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Chapter 7

CHAPTER 7 NOTES - Evolutionary Psych

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PSYC 3420
Irwin Silverman

CHAPTER 7: PROBLEMS OF PARENTING •Two anthropologists - Shepher and Tiger - studied 3 generations living in a Kibbutz, a total of 34,040 k people o They found that the division of labour by gender was actually greater in the kibbutz than in the rest of Israel o There were strong preferences exerted by women: over time, they began to insist that their own children live with them rather than be raised collectively by other women o So the utopian experiment of communal child rearing reverted to the primacy of the mother-child bond - a pattern seen in every human culture •From an evolutionary perspective, offspring are a sort of vehicle for their parents •They are the means by which their parents' genes may get transported to succeeding generations •Evolution, in short, should produce a rich repertoire of parental mechanisms specially adapted to caring for offspring •An important fact about parental care is that many species do not engage in it at all o Ex. Oysters - they release their sperm and eggs in the ocean, leaving their offspring adrift with not a shred of parental care •Parents who protect their young risk their own survival •Given the costs of parental care, then, it is reasonable to expect that whenever we do observe parental care in nature, the reproductive benefits must be large enough to outweigh the costs •Evolution of parental care as seen in animals: Mexican free-tailed bats o After the female gives birth, she leaves the safety and goes out to forage for food o When she returns she is faced with the problem of recognizing her own pup o If selection operated "for the good of the species" it wouldn’t matter which pup she fed o 83% of mothers actually find and feed their own pup •Each mother's evolved parental mechanisms were designed by selection to help her own genetic offspring, not the offspring of the bat species as a whole •Another example is the nesting birds •Tinberg explored why nesting birds would go to the trouble of removing the broken shells from their newly hatched chicks and laboriously take them, piece by piece far away from the nest •He has 3 hypotheses: 1. Eggshell removal served a sanitary function, keeping the nest free of germs and disease that might use the broken shells as a conduit 2. Eggshell removal protected the newly hatched chicks from the sharp edges that come with broken shells 3. Eggshell removal made these nests less noticeable to predators that might be inclined to prey on the young chicks •He found that there was only support for the third hypothesis •The cost of parental care, was outweighed by the benefits of increased survival of chicks though a decrease in predation EVOLUTION CHAPTER 7 page 1 • Selection has designed precisely such that psychological mechanisms - parental motivation designed to ensure the survival of reproductive success of the invaluable vehicles that transport an individual's genes into the next generation WHY DO MOTHERS PROVIDE MORE PARENTAL CARE THAN FATHERS? • John Alcock describes fascinating film on the hunting dogs of Africa that documented the life and hostile forces encountered by one particular dog named Solo o While the mother risked life and limb to save her pups, the father stood by passively and did nothing to protect them • Two hypotheses relevant to humans explaining the predominance of female parental care: 1. The paternity uncertainty hypothesis  From a male perspective there can always be some probability that another male has fertilized the female's eggs  This problem is strongest in species with internal female fertilizations, including: insects, humans, primates, and mammals  Males suffer tremendous costs by channeling their resources to other men's descendants  Resources devoted to a rival's children are resources taken away from one's own  Therefore, it is less advantages for males to invest their resources in parental care  Paternity uncertainty doesn't preclude the evolution of male parental care, it remains one viable cause of the tendency of females to invest more in offspring than males 2. The mating opportunity costs hypothesis  Mating opportunity costs are missed additional matings as a direct result of effort devoted to offspring  The mating opportunity costs are higher for males than for females  The reproductive success of males tends to be limited by the number of fertile females they can successfully inseminate  Therefore, males will be less likely than females to take on parental care  Male parental care should be rare when the opportunity costs of missed matings for males is high  If opportunity costs males suffer from missing matings is low, the condition would be more favourable for the evolution of parental care  Ex. Fish species  Factors explaining these individual differences:  Sex ratio: Men will be more likely to invest in children when there is a surplus of men, and less likely when there is a surplus of women  Attractiveness of the male as a short term mate: more attractive males are predicted to reduce their parental effort and increase their mating effort  Population density: large cities provide more opportunities for males to interact with females than do low-density rural areas EVOLUTION CHAPTER 7 page 2 AN EVOLUTIONARY PERSPECTIVE ON PARENTAL CARE •General rule: selection will favor adaptations for parental care - the preferential allocation of investment to one or more offspring at the expense of other forms of allocating investment - that have the effect of increasing the fitness of the parent •Parental favoritism: mechanisms of parental care will favor some offspring over another •Evolved mechanisms of parental care should be sensitive to three contexts: 1. Genetic relatedness of the offspring 2. Ability of the offspring to convert parental care into fitness 3. Alternative uses of the resources that might be available to invest in offspring GENETIC RELATEDNESS TO OFFSPRING •Study of stepparents in Ohio - only 53% if stepfathers and 25% of stepmothers