David took his role as big brother very seriously. He cared for Melissa as she grew, dressing her for school, making her meals, helping her with her homework, and doing his best to cheer her up. As a little girl, Melissa could be sweet and charming, and David could always make her smile. However, as she grew, she became more moody and distant. Her teacher reprimanded her frequently for her disruptive behaviour in class, and sent her home on two separate occasions: once for maliciously pouring a jar of paint over the carpet, and again for biting another student. At home, Melissa oscillated wildly between temper tantrums, pleading forgiveness, and silent, brooding withdrawal.
As David grew, he began to indulge in the rebellious acts typical of adolescence. He stayed out late, talked back to his parents, took up smoking for a brief period, and drank at the odd party where alcohol was available. But his grades remained fairly high, and his behaviour calmed down near the end of high school, when he became more focused on getting a proper postsecondary education. School didn’t excite him, but he understood its importance. Attending university seemed like an obligation he needed to fulfill; the consequences of not doing so far outweighed the benefits. He studied economics for two years, dropped out, and went to college instead, where he majored in computer science. He got a job shortly after receiving his diploma, and made a modest but happy life for himself.
While David mellowed, Melissa grew increasingly volatile. She partied incessantly, spent days on end away from home, and dated seedy men several years — and in one case an entire decade — older than her. Not content with the more common narcotic offerings of adolescence, she snorted cocaine and took dangerous amounts of ketamine. Sometimes she stayed up for days, or awoke in strange places without any idea of how she got there. On the surface, it seemed she delighted in making her parents worry, and appeared vindicated when she managed to make her mother cry. Her parents scolded her, grounded her, and pleaded with her, but nothing worked. When they told her their concerns, Melissa would scoff.
“Like you even give a shit,” she’d say. To Melissa, her parents’ neglect during her early years was unpardonable. They didn’t care about her then, she thought, so why should they all of a sudden care about her now? David she listened to, to a point, but when he would suggest she straighten up she would accuse him of being a shill for their mom and dad and storm off. He couldn’t reason with her and eventually stopped trying. Their relationship grew cold.
Overreacting
It’s hardly a surprise that siblings in the same family can have very different temperaments; anyone with a brother or sister could tell you that. Yet doesn’t it seem odd that two children raised by the same set of parents in the same household with roughly the same means can come to such radically different ends? It happens all the time, of course, but what exactly causes two children to react so differently to the same caregiving environment?
The answer has, in part, revealed itself through the studies we discussed in our previous chapter. Certain genes (DRD4, 5-HTT, MAO-A, etc.) can, depending on the allele (or version) one possesses, make a person more susceptible to adverse rearing conditions. In our scenario, David would be a low-reactive child, while Melissa would be high-reactive. Perhaps Melissa’s DNA contains the 7-repeat DRD4 allele, or one of the other problematic polymorphisms we’ve explored, making her more likely to act out in the face of her parents’ benign but persistent inattentiveness.
The question, then, is why do high-reactive traits exist at all? From an evolutionary standpoint, it seems unlikely that an increased disposition toward self-destructive behaviour would be selected for in the long run. Over generations, one would expect 7-repeat, s/s 5-HTT and their hypersensitive ilk to be outstripped by their more stalwart allelic brethren. Are these mutations simply too recent to have been selected out, or is our species too buttressed by its advanced technology and social structure for natural selection to take effect? Not likely. Many of the “problem” alleles we’ve discussed so far have counterparts throughout the animal kingdom, from primates all the way down to crustaceans, implying they’ve been around for a very, very long time. But what benefit could high-sensitivity provide?
To provide a possible answer, let’s check in on Melissa’s sister.
Separated shortly after birth, neither twin was aware of the other’s existence. As far as Marcy knew, she was the only child of Roger and Evelyn Davenport, a wealthy couple in their late thirties. Roger worked as an engineer and Evelyn as a travel agent. The Davenports were attentive and loving parents. They had tried for years to have biological children, but they couldn’t conceive on their own, and their repeated attempts at in vitro fertilization all failed. Though adopting was not exactly how they’d expected to have children, their love for Marcy knew no bounds, and they dedicated their lives — and their considerable means — to providing only the best for her.
Marcy went to a private school, took swimming lessons in the family pool, and had a playroom full of educational toys. Her parents hired skilled tutors to give her lessons in French, the piano, and gymnastics. Evelyn read to her from infancy, and Roger took her to every museum within five hours of their house. The family travelled often, and always took pains to experience and learn about the local culture of whatever country they visited. By the age of 10, Marcy was fluently bilingual, was proficient on three instruments, and had visited four continents.
Marcy loved school. She excelled in science, consistently handled mathematics at a grade level above her own, and devoured every book put in front of her. Every teacher she had considered her a natural student. Her grades were always the highest in class, and by the time she finished elementary school she’d amassed an impressive collection of scholastic awards.
In high school, she became an active member of student council, running in every student body election and winning almost every time. No one was surprised when she was elected valedictorian. Though affording school was not going to be a problem for her regardless — Roger and Evelyn had it covered — she was awarded generous scholarships that, supplemented by her savings from her part-time job, allowed her to pay her own way.
Marcy rocketed through university, got accepted to med school, and landed a residency less than two months after earning her degree. She seemed to thrive under pressure, a quality that, coupled with her fierce intelligence and love of challenging work, led her to specialize in neurosurgery. By 30, she was on track to becoming one of the most respected surgeons in her province.
She’d known she was adopted since she was old enough to start asking questions about it — and for a girl as smart as Marcy, this wasn’t very old at all — but it wasn’t until adulthood that she began pursuing her biological parents. It was during this process that she learned she had a twin sister. The news was exhilarating, though a little hurtful — part of her couldn’t help but wonder why her parents had given her up for adoption while her sister got to stay. In spite of these feelings, she sought out her sister, and was surprised at what she found.
Marcy had been told she was an identical twin, and though she knew their differing tastes and circumstances meant that they probably wouldn’t look as similar to one another as she might have imagined, she was nevertheless startled by Melissa’s appearance. She was 20 pounds thinner than Marcy, and dressed in leggings and a tacky jacket made of fake leather. Marcy’s silk blouse, though far from opulent, likely cost more than Melissa’s entire wardrobe.
Melissa clasped a cigarette between two fingers topped with artificial fingernails. Her face resembled Marcy’s but was prematurely lined. A child tugged at her leg and she patted his head distractedly as Marcy introduced herself. The conversation was polite but the two found they had little to talk about. Secretly, they both nursed doubts as to whether they were actually related. It just seemed so improbable that twins could turn out so differently.