 caretaking species. In fact, it might be the defining characteristic of human evolution, or one of the two or three singular shifts in our evolution in becoming who we are today. It took some female evolutionary theorists and primatologists to start to bring this to our attention, like Sarah Blaffer-Hurdy, that we are this profoundly caretaking species. But interestingly, you may not know this, but this was Charles Darwin's thesis about human nature as well. Darwin, in 1871, wrote The Descent of Man, his first book about human beings. He, as Adam Gopnik has argued, was, and I don't know if you know this, he was a beloved dad of a really rambunctious group of children, engaged with his kids a lot, and a defining event in Darwin's life was that one of his most beloved daughters died, and he nursed her to her death at age 10. And out of that, Darwin started to have these deep insights about the place of suffering in human experience and the place of compassion. And it led him to write that sympathy will be increased through natural selection for these communities, which include the greatest number of the most sympathetic members would flourish the best. And in this passage, Darwin says, sympathy is our strongest instinct, stronger than self-interest and that the maximization of self-interest, forgotten by evolutionary science for quite some time. Well, why, how could you make the case that sympathy is our strongest instinct? Well, it has to do with one of the most profound changes in human evolution, which is the dependence of our children, our offspring. This is a little bonobo, isn't he cute? Isn't that great? I'd trade that bonobo for my teenage daughters, no, sorry. And this is a chimpanzee, I love my daughter, so oh my God, I'm in videotape, and I just said that, scratch that, okay. This is a chimpanzee, little baby chimpanzee. What are they doing that's unusual for offspring, babies? They're eating by themselves, average human nurses around the world, nurses their babies four years, average mom. What else are they doing that's unusual? They're sitting up, right? Most babies at this age, like you sit them up and they go, watch out man, my head's really big, whoop, you know. Well, it took a while for evolutionists to appreciate this, but what, you know, as we started to walk upright on the African savanna, our pelvis is narrowed, right, and our birth passage narrowed, as we developed these wonderful abilities with language and music and symbolic representation, we got these big cortexes, which we're about to talk about, and our heads got bigger, and what that means is that our babies, as you all know, are born profoundly premature and dependent upon people to take care of them, right? Our babies, compared to these offspring, are the most vulnerable offspring on the face of the earth, taking seven to 49 years to reach the age of independence, right, and I always say that as a joke, but then half of you are gonna come to me in the break and say, are you sure it's 49? My son's 56, he's still living in the basement, and you know, and when my daughter recently told me, I figured out, dad, what I wanna be, and I was like, Gray, what is it? She's like, I wanna be a writer, and I was like, ah, I'm gonna be paying your bills for 60 years, right? Unless she's as good as Robert Sapolsky, so, but that, as Sarah Blaffer-Hurdy and other people have argued, that simple fact changed everything. It rearranged our social structures, building cooperative networks of caretaking, and then it rearranged our nervous systems. We became this super caregiving species.