I believe Clovis people were the first human inhabitants of the Americas. Why? Here is my reasoning:
1) Widespread extinction of the mega fauna. Worldwide, large animal extinctions are closely matched to first arrival of humans - In the Americas, that event was about 12,000 years ago, in Australia that was about 60,000 years ago, New Zealand around 1000 years ago, Madagascar about 2000 years ago, and so on. This should have happened rapidly in the Americas as the animals would not have had natural fear of humans.
2) Lack of abundant evidence of inhabitants before 12,000 years bp. I believe the few well documented pre-Clovis sites are from erroneous radiocarbon dates. There are many ways the samples can get contaminated. The normal error bar given around radiocarbon dates assumes the samples have not been contaminated.
3) Rapid spreading of the Clovis culture over a short period of time. It is hard for people and culture travel fast when there are existing populations that they must displace or assimilate. It is easy to rapidly expand populations when there are endless bounds to your territory and abundance of food to eat. One of the arguments against Clovis first isthat the preceding population was small, so left few traces. I think it would be hard to argue that there was a pre-Clovis culture in the Americas for a long period of time that would have remained small in population with the vast resources at their disposal.
Other thoughts about this subject are welcome.
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