Social: Why Our Brains Are Wired to Connect (5 page)

Part of what makes it hard to believe that social cognition and nonsocial cognition depend on different neural machinery is that these two kinds of thinking don’t
feel
very different when we use one versus the other.
It’s not like the change we feel when speaking in our native tongue compared with speaking in a recently learned language.
It’s not like the distinct experiences we have when solving a math problem and when imagining being a superhero flying through the air.
These differences feel really different to us.
But when we switch from thinking socially to thinking nonsocially, we feel as if we have simply changed topics, rather than changing the way in which we are thinking.
But that does not mean the differences between social and nonsocial thinking aren’t real.
It means only that the differences aren’t conspicuous to us.

We do have at least one way of intuitively appreciating differences between social and nonsocial thinking.
Most of us subscribe to the common wisdom that book smarts and social smarts rarely go together.
These two kinds of intelligence seem to require different abilities, and the brain has separate networks to support them.
A recent study of children with Asperger’s disorder brings this distinction home.
Asperger’s is considered to be a milder version of autism, but it is associated with many of the same deficits in social cognition and social behavior.
A group of children with Asperger’s
actually performed better on a test of abstract reasoning than age-matched healthy children.
If social intelligence and nonsocial intelligence compete with each other, like the two ends of a seesaw, then it makes sense that deficits that take away some of the strength and power on one end of the seesaw will give the other end greater influence.

Bigger Brains

Most of us have been taught that our bigger brains evolved to enable us to do abstract reasoning, which promoted agriculture, mathematics, and engineering as complex tools to solve the basic problems of survival.
But increasing evidence suggests that one of the primary drivers behind our brains becoming enlarged was to facilitate our social cognitive skills—our ability to interact and get along well with others.
All these years, we’ve assumed the smartest among us have particularly strong analytical skills.
But from an evolutionary perspective, perhaps the smartest among us are actually those with the best social skills.

Before we discuss the reasons why the human brain is larger, we need to know what it means to say the human brain is larger than the brains of other species.
There are countless ways that brains can be compared to one another—total volume, weight, number of neurons, degree of cortical convolution, total gray matter volume, and total white matter volume.
And those are just the tip of the iceberg.

One important preliminary fact is that brain size is predicted very well by body size.
This means that a great deal of absolute brain size is associated with things like maintaining and monitoring the body.
The bigger the body, the more brain tissue is needed to oversee it.
As a result, really big animals tend to have really big brains.
Indeed, if only brain weight is considered, humans are nowhere near the top of the heap.
The human brain weighs in at about 1,300 grams
, just about equal to the brain of the bottlenose dolphin.
African elephants’ brains nearly triple that at 4,200 grams, and some whales have brains that can reach 9,000 grams.
Humans do better comparatively when we consider the total number of neurons in the brain.
We have approximately 11.5 billion neurons, which is the highest known number in the animal kingdom … but just barely.
Killer whales have 11 billion
neurons.
If intelligence were only a matter of the number of neurons we possessed, we would be building eighty-story skyscrapers, and killer whales would be building seventy-five-story seascrapers.

Despite the strong relationship between body size and brain size, some animals have larger brains than their body size would seem to require for the basic maintenance and monitoring functions.
The degree to which an animal’s brain size deviates from what we would expect, based on body size, is called
encephalization
.
It is thought to represent the brain’s spare capacity to do more than control the body—like developing intelligence.
Here, humans are the undisputed heavyweight champions of the animal kingdom.
Human encephalization is 50 percent greater than that of the next closest animal, the bottlenose dolphin, and nearly twice that of any nonhuman primate (see
Figure 2.4
).
And, just as we would expect,
newer parts of the brain, like the prefrontal cortex
, show this enhanced encephalization as well.

Figure 2.4 Encephalization Across Species.
Arrow points to humans.

Adapted from Roth, G., & Dicke, U.
(2005).
Evolution of the brain and intelligence.
Trends in Cognitive Sciences
, 9(5), 250–257.

Making MacGyvers?

So, why did the human brain become so much larger, in terms of encephalization, than the brains of other animals?
Making a bigger brain comes at a great cost in an animal’s time and energy.
It is not much of an exaggeration to say we live in order to feed our brains.
In adult humans, the brain makes up approximately
2 percent of the total body mass, and yet it consumes (that is, metabolizes) 20 percent of its energy.
In prenatal infants, the brain consumes 60 percent of the body’s total metabolism, a rate that continues through the first year of life and only gradually declines to the 20 percent level during childhood.

The brain’s outsized energy budget means that evolution would have selected for brain growth only if brain growth helped primates solve problems critical to survival and reproduction.
Such problems include finding and extracting foods like fruit and meats with higher calorie content than leaf-based diets, avoiding predators, and keeping their young safe.
So what particular kind of cleverness does a larger primate brain offer in the service of solving these ecological problems?
Scientists have come up with three main hypotheses.

