CHAPTER Toward an 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,

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 , 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 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 r 2 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. Br 1 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 Cr 2 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. Genetically measured in one’s own reproductive success plus the based variants contribute to reproduction and sur- reproductive success of kin). If an individual’s genes vival with regard to that environmental condition. are just as likely to be present in a sister as in a Individuals with those variants will be more success- daughter, one would expect the evolution of sororal ful, passing on their “good genes” and the resulting investment in the same way as one expects maternal behavioral repertoire to their off spring. investment. Kinship theory and Hamilton’s under- Although the logic of natural selection is at the standing of it illuminated our understanding of heart of all evolutionary explanations of behavior, social interaction and infl uence, paving the way for there are several concepts that Darwin did not future insights into kinship dynamics. develop fully in his own work that have been more For example, consider confl icts that occur within thoroughly elucidated in recent years. Kinship the family (animal or human). Hamilton ( 1964 ) theory is arguably the most relevant for this volume pointed out that kin are valuable in the genetic on the family. sense (among others senses) and that what contrib- utes to an individual’s inclusive fi tness also may Kinship Th eory contribute to the inclusive fi tness of the individual’s Altruism has long been a topic of interest in the relatives. Th e more closely related are two individu- study of both human and animal behavior. To many als, the greater their shared genetic interests. But, early evolutionary thinkers, it was a puzzle. Why it is important to remember that although there is would individuals be willing to sacrifi ce anything genetic commonality, there also are genetic diff er- for another individual? Th e logic of natural selec- ences, and these can lead to confl icts of interest. tion would seem to suggest that altruism should not Th ese confl icts are often apparent when individuals exist, and yet it is found throughout the natural are competing for the same scarce resources, such as world. Hamilton (1964 ) demonstrated that altruis- mates, food, or social status. Trivers’ (1974 ) analysis tic behavior (behavior performed at a cost to oneself of within-family confl ict made use of Hamilton’s for the benefi t of another) could evolve if the approach. Because the probability of an individual individuals involved were genetically related. Even replicating its alleles through its own off spring is though the direct reproductive fi tness of the donor 0.5 (the degree of relatedness between parent and is reduced, if his actions aid his own genetic kin, off spring), and through its full sibling’s off spring then he receives an indirect fi tness benefi t. Typically, (a niece or nephew) is only 0.25, natural selection this idea is expressed by the equation: will favor individuals that seek a greater share of their parent’s resources. In other words, we expect a Brr >CCr 12 certain degree of sibling competition. In some spe- cies, this competition results in the elimination of a

Where B is the benefi t to the recipient, r 1 is the sibling competitor. In others, it just means a lot of genetic correlation between the donor and the headaches for the parents. From a parental perspec- recipient’s off spring, C is the cost to the donor, and tive, they are equally related to all their children and

