Incognito (33 page)

With the success of the monkey studies, people began to study gene-environment interactions in humans.
²¹
In 2001,
Avshalom Caspi and his colleagues began to wonder whether there are genes for depression. When they went on the hunt, they found that the answer is “sort of.” They learned that there are genes that
predispose
you; whether you actually suffer from depression depends on your life’s events.
²²
The researchers discovered this by carefully interviewing dozens of people to find out what sort of major traumatic events had transpired in their lives: loss of a loved one, a major car accident, and the like. For each participant, they also analyzed the genetics—specifically, the form of a gene involved in regulation of serotonin levels in the brain. Because
people carry two copies of the gene (one from each parent), there are three possible combinations someone might carry: short/short, short/long, or long/long. The amazing result was that the short/short combination predisposed the participants to clinical depression, but only if they experienced an increasing number of bad life events. If they were lucky enough to live a good life, then carrying the short/short combination made them no more likely than anyone else to become clinically depressed. But if they were unlucky enough to run into serious troubles, including events that were entirely out of their control, then they were more than twice as likely to become depressed as someone with the long/long combination.

A second study addressed a deep societal concern: those with abusive parents tend to be abusive themselves. Many people believe this statement, but is it really true? And does it matter what kind of genes the child is carrying? What caught the attention of researchers was the fact that some abused children become violent as adults while others do not. When all the obvious factors were controlled for, the fact stood that childhood abuse,
by itself, did not predict how an individual would turn out. Inspired to understand the difference between those who perpetuate the violence and those who do not, Caspi and his colleagues discovered that a small change in the expression of a particular gene differentiated these children.
²³
Children with low expression of the gene were more likely to develop conduct disorders and become violent criminals as adults. However, this bad outcome was much more likely if the children were abused. If they harbored the “bad” forms of the gene but had been spared childhood abuse, they were not likely to become abusers. And if they harbored the “good” forms, then even a childhood of severe maltreatment would not necessarily drive them to continue the cycle of violence.

Predispositions in the genes. Why do stressful experiences lead to depression in some individuals but not in others? It may be a matter of genetic predisposition. From Caspi et al.,
Science
, 2003.

A third example comes from the observation that smoking cannabis (marijuana) as a teenager increases the probability of developing psychosis as an adult. But this connection is true only for some people, and not for others. By this point, you can guess the punch line: a genetic variation underlies one’s susceptibility to this. With one combination of alleles, there is a strong link between cannabis use and adult psychosis; with a different combination, the link is weak.
²⁴

Similarly, psychologists
Angela Scarpa and
Adrian Raine measured differences in brain function among people diagnosed with antisocial personality disorder—a syndrome characterized by a total disregard for the feelings and rights of others, and one that is highly prevalent among the criminal population. The researchers found that antisocial personality disorder had the highest likelihood of occurring when brain abnormalities were
combined
with a history of adverse environmental experiences.
²⁵
In other words, if you have certain problems with your brain but are raised in a good home, you might turn out okay. If your brain is fine and your home is terrible, you might still turn out fine. But if you have mild brain damage
and
end up with a bad home life, you’re tossing the dice for a very unlucky synergy.

These examples demonstrate that it is neither biology alone nor
environment alone that determines the final product of a personality.
²⁶
When it comes to the nature versus nurture question, the answer almost always includes both.

As we saw in the previous chapter, you choose neither your nature nor your nurture, much less their entangled interaction. You inherit a genetic blueprint and are born into a world over which you have no choice throughout your most formative years. This is the reason people come to the table with quite different ways of seeing the world, dissimilar personalities, and varied capacities for decision making. These are not choices; these are the dealt hands of cards. The point of the previous chapter was to highlight the difficulty of assigning culpability under these circumstances. The point of this chapter is to highlight the fact that the machinery that makes us who we are is not simple, and that science is not perched on the verge of understanding how to build minds from pieces and parts. Without a doubt, minds and biology are connected—but not in a manner that we’ll have any hope of understanding with a purely reductionist approach.

Reductionism is misleading for two reasons. First, as we have just seen, the unfathomable complexity of gene–environment interactions puts us a long way from understanding how any individual—with her lifetime of experiences, conversations, abuses, joys, ingested foods, recreational drugs, prescribed medications, pesticides, educational experience, and so on—will develop. It’s simply too complex and will presumably remain so.

Second, even while it’s true that we are tied to our molecules and proteins and neurons—as strokes and hormones and drugs and microorganisms indisputably tell us—it does not logically follow that humans are best described only as pieces and parts. The extreme reductionist idea that we are
no more than
the cells of which we are composed is a nonstarter for anyone trying to understand human behavior. Just because a system is made of pieces and parts, and just because those pieces and parts are critical to the working of the system, that does not mean that the pieces and parts are the correct level of description.

