the ways that our children’s genes and environment interact.
The Broken Filter
For years, the prevailing metaphor for genes was “the blueprints of development,” a master plan on which every facet of an individual is meticulously drafted. The image fit nicely with the predominant theory of genes at the time, called the genetic dogma, which stipulated that the flow of information from DNA to RNA to polypeptide chains to protein is unidirectional and irreversible. According to the genetic dogma, DNA is strictly read-only; RNA cannot rewrite it, nor can a protein be translated back into RNA. However, the latest research shows top-down, dictatorial genetic dominance to be an incorrect, or at least incomplete, characterization of how genes work.
As important as genes are, they are not the only plan from which a person is built. DRD4, 5-HTTLPR, and BDNF are not genes “for” anything more than the products after which they are named (dopamine receptors, serotonin transporters, and brain-derived neurotrophic factor, respectively). These products can, in turn, regulate physiological and mental development, but there’s a lot of give and take between genetic and environmental factors. The environment works in conjunction with genes, and through changes to the epigenome (a process we will discuss in greater detail later), it can actually influence when and how these genes are expressed. Nor are these influences always obvious or simple. Think of the cumulative effects of the 5-HTT and BDNF genes, or the protective properties of a friendly adult outside of the family, or the ability of children to ignore their parents’ dramatic behaviour while latching onto their inner turmoil. Through the course of this chapter, we’ve learned how ineffably complex and muddled and messy child development can be. Beneath the surface, where nature and nurture spiral, clash, and converge, the concept of anything as neat and orderly as a “genetic blueprint” seems trite, or even absurd.
As scientists became aware of this discrepancy, they adopted a new image: the genetic recipe book. As a metaphor, it is more accurate than the genetic blueprint, as it suggests a set of guidelines that rely on the availability of select ingredients and remain open to a certain degree of flexibility. More importantly, following a recipe creates a product greater than — and distinct from — the sum of its parts. After baking a cake, one cannot pick it apart and prescribe one line or word of the recipe to each individual crumb. The recipe metaphor also concedes some influence to environmental factors, rather than supposing that genes alone dictate the end result. The ingredients may combine correctly, but set the oven to the wrong temperature and the cake will be burnt or underdone.
But even the genetic recipe seems somehow insufficient. It implies a clear and straightforward relationship between genes and environment, one that can be easily replicated by following a few basic instructions. Mix thoroughly to combine ingredients. Apply leavening agent to make baked goods rise. Cook at 400 degrees for 35 minutes, or until golden. It’s too neat, too easy, too comprehensible.
Perhaps genes are too sprawling and complex an idea to be housed in a single metaphor. In that case, we propose a more modest analogy, one that focuses specifically on the gene-by-environment interactions we’ve explored in this chapter. When considering the interplay between genes and the environment, think of a gene as a filter, and the environment as a stream of water passing through it. Should the stream contain some debris — anxiety, obesity, behavioural difficulties, and so on — a functional filter will strain out the impurities. Similarly, a broken filter can cause no harm, should the stream itself be pristine. However, when the water is murky and the filter malfunctioning, environmental pollutants will pass through unrestricted, causing a great deal of trouble for the unlucky individual swimming downstream.
We’re fairly fond of this image, we must admit. But it does place a value judgement on various filters, and that can lead to problems. Remember Joey and Erika from chapter 4? If the broken filter theory is correct, it would suggest that their brains were built from inferior genetic material. Joey’s defiant anger and Erika’s depression may be the result of troubled home lives, but with better supplies of serotonin or dopamine, their symptoms never would have appeared in the first place.
Therein lies the theory’s main problem. If one filter is functional and the other is broken, then one gene is clearly better than another. And if that is the case, why has evolution not selected against the “broken filter” genes? They are not recent mutations — we can find examples of them in almost every animal on earth. Surely such a glaring genetic defect couldn’t survive a billion years of natural selection if it didn’t also carry an equal or greater advantage.
Perhaps our metaphor needs work. What if, instead of a broken filter, we simply had one with looser, more permissive netting? Such a filter wouldn’t do as good a job of catching debris as would a more stringent model, but it may also permit the passage of beneficial materials — nutrients, for instance — that the more functional filter would block. In this case, one filter would not be invariably better than the other. Instead, each would be useful in one environment and detrimental in another. Perhaps, if raised in more supportive environments, Joey and Erika would not only recover, but excel. Their permissive filters,
completely unsuited to troubled environs, would suddenly become a tremendous asset. Such a concept would radically recontextualize the findings we’ve discussed so far, necessitating a lot of research, several well-designed studies, and a revolutionary new theory of gene-by-environment interactions.
For this, we turn to a man named Thomas Boyce.
Chapter 7
The Orchid and the Dandelion
Maria looked at the pregnancy test with disbelief. It couldn’t possibly be right. She was 17, barely three weeks into grade 11, and according to the small plastic rectangle in her hand, her life was about to change dramatically.
She went to her boyfriend’s apartment, resolving to break the news to him over dinner. She made pasta, overcooking the noodles and clumsily dropping a skillet of sauce onto the floor. Her hands trembled and her mind felt shrouded in thick, roiling mist. After 30 minutes of awkwardly puttering around the kitchen, she told him. Her declaration was terse: “I’m pregnant,” she said, the last syllable disintegrating into a long, terrified sob.
Tom, her boyfriend, was stunned but supportive. He’d moved away from home at 16 after a brief and bloody fistfight with his father, and lived on his own in a one-bedroom apartment above a pizzeria. Two years Maria’s senior, he’d finished high school with poor marks and, after a protracted stretch of unemployment, landed a job as a deliveryman for UPS. He told Maria he would stick by her and the baby, and though he wasn’t truly sure of it at the time, he meant it.
Maria gave birth to a baby boy midway through her second semester of grade 11. She named the child David. He was a happy baby. Maria fully intended on returning to school after weaning him, but somehow never got around to it. Instead, she got a job working nights as a waitress, and another as a cashier at 7–Eleven. She and Tom tried to arrange their schedules in such a way that one parent was always home. When this wasn’t possible, an elderly neighbour babysat for them. In exchange, Tom helped her out with a few simple chores. She became a surrogate grandparent to David, whose biological grandparents either didn’t know of his existence or wanted nothing to do with him.
Even with external support, David was often alone. He became self-sufficient at a young age, pouring his own cereal and dressing himself for kindergarten. His parents were kind and loving, but they maintained their social lives and enjoyed smoking pot, which they studiously avoided doing in front of him. As a result David was often left to his own devices, which suited him fine. He was happy entertaining himself and playing with the other children living in his apartment complex. The parents of these children, aware of David’s somewhat peculiar family situation, treated him warmly, feeding him and letting him sleep over and generally looking out for him.
When David was five years old, Maria got pregnant again. The ultrasound confirmed she was carrying twins. Maria panicked. She’d been excited about the idea of having another baby, but even one was sure to stretch her meagre budget to the breaking point. Two seemed utterly unfeasible. After talking things over with Tom, she decided to give one of the children up for adoption.
Maria named the girl she