Toward an Evolutionary Psychology of the Family

CHAPTER Toward an Evolutionary Psychology 1 of the Family Catherine A. Salmon and Todd K. Shackelford Abstract Kinship has been central to evolutionary biological analyses of social behavior since Hamilton (1964) extended the concept of Darwinian fi tness to include an individual’s actions that benefi t not only direct descendents but also collateral kin. No longer were organisms simply reproductive strategists, they also were nepotistic strategists. This concept revolutionized how biologists understand social interaction and infl uence. This chapter provides an overview of some of the ways evolutionary psychologists see humans as nepotistic strategists, introducing concepts that will be important to understanding the chapters on animal and human kinship to follow. Keywords : Adaptation , inclusive fi tness , kin selection Introduction books have been published with the goals of helping What do you think of when you think about family? us understand and improve our family relationships. Parents, children, spouses, or siblings? How about Many focus on parent–child relations or sibling grandparents or cousins? A beloved pet? For most rivalry and how best to get along. people, relationships with those we think of as our Th e current volume focuses on the whys, the family members are an essential part of our lives. As reasons behind people’s behavior and how a greater children, we were dependent on our families for our understanding of “whys” can help us in our own food and shelter. Our families protected us, loved lives, to better understand our own behavior and us, and taught us about the world we were growing that of our family members. It also brings some- up in. Th en, as young adults, many of us moved thing to the table that is often ignored in the study away from our family circles, often to form families of families. Humans are not the only species to have of our own. Sometimes this happened close by; at families. Many other social species live in groups other times, we might move miles away, sometimes and have relationships with their parents, off spring, even to other continents! But many of us retain and siblings. Sometimes these relationships are strong ties to our natal kin. Relationships with short-lived, but sometimes they can last a long time family can be important to our emotional health and often appear to be characterized by strong and can play a signifi cant role in our social success. bonds. Anyone who has read (or seen footage of) Family can be a source of great joy as well as great Jane Goodall’s descriptions of the relationships anguish. Our siblings, for example, can be our between chimpanzee mother Flo and her off spring, strongest allies and our most persistent opponents. especially Flint, the son she nursed until her own We need our families, and yet sometimes we have a death, cannot help but see a bond that many human great diffi culty understanding them. Hundreds of mothers and children feel. 3 01-Salmon-01.indd 3 1/25/2011 1:42:55 PM [N]othing did any good, and about three weeks after point behavior in the direction society views as more Flo died, Flint died too. It seems that because Flo moral or desirable (an excellent discussion of the had been too old to force the spoiled Flint to become naturalistic fallacy and evolutionary moral psychol- independent, he simply couldn’t face life without her. ogy can be found in Holcomb, 2004 ). (Goodall, 1996 , p. 96). What Is an Evolutionary Perspective Goodall also noted that Flint’s older sister Fifi tried on the Family? to help him but eventually had to give up as she had In many ways, early 20th-century thinking about her own infant son to care for. Although we are human behavior embraced Charles Darwin, or at interested in animal families for their own sakes and least his functional approach to the study of life. To hope our readers are too, we also hope that readers modern biologists and animal behaviorists, an will recognize the deeper understanding of human evolutionary approach is second nature. An adapta- families that can be found through an understand- tionist approach to animal families raises no eye- ing of similar phenomena in other species. brows. But the last 75 years or so has seen an almost Th roughout this volume, you will see reference pathological avoidance of biology when it comes to to the evolved motivations that underlie behavior. the study of human behavior. In psychology, neo- In making claims about the evolved nature of behaviorism, humanism, cognitive theory, modern motivations and behavioral mechanisms, we are not psychoanalysis, and an assortment of postmodernist judging whether a behavior itself is good or bad or explanations have come to dictate the way many right or wrong in any moral sense. Human and academics think about human behavior. We believe other animal behaviors exist, and evolutionary sci- it’s time for a rather diff erent approach. We need to entists are interested in understanding why certain remember that people are just another type of behaviors evolved and why they appear in certain animal, subject to the forces of natural selection just contexts. Providing evidence that a behavior is as all other species are. It’s time to revisit the impor- generated by evolved mechanisms — infanticide by tance of our ancestral history and the selection pres- mothers, for example, which occurs in humans as sures that built, not only the organs of our body, but well as many other species — says nothing about the also those of our mind. To explain this approach, we moral nature of such an act. Rather, this investiga- fi rst provide a brief review of the process of natural tive strategy represents an exploration of the cir- selection, the special role of kinship in evolutionary cumstances that would cause such a behavior to analyses, and how adaptations can function as have increased the reproductive success of, in this decision-makers, highlighting this with regard to case, ancestral mothers of the species. It is a consid- kin relationships. eration of what sorts of selection pressures might have caused the evolution of the mechanisms that Natural Selection produce the behavior. In fact, reference to what “is” When we refer to an adaptation, we are talking to justify what “ought to be” is referred to as the about an anatomical structure, physiological pro- naturalistic fallacy . Interestingly, the naturalistic cess, or behavior that made ancestral individuals’ fallacy seems to come into play for humans much more likely to survive and reproduce in competition more frequently than for nonhumans. Few people with other members of their species. Adaptations seem to worry if an evolutionary argument is off ered are shaped, or evolve, through natural selection. Th e for why a pig or a rabbit kills one of its babies. It’s process of natural selection is simply the diff erential not as if we’re condoning the pig’s behavior. But if production or survival of off spring by genetically one tries to explain the evolutionary logic of human diff erent members of the population (Williams, behaviors judged to be immoral or unseemly, the 1966 ). If an individual (whether animal or human) suspicion is that you’re thereby giving it a stamp of is better able to survive and reproduce, he or she approval. But empirical data and the moral realm is more likely to leave off spring that share his or are logically distinct. No matter how desirable some her traits. Darwin’s ( 1859 ) logic can be seen in the behavior may be, that does not mean that wishing following: makes it so, just as the existence of a behavior does not necessarily make it desirable. A better under- Assumption 1: Species are capable of overproducing standing of the evolutionary forces that shaped a off spring. behavior and the cues to which the underlying Assumption 2: Th e size of populations of individuals mechanisms are sensitive may allow us to better tends to remain relatively stable over time. 4 toward an evolutionary psychology of the family 01-Salmon-01.indd 4 1/25/2011 1:42:55 PM Inference 1: A struggle for existence among r2 is the genetic correlation between the donor and individuals ensues. its own off spring (Crawford & Salmon, 2004 ). Assumption 4: Individuals diff er on traits In the equation, r represents the probability that (adaptations) that enable them to survive and the two individuals each have an allele that is a copy reproduce. of an allele in a common ancestor. Such an allele is Assumption 5: At least some of the variance in these called identical by common descent , and the probabil- traits is genetically heritable. ity of such an event is the genetic correlation or Inference 2: Th ere is diff erential production or coeffi cient of relatedness between individuals. Br1 is survival of off spring by genetically diff erent the indirect benefi t to the donor through the recipi- members of the population, which is by ent’s additional off spring, and Cr2 is the direct cost defi nition natural selection. to the helper because of its decreased off spring. Both Inference 3: Th rough many generations, evolution sides of the equation refer to changes in the donor’s of traits that are more adaptive than others will fi tness as a result of his or her altruistic actions. Th is occur through natural selection. was a new way of thinking about fi tness. No longer ( Crawford & Salmon, 2004 ) were organisms simply reproductive strategists (with fi tness being measured in own off spring); now, they In other words, some feature of the environ- were also nepotistic strategists (with fi tness being ment poses a problem for an organism.

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