To accept DeWall's striking results, it is necessary to accept one connection between self-control
and aggression and a second between glucose and self-control:
SELF-CONTROL DOWN ~ AGGRESSION UP GLUCOSE DOWN ~ SELF-CONTROL DOWN
That aggression often follows from a loss of control is backed up by considerable evidence, including clinical studies that link lack of inhibition in psychopaths to extreme violence. Also of interest is the fact that impulsive aggression is more likely to arise when individuals are drunk than sober. Alcohol, as we all know, lowers our inhibitions, but also lowers glucose in both the brain and body. Though scientists such as Baumeister and DeWall have not yet worked out in detail how glucose is used or replenished in the context of self-control, there are far too many studies using different methods and subjects to ignore this relationship. Minimally, these studies indicate that we should think about self-control like a resource, something that can be used up and replenished, something that can be depleted, tipping the scale toward violence.
One of the interesting implications of DeWall’s work is that individual differences in glucose availability are coupled with individual differences in self-control. Diabetes shows a high level of heritability, meaning that some individuals are more likely to develop this problem than others simply based on what genes they receive from their parents. The prevalence of diabetes is on the rise in many countries, with some estimates suggesting that by 2025, there will be 325,000,000 diabetics world wide, more than double current estimates. The genetic disorder that lowers glucose levels arises because of a deficiency in a key enzyme, glucose-6-phosphate-dehydrogenase. This is one of the most common enzyme deficiencies in the world, affecting over 400,000,000 people, and in many cases, triggered by the consumption of fava beans. As with variation in the frequency of MAOA, so too can variation in this glucose-related gene be subject to selection pressures, especially given its link to violence. Once again, we see nature and nurture contributing to individual variation and cultural differences in our capacity to harm others.
Together, these observations of glucose-related disorders speak to a disconcerting reality: we are born with inherent differences in the availability of key resources guiding self-restraint. Some of us start off life better equipped to control our frustrations, wait for future gains, and moderate our temper. These early differences can have long lasting and disastrous effects later in life, a point supported by a study that began forty years ago with four year-old children presented with a marshmallow.
The American social psychologist Walter Mischel recruited four year old children to his
laboratory and sat them down at a table with two objects: a marshmallow and a bell. He then told each
Hauser Chapter 4. Wicked in waiting 130
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