So why did reductionism catch on in the first place? To understand this, we need only to examine its historical roots. Over recent centuries, thinking men and women watched the growth of deterministic science around them in the form of the deterministic equations of Galileo, Newton, and others. These scientists pulled springs and rolled balls and dropped weights, and increasingly they were able to predict what the objects would do with simple equations. By the nineteenth century,
Pierre-Simon Laplace had proposed that if one could know the position of every particle in the universe, then one could compute forward to know the entire future (and crank the equations in the other direction to know everything past). This historical success story is the heart of reductionism, which essentially proposes that everything big can be understood by discerning smaller and smaller pieces of it. In this viewpoint, the arrows of understanding all point to the smaller levels: humans can be understood in terms of biology, biology in the language of chemistry, and chemistry in the equations of atomic physics. Reductionism has been the engine of science since before the Renaissance.

But reductionism is not the right viewpoint for everything, and it certainly won’t explain the relationship between the brain and the mind. This is because of a feature known as
emergence
.
²⁷
When you put together large numbers of pieces and parts, the whole can become something greater than the sum. None of the individual metal hunks of an airplane have the property of
flight
, but when they are attached together in the right way, the result takes to the air. A thin metal bar won’t do you much good if you’re trying to control a jaguar, but several of them in parallel have the property of
containment
. The concept of emergent properties means that something new can be introduced that is not inherent in any of the parts.

As another example, imagine you were an urban highway planner and you needed to understand your city’s traffic flow: where the cars tend to bunch up, where people speed, and where the most dangerous attempts at passing occur. It won’t take you long to
realize that an understanding of these issues will require some model of the psychology of the drivers themselves. You would lose your job if you proposed to study the length of the screws and the combustion efficiency of the spark plugs in the engines. Those are the wrong levels of description for understanding traffic jams.

This is not to say that the small pieces don’t matter; they
do
matter. As we saw with brains, adding narcotics, changing neurotransmitter levels, or mutating genes can radically alter the essence of a person. Similarly, if you modify screws and spark plugs, the engines work differently, cars might speed or slow, and other cars might crash into them. So the conclusion is clear: while traffic flow depends on the integrity of the parts, it is not in any meaningful way
equivalent
to the parts. If you want to know why the television show
The Simpsons
is funny, you won’t get far by studying the transistors and capacitors in the back of your plasma-screen television. You might be able to elucidate the electronic parts in great detail and probably learn a thing or two about electricity, but that won’t get you any closer to understanding hilarity. Watching
The Simpsons
depends entirely on the integrity of the transistors, but the parts are not themselves funny. Similarly, while minds depend on the integrity of neurons, neurons are not themselves thinking.

And this forces a reconsideration of how to build a scientific account of the brain. If we were to work out a complete physics of neurons and their chemicals, would that elucidate the mind? Probably not. The brain presumably does not break the laws of physics, but that does not mean that equations describing detailed biochemical interactions will amount to the correct level of description. As the complexity theorist
Stuart Kauffman puts it, “A couple in love walking along the banks of the Seine are, in real fact, a couple in love walking along the banks of the Seine, not mere particles in motion.”

A meaningful theory of human biology cannot be reduced to chemistry and physics, but instead must be understood in its own vocabulary of evolution, competition, reward, desire, reputation,
avarice, friendship, trust, hunger, and so on—in the same way that traffic flow will be understood not in the vocabulary of screws and spark plugs, but instead in terms of speed limits, rush hours, road rage, and people wanting to get home to their families as soon as possible when their workday is over.

There’s another reason why the neural pieces and parts won’t be sufficient for a full understanding of human experience: your brain is not the only biological player in the game of determining who you are. The brain is tied in constant two-way communication with the endocrine and immune systems, which can be thought of as the “
greater nervous system.” The
greater nervous system is, in turn, inseparable from the chemical environments that influence its development—including nutrition, lead paint, air pollutants, and so on. And you are part of a complex social network that changes your biology with every interaction, and which your actions can change in return. This makes the borders interesting to contemplate: how should we define
you
? Where do you begin and where do you end? The only solution is to think about the brain as the densest concentration of
you
ness. It’s the peak of the mountain, but not the whole mountain. When we talk about “the brain” and behavior, this is a shorthand label for something that includes contributions from a much broader sociobiological system.
^**
The brain is not so much the seat of the mind as the hub of the mind.

So let’s summarize where we are. Following a one-way street in the direction of the very small is the mistake that reductionists make, and it is the trap we want to avoid. Whenever you see a shorthand statement such as “you are your brain,” don’t understand it to mean that neuroscience will understand brains only as massive constellations of atoms or as vast jungles of neurons. Instead, the future of understanding the mind lies in deciphering the patterns
of activity that live
on top of
the wetware, patterns that are directed both by internal machinations and by interactions from the surrounding world. Laboratories all over the world are working to figure out how to understand the relationship between physical matter and subjective experience, but it’s far from a solved problem.