Wired for Culture: Origins of the Human Social Mind (35 page)

The
HAR
s were ranked from
HAR
1
to
HAR
49
, with
HAR
1
being the most rapidly evolving of all the segments. Comparisons between chickens and mice showed that
HAR
1
hardly evolved at all in the 300 million years from the common ancestor of birds and mammals, changing in just two of its 118 bases. But then there was an abrupt acceleration. In just the 6 million years from the common ancestor of chimpanzees and humans to modern humans,
HAR
1
managed eighteen changes. This translates to a 450-fold increase in this bit of DNA’s rate of evolution. But the best part of the story is that this most rapidly evolving segment of our DNA is active in human brain cells.
HAR
1
’s high rate of evolution tells us that it must have granted substantial benefits. Those lucky enough to carry copies of it that had one or more of the beneficial mutations must have enjoyed clear advantages over their less lucky and somewhat dim friends.

What makes
HAR
1
even more extraordinary is that at just 118 bases long, it is about one tenth the length of a typical gene. Genes, as we said, are segments of DNA that contain the code to make proteins, which in turn are the building blocks of bodies. Our hair and fingernails, muscles and eyes, hearts and kidneys, and our skin are all made of proteins.
HAR
1
does not make a protein; in fact, it is not even a gene. Instead,
HAR
1
turns out to be a segment of our DNA that influences or regulates how other genes are expressed, and this might be why it can make such a difference to our brains. In
HAR
1
’s particular case, it influences the ways that neurons in our brain develop and project into new areas. Rather than simply making our brains bigger, it changes the structure, density, and complexity of our brains and the connections their neurons make with each other. The changes that
HAR
1
brings are just such as we might have hoped of a species that supposedly finds it easier to think than the Neanderthals did. Merely adding processors to a computer is not the same as getting these processors to talk to each other and share their information more effectively.

Many of the genes that influence the size of our brain size are located in our genomes near small regulatory segments like
HAR
1
. So, the real wonder of our evolutionary changes since the chimpanzee is how few changes have led to such profound differences and over such a short period of time. Natural selection hit upon just those changes that could make a big difference to our behavior. Many more of these segments and the genes they affect will come to be implicated in our brain growth and development, but one stands out for its possible link to language in humans.
FOXP
2
is a segment of DNA that, like
HAR
1
, regulates the expression of other genes. All mammals have it, and it is expressed throughout the body, including in brains. Unlike
HAR
1
, it has not changed so dramatically since we split from our ape ancestors, but it has recently acquired what appear to be two critical changes that affect the control of facial muscles that are involved in producing speech. Even mice fitted with a copy of the human form of
FOXP
2
are said to squeak differently from those with the normal mouse form!

Very recent evidence shows that the Neanderthals had this same variant of
FOXP
2
, leading many people to conclude that they also had language. But this is premature. They might have had language, but simply having this variant is not proof.
FOXP
2
affects our brains by altering the expression of at least one hundred genes: it is thought to cause about fifty of them to be expressed more and another fifty to be expressed less. So, for
FOXP
2
to work similarly in the Neanderthal brain, we would have to find the same one hundred other genes, and presume that they worked the same way in both brains. But this seems unlikely. My car has an engine and so does a Ferrari. But my car is no Ferrari. We know our brains differed from the Neanderthals’ in having a more fully developed and highly interconnected cortex, the uppermost layer of our brains. But we also have reason to suspect that the social arms race we have suggested is responsible for our unusual brain might not have been so pronounced in the Neanderthals. The archaeological record points to a species with far fewer artifacts, hinting at little social learning of the sort that is so prevalent in our species. And, as we saw in Chapter 2, it is the presence of social learning that established the need for systems of exchange and cooperation; in short, that established the need for a social brain.

DOMESTICATION BY BRAIN GENES

ONE OF
the most surprising effects of our big socially charged brains was to preside over their own diminution. Having steadily enlarged for roughly 2 million years, they have shrunk by around 10 percent in the last 30,000. We also became less robust or more
gracile
—thin-boned—during this time, so it might just be that our brains were adjusting to a reduced stature. But one of the most reliable differences between domesticated animals and their wild ancestors is that the domesticated ones have smaller brains: as a rule, domesticated animals are just a bit dim, or less “street smart.” Could our brains have domesticated us as well?

Domestication is like taking up residence in a protective bubble, and right across the history of evolution it is linked to things becoming simpler. Single-celled organisms that have taken up residence inside the cells of other organisms normally have many fewer genes than their wild ancestors. They jettison genes they no longer need, genes that served functions in their wild state but that are now provided by their host. The structures called
mitochondria
that exist inside each of our cells and that produce energy are thought to be ancient bacteria that took up residence inside cells like ours over 1.5 billion years ago. They probably had around 3,000 genes when they moved in; now they have 16.

The same sort of protective bubble is erected when an animal is domesticated. Now your shepherd looks after you, sees off predators, finds or steers you to food and water, and keeps you warm. The animal’s response seems to be to jettison features it no longer needs, and this includes shedding some of its costly and expensive brain. And why not? It no longer needs so much of it now that the shepherd is doing the thinking. Domesticated rats, mice, mink, cats, dogs, pigs, goats, sheep, llamas, and horses all have smaller brains than their wild ancestors. Wolves outperform dogs on searching tasks. Domestication also tames animals directly as their human handlers preferentially breed the less aggressive ones. Dogs become less packlike; sheep and cows become calm and relaxed around humans, and more dependent on them. They also become less tuned in, or less switched on, because their human masters are doing all the hard work.

