Wired for Culture: Origins of the Human Social Mind (43 page)

Immediately upon admission all eight stopped complaining of any symptoms and acted, to the best of their abilities, normally. Staff described them as “cooperative” and as exhibiting “no abnormal tendencies.” But what followed was a surprise to everyone. All of the fake-insane were given medications (which they secretly did not swallow) and hospitalized on average for just under three weeks, although one of the eight was detained for over seven weeks. Upon discharge they were each given a diagnosis not of sanity, but of “schizophrenia in remission.”

Deception is deeply wired into our genes from birth. Most of us have seen the pictures of human babies in wards, wrapped up in swaddling and placed side by side in a row. The surprising feature of these babies is how much they can resemble each other. Or to put it another way, they don’t appear to resemble anyone in particular. Babies have characteristically round faces and short pug noses, and most infants of European ancestry have blond hair and blue eyes at birth. So anonymous are human infants at birth that observers cannot match photographs of babies to their parents at a better than chance level. Hospitals frequently put both wrist and leg bands on babies, identifying their parents. This is not to prevent the occasional and terrible cases of baby-snatching from neonatal wards; it is a precaution should one band drop off. We have all heard the sad cases of babies being accidentally switched among parents in hospital rooms and then being brought up by the “wrong” parents, only to discover the distressing truth many years later. Who among us would be able to pick out our own child from a group of newborn infants had we never seen it?

Human babies are probably the most dependent of all species of mammal on their parents for survival. Our offspring require something like twenty-four-hour home care for the first year or so of life. It is extraordinary, then, that they do not come into the world with clear marks or some sort of signal that would allow their parents to recognize them. Lambs and newly born goat kids are far more precocious at birth than are human infants and yet even their mothers can recognize them from their calls. So, why are our babies anonymous at birth? One possibility is that babies have round faces, small chins, and pug noses to fit through the small human birth canal. And yet, there is no reason why babies need blond hair and blue eyes to do this, or why they couldn’t have some distinguishing mark or feature. Another possibility is it just doesn’t matter that the baby is anonymous: human mothers are not normally separated from their infants, and they know they are the mothers of the infant they gave birth to.

But this is not necessarily true of human fathers (or for that matter most fathers). The baby in his presence might have been fathered by another man, and without his knowing it. This means that a baby might find itself being raised by a domestic father that is not its
biological
father. Were that domestic father to find out, he might not be willing to spend the time and effort caring for that baby. Worse, he might harm or even kill offspring not related to him, as is true of other mammalian fathers. Infanticide by males is common in mammals; it often occurs when a male lion takes over a pride, or a male gorilla ousts the resident silverback. These new males know they are not the fathers of any offspring around them, and have no interest in rearing them for some other male. They don’t kill these infants to be spiteful, or King Herod–like, to be sure they get a particular one. Killing a female’s offspring will often mean that she comes back into estrus sooner, and the new male will then mate with her and have his own offspring around him instead.

Infanticide by males is rare in humans, but Martin Daly and Margo Wilson have demonstrated that it is around
one hundred
times more likely to occur between male stepparents and their stepchildren than between male biological parents and theirs. This statistic holds even when other factors that might differ between these two kinds of families are taken into account. It must be emphasized that the vast majority of stepparents are not abusive, much less infanticidal, just that both traits are more common in stepparents than biological parents. What scant evidence there is in humans suggests that domestic fathers might not be the biological fathers in 5 to 10 percent of births, without knowing it. Faced with the possibility of reduced investment, or worse, human infants might have fared better if they could hide clues about who their father was and genes for anonymity would have spread. If the domestic father is the biological father, little is lost by this deception. But if the domestic father is not the biological father, potentially much is gained.

