Although magical thinking has been largely abandoned in the West since the nineteenth century, maternal impression is still widely believed in many parts of the world today.3 Some countries have rituals, talismans and customs to ward off harm to protect the unborn child. In India, pregnant women avoid certain individuals such as barren women who may affect their foetus by casting the ‘evil eye’.4 While it may seem absurd that frightening a pregnant woman would have a permanent effect on her offspring, recent findings suggest that we may have been a little too hasty to dismiss maternal impression, or at least the susceptibility of unborn children to traumatic external events.
In this chapter we examine the possibility that early domestic environments not only shape what we learn, but also how we respond emotionally in terms of temperament. Temperament refers to the individual differences people have in their emotional responses. Some of us are more anxious whereas others are more outgoing. Some are more aggressive and others are more fearful. From the very beginning, babies differ in temperamental styles in that some cry more easily or startle suddenly whereas others are more laid-back and placid. Individually, we tend to be more like our parents when it comes to our emotional dispositions, which indicates this dimension of personality has a genetic contribution. However, early environments can also shape the development of temperament in ways that shape who we become as adults, and how well we adapt to domestication.
The day the world stood still
I can still vividly recall it as if it were yesterday. Those of a certain age will remember exactly where they were on that fateful day in 2001. It was a September afternoon in the UK but a bright, sunny morning in New York with crisp blue skies. Colleagues knew that I had a television in my office and had come in to watch the terrifying news unfolding. Two planes had been flown into the World Trade Center and now there was dense smoke billowing out of both. People were jumping to their deaths. If you saw the footage, then you, like me, will probably still have those events emblazoned on your memory as the world changed for ever.
For some, these recollections have become flashbulb memories, as if the scene were lit up in harsh lighting to capture everything – even trivial details of little relevance. Our memories can be supercharged with detail when we experience something terrifying. This is because we become more alert and attentive, on the lookout for danger as our hippocampus, the seahorse-shaped repository for long-term memories in each of the temporal lobes, receives input from the amygdala – a structure the size of an almond, also in each temporal lobe, that is active when you laugh, cry and scream in terror.5 They also don’t let you forget.
Experiences that eventually become memories start out as patterns of neural firing or traces that come flooding into the brain. Raw sensory input is interpreted into representations and given meaning. This in turn updates and changes the knowledge we have about the world by forming memories. Whether details become consolidated into the memory stores of the hippocampus depends on filtering mechanisms that are regulated by the action of neurotransmitters released by the amygdala during surprising, arousing or rewarding events. The neurotransmitters are the molecules that trigger activity in the connecting gaps between neurons. Flashbulb memories stimulate the amygdala to invigorate the activity of the hippocampus, thereby enhancing the memory trace for those events that move us the most.6 As the world watched in helpless shock, a generation would never forget what they saw. But even some from the next generation of unborn babies were left with the legacy of that terrible day.
Post-traumatic stress disorder (PTSD) is an anxiety condition that appears weeks after traumatic events such as rape, battle and other acts of violence. It is characterized by recurrent dreams, flashbacks and flashbulb memories, as if the victim is haunted by the past. After witnessing 9/11, one in five New York residents who lived closest to the World Trade Center suffered from PTSD. Rachel Yehuda, a New York psychiatrist, followed up a sample of pregnant women from this group. She found that these women had abnormal levels of cortisol in their saliva – a hormone that is released as a natural response to stress but depleted in individuals with PTSD.7 Different hormones and neurotransmitters form part of an elaborate signalling system that the brain uses to activate different functions. Some have general effects whereas others seem to be more specific in the roles they play.
The depleted levels of cortisol in the chronically stressed mothers were to be expected. But what was unexpected was the plight of their unborn children. One year after the attack, infants born to the mothers who had developed PTSD also had abnormal levels of cortisol compared to babies of other mothers who did not develop the disorder after witnessing 9/11. Vulnerable mothers had passed something on to their children. As Yehuda put it, children of PTSD victims bore ‘the scar without the wound’.8
It is well known from various disease models that events early in development can have consequences later in life. There is a whole category of substances known as teratogens (literally, ‘monster makers’) that, if the pregnant mother is exposed to them, can result in birth defects. Various drugs, both legal and illegal, as well as environmental toxins such as radiation or mercury can damage the unborn child. However, some diseases resulting from harmful substances take decades to manifest. My own father-in-law died from mesothelioma, a rare form of lung cancer that was probably caused by exposure to asbestos when he was growing up as a child in South Africa. Toxins that enter our bodies can alter the functions of our cells but lie dormant for years. Over a lifespan we may replenish our cells many times, but each reproduction of the cells can carry genetic time bombs that lie in wait for the right circumstances to kill us. Physical substances like asbestos from the environment are obvious candidates as being poisonous to our systems, but what about exposure to psychological toxins? How can our mind’s reaction to non-physical events, such as watching something horrific, produce long-term consequences? How could a mother’s stress in response to 9/11 cross over to the next generation? What could she possibly pass on to her unborn child?
Jerry Kagan, a Harvard developmental psychologist, reckons that around one in eight babies are born with temperaments that make them highly irritable, which is due to their over-reactive limbic systems. They startle easily and respond excessively to sudden noises.9 The limbic system mobilizes the body for action and its circuitry includes the amygdala. It triggers a cascade of hormones and neurotransmitters that prepare the body to respond to threat. Reactivity of the limbic system is a heritable trait meaning that it can be passed on to the child in the genes they inherit.10 These are the highly-strung children who find uncertainty and strange situations upsetting. Depending on how they react to sudden sounds as a four-month-old baby, you can even predict personality many years later.11 Reactivity is like a disposition, which makes some of us twitchy, but others are born more laid-back and chilled. Maybe mothers who developed PTSD after 9/11 gave birth to babies with a nervous nature because of their genes.