall points, but I have to disagree with the specific point about humans causing those mass extinctions. The article you link is
extremely self-serving in pushing a desired narrative, and conspicuously silent about alternative -- quite possibly superior -- explanations for the observed data.
The reasoning followed is that humans moved out of Africa, and then megafauna went bye-bye, and therefore it wuz da humies wot dunnit.
This
rather ignores that the time-table doesn't add up. Humans moved out of Africa way, way, waaaaaayyyyyy before the megafauna started to really decline. And in fact, the human sub-species that (descended from those that) moved out first (most notably the Neanderthals) were using very inefficient "
kill lots of 'em, eat what we can leave the rest to rot" methods. Homo Sapiens in fact represented a trend of greater efficiency ("
kill what we can eat now").
Naturally, the expansion of homo sapiens does represent a period of population growth. But that was also limited until the Ice Age really ended. And
then things got wild. It has been argued (in my opinion, convincingly) that the megafauna was well-suited to the Ice Age, but had trouble adapting to the changing conditions. The population boom of homo sapiens certainly didn't help, but in what I consider to be the most convincing reading of the data, humans merely "finished the job" that the climate had already done for the most part.
As for North America in particular: I find the idea of a Younger Dryas impact event to be at the very least plausible, and as more evidence is uncovered, I find myself leaning ever more
towards this hypothesis. The impact event would have centred on North America, causing pretty terrible conditions in great regions. In a turn of (pre-)historic irony, the climate conditions in North America had been relatively stable. The effect was that up until that point, megafauna in North America did better than in much of Eurasia.
The "humans did it" hypothesis, naturally, points towards the fact that humans arrived late in the Americas, and
that's why the megafauna lasted longer. I don't find that convincing. The megafauna extinction in America started over 10.000 years after humans arrived on the scene, and then happened quite suddenly. With a
bang, one might say.
The idea that humans hunted the megafauna to extinctions becomes shaky when we note that the megafauna extinctions --
everywhere -- occurred between 10.000 and 30.000 years
after homo sapiens showed up; that they happened precisely during a great climate shift; that they occurred earlier where climate shifted earlier, and later where the climate shifts were less severe; and that in a place where a megafauna population did fairly well until relatively recently (North America) this suddenly and dramatically shifted precisely in the period when
something caused a sudden and dramatic thousand-year climate swing that we call the Younger Dryas.
Based on these considerations (which, I admit, I have presented here crudely and hastily) I really think that the megafauna extinctions were chiefly caused by external factors (global climate shifts and quite plausibly a serious impact event), and not by human action. At most, humans played a relatively minor role in the process. More that of a vulture than of a great and ravenous predator, really.
(And in the article you linked, a clue to the true motivations between the "humans did it" hypothesis is found quight away, when the author blames humanity for it all, and then goes on to add "...
much as human activity today is leading to extinctions". This accusation, thrown at the feet of humanity, is politically motivated.)