CHAPTER 8: PROBLEMS OF KINSHIP
Chapter Summary
We started this chapter by delving deeper into Hamilton’s (1964) theory of inclusive fitness, formalized
by Hamilton’s rule c 6 rb. For altruism to evolve, the cost to the actor must be less than the benefits
provided, multiplied by the genetic relatedness between the actor and the recipient. In one bold stroke,
this theory offered one answer to the question of how altruism could evolve. It simultaneously extended
Darwin’s definition of classical fitness (personal reproductive success) to inclusive fitness (personal
reproductive
success plus the effects of one’s actions on the fitness of genetic relatives, weighted by the degree of
genetic relatedness).
Next we drew out the profound theoretical implications of inclusive fitness theory for humans. For
example, (1) there will be a special evolved psychology of kinship involving psychological mechanisms
dedicated to solving the differing adaptive problems confronted when dealing with siblings, half siblings,
grandparents, grandchildren, aunts, and uncles; (2) sex and generation will be critical categories
differentiating kin because
Empirical studies confirm the importance of kinship as a predictor of helping behavior. One study
documented that alarm calling among ground squirrels, a potentially costly endeavor to the caller because
it draws the attention of predators, occurs when close kin are likely to be nearby. Helping kin first
requires the ability to recognize kin. Humans have at least four kin recognition mechanisms: (1)
association; (2) odor;
Concern over close kin also extends to individuals maintaining vigilance over their close kin’s romantic
relationships, especially over female kin. Absence of close kin, on the other hand, has disadvantages.
Growing up without close kin, or in stepfamilies with half siblings, can be stressful, as indicated by the
higher cortisol levels of children in these families.
Grandparental investment is a special arena for testing predictions from inclusive fitness theory. Paternity
uncertainty comes into play. A paternal grandfather has double the risk of genetic relatedness being
severed. First, he might not be the father of his children. Second, his son might not be the father of his
own children. Grandmothers, in contrast, are 100 percent certain that they are the genetic relatives of the
children of their daughters. On the basis of this logic, we should expect mothers’ mothers to show the
heaviest grandparental investment, on average, and fathers’ fathers to show the least. The other two types
of grandparents—fathers’ mothers and mothers’ fathers—should show investment patterns between these
extremes because in each of these cases, there is one opportunity for genetic relatedness to be severed.
A similar logic applies to investment by aunts, uncles, and cousins. The siblings of a sister are sure that
their sister is the parent of her child, so these aunts and uncles are sure that they are the genetic relatives
of their nieces and nephews. The siblings of a brother, in contrast, are not certain because their brother
may have been cuckolded. This leads to the prediction of differential investment by aunts and uncles,
depending on whether the children are their sister’s or brother’s. Maternal aunts, for example, would be
expected to invest more than paternal aunts.
In a study aunts and uncles, two important predictors of investment, were identified. First, aunts tended to
invest more than uncles, regardless of whether their nieces and nephews were the children of a brother or
a sister—a sex effect. Second, the maternal aunts and uncles invested more than the paternal aunts and
uncles, supporting the paternity uncertainty prediction. Similar results were found in studies of helping
cousins
through maternal versus paternal lines.
Although early evolutionary models emphasized harmonious cooperation within members of the family,
recent evolutionary models point to three important arenas of conflict: sibling conflict, parent–offspring
conflict, and conflict between mother and father. Although inclusive fitness theory predicts that genetic
relatedness will be an important predictor of altruism, family members almost never have identical
genetic interests. As a consequence, conflict and competition within families are predicted to be
pervasive.
Suggested Readings
Coall, D. A., & Hertwig, R. (2010). Grandparental investment: Past, present, and future. Behavioral and
Brain Sciences, 33, 1–59.
Cronk, L., & Gerkey, D. (2007). Kinship and descent. In R.I.M. Dunbar & L. Barrett (Eds.), Oxford
Handbook of Evolutionary Psychology (pp. 463–478). New York: Oxford University Press.
Daly, M., Salmon, C., & Wilson, M. (1997). Kinship: The conceptual hole in psychological studies of
social cognition and close relationships. In J. A. Simpson & D. T. Kenrick (Eds.), Evolutionary
social psychology (pp. 265–296). Mahwah, NJ: Erlbaum.
Davis, J. N., & Daly, M. (1997). Evolutionary theory and the human family. The Quarterly Review of
Biology, 72, 407–435.
DeKay, W. T., & Shackelford, T. K. (2000). Toward an evolutionary approach to social cognition.
Evolution and Cognition, 6, 185–195.
Euler, H.A. (2011). Grandparents and extended kin. The Oxford handbook of evolutionary family
psychology. Oxford University Press, New York, 181-210.
Faulkner, J., & Schaller, M. (2007). Nepotistic nosiness: Inclusive fitness and vigilance of kin members’
romantic relationships. Evolution and Human Behavior, 28, 430–438.
