So let's go back to evolution now. And let's look again at certain emotions. And now I'll ask why do we have them? And we talked about emotions like fear, the function of which seems pretty clear. But now let's look at the emotions that incline us to be kind to others, like compassion and gratitude and so on. These have long been seen as a puzzle for evolution. And in fact, many people now say, well, the very fact that we have kindness and morality means the theory of natural selection can't be right. The theory of natural selection guides us to survive on reproduction. As the phrase goes, we capture evolutionary process in terms of nature, red in tooth and claw. So why would we be kind? How could kindness evolve? And one way to put the puzzle is like this. Imagine a population of indiscriminate altruists. And that's just a fancy way of saying a population of creatures whose genes guide them to be nice to everybody. They don't care if their favor's returned. They don't care who they're nice to. They don't care how much it costs. And imagine this society was chugging along, and then a mutation happened. And an animal came into being who accepted the help of others, but didn't contribute. Took the benefits, but didn't pay any costs, and we call this a free rider. In life, a free rider is a roommate who's very happy all the other roommates clean the house, but he or she doesn't do any cleaning. A free rider is a colleague who's very happy to join parties and events, but never helps organize. Somebody who comes to a place and there's a lot of beer there, but never brings the beer. That's a free rider. And you might imagine the free riders would thrive. They would do better by definition. Taking the benefits and not paying any cost does better. And so the puzzle, then, is why did we evolve kindness? How could kindness have survived? How could it be what biologists call an evolutionarily stable strategy? And there's a couple of answers to that question. First, we know it's a problem, because we know there is altruism. We know animals care for their young, they groom each other. Vampire bats, for instance, when they hit it big and bite into a horse or some animal like that, will suck up the blood. Consume some of it themselves, but then come back and regurgitate it into the mouths of their little vampire bat pups, which are adorable. So we know there's a solution to this, and now we'll talk about it. And actually there's more than one solution. Here's part one. And part one involves an idea framed by the biologist, Richard Dawkins. And Dawkins says we are evolved altruists, but we're not indiscriminate altruists. And he took the step of saying, look, let's think about evolution in terms, not of individual animals, but in terms of genes. So what does it mean to say that animals have evolved to survive and reproduce? Actually, a better way of putting it is animals are the vehicles that contain genes. And the genes are the replicators. Think about it. Aren't animals really just survival machines? Well, not when you really think of evolutionary theories seriously. Suppose there's two genes. Gene A makes an animal care for itself and its offspring. Gene B makes the animal care just for itself. So Gene A is going to win out in the long run, when Gene A leads an animal, for when it has offspring, to take care of the offspring and Gene B makes the animal eat its offspring. You don't have to be a mathematical biologist to see that Gene B isn't going to make it. It's reproduction that matters. But more to the point, having kids is just one way to be related to another creature, to share another creature. I also share genes with my brothers, with my uncle, with my aunt, with my cousins, and so on. And so, more generally, the genes that survive, Dawkins argues, are those that make the most copies of themselves. And to use a phrase I used before, animals are vehicles through which genes reproduce. As he puts it, an animal is merely the gene's way of making another gene. And this leads us to kin selection, which is a gene will spread through a population. It either increases the chance that the bearer of the gene will survive. And this is for the genes that lead to emotions like fear. They just help you survive. Or if it increases the chances that other animals that also possess the gene will survive. And so to the extent that a gene exists that motivates helping relatives, that gene will spread quickly. A discriminate gene for altruism then will have a better chance of surviving than either an indiscriminate gene for altruism or a purely selfish animal. To the extent, then, that evolution operates the level of genes, there's no hard and fast distinction between one's self and another. In some way, the title of Dawkins' famous book, The Selfish Gene, is grotesquely misleading, because the way Dawkins intended it to mean is that the genes themselves are selfish. All they want to do, in some metaphorical sense of want, is replicate themselves. But selfish genes lead to unselfish animals. And it follows from Dawkins' theory that pure selfishness, pure doing it for oneself, is biologically untenable. The nature of how animals work suggests that all animals intrinsically have to value the lives of others if only kin. There's a famous story from the biologist, Haldane. Where Haldane is asked, strange conversation I guess, Haldane is asked, would you lay down your life for your brother? And he responds, no, but I would gladly give my life for three brothers, or five nephews, or nine first cousins. Now, he joking, nobody actually does the math, not even a biologist. But the logic of his response is that he's asked whether he'd lay down his life for somebody who contains 50% of his genes. To always do that, would not be a good evolutionary strategy. But it would make sense to give your life for three brothers, 150%, or five nephews, 125%, or nine first cousins, 112.5%. Nobody does the math in their heads, again. But this math has shaped the way our psychologies have developed. And this is one of the ways in which evolutionary theory explains how we could evolve to be kind to others and have emotions that incline us to be kind to others.