Some years ago, I analyzed a mathematical model of this question, which indicated that levels of paternity uncertainty right around the 5–10 percent mark are where anonymity becomes the preferred strategy. We can even speculate that human babies’ strategy of deception extends to their behaviors. They should accept their domestic fathers—biological or not—on equal terms, not relying on physical or olfactory cues to influence their responses. Babies might even deceive themselves the better to cover up their deception. It is just possible, then, that human babies have adopted a deliberate strategy of anonymity to conceal their father’s identity. Women seem to be aware of men’s predicament and the risks this holds for their children, and often collude with their babies in the deception, even if unwittingly. Anthropological accounts reveal that at the birth of a child, the mother, her mother, and other women who might be present are far more likely to say, “It looks like the father,” than, “It looks like the mother.” Fathers need reassuring; the mothers don’t. As time goes on, the risks to the baby decline and they often start to resemble one or the other of their parents, or both. The blond hair and blue eyes so common in Caucasian infants disappear in most of them sometime around the second birthday. As we might expect of a strategy to hide one’s identity, the genes that control our adult eye color are switched off at birth (unless the baby does have blue eyes), but are gradually turned on as the baby matures.

DIVIDED MINDS AND SELF-DECEPTION

AN IMPORTANT
role for self-deception might be to allow the brain to produce a narrative of everyday existence that is somehow consistent, in the face of the gnawing internal conflicts over what to think and how to behave. William Hamilton wrote in the first volume of his
Narrow Roads of Gene Land
that

Seemingly inescapable conflict within diploid organisms came to me both as a new agonizing challenge and at the same time a release from a personal problem I had had all my life. My own conscious and seemingly indivisible self was turning out far from what I had imagined and I need not be so ashamed of my self-pity! I was an ambassador ordered abroad by some fragile coalition [of genes], a bearer of conflicting orders from the uneasy masters of a divided empire. Still baffled about the very nature of the policies I was supposed to support, I was being asked to act, and to act at once—to analyse, report on, and influence the world about me.

What could Hamilton’s lament possibly mean? A
diploid
organism is one that like humans and most animals has two copies of each of its genes, one that it received from its mother and the other from its father. These two copies are called
alleles
. Hamilton had come to appreciate that having maternal and paternal alleles meant there is a fundamentally divided parliament of genes locked up inside all of us. Here is why: males and females combine their genes to produce male and female offspring. This means that most of your genes have spent half their evolutionary history living inside a female body and half living inside a male body. If what works best for a female body is not what works best for a male body, then our genes can be tempted to acquire divided loyalties in their different postings. Human males and females have different physiology, morphology, body size, and shape. Human males and females have different life expectancies (females live longer than males, although this might be a reversal of the pattern in our evolutionary past), and most young women mature physically earlier than men. There might also be differences in risk taking and temperament between men and women, but these are less certain and, even if they do exist, could be learned rather than influenced by genes.

So different are the two sexes that it is useful in some respects to think of males and females as slightly different species pursuing divergent lives, only coming together every now and then to mingle their genes. If the metaphor seems strained in humans, consider the case of the group of insects known as the
Strepsiptera
. They are
endoparasites
, meaning parasites that live inside the body of another animal. In a few
Strepsiptera
species, males and females have evolved to live inside the bodies of different hosts—females lives inside an ant, males inside a cricket. Females spend their entire lives dwelling in their host’s body, never emerging. They have lost their eyes, wings, antennae, and legs. Males on the other hand must emerge every now and then from their cricket hosts to find these submerged females to mate, and so they retain all these features. How can the same genes be expected to produce such different outcomes?

Natural selection will often have little choice but to mold our genes to do the best job they can by somehow averaging the demands and the payoffs of living in male and female bodies; but that averaging can be tipped toward one sex more than the other. For example, the genes that reside on the chromosomes that determine your sex do not divide their time equally between the sexes, and this can cause them to have sharply divided loyalities. Women have two X chromosomes, one inherited from their father and one from their mother. Men have one X and one Y chromosome, the Y always inherited from their father, the X from their mother. Assuming equal numbers of males and females in a population, this means that Y chromosomes at any given time make up one quarter of the sex chromosomes, the other three quarters being Xs. The Y chromosome only ever resides in men, but X chromosomes divide their time between men and women (technically some parts of the Y can find their way onto the X but this is not important for this example).