salmon, shackelford 5

01-Salmon-01.indd 5 1/25/2011 1:42:55 PM grandchildren, so parents have typically been under with information about their paternal origin. Th is selective pressure to resist a particular off spring’s can create additional confl ict if the mother has off - demands, especially when off spring are trying to spring from diff erent fathers because paternally extract more than their fair share of resources. active genes in the current off spring have no stake in Consider the case of weaning confl ict in a species the off spring sired by other males. Haig’s work that produces one off spring at a time. When an off - addresses the infl uence of these confl icts on the evo- spring is very young, parental fi tness typically ben- lution of the female reproductive system and how efi ts most from investing highly in this current serious health problems for mothers, such as gesta- off spring. It’s in the off spring’s best interests to tional diabetes and preeclampsia, can arise. extract as many resources as possible, up to a certain point, even at the expense of future siblings the Adaptations as Decision-makers mother could be having. At some point, the value Adaptations can be anatomical, physiological, or to the off spring (who may be reaching a state of behavioral. Th e beaks of Darwin’s fi nches, often greater independence, able to obtain food on its used to characterize the diff erent species of fi nches own, etc.) of monopolizing such resources is out- living on the Galapagos, provide a classic example weighed by the costs in terms of its own inclusive of an adaptation that is anatomical in nature (for fi tness. Typically, the mother reaches her own point review, see Grant & Grant, 2007 ). Th e dietary of diminishing returns before the off spring does options available infl uenced the survival of birds of (after all, she is equally related to each of her off - varying beak types and sizes, so that today we see spring, whereas her current off spring is more closely fi nch beaks that are well suited to cracking large related to itself than to future siblings). Th e period seeds in some areas, whereas fi nches in other envi- between when the mother’s fi tness is best served by ronments have beaks that take advantage of other decreasing investment in the current off spring and food sources, such as insects. But adaptations can investing in future off spring (in reproducing again) also be understood in terms of processes that carry and when the current off spring’s fi tness is also best out the cost–benefi t analyses that an ancestral organ- served by the mother investing elsewhere is known ism required to survive environmental challenges. in mammalian species as weaning confl ict (see For example, the fever adaptation can be described Trivers, 1974 ). Th e mother’s fi tness returns are as a set of decision processes for dealing with certain decreasing, but the off spring isn’t quite ready to give types of invading organisms. If you are being up any investment. Confl ict is most intense at such invaded by bacteria M, raise your body temperature a stage. During this period, the mother’s fi tness is by X degrees. Th e increase in body temperature may increased more by investing in additional off spring, be enough to destroy the invader, which is benefi cial whereas a particular off spring’s fi tness is increased to the individual (which is why when fever is pre- more by continued maternal investment. Th e con- vented by drugs, resistance to infection is lower). fl ict ends as the fi tness benefi ts of weaning shift to But the adaptation is not cost-free. It takes a non- both mother and off spring (Drake, Fraser, & Weary, trivial amount of energy to raise body temperature. 2008 ; Humphrey, in press; Rehling & Trillmich, Perhaps more importantly, and especially in young 2007 ). children, the rise in body temperature can damage Harvard professor David Haig ( 1993 ; and see other systems if it is excessively high and prolonged Haig, 2002 , for review) has investigated parent– in duration (Williams & Nesse, 1991 ). off spring confl ict at a further level of analysis by From a decision-maker perspective, adaptations considering that there are three sets of genes, each can be seen as decision rules or mental mechanisms set of which may have diff erent interests. Th ey designed by natural selection for producing the include genes in the mother, maternally derived diff erent behaviors required for ancestral survival, genes in the current off spring, and paternally derived growth, and reproduction. Buss (1999 ) has sug- genes in the current off spring. With maternal genes gested the term “evolved psychological mecha- having an equal stake in each off spring, they will be nisms” for the specialized information-processing selected to transfer resources to off spring as a func- mechanisms that organize experiences into adap- tion of the off spring’s likelihood of reproducing. tively meaningful schemas. Th ese mechanisms focus Genes in the current off spring have a greater interest attention, organize perception and memory, and in the current off spring than in future siblings and recruit specialized procedural knowledge that leads will be selected to maximize transfer of resources to to domain appropriate inferences, judgments, and the current off spring. Some genes can be imprinted choices when activated by a relevant problem.