The word “bovine” technically just means cowlike but is used as an adjective to mean stolid, slow-moving, and dim-witted. Maybe our big brains have made us more bovine by cosseting in us technologies built from social learning. Remember it was this social learning that we thought removed much of the need for us to be inventive in the first place. Who among us is good at tracking game, lighting a fire without matches, or finding edible plants in the local wood? Technology and mastery of the environment are great levelers of people, and this acts as a further boost to domestication. The anthropologist Robert Lee reported that among the San Bushmen of the Kalahari, when disputes reach a point where there might be open conflict, someone will often declare, “we are none of us big, and others small; we are all men and we can fight; I am going to get my arrows.”

Our brains might also have domesticated our outward appearance, making us one of the more peculiar-looking of the mammals. Mammals are really only distinguished from the other animals by two key traits. Mammals have fur—no other kind of animal does—and we evolved the ability to lactate or nurse our young, again something no other animal does. But nearly all of our other features we share with other animals. Now, fur, like feathers in birds, is a valuable invention for its combination of being breathable, its ability to shed water and snow, and for being an excellent insulator, and an insulator that works even when wet. These are just the qualities you might expect of a material natural selection devised to cover warm-blooded animals that sweat, get rained on, and often live in cold climates.

But humans are naked. We have jettisoned this valuable fabric. An even greater irony is that having done so, we now hunt mammals and kill them so we can wear
their
fur. Even in our modern world, fur spun into the form of wool is still the preferred fabric as a base layer for skiing and other cold weather pursuits, and wolverine ruff is still the preferred insulator on the hats of polar explorers. So, why would humans have got rid of their fur, especially as being naked makes us more susceptible to cuts and bruises and to exposure to the sun? Surreptitiously look around you now if you are reading this book somewhere in public. Those bare patches of smooth skin you can see, and that appear self-evidently normal and even attractive in a human, seem ludicrous in any other mammal. Imagine your dog sheared of all its fur or a polar bear naked as a human. The ridiculous-looking image you have in your mind is what you look like to other animals.

One suggestion is that we lost our fur when we moved out onto the savannah, early in our evolution, so that we could cool our bodies more effectively. Our
Homo erectus
ancestors were upright hunters and foragers, who would have spent much of the day baking in the hot sun, and so losing their fur and becoming naked might have been beneficial. For instance, no one knows how far back in time the persistence running style of modern-day San Bushmen existed, but if
Homo erectus
used it, then shedding their fur might have been an important way to protect themselves from overheating, although as it is males that do this hunting, this explanation fails to tell us why both males and females became naked. Another difficulty with this idea is that becoming naked should also then have benefited those other animals that lived in the noonday sun, and especially those that we chased, but they haven’t lost their fur. There are also some calculations that animals without fur would lose more heat at night—when they need to retain it—than they could give off during the day, returning a net loss for being naked. Finally, there is the problem that when we left the savannah and travelled around the world, our hair did not grow back as we inhabited colder climes. Natural selection would have had plenty of opportunities to pick people out who were slightly more hairy than others—they are easily spotted at the nearest swimming beach or public pool.

A different idea to explain our nakedness gets our brains involved, but the link won’t be immediately apparent. It is a little-known fact that the single largest cause of death in animals, and probably all organisms, is parasites—viruses and bacteria, but also things like biting flies, or lice, ticks, worms, and other infectious organisms that transmit disease, suck our blood, and live in our guts where they eat our food. Because these parasites reproduce so quickly they can always stay one step ahead of our immune systems. Malaria, transmitted by a mosquito bite, still kills far more people around the world each year than wars. Recent estimates put the figure at around 1 million per year in Africa alone. The human immunodeficiency virus or HIV kills even more people than malaria, currently around 3 million per year. Few of us realize just how much energy we give over to our immune systems to fight these and other parasites, but farmers know that cows fed antibiotics get bigger. What? They get bigger because they do not have to use up precious energy fighting off infectious diseases, and freed of that burden they turn the excess energy into growth.

Fur is a convenient and safe home for the parasites known as
ectoparasites
, creatures such as flies and ticks that plague us either by living on the outside of our bodies or by biting us and transmitting diseases such as Lyme or malaria. A measure of the burden of these flies is that many animals spend large portions of their days—over 25 percent in some cases—trying to remove ectoparasites. Monkeys huddle in groups to groom each other, not as a way to look better but to remove parasites. So bountiful is the harvest that one possible motivation for grooming someone is to be able to eat the parasites you get. But the more probable reason is to “curry favor”—the word “curry” here appropriately being an old expression for brushing a horse—by removing someone else’s ticks. Grooming is not always an option, and horses, cows, bears, and just about all large mammals rub themselves against trees at least partly to remove parasites. Some animals—horses among them—even have specialized muscles for twitching their skin to make flies jump off, or they can switch their tails to swat at them.

Now, the connection between our brains and our nakedness is that our lack of hair might be a form of domestication by intelligence. Walter Bodmer and I have suggested that humans might have lost their fur as a way to reduce the burden of these annoying and disease-carrying ectoparasites. Our great intelligence—or our abilities at social learning—would have made us uniquely suited to replace the functions of hair or fur with our technologies. We can build fires, create shelters, and make clothes as ways of avoiding the loss of heat when we needed to retain it, or as a way of blocking the sun when its baking rays become too hot. Unlike fur, clothes can be changed and washed or even discarded if they get infested. Having these technological replacements for fur available at our fingertips might have set us on a trajectory of becoming less hairy as natural selection favored people who carried around fewer infections.