Many years ago I put two and two together and discovered the Penis Theory: that human sexual anatomy, physiology, deposit viscosity change after deposit, and behavior are mysterious unless understood as derived from an evolutionary arms race in the context of a normal mode of human reproduction involving multiple sequential male sexual partners for a single female within 5 minutes of one another. If the female consented or not is unknown, but a gang rape theory of human reproduction cannot be ruled out. Group sex (multiple males with one female in immediate sequence) as a normal mode of human reproduction is proven, in my opinion. I'm not saying I like it; nor that it's not repulsive and revolting, not to mention tragic. Just that it's true. Please ask me to put the whole argument out there, it's 25 years old now and I shouldn't be so chicken to tell people if it's true, even if it is disgusting and morally wrong.
Then I saw the blond water buffaloes from the train window in India, and independently came up with the Theory of the Aquatic Ape. Both water buffaloes and humans evolved to have a matt of hair on the tops of their heads. This makes sense if both wallowed in shallow water under hot sun much of the time; if it makes sense for water buffaloes who we witness doing that, then it makes sense for humans to. At least plausible.
Earlier I wrote A Theory of Humor, and in 2012 hearing talks at a Humor Theory conference the idea came to me that human evolution is mainly a matter of female sexual selection of males based on humor. Girls think funny boys are sexy, whereas boys don't include funniness in what makes them think a girl is sexy. If humor correlates with intelligence generally or social intelligence more specifically, and if female sexual choice exists (obviously it does, in our species as much or more than any other), then this quality will drive a species in the direction of greater intelligence or social intelligence.
This certainly has a different feeling from male gang rape of females as normal reproduction among humans. Perhaps these are competing modes of reproduction. The incels band together and go murder, pillage, and rape in the next villeage; meanwhile the emotionally intelligent women with any ability to choose their own partners are having babies with the funny men. In general it seems the emotionally intelligent and powerful women have largely won the war for the species, since we are all so smart and emotionally smart, because those women picked smart, and emotionally smart men, and evidently the raping and pillage became less common, not to say zero. Our species is quite regulated by and for women, and male intelligence itself is a part of that regulation.
Some other items to sequence into the human story:
Evolution of white eye whites. Gorillas don't have this. It lets you see where you fellows are looking, and improves the cohesion of a society that demands a higher degree of shared attention, shared goals. Seems like this is late, might separate neaderthals from humans.
Fire. This is early. Homo erectus had fire. 2M years? Fire means everyone sitting around the fire after dark. Hang around the fire to do what? Tell jokes, be funny, connect socially. Use your growing intelligence, especially to increase affiliation. Social forces become more and more urgent in such a space. Rejected from the group, in a world with fire, means you are out in the cold, vulnerable to any predator, social rejection suddenly means death in a fire-centered species. Apes without fire can sleep in any tree, even rejected apes can find a remote tree and survive the night. But humans who grew up sleeping around a fire for warmth and safety cannot so easily start their own fire without the cooperation of others. So the mean undiplomatic people gradually get winnowed out.
Female hidden estrus. See below.
Female sexual selectivity. Maybe this came as a revolution against the gang rape? Maybe gang rape was a protest movement which changed our genitalia but stopped being a normal mode of reproduction after a while. They clearly have some interaction since group sex is the polar opposite of female selectivity.
Neoteny. This is just an implementation mode of the evolution toward intelligence via female selection of funny male partners. Pick funny partners, you're picking younger-at-heart partners, younger-as-adult partners, adults who maintain childlike features longer into adulthood. Neoteny.
Language. In my opinion, language came about as a means of being more funny, by people who became more and more intelligent due to humor-based sexual selection. Once you get pushed up high enough in the intelligence spectrum, you get more and more layers of symbolic mapping in the neural nets, then functional grunts get elaborated to finer degrees of functionality. All driven by spare unnecessary intelligence selected for by girls who prefer and will have sex with the funniest boys.
Group size: Neanderthals are small group folks, sapiens go to 150 functionally. This also comes out of social intelligence and perhaps after language.
Fully standing posture: can be tracked by physical anthropologists. You only need a few to run down a horse, so it can occur any time, long before you have 150 people in a group.