6 toward an evolutionary psychology of the family

01-Salmon-01.indd 6 1/25/2011 1:42:56 PM Kinship and Human Psychology maternal eff ort. Th e evolved motivational mecha- Anthropologists have long recognized the impor- nisms that direct maternal investment decisions are tance of kinship to the study of human social behav- sensitive to a number of off spring attributes, to the ior, as illustrated by several chapters in this book by material and social situation, and the situation/ anthropologists and the evidence for runaway social condition of the mother herself (see Daly & Wilson, selection elegantly presented in Flinn’s chapter on 1995 , for a review). an evolutionary anthropology of the family. One However, mothers are not the only interested might have assumed the same of psychologists. party. Off spring themselves have a role to play in And, it is true that attention to the family has been shaping resource allocation. Parent–off spring con- paid in areas such as developmental psychology and fl ict (Trivers, 1974 ) is a feature of sexually repro- counseling psychology. However, it has been largely ducing species because of the resultant genetic ignored in many other areas of psychology, includ- asymmetries in family relationships. A mother is ing those areas in which its importance might have equally related genetically to any two of her off - seemed obvious, such as (see Daly, spring, but each off spring is more closely related to Salmon, & Wilson [ 1997 ] for a discussion of the itself than to a sibling (except in the case of identical absence of the family in much of social psychology; twins). As a result, mother and off spring do not see see Burnstein, Crandall, and Kitayama [1994 ] and eye to eye on the relative fi tness value of other off - Michalski and Shackelford [ 2005 ] for examples of spring or on the allocation of maternal resources. evolutionarily informed social psychological research Th is confl ict over maternal resources provides an that takes kinship into account). explanation for some puzzling aspects of mother– Although some areas of psychology do attend to off spring interaction, such as weaning confl ict the importance of understanding familial relation- (Trivers, 1974 ) and the dangerously high levels of ships and the roles they play in our lives, the major- substances of fetal origin that sometimes accumu- ity have failed to recognize the relevance of the late in the blood of pregnant women, including pla- qualitatively distinct types of close relationships cental lactogen, which up-regulates the fetus’s access found within the family domain. A proper, evolu- to maternal glucose stores, resulting in gestational tionarily informed approach to a psychology of the diabetes (Haig, 1993 , 2002 ). Such areas of confl ict family is by necessity a relationship-specifi c approach between parent and off spring are explored further in (Wilson & Daly, 1997 ). Humans, along with other Chapter 6 by Salmon and Malcolm, as are parent– species, have evolved specialized mechanisms for child relationships more generally in Chapter 5 by processing information and motivating behavior Del Giudice and Belsky. relevant to the specifi c demands of being a mate, father, mother, sibling, child, or grandparent. Th is Fatherhood type of evolutionary perspective on the nature of Signifi cant similarities exist between paternal solici- distinct family relationships provides an insight tude and maternal solicitude, but there also are into our behavior that cannot be found elsewhere. several substantial diff erences. Parents have been Kinship is not one relationship. It is many diff erent selected to assess off spring quality and need, and for relationships. Th e challenges that face mothers are both fathers and mothers, mechanisms motivating diff erent from those that face fathers or siblings. solicitude evolved to generate solicitude in relation to cues of the expected impact of any parental Relationship-specifi c Adaptations investment on the off spring’s future success. Both Motherhood father and mother have been selected to discrimi- Th ere is no more essential mammalian relationship nate with respect to cues that the off spring is their than that between mother and off spring. It should genetic child. But it is true that for mammalian not be surprising, therefore, that it may be the mothers the evidence is clear. If you gave birth to it, relationship with the most specialized anatomical, the baby is yours. For men, due to internal fertiliza- physiological, and psychological mechanisms (Hrdy, tion and relatively concealed ovulation, paternity 2000 ). Th e demands of motherhood go beyond is never certain (or wouldn’t have been in our ances- conception, gestation, and nursing. Not all off spring tral past). Putative fathers must depend on sources are created equal. Th ey are not all equally capable of of information about the mother’s likely fi delity, transforming parental care and investment into the or the child’s resemblance to his relatives or to long-term success of parental genes. Th e result has himself. From this, one might predict that paternal been strong selection for the strategic allocation of aff ection will be infl uenced by paternal perceptions

