I don't think you actually know that. I don't think anybody actually knows that.

I'm basing it on observable behavior. If you want to retreat into solipsism then you are just avoiding reality.

I think the way morality has evolved completely reflects my theory on empathy. We used to be more moral towards our tribe or our family because it's easier to see our selves in them. But as awareness and knowledge expands through our ability to self analyze, we start seeing our selves in other groups that aren't superficially or immediately connected to our own identity.

You're basing it on assumptions derived from observable behavior with no real proof to the claim.

Saying that I'm retreating into solipsism is a huge strawman and it made me have to read. Oh, ****, I'm already reading.

I don't think you are taking into account how evolution actually works. How would that work, genetically?

We evolved in the tribal context based on kin selection and reciprocity because
1) kin selection - your close relatives share your genes
2) the people in close proximity to you make for useful and reliable trading partners.

The selective pressures that selected for these traits made basic assumptions that are no longer true, but were true for the vast majority of human history

E.g. that your brother is always going to be genetically related to you. You can have an adopted brother and feel the same way about them. That's not cause you're more evolved. It's cause the forces that drove your evolution simply assumed brothers were related and, in the vast majority of cases, they were.

When I say evolved I don't mean in a genetic sense, I mean how our understanding of morality has developed. I don't think morality is genetic, I think it's a product of varying things that are genetic that I can't pin point because I'm not a neurologist. I think time has given us the ability to analyze ourselves and gain a better understanding of morality just like it has in many different things.

That's negative utilitarism, to be exact. I think that it is actually what most modern people's morals are based on (that's how it is for me anyway), but it's probably true that our natural instincts obey a different morality: one that's purely based on the successful survival of ourselves and our kin. However, I guess that nurture has wired us to try to act utilitarian.
By the way, it's funny how much human morals change throughout history

it arises as a function of human society (i.e. the tribe) and is based largely on the genetic mechanisms I spoke of.

The extent to which it is variable is the extent to which different human societies sieze in the same instincts to enforce different rules.

There is a lot of evidence for it. In fact, if you believe in evolution, it's really hard to explain how some mechanism for regulating human behavior which always serves the good of a given society and is present in every human society on Earth would not have some basic evolutionary explanation. It's just yet another arena where science makes is uncomfortable when it hits too close to home.

what serves society first and foremost is having a common moral framework by which you can regulate the members of said society

Society A and society B might have different specific morals, but the purpose those morals serve are much more identical.

E.g. I remember a study from years back about how they determined that certain neural activity resembled someone pondering a moral question vs a strictly logical question.

And they asked a group of people about stoning a woman for adultery, some of whom were Western and some of whom were middle Eastern. The people answered the question predictably, of course. The striking thing was that in both the Western and middle Eastern patients, the same neural patterns manifested. The Westerners were disgusted at the murder a woman, the middle easterners week disgusted at her betrayal of her husband. Both were following the same instincts, though informed by different cultures so they came to very different conclusions.