claimed to have any "parental feelings" at all toward their stepchildren •Flinn found: in Trinidadian village, stepfather's interactions with their stepchildren were less frequent and more aggressive than those involving the genetic fathers and children •Parental love and resources are substantially less likely to be directed toward children by stepparents than by genetic parents •Webster's dictionary definitions of "stepmother": 1. The wife of one's father by a subsequent marriage 2. One that fails to give proper care or attention •Cross-culture summary of folk literature, depicts stepparents as villains and evil • A man has at least two sources of information to consider the likelihood that he is the father: 1. Information about his partner's sexual fidelity during the period in which she conceived 2. Perceptions of the child's resemblance to him WHO ARE BABIES SAID TO RESEMBLE? •Daly and Wilson suggested that mothers should be motivated to promote a putative father's certainty of paternity by remarking the newborn's similarity in appearance to him •Experiment: videotaped 111 U.S. births that were 5-45 minutes long, to examine these efforts made by mothers o 68 tapes contained explicit references to the baby's appearance o The mother's remarks about the resemblance to the father were 4 times as frequent (80%) as her remarks about the baby's resemblance to her (20%) •Experiment: sent out 526 questionnaires to new parents o The result of this second study confirmed the results of the first study EVOLUTION CHAPTER 7 page 3 o 81% of mothers said the baby looks more like the father, and only 19% of mothers said looked like themselves •Findings suggest that contrary to the initial indications from one study, children at ages 1, 3, and 5 do not resemble their fathers more than they resemble their mothers •Study: perception of resemblance might affect men's subsequent investment in the child o Men found the faces into which their photo had been morphed to be the most attractive and indicated that they would spend more time with this child, invest more money, and be least resentful of paying child support o In contrast, women were much less affected by the child's resemblance to themselves •Research using fMRI brain-scan technology has discovered that men show greater cortical activity than do women when shown images of children's faces that resemble their own •Men who perceive that their children do not look like them inflict more abuse on their spouses •Perception of a child's resemblance to the father might be one of the critical cues that affect both his degree of investment in the children and the magnitude of the costs he inflicts on his spouse PARENTS' INVESTMENT IN CHILDREN •Study on evaluating the effects of men's paternity uncertainty on their investment in children's college education •3 predictions were made: 1. Men will allocate more resources to their genetic children than to their stepchildren 2. Men who are uncertain about whether children are genetically their own will invest less than men who are certain the children are their own 3. Men will invest more in children when the child's mother is their current mate than they will in children from former relationships •Prediction 1 and 2 follow directly from the evolutionary theory of parental care and from the premise of genetic relatedness • Prediction 3 is based on the hypothesis that men use parental care as a form of mating effort •The researcher collected data on 3 dependent measures: 1. Whether the child received any money at all for college from the respondent (69% did) 2. The total amount of money each child received from respondent (avg. of $13,180) 3. The % of child's college expenses that were paid by respondent (avg. 44%) •Results supported all three predictions; genetic children: 1. 5.5 times more likely to receive money for college 2. Received $15,500 more for college 3. 65% of their college expenses was paid for EVOLUTION CHAPTER 7 page 4 • Study of American men, found that men with low paternity confidence spent less time with their putative children and invested less in their education • Study of French families, found that fathers of children whose faces resembled their own reported being much more "emotionally close" to them • Mother's facial resemblance was unrelated to how emotionally close they felt • Study of Dutch men found that fathers show more affection and attachment to children whose smell they can easily recognize • Facial resemblance and odor recognition are two cues men use to gauge paternity • Study of men's investment in Xhosa high school students in Cape Town, South Africa o When asked directly about their feelings, stepfathers admitted that their positive feeling were considerably weaker for their stepchildren than their natural children CHILD ABUSE AND OTHER RISKS OF NOT LIVING W/ BOTH PARENTS • Parental care may be viewed on a continuum o At one end of the extreme is self-sacrifice o At the other end of the extreme is infanticide • Daly and Wilson surveyed 841 households that included children age 17 or younger, and 99 abused children from a children's aid society • The data showed that children living with one genetic parent and one stepparent are roughly 40 times more likely to be physically abused than children living with both genetic parents CHILD HOMICIDE AS A FUNCTION OF GENETIC RELATEDNESS TO OFFSPRING • Daly and Wilson have explored the link between genetic relatedness and child homicide • The rates of child murder are far higher for stepparents than for genetic parents • The risk is highest for very young children (specially age 2 and below) • Cross-cultural data on child abuse and homicide as a function of stepparenthood are sparse SEX DIFFERNCES IN PARENTING ADAPTATIONS • The primary caretaker hypothesis: women will have evolved adaptations that increase the odds that their children will survive • One study found that females had a greater preference than males for viewing photos and silhouettes of infants • Women are better than men at recognizing infant facial expression of emotion
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