salmon, shackelford 7

01-Salmon-01.indd 7 1/25/2011 1:42:56 PM of resemblance. And, in fact, people do pay more dynamic. He endures two relationship links that attention to paternal resemblance than to maternal can be broken by nonpaternity: the grandchild resemblance, with mothers and their relatives might not be his son’s child, and his son might actively promoting perceptions of paternal resem- not be his own biological child (see also Michalski & blance (Daly & Wilson, 1982 ; Regalski & Gaulin, Shackelford, 2005 ). Euler (Chapter 12) addresses 1993 ). Issues of paternal investment are discussed the nature of grandparental and extended kin by Anderson (Chapter 7), and issues of investment relationships. by mothers and fathers in unrelated off spring are addressed by Volk (Chapter 8). Mateship Although mates are rarely close genetic relatives, Sibship their relationship is usually considered a family one, An evolutionary perspective also can generate with both parties having a shared interest in their insight into our understanding of sibling relations joint off spring. Th e longer the duration of the (Mock & Parker, 1997 . Hamilton’s ( 1964 ) analysis union, the more likely that they share a similar of the evolution of sociality and altruism in haplo- perspective on the optimal allocation of resources. diploid insects had at its core the shared genetic What is best for one is usually best for the other. But interests of sisters in such species. But although such a harmony of interests can be shattered by siblings, our close genetic kin, can be major allies, extrapair relations. Studies of marital confl ict and they also can be our fi ercest competitors, especially violence make this point clear. Suspected or actual for parental resources (Salmon, 1998 ; Sulloway, infi delity is a powerful source of severe confl ict and 1996 ). Th e result is sibling relationships that are spousal violence (Daly & Wilson, 1988 ; Wilson & often somewhat ambivalent across the lifespan. Daly, 1993 ; for recent reviews, see Goetz & Th omas Pollet and Ashley Hoben (Chapter 9) Shackelford, 2009 , and Kaighobadi, Shackelford, illuminates the cooperative and rivalrous nature of & Goetz, 2009 ). Step-relationships bring another sibling relationships. factor into the mix. In this case, there is a child who is a potential vehicle of fi tness for one partner but Grandparenthood not the other. Both parties are aware of the asym- Do we have adaptations designed specifi cally to metry in relatedness (as contrasted to instances of deal with the problems faced by grandparental female infi delity and subsequent cuckoldry) at the relationships? Or, do these relationships merely start of or at least very early in their relationship. co-opt adaptations for parenting? Postmenopausal Nevertheless, stepchildren are at an elevated risk women make signifi cant contributions to the wel- of neglect, abuse, and homicide (Daly & Wilson, fare of their grandchildren in many cultures 1988 , 1995 ), a reminder that the motivational (Lancaster & King, 1985 ; Sears, Mace, & McGregor, mechanisms of parental feeling are designed to pref- 2000 ). Th us, it is reasonable to suspect that mental erentially direct aff ection and investment toward processes specifi c to the allocation of grandparen- one’s genetic off spring. Kermyt Anderson (Chapter 7) tal investment may have been the targets of natu- discusses stepparenting, divorce, and parental ral selection (Hawkes, O’Connell, Blurton Jones, investment. Alvarez, & Charnov, 1998 ; Smith, 1988 ). Daly and Wilson ( 1984 ) also have suggested that Euler and Weitzel ( 1996 ) noted that paternity motivational diff erences produce diff erent methods certainty could infl uence grandparental investment when it comes to how stepparents or genetic parents (in addition to its impact on paternal investment). kill. Daly and Wilson found, in both Canadian and To test their hypotheses, they asked adults to rate the British national-level databases, that stepfathers degree of grandparental solicitude they experienced were more likely than genetic fathers to commit from each of their four grandparents. Th e results fi licide by beating and bludgeoning, a window into were striking, indicating a strong link between relat- stepparental feelings of bitterness and resentment edness/paternity certainty and solicitude. Maternal not seen in genetic fathers. Genetic fathers were grandmothers were rated the highest on solicitude, more likely than stepfathers to commit fi licide by followed by maternal grandfathers, paternal grand- shooting or asphyxiation, which often produce a mothers, and fi nally paternal grandfathers. From relatively quick and painless death. Weekes- a theoretical perspective, a maternal grandmother Shackelford and Shackelford ( 2004 ) replicated and has the greatest certainty of her grandchild’s related- extended these fi ndings using a U.S. national-level ness to her. A paternal grandfather faces a diff erent database of over 400,000 homicides. Th ey also

