If you understand ant reproduction you'll understand why they work that way. Males are born from sterile eggs, they inherit genes only from their mother. Females inherit from both, just like all humans.

This means, female ants are closer related to their siblinfs than their children. They share 75% of genetic material with their siblings vs 50% with their children. The selfish gene and all that, there is a selective pressure in such an organism to become eusocial.

I can see calling it 3 genders, but it isn't quite right, there are still 2 sexes, and female workers are capable of reproduction. But in a eusocial species, the individual isn't the organism, the colony is. The individuals are like somatic cells, and the queen is the germ line.

Humans are not eusocial, just social. We show characteristics of eusocialty, but we aren't quite there. Above, you talked about the tribe and a reproductive aged girl spitting out kids until she was unable, and you're right, a tribe doesn't want to grow as much as possible, but it isn't as simple as that. People like to reproduce as much as is successful. Human children require care, we aren't alligators, so spitting out babies is not the most efficient approach, they all die. The most efficient approach is to spit out as many as you can rear with the resources available to you, and doing your best to maximize their survival. But the tribe, the tribe is something like an organism all it's own, I'm sure you're familiar with Dunbar's number, a tribe with too many people is unhealthy, as is a tribe with too few. So the tribe's goal is to reproduce, to splinter, to form a separate related tribe to cooperate with. And a tribe's behavior is a result of it's culture, it's culture is a result of which behaviors led the tribe to be healthiest, there's a natural selection there as well, its turtles all the way down. If a tribe is capable of managing resources maximally, it's members will reproduce maximally, and the tribe will grow and split, leaving 2 tribes with such successful culture and so on. Humans do attempt to reproduce successful adults as much as possible.

I think you're probably right, from an evolutionary and reproductive standpoint, about homosexuality and other deviations from the norm with regard to sexual behavior.i