1) You state “The brain, like other organs, is pretty much the same around the globe.” This cannot possibly be true for the following reasons:

First, it would require that human characteristics do not abide by the same law of normal distribution (bell-curve variation) that all other natural characteristics abide by–with such variations occurring both within and between groups of organic and inorganic structures alike. Such variation dynamics will necessarily apply with regard to genetics and environmental effects alike. Twin studies from around the globe have confirmed that human attributes range from 90 percent genetic for physical characteristics, such as height, to 25 percent genetic for highly pliable personality characteristics. And average of 50 percent can often be applied for overall illustrative purposes.

Second, it denies the effects of evolutionary history that would inevitably produce both specialized and general differences between groups, as each group will have experienced varied selection pressure(s). For example, it is well known that different races have different susceptibilities/immunities with regard to particular microbial threats (e.g., diseases). In terms of general differences, an evolutionary history that has included a greater variety, intensity and/or sequence of threats will produce a higher level of advancement with regard to generally adaptive attributes, such as intelligence (for higher-level species) and the cooperative instincts required to compete in a strength-in-numbers-based arms race.

2) This renders your second point almost correct, as ecosystem demands definitely create these differences. But, of course, you seem to deny that genetic variation exists, which effective denies the fact that genes serve largely as a mechanism for creating species adaptation (as necessary to facilitate perpetuation) by virtue of their variability.

3) From the evolutionary perspective, a social behavior that proves functional will increasingly be considered moral within a population–for all higher-level social species. This is because those group behaviors that are not functional will lead to the attrition and/or eventual extinction of the members of the group that displays them. As human existence has changed dramatically over the last 10,000 years, both with the dawn of agriculture and, especially, with the dawn of civilization (tribal mergers), dramatically different social demands have increasingly selected for modified human cooperative instincts (emotions and feelings as part of the human biocultural (genetically and environmentally adaptive as part of a total functionality package) profile. The most important change here is that larger, more-diverse human populations have increasingly had their tribal instincts purged as the benefits of functional cooperation, including greater strength in numbers and specialized contribution have been realized. And perhaps most importantly here is that civilized behavior/morality is generally better–not just different based on particular “ecosystem demands.” For confirmation of this, we must only consider that one or more individuals with civilized instincts would have no trouble interacting cooperatively within a tribal population (say, living by the “golden rule”). But the same would not be true in reverse, as tribal instincts compel individuals to highly loyal to those genetically related and very distrustful of, and ofter aggressive toward, those from different kin-groups. Or, viewed in reverse, those from a particular tribe will typically be welcomed into a modern “melting pot” society, while those who are non-kin will not typically be welcomed into a particular tribal society, and could easily end up dead in short order. This can be seen everyday in the Middle East to some degree, but would be far more visible to any who observe tribal interactions in New Guinea.

As we return to you initial declaration of what seems “prudent, parsimonious, and fair.” In light of the facts of the natural world described above, it is your ideological underpinning that becomes most apparent; one centered upon the quite-popular notion of relativism–where all are instructed to consider all varied human features to be equal in their merits in hope that all peoples will live in peace and harmony with each other and with Mother Earth. This may be an appealing construct for many who have been convinced that good intentions and postmodernist philosophy will allow humankind access to the Utopian Ideal. But it is so detached from, and antithetical to, what is real that this artificial moral framework will lead to the self-destruction of any society that adheres to it. For again, over time it will be natural selection that determines what is moral, based on what is functional, as all else is tossed into the dustbin of history and/or is dispatched to the fossil record. For a more-detailed explanation of all that is described here pick up a copy of Living With Evolution or Dying Without It: A Guide to Understanding Humanity’s Past, Present, and Future.

Humankind can maximize its ability to play within the rules dictated by evolutionary reality, but it cannot make its own rules, as many have been led to believe.

Likely yucki behaviors and traditions, that’s a technical term, had a reproductive advantage. This is pretty much by definition.

If the behaviors didn’t produce more offspring they would be, like, gone.

Now the, universal, reflex of disgust is an imperative so reasoning about disgusting acts or people, etc. is pretty much impossible. Disgust for others is not ideological but the reasons we make up to rationalize the feeling are — just pretend. But also adaptative, at some point, likely in the past and not so much now.

And isn’t that the tragic 4 word summation for so much human behavior — not so much now.