I would be every interested in reading this evidence :) The "Black Hole" hypothesis certainly explains close overlaps between "humans arrive and increase on population" and "megafauna go extinct".
But then I'm not claiming that it was all Homo sapiens - rather, climatic change had already placed species under stress, then man was the final stressor that pushed them over the brink.
And a single discrete coincidental event would not explain why the pattern "modern humans arrive, megafauna disappears" occurs repeatedly, throughout the fossil record, over 50kY.
Humans had been in the Americas for thousands of years, yet these 32 genera vanished all at the same geologic instant, simultaneously with the Clovis culture itself.
This does not mean humans have not also participated in numerous extinctions, ancient and modern. It only means we cannot be responsible for the sudden American extinctions.
Given more time, we would no doubt have wiped out many of the species. But horses and camels survive on other continents, exposed to humans. Why would Americans have, uniquely, chosen them to wipe out?
> This does not mean humans have not also participated in numerous extinctions, ancient and modern. It only means we cannot be responsible for the sudden American extinctions.
This is a may, not a can: a trivially fitting hypothesis is that the clovis culture was based around that megafauna, and when it finally went through everything it ended with them.
This also explains the synchronicity of the disappearance, because any megafauna hunted to extinction would lead the hunters to fall back on the next genera, increasing hunting pressure on it and thus accelerating its disappearance.
> Given more time, we would no doubt have wiped out many of the species. But horses and camels survive on other continents, exposed to humans. Why would Americans have, uniquely, chosen them to wipe out?
Either coevolution (meaning the megafauna would have had the time to adapt its reaction pattern to the rise of humanity), or environments which allow them to evade hunters and avoid extinction which may not have been available in the americas.
But did humans coexist with megafauna in America / Asia / Australia / Aotearaoa for thousands of years before they all died out?
As I'm a New Zealander, I'm far more familiar with mass extinctions in NZ, and let me just say, to paraphrase a Smash Mouth song, well, after the arrival of humans, the extinctions start coming and they don't stop coming.
For a few reasons.
1) Introduction of the kiore (Polynesian rat) - while now, somewhat ironically, nearly extinct in NZ due to competition by Norwegian and black rats, its predation of chicks and eggs was instrumental in pushing some endemic species to extinction.
2) Unsustainable hunting, and collection of eggs. The most prominent example is the thousands of moa and their eggs found in the middens of what was probably the first archaic Māori (aka "moa hunter") settlement on Te Waipounamu/South Island. Given that moa, like other large birds, were slow breeders, it was inevitable that moa populations would collapse shortly after human arrival given the level of exploitation seen in the middens.[1]
3) Fire. Archaic Māori used fire to drive forest dwelling moa for hunting, which destroyed large areas of old forest that were stable, but unable to re-establish under changed climatic conditions. For an example, the Mackenzie Basin[2], and the Torlesse Range[3], both now known for their extensive tussocklands, were previously covered in dense forest, which no longer existed by the time of European colonisation. With a loss of habitat comes increased risk of extinction.
4) Desperation - as moa became scarcer, the archaic Māori switched to alternative food species, and extinctions rapidly followed (e.g., the flightless South Island goose[4]). This is also the period where (most archaeologists agree) the ancestors of the Moriori[5] departed from the South Island and settled the Chatham Islands/Rēkohu, as archaic Māori society entered collapse.
I highly recommend this book[6] for insights into at least one confirmed example of the black hole theory. You can also explore the art of that book in the national museum's collections[7]. The fact that there's six pages of that art is rather depressing.
Island ecologies are fundamentally different from big continents, for obvious reasons. Even Australia displays island-like extinctions. So, yes, arrival of humans, with their animals, always has profound effects on islands. But that has little resemblance to what happens on continents.
But then I'm not claiming that it was all Homo sapiens - rather, climatic change had already placed species under stress, then man was the final stressor that pushed them over the brink.