more when it is young and helpless than when it can fend for itself. The child sees things differently. Though an offspring has an interest in its siblings’ welfare, since it shares half its genes with each full sib, it shares all of its genes with itself, so it has a disproportionate interest in its own welfare. The tension between what a parent wants (an equitable allocation of its worldly efforts to all its children) and what a child wants (a lopsided benefit to itself compared to its siblings) is called parent-offspring conflict. Though the stakes of the conflict are the parents’ investment in a child and its siblings, those siblings need not yet exist: a parent must also conserve strength for future children and grandchildren. Indeed, the first dilemma of parenthood—whether to keep a newborn—is just a special case of parent-offspring conflict.
The theory of parent-offspring conflict says nothing about how much investment an offspring should want or how much a parent should be prepared to give. It says only that however much parents are willing to give, the offspring wants a bit more. Children cry when they are in need of help, and parents cannot ignore the cries. But children are expected to cry a bit louder and longer than their objective need calls for. Parents discipline children to keep them out of danger, and socialize them to be effective members of their community. But parents are expected to discipline children a bit more for their own convenience, and to socialize them to be a bit more accommodating to their siblings and kin, than the levels that would be in the interests of the children themselves. As always, the teleological terms in the explanation—“wants,” “interests,” “for”—don’t refer to literal desires in the minds of people, but are shorthand for the evolutionary pressures that shaped those minds.
Parent-offspring conflict explains why child-rearing is always a battle of wills. What it does not explain is why that battle should be fought with rods and birches in one era and lectures and time-outs in another. In retrospect, it’s hard to avoid sorrow for the millennia of children who have needlessly suffered at the hands of their caregivers. Unlike the tragedy of war, where each side has to be as fierce as its adversary, the violence of child-rearing is entirely one-sided. The children who were whipped and burned in the past were no naughtier than the children of today, and they ended up no better behaved as adults. On the contrary, we have seen that the rate of impulsive violence of yesterday’s adults was far higher than today’s. What led the parents of our era to the discovery that they could socialize their children with a fraction of the brute force that was used by their ancestors?
The first nudge was ideological, and like so many other humanitarian reforms it originated in the Age of Reason and the Enlightenment. Children’s tactics in parent-offspring conflict have led parents in every era to call them little devils. During the ascendancy of Christianity, that intuition was ratified by a religious belief in innate depravity and original sin. A German preacher in the 1520s, for instance, sermonized that children harbored wishes for “adultery, fornication, impure desires, lewdness, idol worship, belief in magic, hostility, quarreling, passion, anger, strife, dissension, factiousness, hatred, murder, drunkenness, gluttony,” and he was just getting started.166 The expression “beat the devil out of him” was more than a figure of speech! Also, a fatalism about the unfolding of life made child development a matter of fate or divine will rather than the responsibility of parents and teachers.
One paradigm shift came from John Locke’s Some Thoughts Concerning Education , which was published in 1693 and quickly went viral.167 Locke suggested that a child was “only as white Paper, or Wax, to be moulded and fashioned as one pleases”—a doctrine also called the tabula rasa (scraped tablet) or blank slate. Locke wrote that the education of children could make “a great difference in mankind,” and he encouraged teachers to be sympathetic toward their pupils and to try to take their viewpoints. Tutors should carefully observe the “change in temper” in their students and should help them enjoy their studies. And teachers should not expect young children to show the same “carriage, seriousness, or application” as older ones. On the contrary, “they must be permitted . . . the foolish and childish actions suitable to their years.”168
The idea that the way children are treated determines the kinds of adults