Emotions act to simplify the world, summarizing our experiences into a few metrics. So, for example, when you are trying to decide whether or not to eat an apple you don’t have to first recall every past experience involving apples. Instead your emotions have already summarized each event and the results have been pooled into one value characterizing your past experiences as somewhere between very rewarding or very detrimental on average. The general rules, such as both joy and pleasure increase trust, will remain fixed among individuals and species. What will change are the parameters of those rules: how much weight is placed on pleasure versus trust, old versus recent experiences. These parameters constitute our personality and while they will change overtime due to learning they must have an initial condition: our base personality, the component of our emotions most susceptible to evolution.
Current adaptations are the result of historical conditions; we need to look at the world of our ancestors to understand our personalities. The first question we need to address though is how far back in time do we need to go. Are our personalities adapted to the world of the cave men, small hunter-gatherer kinship tribes which are too dispersed to regularly interact, or the world of cities and nations, very large aggregations of specialized individuals which are relatively unrelated and largely unknown to each other? The answer is likely somewhere in the middle, varying depending on the specific aspect of personality in question, but I think a fallacy in current socio-biology and evolutionary psychology is underestimating the rate of adaptation.
Populations have been shown to have drastic changes in traits in only a few generations, termed rapid evolution. The conditions for this rapid change are sufficient standing genetic variation and strong selection. Standing genetic variation means that the new majority trait already existed in the population as a small minority rather than requiring a new mutation. Strong selection on the other hand requires both that the different variations strongly change how an organism responds to the environment and that the environment has changed. In the majority of documented cases, rapidly evolving traits are those associated with predation, either capturing prey (e.g. beak or jaw size) or avoiding predation (e.g. body size or camouflage). This is likely because the interaction with other species causes these traits to have a high degree of specificity as well as the potential for rapidly changing conditions (e.g. the arrival of a new predator).
The predator-prey interactions for humans are very different from most other animals: the majority of us obtain prey and avoid aggressors indirectly through interactions with other humans. Traits like body size, speed, or coordination are no longer the dominant factors in determining our growth, survival, and reproduction. In humans the weight of this burden falls to the way in which we interact with our fellow man and these interactions are shaped by our personalities. Additionally, how we should interact continues to change as the size and structure of the society in which we live also evolve. Together these suggest strong selection on our emotional predispositions (our base personalities). Acknowledging the large variation in personalities, then, I think that it is likely that our emotions have undergone (and are undergoing?) rapid evolution; human personalities are more adapted to historical than pre-historical social conditions. To take it one step further, it is not an evolutionary fallacy to say that we are emotionally adapted to (relatively) modern conditions.
The final point I wish to make while laying the evolutionary ground work concerns why there is such a large amount of variation in personalities. If I am suggesting that we are (relatively) well adapted to modern conditions then shouldn’t that historical selection have “weeded out” all the variation, leaving only the one optimal strategy? The answer is what is called frequency dependent selection and it is a concept that I will return to often. Frequency dependent selection means that the fitness of a trait depends on the traits of others in the population. Negative frequency dependence means that rarer types have an advantage, the most ubiquitous example being sex: if you are a male in a female biased population, or vice-versa, life is pretty good. This negative frequency dependence acts to maintain diversity in the population, a 50:50 sex ratio in the previous example. Conversely, positive frequency dependence benefits common types, reducing diversity. For example, if everyone goes to site A for the mating season you aren’t going to do very well going to site B no matter what sex you are. As members of a structured society there is a diversity of emotional roles which we can fill and those in proportionally unfilled roles will fair relatively better (negative frequency dependence). So, for example, if you live in a society of very curious individuals (high trust for unknown targets) you can benefit from their experience and be cautious yourself, avoiding the risks, while if you live amongst very cautious individuals your curiosity can uncover substantial rewards.
So, to summarize: the emotions described in 2b are general across all learning organisms it is the personality, the parameters of the emotional rules, which differs between organisms. To understand the (average) human personality we have to look at the conditions under which we evolved. Due to the importance of our emotions in shaping social interactions, which strongly determine our fitness, it is likely that our personalities have undergone rapid selection suggesting that we can understand our personalities by looking at relatively modern conditions. Finally, the diversity in human personalities is maintained by negative frequency dependence where-by rare types have an advantage. The next section will explore how our social interactions have shaped our base personalities.
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