this in mind, it is interesting to note the number of studies that link 5-HTT to a host of behavioural disorders in humans and other primates, including both anxiety and excess aggression. There is a wide gulf of evolutionary difference between people and prawns! But the effect of certain chemicals on the neurological system can be remarkably similar across species. The connection is purely speculative, but worth considering.
Unlike DRD4, 5-HTT is not itself a gene, but only a section of one. It sits on the promoter region of SLC6A4, which codes for a group of serotonin transporters. They affect the efficiency with which the human body can reabsorb and reuse serotonin after it has sent its first chemical message to the receptors. Since 5-HTT codes for the SLC6A4 promoter, it decides how much serotonin the body can reclaim. There are only two allelic variations — long (l) and short (s) — but they work in conjunction. Each person has two alleles of any one gene. With two copies of the gene and two possible forms the gene can take — long and short — there are four possible combinations a person can have: long/long, long/short, short/long, and short/short. For the sake of brevity, we will refer to these as l/l, l/s, and s/s (l/s and s/l amount to the same thing, so there is no point in distinguishing between them).
MAO-A
Though less of a key player than either DRD4 or 5-HTT, the MAO-A gene bears consideration, especially since its function is tied into that of the other two genes. MAO-A codes for monoamine oxidase A, an enzyme that breaks down neurotransmitters like serotonin and dopamine. Its function, or lack thereof, directly affects the amount of dopamine and serotonin in the human body.
Like DRD4, MAO-A has multiple allelic variations based on the number of times it repeats a particular sequence of nucleotides — in this case, one 30 base-pairs long. Humans can have anywhere from 2 to 5 repeats. Of these, the 4-repeat allele is considered high reactive, meaning it devours serotonin and dopamine more readily than its low-reactive counterparts.
MAO-A has been dubbed “the warrior gene,” as recent studies have discovered a correlation between its low-reactive allele and aggressive behaviour in response to provocation. Researchers Rose McDermott and Dustin Tingley devised a study to document the interaction between a person’s MAO-A genotype and his response to a perceived wrongdoing. Or, more accurately, a man’s MAO-A genotype. As MAO-A sits on the X chromosome, focusing the study solely on males reduced the list of possible genotypes to either high or low. Girls have two X chromosomes, making their MAO-A alleles significantly more complicated (instead of high or low, you have h/h, h/l, and l/l). We do not currently know if one or both of women’s MAO-A genes function at any one time, or whether a high-reactive allele trumps a low-reactive allele, or vice versa. As a result, our knowledge of MAO-A-by-environment interactions pertains only to men.
Ostensibly, men completed vocabulary tests in exchange for financial rewards. However, these tests were only a pretext for a subsequent game, during which an anonymous opponent could steal a certain amount of the man’s earnings. In retaliation, men were given the ability to inflict on the thief a somewhat bizarre punishment: making them ingest an unpleasant quantity of hot sauce. If the men chose not to use the hot sauce, it could be redeemed at the end of the game for money. Punishment, therefore, held negative consequences for both the thief and the victim. The thief would be subjected to a dose of hot sauce and the victim would use up a resource that could have otherwise earned back some (but not all) of the money the thief had stolen.
But here’s the trick: the thieves didn’t exist. Experimenters manipulated the rounds in order to divide men into different test and control groups. Some men had only a small amount of their earnings “stolen” from them, while others faced significantly greater losses. The reactions of each man were recorded and compared to their level of provocation — how much was stolen from them — and their MAO-A genotype.
Not surprisingly, men with either genotype who’d had significant portions of their earnings stolen from them acted more aggressively than men who’d lost less. However, among the men who’d lost considerable amounts, those with a low-reactive MAO-A were far more likely to pursue vengeance than those with a high-reactive version of the gene. This implies that men with low-reactive MAO-A only display greater aggression when provoked by a perceived slight, and not as a result of having an inherently domineering personality.
The warrior gene theory has garnered significant criticism since its inception, particularly because low-reactive versions of the MAO-A gene are less prevalent among Caucasians than other races, lending the research an unfortunate air of racial divisiveness. It’s not within the stated purpose of this book to weigh in on that particular debate, but whether the “warrior gene” exists or not, it is, at most, only half the story. For behaviours cannot be dictated by genes alone. Genetics may determine how easy it is to push a person’s buttons, but the finger that actually pushes them belongs to the early caregiving environment — how a person was parented.
Section 2
The Broken Filter
“Genes and family may determine the foundation of a house,
but time and place determine its form.”
—Jerome Kagan
Chapter 4
Messy Metaphors
Mrs. Munroe has a good group of students this year. Grade eights can be a challenge — precariously balanced as they are between childhood and adolescence, their hormones overcharged and as volatile as nitroglycerin — but for the most part, she can’t complain. Only two of her students trouble her, and for very different reasons.
Joey is pure energy. Unfortunately, he rarely puts it to good use. He disrupts classes, swears at teachers, and bullies his classmates mercilessly. Over half a dozen students have complained to Mrs. Munroe about him. One claimed Joey stole his backpack and threw it onto the school roof. Another said Joey shoved her in the janitor’s closet and held the door shut until after the second period bell rang. Still another showed Mrs. Munroe her binder, which had been stabbed repeatedly with a pen and defaced with permanent marker. She claimed Joey did it.
Though Joey terrorizes his peers more or less without prejudice, a few students actually look up to him. He flouts rules with an abandon they find hopelessly alluring. He chain-smokes during his lunch hour, standing defiantly just a few feet off of school property, where the teachers are powerless to stop him. He regales anyone who will listen with stories of binge drinking and illicit sex. Mrs. Munroe is pretty sure the sex talk is pure bravado, but the drinking, at least, she believes to be true. Joey has shown up to school flush-faced and giddy on more than one occasion, the smell of stale beer on his breath. None of her punishments seem to have any effect on his behaviour. He careens through life like a transport truck with its brakes cut, flirting with disaster and constantly gaining speed.
Mrs. Munroe’s other problem child is Erika, though a less empathetic teacher would hardly consider her a problem at all. She never acts out, or breaks rules, or draws any attention to herself whatsoever. This is not to say she’s an ideal student — she doesn’t participate in class, and often fails to do her homework. Her test performance is spotty; sometimes she scores very well, but at other times she hands tests in with many questions left unanswered.
For the first few weeks, Mrs. Munroe suspected that Erika had some sort of learning disability, but she has become convinced this is not the case. The work Erika does complete is of exceptional quality. She writes eloquently, and can solve fairly complex math problems without struggle. The trouble is that, more often than not, she simply doesn’t bother to do the work. She doesn’t seem to have the energy. She smiles wanly when Mrs. Munroe talks to her about her assignments, shrugs off her teacher’s concerns, and completes just enough of her schoolwork to get by and stay under the radar.
The
