Blueprint: The Evolutionary Origins of a Good Society, by Nicholas A. Christakis, Little, Brown, 544 pages, $30
We finally have an answer to the nature/nurture debate, and it appears to be yes.
It took billions of years of biological evolution for bacteria to morph into humanity, but the human ability to learn and to teach each other new tricks means that useful behaviors and ideas don't have to take biological time to spread through the species. Their emergence, the ways we spread them, and the ways they change over time amount to a kind of cultural evolution.
A cultural discovery—our pre-human predecessors' capture of fire—externalized the digestive system that evolution had shaped for our variety of ape. That freed biological energy to grow a big brain. In Blueprint: The Evolutionary Origins of A Good Society, Nicholas Christakis argues that this coevolution has equipped us with a "social suite" of traits that arose through genetic evolution and that have been amplified by cultural evolution, which has in turn influenced our genetic evolution toward propensities that support the social suite. These include the "capacity to have and recognize individual identity," "love for partners and offspring," friendship, social networks, cooperation, "preference for one's own group ('in-group bias')," "mild hierarchy (that is, relative egalitarianism)," and "social learning and teaching."
Christakis, a physician and a sociologist at Yale, buttresses his arguments with evidence from social science, evolutionary biology, genetics, neuroscience, and network science. He presents evidence from beyond the laboratory, drawing examples from the history of shipwrecks and communes and from studies of elephants, bonobos, and dolphins. He even addresses philosophical objections to his claim that our genetic and cultural history prepared humans "to make a particular kind of society—one full of love, friendship, cooperation, and learning."
(If you're familiar with the "Halloween incident" at Yale, you might be surprised at Christakis' optimism: After his wife, at the time also a member of the Yale faculty, wrote an email to students pushing back against warnings about "culturally unaware and insensitive" costumes, both spouses were confronted and shouted at by students. He eventually stepped down from his role as head of a residential college but retained his tenured professorship, while she stopped teaching at the university altogether.)
Christakis embraces a "glass is half full" interpretation of human sociality, but he doesn't shy away from the inseparable shadow consequences of the same traits: Our ancestors learned to be kind when they learned to be more effective groups of killer apes. People all over the world observe social norms of fairness and reciprocity, even without direct reward, in part because our otherwise different societies punish non-cooperators. We cooperate with others in our in-group in order to compete with out-groups. In gene-culture coevolution, contradictory and conflicting behaviors can power a kind of evolutionary arms race. Nature (pre-wired capabilities, such as the capacity for cooperation and social learning) and nurture (cultural development of teaching) can act as complementary forces, together driving the elaboration of cultural forms and the expansion of the social suite.
"Evolution," Christakis writes, "provides the underlying foundation for human culture by equipping us with the ability to cooperate, make friends, and learn socially."
Key to Christakis' arguments are the concepts of pre-wiring and exaptation. While a hardwired trait might equip a species of bird to voice the same tune everywhere in the world, a species pre-wired for birdsong might invent different songs in different environments. The former is often used to describe traits that are reflexive or instinctive. Hardwired compels; pre-wired enables.
Exaptation is an evolutionary trick that human beings are not alone in exploiting, although we are particularly good at it. It means that a species can repurpose a trait like feathers, which probably evolved as a form of thermal insulation, to do other things, such as fly. Exaptation also bridges genetic and cultural forms of evolution. While long, slow, biological evolution provides us (and other species) with a strong tendency for parents to form lasting partnerships—"pair-bonding"—human cultures provide a wide variety of cultural forms, such as monogamy, polygamy, and polyandry.
The biological advantage of pair-bonding is that the father stays around to help the mother take care of the offspring they have produced. This close partnership assures the father that he is indeed helping raise his own children, which is particularly useful in our species, which requires an investment of years of care before a child can act as an adult. And it assures the mother that she has help finding food and shelter while she births and nurtures offspring. As Christakis puts it: "The evolutionary psychology of both men and women is to exchange love for support."
Christakis claims that over time, humans learned to extend the affection and partnership we have with our mates to our kin, then to our kin's friends, then to all the members of a strongly defined group—an expanding circle of attachment that enables us to form social networks and complex societies. When maternal love becomes marital love and those forms of love expand to create friendships, a norm of expectations spreads through the group: Friends expect reciprocity, a balance of favors asked and offered. Relationships with in-laws take a variety of forms in different human societies, but in all cases they expand the circle of people one expects to trust. As networks of trust grow, a norm of cooperation emerges: Everybody expects others to help further the aims of the in-group. I may do favors for people in my group, even if they aren't kin and even if they haven't done anything for me, because I know that I can also count on other members of my group to do me favors.
In any group, some people will be willing to cooperate and others will "free ride" on the work of the cooperators. When free riding reaches a certain point, cooperation breaks down. Extensive research suggests that "altruistic punishment" may be a kind of social glue that maintains an acceptable level of cooperation. Think of how you'd like to tell off that person who cuts in line ahead of you. That's altruistic punishment—a norm upheld not by a police force but by public opinion.
Culture, as Christakis defines it, is "knowledge that is transmitted between individuals and across time, that can be taught and learned, and that is distinctive to groups…a set of beliefs, behaviors, and artifacts that are shared by members of the group and are typical of it, and that are socially transmitted." Other species exhibit social learning, but human beings are by far the best at deliberately inculcating other members of our group with useful knowledge. In other words, we're the best at teaching.
Human beings have compulsions and talents—some that most would consider "good," and some that most would consider "not good." We also have tools to create workarounds for the "not good" part: norms that enable people in groups to cooperate, even if they don't know each other; punishment that keeps "free riding" low enough that people will contribute to public goods; reputation that enables trust among people who may not have dealt with each other before.
The critical uncertainty is choice: Will our pre-wiring—together with toxic cultural forces, such as racism—lead to fiercer, meaner, better-armed tribal conflict? Or will the part of us that expands love from mates to friends to shipmates come to dominate? Christakis is optimistic. I hope he's right.