We evolved from primates. And generally that story follows a simple path: we started to walk upright, then we started to talk, then we started to use tools, then we hunted down bigger-but-dumber animals, then we got married and monogamy became a thing, and then, generally, we were the humans we are today. It's easy enough to track and makes sense considering the way most people live(d). Echoes from the past in society of the present.
But those echoes might actually just be sounds from a bonobo orgy.
As Jack Hitt writes for Lapham's Quarterly:
In the heart of Africa, in a swamp forest near Lake Tumba in the Congo, a frolicking species of ape called the bonobo has long upset the Frazetta picture of our past. These apes, who, along with chimpanzees, share up to 98 percent of our DNA, confounded the first primatologists who observed them. Over time, they have created a colony far different from that of their intensely competitive, often violent, chimpanzee cousins. Bonobo society is based on cooperation and empathy; the culture is a matriarchy where competition is redirected into a communitarian sexual appetite. Bonobos also shocked these earliest scientists because they possessed a cheerful sense of general promiscuity, weaving wanton sex into their society, and they boasted a sexual repertoire once thought to be the exclusive property of Homo sapiens—deep kissing, foreplay, oral sex, homosexuality, and polyamory.
There is more:
Throughout the day, males and females, adolescents and elders alike greet one another sexually for apparently almost any reason—and do so with everything from a quick feel, to porn-style choreographies, to elaborately athletic couplings. This feature—the variety of their easygoing sex life—is what led Duke primatologist Vanessa Woods to cheekily title her book about them Bonobo Handshake. Bonobos have deployed their elaborate sexual toolkit to ease all kinds of social transitions—ranging from saying good morning to giving the blessing before dinner to expressing a hearty welcome to a new member of the group. Females will casually present themselves to males. The male will walk right up to a female without any hesitation. All bonobos frequently have homosexual sex—the males being quite fond of hanging upside down, face to face, from a tree and engaging in what the gay community calls frottage (some primatologists call it “penis fencing”; to most teenagers it’s better known as dry humping).
There's way more and you can/should read it here. But bonobos—and their sexual appetite—had long been ignored by researchers for all of these reasons. They didn't fit it with the human-evolution story, while Jane Goodall's chimpanzees did. And the bisexuality, casual sex, and non-aggro males didn't fit in with the way society was. Yet, bonobos seem more like humans in almost all of these ways. Pleasure and cooperation may have been more important in human evolution than we've ever realized, and as Hitt's story shows, that's pretty great.