effect. Likewise, most people get enough copper in their diet, as it can be found in a wide number of dietary staples, including fish, whole grains, nuts, potatoes, leafy greens, dried fruit, cocoa, black pepper, and yeast. Because it is almost universally consumed in sufficient quantities, copper’s contribution to hair colour goes largely unnoticed. Somewhat paradoxically, the ubiquity of its influences renders them invisible. Such is the case with thousands of environmental factors we take for granted. It isn’t until a radical change in the environment depletes once-plentiful resources that we realize how much those resources contributed to our development. In the words of Joni Mitchell, you don’t know what you’ve got ’til it’s gone.
A dramatic example of this occurred in Europe in October of 1944. The tides of war had turned on the Germans, who found their once seemingly invincible army forced back on all sides. Allied forces had reclaimed the southern part of the Netherlands, but the Germans maintained control of the rest. In an attempt to demoralize the Dutch, who had been emboldened by the partial liberation of their country and threatened a violent uprising, the Germans placed an embargo on all food supplies heading into the country and flooded the surrounding fields, spoiling the season’s harvest. To make matters worse, November proved the start of a very harsh winter. The Dutch canals were frozen solid, thwarting Allied attempts to ship in supplies by barge. Thus began the Dutch Hunger Winter, a devastating famine that lasted into the spring of 1945 and was responsible for 18,000 deaths by illness and starvation. Though the tragedy of the famine was harsh and immediately felt, the full brunt of its impact did not appear until long after the embargo was lifted and food supplies returned.
Almost immediately after it ended, researchers saw in the Hunger Winter the potential for a large-scale natural experiment. A population of well-fed people with documented medical histories had undergone severe malnutrition for a precisely delineated amount of time, and then quickly reverted to a normal diet. Over the following decades, researchers studied the medical records of individuals who had gestated (were growing in their mothers’ uteruses) during the famine, noting any statistical abnormalities between them and other Dutch nationals who had not been so affected. The results were fascinating. Children whose mothers had been malnourished during the first trimester of their pregnancy were unusually likely to suffer from spina bifida,[5] cerebral palsy, and other conditions of the central nervous system. Additionally, girls from that cohort were twice as likely as the general population to develop schizophrenia. Clearly, malnutrition during those first few months of development impinges on the brain’s ability to properly develop.
However, perhaps the most surprising finding involved men born to mothers who had been malnourished during the first two trimesters of their pregnancy. A 1976 study found that these men, now in their thirties, were significantly more likely to be obese than other men of their age and background whose mothers had not experienced the Hunger Winter. Further studies, though performed on rats instead of people, have helped us to understand the mechanism behind this strange phenomenon. Mothers’ malnutrition during the first two trimesters of pregnancy leads to unusually high insulin levels in male fetuses during the third trimester, which can affect the development of the fetus’ brain. We don’t yet know for sure why this occurs, and why it doesn’t affect females, but it does make sense from an evolutionary standpoint. Mothers experiencing famine could be hormonally conditioning their children’s metabolism to most effectively function in an environment where sources of nutrition are scarce. If a child is born into an environment plagued by famine, the ability to readily store fat would be a significant advantage. However, once the boys were born and the problem of food scarcity was solved, they nevertheless retained their prenatal conditioning despite the fact that their evolutionary advantage had become a disadvantage.
The Hunger Winter provides a good example of how environmental influences on development can easily remain buried beneath the surface of human development, only to be unearthed generations later by a dramatic change in the landscape. Had the Hunger Winter not occurred, we may never have learned that the prenatal environment can affect an individual’s propensity to store fat, and the men studied would likely have developed a body type similar to those of their relatives (though, as always, diet and exercise would have played an important part).
Admittedly, the Hunger Winter is an extreme example. Under normal circumstances, attributing environmental influence to height or hair colour may seem unnecessarily pedantic. After all, if the environmental factor contributing to a trait’s development is present everywhere on Earth, isn’t it fair to say that said trait is genetically determined? If someone’s genetic makeup dictates they will have green eyes, they’re almost certainly going to get them, whether they live on the streets of inner-city Baltimore or in a mansion in Beverly Hills. Likewise, for certain conditions, a single aberrant gene really is the root cause. One could reasonably argue that calling CFTR[6] “the gene for cystic fibrosis” is accurate shorthand, as cystic fibrosis occurs when an individual inherits two mutated versions of that specific gene. The environment in which the affected child is raised will not alter how the gene behaves.
Nevertheless, relying on terms like “the gene for X” can be dangerously reductive, as it blinkers our thinking and encourages limited, simplistic approaches to complex problems.
Let’s consider the scene that began this chapter. Remember Thomas? Was his facility with the guitar purely the result of his genes? It would be difficult to argue that environmental influence didn’t play some part. No one picks up an instrument and plays Bach on the first try. It takes hours and hours of practice to develop the requisite agility, finger strength, and muscle memory. Despite what anyone with particularly accomplished parents may hope, skills and knowledge do not come prepackaged inside our chromosomes. Bodybuilders do not sire toned, muscular children, nor do the offspring of computer programmers enter the world knowing how to code in C++. Every generation must develop these skills from scratch.
Okay, so Thomas’s talent was tempered by hours of dedicated study. But what about Amelia? An instrument may require extensive experience to be played competently, but some people are blessed with a natural singing voice. Amelia’s father, we are told, is an excellent singer, and so too are most of his immediate family. It stands to reason that their musical aptitude was passed down through the generations. Thomas had to work to develop his skills, but Amelia was simply fortunate enough to inherit a gift. Right?
Genetically speaking, it is possible that Amelia was born with certain traits advantageous to a burgeoning singer. If her father’s family has truly abounded with talented vocalists throughout the generations, then perhaps their genes code for better-than-average lung capacity, a strong diaphragm, or exceptionally dexterous vocal cords, and these predispositions are what drew her ancestors to singing in the first place. This could be the case, but to assume it must be — and to cite Amelia’s proclivities as the only evidence — is tremendously naive. It is equally possible, perhaps even probable, that Amelia possesses no physiological advantage as a singer whatsoever. Half her genes come from her mother, after all, who readily admits that her whole family is tin-eared and musically inept. This is not to say that Amelia’s talent wasn’t inherited, only that we mustn’t limit our idea of inheritance to a transaction involving a few dozen molecules.
If Amelia is from a musical home, she probably grew up with music as an important part of her life. We can assume the record player was running often, and that her father regularly sang around the house. In this case, her musical education began before she was even born.
Children develop an aural connection with the outside world as early as six months after conception. Researchers recruited a group of pregnant women and had them read one of two stories — The Cat in the Hat or The King, the Mice, and the Cheese — aloud twice a day from the time they were seven months pregnant until the day they gave birth. Two days after they were born, the children of these mothers were tested to see which story they preferred, using a fairly ingenious device that measured how often they sucked on a pacifier. Sucking is a reflex ingrained in children from birth, and one of the few motions over which infants have conscious (or close to conscious) control. By adjusting the speed of their sucking, the babies could choose
