All the biggest land animals — elephants, rhinos, hippos, giraffes — live in Africa. Asia also has elephants and rhinos, but they are both smaller and less abundant than their African cousins, and no other continent is even a contender in terms of megafauna.
Even if we define megafauna more liberally and look only at abundant species, Africa still wins hands-down. I made a list of wild land mammal species which weigh 100 pounds or more and which are listed as “least concern” on the IUCN Red List. Even though many of Africa’s trademark megabeasts (elephants, rhinos, hippos, gorillas, and lions, among others) are excluded by the latter criterion, Africa still comes out on top. A full 50% of the species on the list (37 out of 74) live only in sub-Saharan Africa. By comparison, Eurasia (including North Africa) has 20 abundant megamammals, the Americas have 17, and Australia has 5. (The total is only 74 because 5 of the species are common to Eurasia and America.) The four heaviest species on the list (giraffe, Cape buffalo, and two species of eland) are all African. If I relaxed the conservation criteria a little, Africa’s dominance would be even more overwhelming.
Africa has not always been so exceptional, though. Until quite recently (geologically speaking), the other continents had significant megafauna of their own. North America in particular was home to several species of elephant, ground sloth, horse, and big cat. In his hunting memoir Green Hills of Africa, Hemingway comments on this and offers an explanation:
Looking at the way the [elephant] tracks graded down through the pleasant forest I thought that we had the mammoths too, a long time ago, and when they travelled through the hills in southern Illinois they made these same tracks. It was just that we were an older country in America and the biggest game was gone.
Hemingway surprises us a little here, turning our familiar ideas upside down and calling the New World “an older country.” What he presumably means is that humans have been hunting there for a longer time than in Africa and have killed off most of the big game — which is the exact opposite of the truth. Our species evolved in Africa, and the Americas were the very last continents we colonized. So why, if Africa has been subject to human hunting for so much longer than America, does America seem to be “hunted out” while Africa still abounds in big game? Later in Green Hills Hemingway writes:
A continent ages quickly once we come. The natives live in harmony with it. But the foreigner destroys . . . . Our people went to America because that was the place to go then. It had been a good country and we had made a bloody mess of it and I would go, now, somewhere else and as we had always gone. You could always come back. Let the others come to America who did not know that they had come too late. Our people had seen it at its best and fought for it when it was well worth fighting for. Now I would go somewhere else. We always went in the old days and there were still good places to go.
Nothing surprising here, at least at first glance. “The natives live in harmony with it. But the foreigner destroys” sounds like the familiar cliché about how every country was an ecological paradise until the white man showed up and ruined everything — a cliché to which there is admittedly some truth, since whites did in fact decimate the megafauna of both America and Africa. Whites couldn’t have killed off America’s mammoths, though, or her ground sloths and horses and the other Pleistocene megafauna, all of which went extinct millennia before Columbus sailed the ocean blue. If humans are to blame for those extinctions (and circumstantial evidence certainly points to us), the culprits were the Clovis people — Paleo-Indians, the ancestors of “the natives.” They were still “foreigners” when they killed off the mammoths, though, having recently arrived from Siberia. When “natives” and “foreigners” are understood in a general sense, rather than as referring to specific ethnic groups, Hemingway’s point makes sense and is consistent with his earlier reference to America as “an older country” — that is, a country with a longer history of depredation by foreigners — than Africa.
In the big picture, Africa is the only land that can properly be said to have natives, the only place on earth where humans are not an invasive species. Humans and the African megafauna evolved in tandem, adapting to each other; the game animals evolved the instincts they needed to survive in an environment which included human predation, and the humans developed sustainable hunting practices.
In America, on the other hand, the Clovis suddenly showed up in a land whose wildlife had no evolutionary history of living with humans, and the results were disastrous. Over time, the Paleo-Indians learned to live in harmony with their new habitat and became naturalized “natives,” and the surviving megafauna presumably evolved as well, developing an instinctive fear of humans and other adaptations which would help them survive in the new (humanized) America. Millennia later, when the next wave of “foreigners” arrived in the New World, there was to some extent a repeat of the Clovis apocalypse, but on a much smaller scale. After all, the animals had already adapted to living under human predation in a general sense and only had to deal with the somewhat different behavior and technology of the Europeans. Though the Europeans greatly reduced the numbers of several species (bison, wolves, etc.), there were few all-out extinctions. In comparison to the totally foreign Clovis invaders, the Europeans were only somewhat foreign and therefore easier to adapt to — like adapting to a new strain of flu, as opposed to a completely novel pathogen.
It would be hard to overstate the difference between Africa and America in terms of big game. America (North and South) is over twice as large as Sub-Saharan Africa in terms of land area; it includes a wider variety of climates, which should be conducive to the evolution of more species, and it includes the colder climates which Africa lacks and which (based on Bergmann’s rule) should tend to produce physically larger species — and yet Africa has over twice as many abundant species of large mammal as America. Perhaps the reason lies in the fact that Africa, alone among continents, has never been invaded by a truly foreign human population like the Clovis in America, only by foreign strains of a locally evolved species.