yes, but I believe we are using different interpretations fairness. as someone already pointed out, for fairness to be innate to humans it would need to be a better genetic trait compared to unfairness. so we are not arguing about how and if it is a good behavioural strategy, as it needs to be a better gene to have vs 'the-unfairness-gene'. so you might be genetically unfair and act fair as long as it is a valid behavioural strategy and revert to your genetic inclination when the situation requires you to (in case of serious danger for example). based on that it would be also possible to say that people are genetically fair and act unfair when in need, but that would not be fairness in my opinion.

Yes, TIT-FOR-TAT is the winning strategy in iterated Prisoners' Dilemma.

Basically, start off nice. If people are mean, punish them by getting mean. If they are nice, treat them in kind.

as I said to dasil003, it's not really about behaviour, it's about genes. to reply to your post: we have a better understanding of the world compared to the other animals so maybe it simply happened that at a given time we understood that cooperation allows you to gain an unfair advantage vs single individuals and so on (in some way you need to keep that cooperation going).

my point is that it seems to me that exploitation of weaknesses is the central theme of evolution and it doesn't mix well with fairness. then again, I don't study biology so take my words with a grain of salt.