"I don't think it's enough, Arb," Malcolm said. "I think more is involved - I think there has to be more, even to explain how our own species arose."
"About three million years ago," Malcolm said, "some African apes that had been living in trees came down to the ground. There was nothing special about these apes. Their brains were small and they weren't especially smart. They didn't have claws or sharp teeth for weapons. They weren't particularly strong, or fast. They were certainly no match for a leopard. But because they were short, they started standing upright on their hind legs, to see over the tall African grass. That's how it began. just some ordinary apes, looking out over the grass.
"As time went on, the apes stood upright more and more of the time. That left their hands free to do things. Like all apes, they were tool-users. Chimps, for example, use twigs to fish for termites. That sort of thing. As time went on, our ape ancestors developed more complex tools. That stimulated their brains to grow in size and complexity. It began a spiral: more complex tools provoked more complex brains which provoked more complex tools. And our brains literally exploded, in evolutionary terms. Our brains more than doubled in size in about a million years. And that caused problems for us."
"Like what?"
"Like getting born, for one thing. Big brains can't pass through the birth canal - which means that both mother and child die in childbirth. That's no good. What's the evolutionary response? To make human infants born very early in development, when their brains are still small enough to pass through the pelvis. It's the marsupial solution - most of the growth occurs outside the mother's body. A human child's brain doubles during the first year of life. That's a good solution to the problem of birth, but it creates other problems. It means that human children will be helpless long after birth. The infants of many mammals can walk minutes after they're born. Others walk in a few days, or weeks. But human infants can't walk for a full year. They can't feed themselves for even longer. So one price of big brains was that our ancestors had to evolve new, stable social organizations to permit long-term child care, lasting many years, These big-brained, totally helpless children changed society. But that's not the most important consequence."
"No?"
"No. Being born in an immature state means that human infants have unformed brains. They don't arrive with a lot of built-in, instinctive behavior. Instinctively, a newborn infant can suck and grasp, but that's about all. Complex human behavior is not instinctive at all. So human societies had to develop education to train the brains of their children. To teach them how to act. Every human society expends tremendous time and energy teaching its children the right way to behave. You look at a simpler society, in the rain forest somewhere, and you find that every child is born into a network of adults responsible for helping to raise the child. Not only parents, but aunts and uncles and grandparents and tribal elders. Some teach the child to hunt or gather food or weave; some teach them about sex or war. But the responsibilities are clearly defined, and if a child does not have, say, a mother's brother's sister to do a specific teaching job, the people get together and appoint a substitute. Because raising children is, in a sense, the reason the society exists in the first place. It's the most important thing that happens, and it's the culmination of all the tools and language and social structure that has evolved. And eventually, a few million years later, we have kids using computers.
"Now, if this picture makes sense, where does natural selection act? Does it act on the body, enlarging the brain? Does it act on the developmental sequence, pushing the kids out early? Does it act on social behavior, provoking cooperation and child-caring? Or does it act everywhere all at once - on bodies, on development, and on social behavior?"
"Everywhere at once," Arby said.
"I think so," Malcolm said. "But there may also be parts of this story that happen automatically, the result of self-organization. For example, infants of all species have a characteristic appearance. Big eyes, big heads, small faces, uncoordinated movements. That's true of kids and puppies and baby birds. And it seems to provoke adults of all species to act tenderly toward them. In a sense, you might say infant appearance seems to self-organize adult behavior. And in our case, a good thing, too."
Thorne said, "What does that have to do with dinosaur extinction?"