8 toward an evolutionary psychology of the family

01-Salmon-01.indd 8 1/25/2011 1:42:56 PM identifi ed similar diff erences in the methods by which Japanese macaques (Glick, Eaton, Johnson, & stepmothers and genetic mothers committed fi licide. Worlein, 1986 ) and in alarm-calling in Belding’s Aaron Goetz and Gorge Romero (Chapter 11) dis- ground squirrels (Sherman, 1977 ; alarm-calling is cuss the nature and scope of family violence, with done typically by females living near female kin), particular attention to the role played by paternity recognizing relatives has been a hot topic in animal uncertainty. family research. Do animals recognize each other as kin by frequency of contact? Phenotypic resem- Kinship and Animal Psychology blance? Smell? Th e research in this area is brought to When most people think about family, they think light in Chapter 13, by Hepper. about their own relationships, their parents, siblings, And, like humans, not all family relationships and children, maybe cousins, aunts and uncles, and are bright and rosy. Books on how to deal with grandparents, too. But we are not the only species sibling rivalry between one’s children abound, and that has families and for which kinship plays a sig- in some animal species such sibling confl ict is taken nifi cant role. Much of our understanding of human to Cain and Abel–like heights, with siblicide occur- families and the mechanisms that infl uence family ring in many species of birds. Siblicide in these cases relationships was facilitated by the study of animal has been interpreted as an adaptive strategy that behavior and how animals invest in their own off - benefi ts the surviving off spring and the parents, spring (and sometimes in siblings or in the off spring as grisly as this may seem (Mock, Drummond, & of others). From work on the breeding success of Stinson, 1990 ; Mock & Parker 1997 ). birds, to the strategic allocation of reproductive eff ort to parenting or mating, to sibling competi- Fictive Kinship tion and helpers at the nest, animal families not When we refer to fi ctive kinship, we are focusing only are interesting in and of themselves, but also on relationships that appear to be modeled on those are important for the light they shed on human of genetic kinship. Godparents or blood-brothers family relationships. are examples many readers will be familiar with. Th e focus is on relationships that are kin-like but Animal Parenting that are not defi ned by actual genetic relatedness. In Consider the killdeer, a familiar bird in the grass- many cases, these relationships may replace missing lands of America. It is perhaps best known for its kin relationships and co-opt the adaptations predator distraction display used to protect its chicks. designed to manage those of genetic kinship. How If a predator gets close to its nest, it will attempt to many people have heard others refer to their pets as lure the predator away with a display of vulnerabil- their babies? Many people treat their pets like chil- ity, behaving as though its wing is broken. Th e dren, buying them toys and treats, showering them energy cost may be low but there is a risk (part of with aff ection and investment. Th e special bond the bird’s investment) that the predator will make between people and their pets is addressed by Archer the parent into a killdeer lunch (Brunton, 1990 ). (Chapter 16) and Serpell and Paul (Chapter 17). How easy it is to appreciate such parental protec- Friendship is often treated as a special form of tion, seeing the connection between that and the kinship. Close girlfriends may refer to each other as protective behavior of human parents, as well as sister, and birthday cards for female friends contain that of many other animals. phrases such as “You’re like a sister to me.” Park and Although many species of animal, particularly Ackerman (Chapter 19) refl ect on the connections some aquatic ones, make no after between kinship and friendship. Others have spawning, many do invest in their off spring. Among pointed out that cues of kinship infl uence the way mammals, it is typically the female who invests the we interact with others. Cues of kinship can make most through provisioning and protection, although us more likely to cooperate with others (as discussed it is true that some males contribute signifi cantly by Krupp, DeBruine, and Jones, Chapter 20), and as well. Several chapters in the current volume appeals to the shared interests of kinship (“My address issues related to animal parenting, including brothers and sisters . . . ,” “For he who sheds his blood Chapter 15 by Berman; and in Chapter 6, Salmon with me today shall be my brother.”) have been used and Malcolm consider parent–off spring confl ict over over and over again in political and rhetorical speech investment in both animals and humans. (Salmon, 1998 ; Johnson, 1987 ). In this volume, Because animals sometimes behave nepotistically, Hector Qirko touches on how the power of fi ctive engaging, for example, in cooperative grooming in kinship plays a role in our lives today.

