I do agree that humans were almost certainly responsible for the successive waves of extinctions that coincided with their first appearances in new territories. One particularly compelling bit of evidence concerns the North American mammoths. There had always been a debate over whether the primary cause of their extinction had been human over-hunting or the climate changing from glacial to interglacial conditions. I had always had my doubts about climate change, since the glaciers had retreated dozens of times before without significant elevations of the rate of extinctions, so why the huge increase on the first interglacial that included humans?
But recently the debate has been definitively resolved (in my opinion). A study has looked at the bone structure, and the population demographics, of the most recent mammoth fossils. The two scenarios under consideration would lead to very different evidence. If the culprit was climate change and resulting lack of food resources, then you would expect to see poor bone structure with evidence of numerous periods of malnutrition. You would also expect to see few infants, as the birth rate would plummet to conserve the mothers' resources, in a typical response to famine conditions. On the other hand, if over-hunting was the primary culprit, you would expect to see good bone structure, since there would be plenty of food for the few surviving mammoths, and many infants, as the population would be producing new members as quickly as possible to replace the numerous deaths from hunting.
So what to we see in the fossil record at the end of the time of mammoths? Good bone structure and many infant and young mammoths. Combined with the fact that this was also the beginning of human occupation of North America, and it's a settled case to me. Humans over-hunted the mammoths to extinction.
But recently the debate has been definitively resolved (in my opinion). A study has looked at the bone structure, and the population demographics, of the most recent mammoth fossils. The two scenarios under consideration would lead to very different evidence. If the culprit was climate change and resulting lack of food resources, then you would expect to see poor bone structure with evidence of numerous periods of malnutrition. You would also expect to see few infants, as the birth rate would plummet to conserve the mothers' resources, in a typical response to famine conditions. On the other hand, if over-hunting was the primary culprit, you would expect to see good bone structure, since there would be plenty of food for the few surviving mammoths, and many infants, as the population would be producing new members as quickly as possible to replace the numerous deaths from hunting.
So what to we see in the fossil record at the end of the time of mammoths? Good bone structure and many infant and young mammoths. Combined with the fact that this was also the beginning of human occupation of North America, and it's a settled case to me. Humans over-hunted the mammoths to extinction.