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Robert M. SapolskyA modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
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Evolution is the change of individual species over time based on the reproductive selection of traits more adaptive to the environment. Evolution does not only work on physical traits, but it also selects for more adaptive behaviors. The study of evolution’s effect on behavior, including human behavior, is sociobiology.
Individual and Group Selection for Behavior
It was once believed behavioral traits evolved to create behaviors for the good of the group (i.e., group selection). However, research shows behavioral traits are selected for in the same way as physical traits: We have evolved to behave in ways that put us at a greater chance of passing on our genes. In other words, our behavior is not governed by group selection but by individual selection. This can lead to quite brutal behavior. For example, male langur monkeys live in male-dominated groups, and whenever a new male takes over, it kills the infants of the group to incite the females into ovulation and then impregnate them to pass on his own genes as opposed to the genes of his failed competitors. This competitive infanticide, first discovered in 1977, has been documented in 119 species. Now accepted, findings on this behavior were once widely criticized. Sapolsky reiterates that scientists, like everyone else, are guilty of bias and did not want to believe such behavior to be true.
Evolution inspires behaviors that help us pass on our genes. However, since our relatives share the majority of our genes, evolution also favors behaviors that assist our relatives in reproducing. This is “kin selection,” observable throughout primates.
The closer someone is to us genetically, the more we are likely to help—or even sacrifice ourselves—for them. Such is evidenced in the rarity of mothers nursing the infants of others in mammalian groups.
Reciprocal Altruism
If evolution is all about individual advantage, why do large, multi-kin groups of organisms regularly cooperate? This is the domain of reciprocal altruism: “incurring a fitness cost to enhance a non-relative’s fitness, with the expectation of reciprocation” (345). Because we are always looking for individual advantages, the presence of reciprocity systems leads to cheating. Primary among natural strategies to inhibit cheating is the “Tit for Tat” strategy: cooperating the first round, and then mirroring what the opponent does thereafter.
Tournament Species and Pair Bonding Species
Two major types of social organizations exist in primate species, and division is based on their styles of sexual selection: tournament species and pair-bonding species. In tournament species, males compete for partners with one male winning the right to all the females. This leads to selection for larger, more aggressive males with prominent secondary sexual characteristics (features that appear during puberty but are not directly involved in reproduction, such as facial hair) do not that display their health and strength to potential females. It also leads to lack of male care for offspring. In pair-bonding species, each male couples with one female, and males do not compete. This leads to equitable size between males and females and male involvement in parental care.
Genes are the basic unit of evolution, but one can argue that phenotypic traits (i.e., the physical product of genes in the body) are what is actually selected for by environments or individuals. The idea of multilevel selection is that the best understanding of why something evolved in a certain way requires investigation at the levels of individual genes, the expressed trait, and the organism’s complete collection of traits.
One example of multilevel selection is neo-group selection, which acknowledges traits that are individually adaptive, such as high aggression, are maladaptive at the group level. Therefore, this group can be outcompeted by other groups composed of less aggressive individuals. Though this may be rare in the animal world, it is quite clearly common in human cultures, where factors, such as ideology, increase competition between groups and can lead to the genetic extermination of one group over another.
And Us
Humans exhibit traits of both tournament and pair-bonding species. We exhibit clear kin selection with strong kinship relations existing throughout all human cultures. However, our understanding of who our kin are often diverge from biological relatedness and deal with “ideological” kinship. This is because humans create kinship cognitively: We reason it out based on factors we deem important, such as culture, religion, personal history together, and racial markers.
Importantly, human cultural and technological innovations can trigger sudden bursts of variation in the gene pool. For instance, the enzyme lactase, which helps infants digest their mother’s milk and goes away with maturity, persists in some humans in adulthood as a result of our domestication of livestock and incorporation of their milk into adult diets. Those who developed lactase persistence could digest this milk and could get the nutrition necessary to increase their rates of survival and reproduction, which altered the human gene pool.
Is Everything Adaptive?
Not all traits exist because they are adaptive. Some evolve for one purpose but then are coopted toward another purpose and survive that way (exaptation). For instance, feathers evolved for insulation but then were exapted for flight. Other traits may just be evolutionary “baggage,” packaged together in organisms or trait groups that survive due to the adaptive capacity of other traits (spandrels).
If we explain why things exist evolutionarily, we may be subject to the “naturalistic fallacy,” the idea that since a trait is adaptive in our history, it belongs there and is “good.” Therefore, infanticide, war, and many other terrible acts can be deemed acceptable because they have evolved. This, of course, is not the claim made by sociobiologists: “Saying that we advocate something just because we report it is like saying oncologists advocate cancer” (385). Importantly, it is also not the claim made by Sapolsky. Throughout Behave, Sapoksly has given us several examples of behaviors that were logical in our evolutionary environs but have become maladaptive today. Some examples from Chapter 2, 3, and 4, respectively, are our dopaminergic system making us always want more (a dangerous desire into today’s world of processed sugars and fats), automatic aversion to faces of other races, and our stress response’s diversion of energy from immune system function and tissue repair. Because something was adaptive to us evolutionarily does not mean it is good for us today. This brings yet another meaning to the science of our “best and worst:” Although a trait survived in evolution because it was best in our environment, it does not mean we should want it today.
This is true of our social behaviors as well, as supported by Sapolsky’s discussion of the naturalistic fallacy. Higher aggression, larger size, and more selfish sexual selection behaviors in males is one aspect of humanity that does correspond with tournament species. It is also a set of traits at the root of our cross-cultural preponderance for domestic violence of men against women. Evolution has in some sense structured us this way, as those who had such genes and behaved in such ways were more successful at reproducing in our ancestry. This does not make the behavior “good” or correct. But understanding such behaviors do have evolutionary purposes and genetic correlates is the first step to reducing them in our species.
Evolution incorporates both the science of genetics and the science of culture and is the crucial way to think about how behaviors and their genetic impacts are passed down generation to generation. It also connects to how behaviors of our ancient ancestors impact our own behavior today and is the concept by which a study on a rat in a lab can be extrapolated to the behaviors of humans in New York City: They both share a common ancestor for which the genes controlling whatever behavior is being studied were adaptive. This closes the first part of the book, a study of the many inter-related factors that determine behavior with evolution being the largest and most encompassing. Next comes Part 2, which is engaged in “synthesizing this material in order to look at realms of behavior where this matters most” (386): aggression, crime, war, prosociality, empathy and peace.
By Robert M. Sapolsky