salmon, shackelford 9

01-Salmon-01.indd 9 1/25/2011 1:42:56 PM Conclusion and close relationships . In J.A. Simpson and D.T. Kenrick Th is volume is intended to illustrate the many ways (Eds.), Evolutionary social psychology (pp. 265 – 296 ). Mahwah, NJ : Erlbaum . in which an evolutionary perspective on the family Darwin , C. ( 1859 ). On the origin of species by means of natural can contribute to our understanding of behavior, selection or the preservation of favored races in the struggle for not only of our own family relationships but also life . London : John Murray . of how our evolved psychological mechanisms infl u- Drake , A. , Fraser , D. , and Weary , D.M. ( 2008 ). Parent-off spring ence how we react to friends, allies, and our pets. resource allocation in domestic pigs . Behavioral Ecology and , 62 , 309 – 319 . We also hope that it provides insight into the kin- Euler , H. , and Weitzel , B. ( 1996 ). Discriminative grandparental ship psychology of animals and how similar (and at solicitude as reproductive strategy. Human Nature , 7, 39 – 59 . times diff erent) they are in comparison to our own Glick , B.B. , Eaton , G.G. , Johnson , D.F. , and Worlein , J.M. kinship psychology. Much of the pleasure and pain ( 1986 ). Development of partner preferences in Japanese of family life has been with us over the course of macaques (Macaca fuscata ): Eff ects of gender and kinship during the second year of life . International Journal of human evolutionary history. Our modern behavior , 7 , 467 – 479 . is the product of our evolutionary response to the Goodall , J. ( 1996 ). My life with the chimpanzees . New York : pressures of living as a social species, just as the Alladin . behavior of other social animals is a product of such Goetz , A. T. , and Shackelford , T. K. ( 2009 ). Sexual confl ict in pressures. Th e next three chapters in this opening humans: Evolutionary consequences of asymmetric parental investment and paternity uncertainty . Animal Biology , 59 , section of the volume, by Mark Flinn, Bernard 449 – 456 . Chapais, and Doug Mock, elaborate on the benefi ts Grant , P. R. , and Grant , R. ( 2007 ). How and why species multi- of bringing an evolutionary perspective to the ply: Th e radiation of Darwin’s fi nches (Princeton Series in study of human and animal families. In our fi nal Evolutionary Biology) . Princeton, NJ : Princeton University chapter, we return to a consideration of the future Press . Haig , D. ( 1993 ). Genetic confl icts in human pregnancy. of evolutionary approaches to the study of family Quarterly Review of Biology , 68 , 495 – 532 . relationships. Haig , D. (2002 ). Genomic imprinting and kinship. New Brunswick, NJ: Rutgers University Press. Hamilton , W.D. ( 1964 ). Th e genetical evolution of social behav- References iour. I and II . 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01-Salmon-01.indd 10 1/25/2011 1:42:56 PM Regalski , J.M. , and Gaulin , S.J.C. ( 1993 ). Whom are Mexican Sulloway , F.J. ( 1996 ). Born to rebel: Birth order, family dynamics, infants said to resemble? Monitoring and fostering paternal con- and creative lives . New York : Pantheon . fi dence in the Yucatan . Ethology and Sociobiology , 14 , 97 – 113 . Trivers , R.L. ( 1974 ). Parent-off spring confl ict . American Rehling , A. , and Trillmich , F. ( 2007 ). Weaning in the guinea Zoologist , 14 , 249 – 264 . pig (Cavia aperea f. porcellus ): Who decides and by what Weekes-Shackelford , V.A. , and Shackelford , T.K. ( 2004 ). measure? Behavioral Ecology and Sociobiology , 62 , 149 – 157 . Methods of fi licide: Stepparents and genetic parents kill Salmon , C. ( 1998 ). Th e evocative nature of kin terminology in diff erently . Violence and Victims , 19 , 75 – 81 . political speech . Politics and the Life Sciences , 17 , 51 – 57 . Williams , G.C. ( 1966 ). Adaptation and natural selection: A cri- Salmon , C. ( 2003 ). Birth order and relationships: Family, friends, tique of some current evolutionary thought . Princeton, NJ : and sexual partners . Human Nature , 14 , 73 – 88 . Princeton University Press . Sears , R. , Mace , R. , and McGregor , I.A. ( 2000 ). Maternal grand- Williams , G.C. , and Nesse , R. ( 1991 ). Th e dawn of Darwinian mothers improve nutritional status and survival of children medicine . Quarterly Review of Biology , 66 , 1 – 22 . in rural Gambia. Proceedings of the Royal Society of London. Wilson , M. , and Daly , M. ( 1993 ). An evolutionary psychological Series B. Biological Sciences , 267 , 1641 – 1647 . perspective on male sexual proprietariness and violence Sherman , P.W. ( 1977 ). Nepotism and the evolution of alarm against wives . Violence and Victims , 8 , 271 – 294 . calls . Science , 197 , 1246 – 1253 . Wilson , M. , and Daly , M . ( 1997 ). Relationship-specifi c social Smith , M.S . (1988 ). Research in developmental sociobiology: psychological adaptations . In G. R. Bock & G. Cardew Parenting and family behavior. In K. MacDonald (Ed.), Socio- (Eds.), CIBA Foundation symposium on characterizing psycho- biological perspectives on human development (pp. 271 – 292 ). logical adaptations (pp. 253 – 263 ). Chichester, UK : John New York: Springer . Wiley & Sons .

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