Why are we eating too much?

Follow the causal chain from top to bottom.

The reason why we are perpetually eating too much today is that in the environment that we evolved in, food was so scarce that the chances of dying through malnutrition were vastly higher than the chances of dying from becoming too fat.

Our brains use sloppy analysis, which is nice and fast, and good enough in most circumstances. The downside of the occasional error is outweighed by the upside of making quick decisions in the really important situations. But we still make errors, and because it is not good to make errors, natural selection has biased us towards the safer errors; for instance, when it comes to threat detection we are biased towards false positives. This is the “smoke detector principle” described by Randolph Nesse, in which we overreact to potential dangers (241). It is better for us to incorrectly think that a tree is a bear, than think that a bear is a tree (running away, shrieking, from a tree is embarrassing, but urinating against a bear is fatal). This Error Management theory, developed by Haselton and Buss, has been supported by numerous studies (242; 243). As another example: when hunting back in the Pleistocene, the consequences of being too timid (missed opportunities for shelter, or a pleasant meal, perhaps) are less severe than being too confident (finding yourself in a shark’s belly, still clutching the ineffectual weapon that you wove from reeds). Number one on our list of things to do is: avoid getting eaten (244; 245).

The propensity to see faces when they are not there , is accentuated by this bias towards false positives; it is far better to see faces when they are not there than to fail to see a face when it is there (since we are always on the lookout for potential enemies). This is why we hear stories of the Virgin Mary’s face appearing on a grilled cheese sandwich, and why the naturally carved shape of a mountain in the Cydonian region on Mars looks so like a face to us. We are extremely prone to seeing faces in particular because of the sophistication of the facial gap-filling rules of thumb that we have in our heads (mentioned in the last chapter); we only have to see a few lines and shapes that look a bit face-like and the routines in our head fill in all of the missing features.

In general, then, natural selection has made us particularly sensitive to errors with potentially severe consequences. We are more likely to overeat than undereat because starving to death is worse than getting a bit fat. Miller and Kanazawa (94 p. 76) illustrate this phenomenon with the example of male sexual interest: if a man mistakenly thinks that a woman is interested when she is not, then all he loses is some pride, but, if he fails to notice when a woman really is interested, then the costs are potentially more serious (a lost opportunity for sex, children, marriage and eternal bliss); natural selection should thus bias men towards thinking that a woman is interested when she is not. In practice, of course, this drive to pursue women has to overcome the Fear of rejection, the Fear that we will lose status in the tribe or damage our self-image (the Facade that will be discussed later in this chapter), which we need if we are to be successful in the mating competition.

The optimum error analysis is different for women: if they think a man is interested when he is not then he might have sex with her and run off, while she is left holding the baby. These are more severe consequences than just missing out on romance, so natural selection should bias women the other way: to think that a man is not interested when he actually is. Determining whether these biases do actually exist is left as a rather dangerous exercise for the reader.
Natural selection makes us play it safe; it drives us to avoid bad things more than it encourages us to pursue good things because the consequences of failing to avoid a bad thing can be much, much worse than missing out on a good thing. We may love eating steak, really love it, and really, really hunger for a beautifully cooked, freshly cut rib-eye, but not nearly as much as we really, really, really do not want to eat a rotten steak covered in maggots that we have found in the gutter. The repulsion of the latter far outweighs the attraction of the former. Being fired feels bad, more than being promoted feels good. Threats seem more important to us than opportunities. A small, fast-approaching object seen out of the corner of our eye immediately generates a panic response, on the assumption that it might be a missile of some sort; we do not consider that some kind person might be throwing a roll of dollar bills, or a doughnut, at us.

Elevating our position in the tribe is good, but it has a less dramatic influence on our survival chances than eviction from the tribe; going from some-sex to lots-of-really-stunning-sex is not as important as going from some-sex to no-sex-at-all. As a result, we obsess about losing status more than gaining status; we do not want it to drop below the level at which the tribe throws us out to fend on our own. Life has many such aspects in which not meeting a minimal level can have fatal consequences: if we are not strong enough, or not smart enough, or not sociable enough, or do not have enough of an understanding of flames, then respectively we will be unable to hunt, unable to find our way home, unable to find a mate, or unable to cook without setting ourselves on fire. As a result, we need drivers that shout at us whenever an important trait is dangerously low.

Having a low-level alarm is much more efficient than our brain continually reminding us about all of the traits that we have in abundance. The latter system would create a lot of signal chatter that could drown out the dangerous failing in one area. Our thoughts are thus biased towards the negative. Considering the analogy of physical pain: one could argue that a positive feeling that you got when your hand was not in the fire would do just as well as the negative feeling when it was (in other words you would feel continual joy that your hand was not being burnt at the moment). However, we have a lot of body parts and feeling continuous joy about the lack of pain in every bit of our bodies would be confusing, and a waste of valuable brainpower. The actual system is much more efficient; our feelings stay silent when things are okay but scream at us to attend to the part of us that is being damaged. The Nazi interrogator tortures the plucky British airman, rather than offering him a delicious soup and a back rub. As Freud would have it, humans do seek pleasure, but they will work harder to reduce pain (235). Indeed, we have twice as many negative emotions as positive ones and evidence shows that we hate losses, more than we enjoy gains (the principle of loss aversion) (211). Just as comfort is not as strong a driver as agony, confidence is not as strong a driver as Insecurity (our concern over future pain). When natural selection wants to guide us, it prefers the stick to the carrot.
To reiterate, natural selection has made us more concerned about threats (because many threats can end our life), than opportunities (which at best can improve your life) (94 p. 160; 245). A study that illustrates this principle showed that when presented with research on health risks (such as food coloring or electromagnetic fields), those surveyed found the research more credible if the findings showed a hazard, than if they showed no risk (246). Natural selection has given us a Negativity Bias; we are more likely to believe a threat than an opportunity.