Multiple Choice Questions
(a) their past mate value
(b) their genetic relatedness
(c) how needy they are of financial aid
(d) how long it takes that help to translate into fitness benefits
(a) r < cb
(b) b > cr
(c) c > rb
(d) c < rb
(a) the conditions under which mechanisms favoring altruism can evolve
(b) the conditions under which mechanisms favoring altruism cannot evolve
(c) both (a) and (b)
(d) neither (a) nor (b)
(a) a benefit given to a full sibling must be twice the costs to the actor for altruistic decision rules
to evolve
(b) a benefit given to a half sibling must be twice the costs to the actor for altruistic decision rules
to evolve
(c) a benefit given to a first cousin must be half the costs to the actor for altruistic decision rules
to evolve
(d) a benefit given to a first cousin must be four times the costs to the actor for altruistic decision
rules to evolve
5. The fact that only genes that code for traits that fulfill Hamilton’s rule can spread throughout the
(a) evolvability stipulation
(b) evolvability condition
(c) evolvability restraint
(d) evolvability constraint
(a) Firstborns; middleborns and lastborns
(b) Lastborns; firstborns
(c) Firstborns; middleborns
(d) Middleborns; firstborns and lastborns
(a) firstborns will be more rebellious than laterborns
(b) laterborns will be more conservative than firstborns
(c) children will inhabit different niches depending on their birth order
(d) children will compete for the same niches to signal their competitive abilities relative to their
siblings
(a) Firstborns always receive the most parental investment in families with three or more
children.
(b) Middleborns end up receiving less total parental investment even if the parents divide their
investment equally among all the children present in the household at a given time.
(c) Lastborns always receive the least parental investment if the parents divide their investment
equally among all the children present in the household at a given time.
(d) Middleborns end up receiving more total parental investment, particularly if the parents divide
their investment equally among all the children present in the household at a given time.
9. Among ground squirrels, __________ were more likely than ___________ to cooperate in mutual
(a) half brothers; full brothers
(b) full brothers; half brothers
(c) half sisters; full sisters
(d) full sisters; half sisters
(a) states that menopause evolved as a means of ceasing direct reproduction, to force women to
invest in children and then grandchildren
(b) states that grandmothers should invest more than grandfathers because of greater certainty of
genetic relatedness to their grandchildren
(c) has not been supported empirically
(d) has been empirically documented only in Western cultures
(a) kin will be classified in reference to the peripheral individual
(b) kin relationships will be arrayed on a dimension of closeness
(c) cooperation between kin will be a function of their closeness and will be linked with genetic
closeness
(d) younger members of extended kin will encourage older members to behave more altruistically
toward collateral kin
(a) younger members of extended kin will encourage elder members to behave more altruistically
toward collateral kin
(b) elder members of an extended kin family will encourage younger members to behave more
altruistically toward collateral kin
(c) kinship terms will maintain special connotation and will not be co-opted into use by non-kin
(d) people somehow know exactly how genetically related they are to other individuals, even
those they have just met
(a) inclusive fitness hypothesis
(b) predator confusion hypothesis
(c) bait-and-Switch hypothesis
(d) parental investment hypothesis
14. Of the three hypotheses that Sherman offered to explain calling in ground squirrels, the
(a) inclusive fitness hypothesis
(b) predator confusion hypothesis
(c) bait-and-switch hypothesis
(d) parental investment hypothesis
(a) prefer the scent of their father to that of their mother
(b) prefer the scent of their father to other men
(c) prefer the scent of their mother to other women
(d) prefer the scent of non-related women to that of their father
16. Which of the following is not a primitive of Doug Jones’s proposed universal grammar which governs
(a) genealogical distance
(b) group membership
(c) social rank
(d) geographical distance
17. What is the adaptive value of distinguishing between different kin members in terms of their social
(a) It provides a means for identifying individuals from whom we are likely to receive altruism
and those to whom we might channel our altruistic acts.
(b) It allows us to identify those who are more capable of giving altruism and those who are more
likely in need of altruism.
