Wired for Culture: Origins of the Human Social Mind (44 page)

The best-known cases of genomic imprinting involve genes that influence how large a baby grows in the mother’s womb. Normally, at least up to a point, larger babies are healthier. Nevertheless, a mother might wish to limit the growth of her babies
in utero
because a baby that is too large could harm or even kill her during childbirth, or affect her chances of reproducing successfully in the future. All women face this trade-off between what evolutionary biologists call their
current
and
future reproductive success
. Fathers, on the other hand, in an evolutionary sense have been less concerned about how the baby’s size might affect the mother. So long as the mother (and thus the baby) survives, men will prefer somewhat larger babies because they tend to fare better. Men won’t mind as much—again in an evolutionary sense—if this limits the mother’s future reproduction because they can in principle always have children with other women. This results in a conflict of interest between paternal and maternal genes, with the father’s genes wanting slightly larger babies than the mother’s genes.

Careful genetic studies show that mothers and fathers imprint their genes in just the ways we would predict if they are in conflict over how large they want their babies to be. For instance, we all carry a gene called
insulin-like growth factor 2
, or
Igf2
.
Igf2
produces a protein that, as its name suggests, increases the volume of nutrients the developing embryo receives, causing it to grow larger. If our conflict story is correct, we might expect that fathers will leave their paternal copy of this gene on in the developing fetus, but mothers will switch their maternal copy off by imprinting it. And this is exactly what happens. Another gene, called
Igf2-R
, adds evolutionary intrigue to this story. Standing for insulin-like growth factor 2
receptor
, this gene captures the product of the
Igf2
gene: it seems to have no other purpose than to nullify
Igf2’s
effects. It is as if mothers and fathers have been locked into an evolutionary arms race over the size of the baby and
Igf2-R
exists to help the mother. If so, we would expect the maternal copy of
Igf2-R
to be switched on, but the paternal copy to be imprinted and thereby switched off. And, again, this is exactly what happens. Neither side (mother vs. father) “wins” this evolutionary competition outright; rather, they remain locked into their respective strategies as the best things they can do for their respective genes.

Whether this conflict between the mothers and fathers is also felt within each of their minds is not known, but it could be. Male and female babies grow up to be fathers and mothers, and both sexes will carry these imprinted genes that influenced their growth. Either way, conflicts that might manifest as the sort of divided consciousness Hamilton spoke of can be imagined and might even operate routinely in our minds because of genomic imprinting effects. The founder of psychoanalysis, Sigmund Freud, would have known nothing about genomic imprinting, but it might form the basis of one of his better-known ideas. Freud proposed that a squabbling triumvirate of the
id
,
ego
, and
superego
rule our conscious and subconscious minds. To Freud, your id is your impulsive and self-interested side, your superego is your moral and ethical side, and your ego is left in the middle to arbitrate between these two opposing factions. Freud is rightly criticized for the descriptive, subjective, and elusive nature of these definitions, and yet all of us sense that there is something to them. We have all known the impulsivity and hyperactivity of someone with an overactive id (in Freud’s terminology) or the balefully moralizing tone of someone with an overactive superego. One says, “C’mon, just do it!” The other says, “You know, we really shouldn’t, it’s not right.”

To the less Freudian inclined, Freud’s id-superego battle is just the familiar tussle between passion and reason. But why is this tussle such a fundamental and unresolved part of us? Extraordinarily, we can construct an expectation for something like id versus superego conflicts from a knowledge of how imprinting works. In most mammal species, upon reaching sexual maturity, one or the other sex—but not both—typically leaves the group it was born into, to find a mate elsewhere. In most mammals it is males that disperse at sexual maturity and these males must then go off on their own, or sometimes in pairs as brothers, leaving their natal territory to seek a new territory in which to live and reproduce. This pattern in the mammals accounts for the familiar stories of male lions taking over prides of lionesses or male gorillas that take over and displace silverback males from the groups they dominate. In birds, it is often the reverse, with females dispersing and having to go off and find a male’s territory to join. In humans, the usual mammal pattern is reversed, and so, as with many bird species, it is typically females that leave the group. This is not a prescriptive social statement but rather one based on patterns of female movements in traditional hunter-gatherer societies. Even until recently, we recognize this pattern in the tendency of women to join their husband’s household and adopt his surname.

Female dispersal is an unusual trait but one that we also happen to share with chimpanzees, and it seems with Neanderthals. The twelve cannibalized Neanderthal skeletons mentioned earlier were well enough preserved to yield ancient DNA. Analysis of their genes shows that the men were brothers, but the women, as would be expected if they have left their natal territories, were unrelated to each other. Now if, as the chimpanzees and Neanderthals suggest, this difference in which sex leaves the group has been true of our past, then the males in human social groups will tend to be more closely related to each other than they are to the adult women, or the women are to each other. The men are mostly fathers, sons, uncles, nephews, cousins, and brothers; but the women are mostly immigrants from other groups. This difference in average relatedness sets up the potential for a conflict of interest between the genes the mother and father transmit to their offspring. A father might wish his offspring to behave altruistically toward other group members, especially toward children and adult male members of that group. Mothers, on the other hand, being less related to other people in their group, might wish these same offspring to be less altruistic and more self-interested.

And this is where genomic imprinting steps in. If we imagine a gene involved in helping or favoring relatives, including the conscious expression of the emotions and beliefs that support these behaviors, your mother might wish to have her genes switched off to make it less likely they provide aid to genes not related to hers. For the opposite reason, your father might wish to have his switched on. Now since half of your genes come from your mother and half from your father, this sets in place the potential for an enormous tug-of-war between opposing factions of genes—some predisposed to be helpful and cooperative, others less so. If we wish to put this scenario in Freudian terms, there will be a struggle within you between superegolike tendencies to be helpful and idlike tendencies to be more selfish in your outlook. It is then up to your conscience, or ego, to arbitrate.

