37% includes "incidental" and is definitely a maximum as far as I've seen. I think it's probably safe to say statistically under half. A reanalysis of the same data put that down to 30%. More modern data has that rate much lower. https://kinseyinstitute.org/research/publications/historical-report-diversity-of-sexual-orientation.php
Including "incidental" is pretty generous too. 14% had "more than incidental" which is the data I was using.
As for the Nambikwara - very cool, and very interesting. Very proscribed, though. I don't think a single counterexample provides a very convincing contradiction of the overall claim, that heterosexuality is the default. In each of these cultures, homosexuality occurs under very specific rules and the men still have "traditional" marriages with women.
Because instead of making the argument, "it's not you, it's me," he made the argument, "it's you, because I'm just like every other guy on Earth."
Indeed. Archaeological study of the grounds surrounding Stonehenge shows evidence of what appears to be a prolonged conflict between two neighbouring settlements, which lasted several hundred years- during which time there were no new religious monuments made in the area (suggesting that most energies were devoted to this conflict). There's evidence of several major battles.
I suppose I should have said, "where group selection works in nature."
From the paper you cited: "Unlike these closed laboratory populations, populations in nature would often be open to emigration." Evidence of group selection occurring or having occurred in real populations has never been observed.
4 does work. In Australia they have a near-perfect voter turn out. It makes voting rational, in order to avoid the fine.
The case you described, where the cancer cell resulted in the death of the individual human, could equally well be described as kin selection. An individual that hurt its close genetic relatives- and actually actively kills them- also hurts its individual reproductive success.
The argument against group selection is an argument against its usefulness as a concept. Where group selection works, it is mathematically indistinguishable from kin selection, so you might as well use kin selection as your conceptual model. Additionally, it can be confusing for people who don't understand the circumstances where it definitely cannot work, which is any case where the individuals are not closely related.