I usually associate the abundance of Mega-fauna in Africa to the African's shortcomings as a hunter - however the co evolution thesis makes much more sense. In the new world, the mega fauna would be like low hanging fruit (especially sloths). Bison must have lucky enough to have existed in large enough herds to have avoided a similar extinction: having attained some sort of critical mass.

If one buys into the African co evolution theory, the next question is, how might Africans themselves differ from non Africans since they co evolved with the African Lions, Elephants, etc. ?

One hypothesis: hunting African elephants is a lot more dangerous than hunting wooly mammoths, hunting Thompson's gazelle harder than white-tailed deer. If it's really hard, don't do it. Don't form hunting parties, don't form cooperative male groups.

I usually associate the abundance of Mega-fauna in Africa to the African's shortcomings as a hunter

also might have to do with low population density. hard to tease apart the variables.

Nomads coming in from Asia to N. America would have also had low population densities.

If I didn't make it clear, the article implies that the N. and S. American mammals did not know what had hit them. Sloths would be particularly vulnerable: only able to survive hidden in dense rainforests. The African mammal evolved defenses against man the hunter over many (millions of?) years (until firearms came along).

Next question: what happened to the big mammals in Eurasia? They’re gone. Man must have arrived there recently as well. Perhaps proper co evolution takes 200-300 thousand years. So Eurasian big mammals suffered hunter-aided suffered extinction for the same reason as New World mammals: Arriving humans were too great an ecological shock.

i don't think we need to look for a one-size-fits-all solution. re: population density, i don't know, if humans hit a new continent with naive animals and few human parasites, why shouldn't their population quickly overshoot carrying capacity? note also that humans weren't the only mammals to invade via berengia, north and south america were repeatedly invaded by species from eurasia for the past tens of millions of years. each wave tended to result in extinctions as newer more resilient eurasian mammals overcame the new world species.

It was the overkill of the asian megafauna by north american hunter gatherers that caused the clovis point to be restricted by the SALT II treaties.