Thumbs: also dateable by the physical anthropologists. Could be adaptive after intelligence ratcheted up a bit, then the people who could tool up better with thumbs might do better than the no-more-intelligent ones without.
Running endurance: came after the standing posture. A hunting adaptation. Perhaps early. To me it reminds me of the water thing. Men are hairy, because they leave the safe wallow and go out into the bush and hunt all day, so they need sun-protecting hair on their bodies more than the girls do who wallow longer under a layer of water or mud.
These are just a few of the steps on the ladder. My current ordering?
Hairlessness interacts with Fire since you can dry off easily by a fire if you aren't very hairy.
Fire forces sociability, precedes Funny=Sexy which has a bigger impact around a fire.
Put them all in order, okay?
It seems true to the degree that if you want to disagree then you have to come up with alternative explanations for each of a constellation of many features in this theory all pushing in a single direction.
Furthermore, humans have organized social aggression on a scale and distance qualitatively different from other species which instead merely police local territory or fight for direct mating rights or for direct personal status within a local dominance hierarchy; is that unrelated to a species characteristic of organized sexual aggression? Perhaps not: gang war supports gang rape.
Sadly the selection for social intelligence in males by females may have empowered those later generations of increasingly socially intelligent males to organize themselves together to do male-type things on a larger social scale: like organizing for war. The intelligence acquired by female preference for humor, which could be seen as aiming for a more female-supportive social world, has led to the nuclear-powered ability to destroy everything. In short, we can't let men and dicks be in charge of everything.
Compare in a thought experiment three versions of the same species.
The Alpha-Covert system is the worst of the three. Just consider what a terrible system design is would be for a reproducing species (and aren't they all). Admitting it concieveable that the alpha could actually do such a monumental task, still the continuous vigilance and enforcement required would demand either locks (only possible for humans) or complete loss of sleep (not possible for any animal). It would take so much out of the alpha that the alpha would have little ability to do anything else, whatever alphas do, like protect the herd, investigate threats, discipline other kinds of violations, etc.. The number of females that the alpha could manage would be much decreased, meaning that his alpha status would be actually far lower than that of a true alpha species, where a whole herd is jealously governed by a single male. An Alpha-Covert system seems evolutionarily unstable for this reason: The alpha would do a suboptimal job as an alpha, would not have much scope for his domination (ie a small harem), some female will certainly run away, some beta will go with her, the Alpha thing falls entirely apart, and the genetic drift of the species will go away from Alpha reproductive dominance because betas are getting reproduced. Unless female fertility becomes again Overt in order to take the load off the alpha.
So this is not exactly an argument for why humans do have covert fertility in the female, but it does put something of a constraint on the system: there is a natural tradeoff between the covertness of female fertility and the alphaness of the male social and reproductive rights system. Since humans have covert female fertility, it would seem we are not very much of an Alpha dominant type of species. Except for the unfortunate innovation of locks.
Female orgasm: Well I consider this still quite a mystery, but perhaps the obvious facts are enough of a story. They are hopeful enough. The basic fact is that orgasm through imposed experience of inner surrender produces emotional well-being and pro-social relationships. The main physical fact is that the primary orgasmic sense organ for females, the clitoris, is so far separated physically from the vagina that penetrative copulation mostly gives at best minor pleasure to the female. For the female to get the benefits of orgasm, the male must actually seek to give it to her: to a first-order approximation, altruistically. Therefore barring other concerns the female will prefer to have sex with those males who have, let's call it, socio-emotional intelligence. A little less selfishness. If you're not willing to focus on your partner's pleasure, why should she be so interested in yours? This is built into the anatomy of the species, because the male can take all the pleasure he wants giving nothing to the female, or be the kind of guy who is willing to give pleasure to the female. In a species characterized by female choice of sexual and reproductive partners, this logic results in a force for evolutionary selection for male socio-emotional intelligence.
Is it a coincidence that sexy=funny boys is also a force for evolutionary selection for socio-emotionally intelligent males? Can multiple forces push in the same direction? We do seem to have some socio-emotionally intelligent males in the species, there are plenty of funny betas around, generally speaking, and there is a good degree of female choice also. So I'm going to say that the species has evolved toward its social and intellectual capabilities by means of the separation of vagina from clitoris and the sexiness of funny men.