Some simple arithmetic tells us that over many generations X chromosomes will spend two thirds of their time in women and one third in men (think of the sex chromosomes in a man and a woman as being numbered from 1 to 4, three of which are X chromosomes and one is a Y chromosome. Then, again assuming equal numbers of men and women, any given X chromosome has a two-thirds chance of being in a woman and a one-third chance of being in a man, because a woman always gets two Xs and a man one). We might expect genes on X chromosomes, then, to be better at making women than at making men even though they can reside in both.

In extreme cases, the loyalties get tipped entirely to one sex, even though the gene can appear in males and females. You inherit a small amount of DNA in the structure known as the mitochondrion that resides in each of your cells. Mitochondria are inherited solely from mothers, even though mothers and fathers both have them. This means that even though the mitochondrion spends exactly half of its time in each sex, this small piece of DNA is at a dead end when it finds itself in a male because it knows it will not be transmitted to his offspring. This puts it in direct conflict with the male’s body. There are remarkable instances in the animal kingdom in which genes on the mitochondrion feminize males to such an extent that they become females, thereby ensuring this mitochondrion does get transmitted.

It gets worse. Bacteria known as
Wolbachia
live inside the cells of some ladybird, fruitfly, butterfly, and woodlice species. As with mitochondria, only mothers transmit these
Wolbachia
to their offspring. Now, females of these species lay a large clutch of brother and sister embryos, each carrying the mother’s
Wolbachia
. As with the mitochondria, the
Wolbachia
in the male embryos are at a dead end. In some ladybird species, these
Wolbachia
commit suicide by killing the male embryos in which they reside. Why? In ladybirds at least, the surviving sisters (who carry identical copies of the suicidal
Wolbachia
) feast on their dead brothers. This improves the sisters’ survival and therefore the survival of the
Wolbachia
in them. Suicide can be a useful policy for spreading copies of your genes.

Our divided loyalties do not begin or end with differences that arise from genes spending differing amounts of time in the sexes. For example, all of our genes have spent a good part of their lives living inside children who try to manipulate their parents in the persistent ways that children do, and another part of their lives as parents trying to resist those charms. Which period of our lives wins? Most people think it must be parents, as they are bigger, stronger, more intelligent, hold the reins of power, and are more devious. Or is it children because their needs are greater? The answer is neither, or more accurately, the answer is that it is the wrong question. Our genes have been selected to influence us in the ways that best suit them at the different times of our lives. That is why the begging and nagging you as a child turns into the scolding and strict parent. As a child it serves your genes to beg, but when you become a parent it often serves those same genes to try to stand firm. Just as was true of the stand-off between deception and the ability to detect it, it is not
you
that wins in the end but your genes. You are just their carrier and the organ that expresses their wishes, and otherwise mostly irrelevant.

A phenomenon known as
genomic imprinting
could mean that the possibilities for a divided mind are far greater than anyone might previously have imagined. Even people who instinctively recoil from the thought that they are just a vehicle for their genes must acknowledge some beauty in the precision of its effects. For the most part, the paired genes that you inherit from your mother and father are identical or nearly so, and normally both the maternal and the paternal copies are “expressed” or used. But the hallmark of genes that are “imprinted” is that some are expressed only when inherited from the mothers, and others are expressed only when inherited from the father, with the other copy in both cases remaining silent. The imprint itself is a chemical tag that gets applied to the gene when the mother makes an egg or the father makes sperm, and its action is to switch the gene off. Now, if for some reason there is a conflict of interest between the same genes, depending upon whether they are inherited from the mother or the father, such that one wants to be on and the other off, genomic imprinting can make that conflict happen.