Next time you feel that tension between the half-crazed side of you that wants to leap recklessly at some opportunity and that annoying other side of you that says, “Whoa!”, give a moment’s thought to the possibility that it all comes from a genetic tug-of-war inside your brain. I use Freud’s ideas here metaphorically and even whimsically, and I don’t take these examples to be evidence for his theories. But for purposes of understanding our selves, we can now see the wisdom of Hamilton’s statement—there is an inescapable conflict within us, and it might even be played out at the level of our conscious awareness and dispositions toward others. The “I” that we see when we look inside us is perhaps little more than a construction of these interested parties inside our minds, trying to get us to behave in ways that promote them, given the makeup of our social groups.

If this all sounds a bit dubious or incredible, it is worth bearing in mind what Daniel Dennett has called Orgel’s “second rule,” named after the molecular biologist Leslie Orgel: “evolution is cleverer than you are.” And, indeed, a gene has recently been found in mice to have the characteristics predicted if there is conflict between paternal and maternal alleles over how altruistic to be. The gene is called
growth factor receptor-bound protein 10
or
Grb10
, and it is imprinted—paternal copies of this gene are expressed, while the maternal ones receive the imprint and are switched off. It also influences social behavior. When researchers remove the paternal copy of the gene, offspring become more socially dominant—more altruistic in this case—in their interactions with others. This suggests that the paternal copy normally acts to suppress altruism rather than promote it, as in our scenario for humans. Intriguingly, though, in mice it is males who normally disperse from their groups rather than females, so this is the effect we expect. It is too early to know if this finding bears directly on the idea of conflict inside human minds. But it does show that imprinting related to conflict within genomes over how just how altruistic maternal and paternal genes “want” to be can indeed be observed.

CONSCIOUSNESS AND SELF-AWARENESS

THE IMPRESSION
that we are able to choose freely between different possible courses of action is fundamental to our self-image as beings with free will. But as we have seen, our obsession with free will might be misplaced. Natural selection should have created in us a tendency to do what is good for our survival and reproduction, and not necessarily a tendency to do what we “want” to do. The situation might even be worse for free will than this explanation suggests. Our subjective experience of freedom—or at least more of it than we might imagine—might be little more than an illusion. This is a statement that we all instinctively and intuitively reject, but there is a growing evidence that our actions can be initiated by unconscious mental processes that occur long before we become aware of them.

Sophisticated experiments which measure activity in people’s brains while they are asked to perform a task show that our brain can make decisions up to ten seconds before the decision enters our awareness. In one of these experiments, you might be asked to focus your attention on a screen where a stream of letters is presented, such as:
b
…..
c
…..
f
…..
d
….. You are told that when you feel the urge to do so, you should freely decide to push one of two buttons in front of you—one operated by your left-hand index finger, the other by your right—and then press it immediately. After pressing one of the buttons, a screen appears that replays the last few letters in the stream you just viewed. You are then asked to indicate which letter was being displayed when the idea to push the button came into your mind.

People who participate in these tasks use the left and right response buttons about equally often. This is important because it shows they are making choices. But the surprise is that people’s brains seem to know what they are going to do before the owners of those brains are made aware of the decision. This unsettling conclusion was apparent from the patterns of the volunteers’ brain activity. These patterns changed five to ten seconds
before
the letter the volunteers had indicated was being displayed on the screen when the idea to push the button came into their minds. Imagine yourself in this setting: You might have got the idea to push the button when
d
was on the screen, but your brain activity would tell a different story. It would show changes happening earlier, say, when
b
was on the screen. The researchers know that this was when the decision was made to press the button because the patterns of brain activity can predict which of the buttons—left or right—you would later push. At the time these events were happening, you would not have yet had an inkling of what you were going to do.

These are careful neurological studies by leading scientists using the latest neuro-imaging techniques. They are not the sort of crackpot research studies—such as those on so-called subliminal messages—that unnerved moviegoers in the 1950s, worried that they had been manipulated by some “hidden persuader,” in Vance Packard’s memorable phrase. His compelling and worrying book of the same title convinced millions they were powerless to escape instructions being inserted into their minds—to buy Coca-Cola and popcorn—by messages flashed so quickly onto movie screens that their conscious minds were not even aware of them. Campaigners opposed to the use of subliminal messages in advertising produced advertisements showing hordes of slightly manic people, manipulated by the invisible hands of subliminal messages, streaming to buy soft drinks and popcorn. But later research showed Packard’s claims to be false. Truly subliminal messages—messages that appear for such a short period that we don’t perceive them—don’t influence us, or if they do, the effects are weak. It is only when they are shown long enough for us to become aware of them—that is, they are no longer
subliminal
—that we rush out and buy the Coca-Cola or the popcorn. We are being persuaded, but the persuaders are not hidden.

What, then, could the results of the neuro-imaging studies possibly mean? Are we mere observers being diligently, if belatedly, informed of what our brains are up to? The simple answer to that question is almost certainly yes. To a degree that far exceeds what we might have thought, we cannot merely assume that “we” initiate the thought processes that lead to the decisions we make, such as to buy Coca-Cola or popcorn. Instead, our subconscious brains might set to work on problems that it later gives us answers to, and when it does so, this feels like free choice or an action “we” chose. In fact, whenever some thought just seemingly pops into your brain, it might be the result of the sort of subconscious thinking that occurred in the button-pushing experiments.