The first is the one most of us think of intuitively: individual innovation.
The television character MacGyver is the archetype of this sort of intelligence.
He is a secret agent who is always getting into sticky situations and manages to innovate his way out of them by combining available household items in novel ways to produce exactly what he needs.
In one episode, he stops a dangerous sulfuric acid leak using only a candy bar and its tin foil wrapper.
Though our lives probably involve fewer explosive situations, we are all MacGyvers in our own way.
We are problem solvers, whether the problem is what to cook for dinner given the ingredients we have on hand or how to structure a spreadsheet most effectively.
To differing degrees, all primates are problem solvers.
When we think about having big brains, we think about how smart they make us, as individuals,
at learning and solving problems.
But despite this being an obvious answer—and perhaps the answer you might have been taught in high school science—it’s not the right answer.
Whether a species innovates more or less is not the best predictor of brain size across species.

The second hypothesis focuses on our social abilities.
Although humans as a species are very good at inventing solutions to problems, individuals don’t always do as well on their own.
When my son, Ian, was four, he loved to play the videogame
Super Hero Squad
.
My wife, Naomi, and I would always have to play with him because he would get stuck very easily.
The game involved solving a series of puzzles, and Ian wasn’t old enough to solve them on his own.
Out of every five puzzles in the game, Ian might have been able to solve one.
Of the same five puzzles, Naomi and I could solve only two or three.
Generating the solutions was just too hard.
Apparently, we were too old to solve the problems because the way we would move forward is by watching YouTube “walkthroughs” of a young boy getting through the puzzles successfully and explaining the tricks as he went.

In other words, humans don’t excel as a species because we are all innovators.
Rather, one or more of us (in this case, a young videogame wizard) devise a solution to a common problem, and the rest of us learn the solution from that person by imitation or instruction.
Perhaps we developed larger brains to improve our capacity for imitation or social learning?
While species that engage in social learning more often do have bigger brains, it turns out that this is not the best predictor of brain size across species either.

The Social Brain Hypothesis

The third hypothesis for why we have bigger brains suggests that we have them so that we can connect and cooperate with one another.
If you needed to build a home on your own, how well would you
do?
Could you build yourself a log cabin?
Cutting and lifting logs is a lot easier with a couple extra pairs of hands.
In a sense, the basis of society could be seen as an agreement that if you help me build my log cabin, I’ll help you build yours in turn.
Everyone gets a better home, and we all benefit.
Nonhuman primates aren’t in the business of building log cabins, but their success at dealing with ecological problems can also be profoundly improved by dealing with their problems together—through coordinated cooperative action.
Survival turns out not to be a zero-sum game for primates.

In the early 1990s,
evolutionary anthropologist Robin Dunbar made the provocative claim
that the primary reason the neocortex grew larger was so that primates could live in larger groups and be more actively social.
Neocortex ratio
refers to the size of the neocortex
relative to the size of the rest of the brain.
The evidence that Dunbar and others have marshaled is impressive.
When the relative size of the neocortex is correlated
with differences in the three potential drivers of brain size (individual innovation, social learning, and group size), group size is the strongest predictor of neocortex size.
In his first study, Dunbar pitted group size against indicators of nonsocial kinds of intelligence, and he found that although both correlated with the neocortex ratio, group size was the better predictor.
Later work demonstrated that these effects
were strongest among the frontal lobes.

Using the equations that emerged from this line of work, Dunbar was able to estimate what the largest effective, coherent social group should be for each kind of primate, based on its neocortex ratio.
His analysis suggests that for humans the number is around 150, the largest for any primate.
This is referred to as “Dunbar’s number,”
and it turns out that a striking number of human organizations tend to operate at around that size.
For instance,
village size, estimated from as long ago as 6000 BC
and as recently as the 1700s, converges around the 150 mark.
Ancient and modern armies also organize around units of about 150 people.

The human brain didn’t get larger in order to make more MacGyvers.
Instead, it got larger so that after watching an episode of
MacGyver
, we would want to get together with other people and talk about it.
Our social nature is not an accident of having a larger brain.
Rather, the value of increasing our sociality is a major reason for why we evolved to have a larger brain.

Making Groups Worth It

What is so beneficial about living in larger groups?
Why would evolution foster an increase in our typical group size by increasing the size of our brains?
The most obvious advantage to larger groups
is that predators can be strategically avoided or dealt with more successfully.
It’s hard to keep your mind focused on finding food when you are worried about being food, and it’s dangerous to be out in the open looking for food by yourself.
Groups of apes, in contrast, can trade off time looking for food and watching out for predators.
That is a big advantage.

The downside of larger groups is that there is increased competition for food and mating partners within the group.
If you are on your own and you manage to find food, it’s yours.
The larger your group, the more likely it is that one of the others in your group will try to poach it.
Primates with strong social skills can limit
this downside by forming alliances and friendships with others in their group.

Consider two chimpanzees, Smith and Johnson.
Johnson gets bullied regularly by Smith.
Johnson is a relatively low status ape.
But if he can form an alliance with Brown, a high status ape, this will help protect him from Smith.
Because Brown is high status, he knows that if he takes Johnson’s side in a skirmish with Smith, Smith will stand down immediately, not wanting take on a higher status chimp.
This is a great deal for high status Brown because he
will get more favors (for example, grooming) from his low status partner, Johnson, without really putting himself at risk in confrontations with Smith.