(c) both (a) and (b)
(d) neither (a) nor (b)
(a) Los Angeles women were equally likely to report helping close kin and distal kin
(b) Los Angeles women were more likely to report helping close kin than distal kin
(c) acts of helping flow from younger to older more than from older to younger
(d) Los Angeles men were less likely than women to bequeath their estate to more kin
(a) women recall more family members than men
(b) helping is greater as a function of increased genetic relatedness and decreases in the
reproductive value of the relative
(c) helping is greater as a function of increased genetic relatedness and increases in the
reproductive value of the relative
(d) women are more helpful than men
20. Burnstein and colleagues (1994) reason that helping should decrease as the genetic relatedness
(a) helping that is relatively trivial is a better test of the inclusive fitness hypothesis
(b) inclusive fitness theory is the best of competing hypotheses for differences in helping
behavior as a function of genetic relatedness
(c) no other theory besides inclusive fitness hypothesis predicts a helping gradient that follows
from the amount of genetic overlap
(d) many theories in psychology predict a helping gradient that follows from the amount of
genetic overlap
(a) one; the ten-year-olds are higher in reproductive value
(b) eighteen; ten-year-olds are lower in reproductive value
(c) forty-five; ten-year-olds are lower in reproductive value
(d) seventy-five; ten-year-olds are higher in reproductive value
22. Korchmaros and Kenny identified ____________ as a psychological mediator of helping behavior
(a) temperament
(b) agreeableness
(c) intelligence
(d) emotional closeness
(a) the person’s sex
(b) whether or not one has recently done a favor for that person
(c) frequency of contact
(d) psychological grief experienced when that person dies
(a) younger; elder
(b) female; male
(c) healthy; sickly
(d) sickly; healthy
(a) their peers compared to their kin
(b) their distant kin compared to close kin
(c) their paternal kin compared to their maternal kin
(d) their female kin compared to male kin
26. Flinn’s study of children’s cortisol levels based on household composition revealed that children
(a) nuclear family with father absent over half the time
(b) stepfather and half-siblings present
(c) stepfather
(d) single mother with other kin present
(a) People leave more of their estate to non-kin than to kin
(b) People leave more of their estate to offspring than to siblings
(c) People leave more of their estate to siblings than to offspring
(d) People leave more of their estate to brothers than to sisters
(a) use a previous spouse’s resources to attract a new mate
(b) use resources on additional offspring rather than on mutual children
(c) both (a) and (b)
(d) neither (a) nor (b)
(a) more likely than women to allocate resources to children
(b) more likely to allocate resources to children than to spouses
(c) more likely to allocate most resources to a spouse if she was of post-reproductive age
(d) more likely to allocate most resources to a spouse if she was of reproductive age
(a) decision rules exist which are byproducts of parental mechanisms designed to operate earlier
in the life of the parent
(b) humans have evolved psychological mechanisms of resource allocation
(c) evolved psychological mechanisms are sensitive to genetic relatedness
(d) evolved psychological mechanisms operate on relatively recent types of resources: those
accumulated over one’s lifetime
31. Paternal grandfathers face _________ the chance of genetic relatedness being severed when compared
(a) half
(b) three-quarters
(c) double
(d) triple
32. Based on certainty of relatedness to grandchildren, __________ should invest more than
(a) paternal grandparents; maternal grandparents
(b) maternal grandmothers; paternal grandfathers
(c) paternal grandmothers; maternal grandfathers
(d) maternal grandfathers; paternal grandmothers
(a) should follow the degree of relational certainty inherent in the different types of grandparental
relationships
(b) means that grandparents should invest more when they are consciously certain of their genetic
relatedness to grandchildren
(c) does not follow patterns predicted by an evolutionary perspective and thus requires future
work to further refine evolutionary hypotheses
(d) has changed dramatically as a result of the modern circumstance of living distally from
grandparents
34. Gaulin, McBurney and Brakeman-Wartell found that ___________ invest more than ___________.
(b) maternal aunts and uncles; paternal aunts and uncles
(c) paternal aunts and uncles; maternal aunts and uncles
(d) aunts and uncles; siblings
35. Which grandparent’s survival best predicted the survival of the grandchild, according to a study
(a) paternal grandmothers
(b) maternal grandfathers
(c) paternal grandfathers
(d) maternal grandmothers
36. Altruism toward cousins should fall into which of the following patterns, according to inclusive
fitness theory? (FaBro = father’s brother’s children; FaSis = father’s sister’s children; MoBro = mother’s
(a) MoSis > FaSis, MoBro > FaBro
(b) MoSis > FaBro > FaSis > MoBro
(c) FaSis >MoSis, FaBro > MoBro
(d) FaBro > FaSis, MoBro > MoSis
(a) familial remuneration model
(b) familial benefits model
(c) ecological benefits model
(d) ecological timing model
(a) birth order differences
(b) access to parental resources
(c) inclusive fitness theory
(d) the personality differences between siblings
(a) disgraced the family
(b) engaged in or solicited incestuous relations
(c) competed for the same woman
(d) refused to introduce him to female friends
(a) how much parental investment each parent will give to the offspring within the family
(b) how many children would be ideal for the pair
(c) how much investment grandparents make in their offspring
(d) why children do not resemble the father or his kin
(a) people use facial averageness to make kinship determinations
(b) people use facial symmetry to make kinship determinations
(c) the top half of the face is particularly important for kinship detection
(d) the bottom half of the face is particularly important for kinship detection
(a) to detect which individuals will ally together based on kinship
(b) to determine whether an individual is exploitable due to lack of nearby kin
(c) to determine whether an individual is protected by kin
(d) all of the above
43. Recent studies on the effect of genetic relatedness on helping behavior have demonstrated that
(a) individuals help relatives more than friends and mates only when the cost of the help is very high
(b) individuals help relatives more than friends and mates only when the cost of the help is very low
(c) individuals are more altruistic to non-relatives than relatives, due to fear of retribution
(d) individuals are most altruistic to relatives who are sickly or in need of much help
(a) replaces the grandmother hypothesis
(b) predicts that children will receive more care from their mother during menopause if their father is
not present
(c) proposes that menopause occurs because women tend to lose their mates, either to death or to a
younger woman, after middle age
(d) all of the above