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Chapter 13

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University of Guelph
PSYC 3100
Hank Davis

Chapter 13: Families and Development It Takes A Village to Raise A Child  Parents are generally only the leading actors in a family drama with a large supporting cast  The people our ancestors knew and interacted with the most were Kin, who shared a fitness interest in them and their children  Two types of altruism: o Reciprocal altruism (see chapter 7) o Kin Selection  W.D Hamilton: Genes have two routes to the next generation, direct and indirect  Direct: gene somehow makes its surrounding body more fit is more likely to be copied than one that doesn’t o Its fundamental problem is that it makes the surrounding body less fit  Indirect: altruism gene can be passed to the next generation by having one person induce altruism and aim the benefits to another person who carries the same gene due to common ancestry o If the fitness lost to the altruist is low enough and the fitness benefit to the recipient was high enough there is a net benefit for the gene o Biologists use the phrase Kin Selection to refer to this idea o This theory is used because kin carry many identical genes from common ancestry o (all humans have identical genotypes at 2/3 of their loci, which cancel out A Formal Model of Kin Selection: Hamilton’s Rule  In any encounter there is an altruist (who gets a cost) and a recipient (who gets the benefit) o Size of cost is C o Size of benefit is B o Probability that two people share a gene by virtue of their sharing a common ancestor  This is R, the Coefficient of Relatedness  This is a fraction between 0-1 o Hamilton’s rule: A gene will spread if it induces altruistic behaviour when: rb>c  The term on the left, rb, has to be greater than the cost to the altruist  The product term is simply the benefit to the recipient multiplied by the probability that the recipient also carries the gene  Kin selected genes should induce altruism whenever the benefit devalued by the degree of relatedness outweighs the cost (when rb>c) Can Animals Do Algebra  Selection is pragmatic: it gets the job done  Selection provides animals with rules of thumb: a simple, pragmatic way of solving a complex problem o B must always be largely greater than C since R is always less than one  Examples: I have $5 million in the bank, you’re starving. Me giving you $5 is trivial to me, but life-saving to you (c is very small, b is very large) o Animals can identify who is related, or Kin, by observing behaviours or by scent patterns given off by others of their species What Is A Family  Steven Emlen: a family is a group in which there is continuous interaction between sexually mature offspring and their parents o When the offspring stick around their natal home instead of seeking their fortune: it’s a family What Keeps Families Together  Families will be unstable, disintegrating when individuals can further their fitness better by forming their own families o Reasoning is families form only when individuals delay their own reproductive efforts in favour of supporting those of relatives  Families with access to many resources will be more stable than poorer families Are Human Families Similar to Animal Families  Parallel effects occur in human families o During good times, children leave and marry. During bad times children remain at home  Decisions are sensitive to expected reproductive consequences and not just economic ones o Example: people who immigrate to another country had a much higher probability of marrying, but their standard of living was often lower than the one they left behind Evolutionary Theory Predicts Conflict Within Families  Traditional psychology describes families as either functional (harmonious) or dysfunctional (exhibit internal conflict) o We are related to ourselves 100%, our parents and siblings 50%  This is the basis for sibling rivalry, we see ourselves as twice as valuable genetically as we are 100% likely to pass our genes on and they are only 50% likely Parent-Offspring Conflict  Trivers analyzed parent-offspring conflict o A mother is a source of effort and resources (investments) that can be distributed among offspring o Conflict often revolves around optimal distribution of the investment  Should a mother devote all her investments towards one child, or should she invest in her other (or future) offspring  All her children are equally valuable as they all have the same chance to pass on her genes  To the children, they are twice as valuable than the other siblings so they deserve more of the resources  This is because we have 100% chance of passing on our genes, we don’t see it as 50% chance of passing on our mothers genes  This occurs for every single child: A sees itself as twice as valuable as B, B sees itself as twice as valuable as A, but mom sees them as equally valuable o This level of conflict increases when half-siblings are added into the mix  This is universal among all mammals  This also explains why children tend to become more immature and needy when a new baby arrives in the family o The mother wont wean an insufficiently mature child  This conflict begins before birth, the fetuses has hormonal ways of manipulation to obtain more resources from the mother than is good for the mother to give to the baby  This results in maternal diabetes and maternal high blood pressure Sibling Rivalry  This is the same mechanism as parent-offspring conflict o We see ourselves as better than our siblings so we believe we should get more resources o Studies have shown that identical twins are less selfish to each other than fraternal twins  This is because identical twins carry the same genetic make-up  We would have expected this selfishness to be nonexistent as these twins are genetically identical  The reason this is not nonexistent is because twins are so rare, we have not evolved to recognize twins as identical genetically, but we do recognize them as close kin (perceived similarity) Why Parents Teach Their Children to Share  Its in the parents best interests for their children to share and be nice to each other, this insures the greatest chance for grandchildren  Also be nice to cousins when they can be nice back (when the benefit exceeds twice the cost to the offspring)  Furthermore, we should be nice to nonrelatives if there is any likelihood that they can/will retaliate  Parents are designed to enforce altruism to advance their own interests (not purely for altruism’s sake) o The fact that children and parents have different interests inevitably leads to conflict o Harmony is not to be expected, it is expected that parents will enforce their own self-interests (which they like to call harmony) Neglect and Infanticide  Remember naturalistic fallacy (chapter 1)  Discriminative Parental Solicitude: investment in offspring that is conditional on parental resources and offspring’s relatedness, need, health etc.... o Should a mother invest in a child who is very unlikely to make her a grandmother?  In many societies babies are not named for several days once it becomes apparent that it is viable (will survive and worth the investment) o Daly & Wilson: postpartum blues and depression is part of a mechanism to allow mothers to objectively evaluate whether the child is worth keeping or not o Infanticide may be condemned in our society but examples of it still remain throughout the world Conflict Between Father and Mother  The level of conflict between father and mother depends on the fathers confidence that the children are his  If he is sure the children are not his, the father will either minimize the resources the mother will give the children, or he will invest in the children to win her affection and have children of his own  In some species, when a male takes a new female he kills all her existing dependant offspring o This is especially true of cats (including the common house cat)  This is due to the incentive for the female to stop raising other offspring and bare the male’s children ASAP  Sibling rivalry increases when paternal confidence is low because: o The less certain the father is of his paternity, the less interest he has in seeing the children receive resources, thus less interested in enforcing harmony o If the children are related by .25 instead of .5 (half siblings) they will want to share only when the benefit to the sibling is 4X the cost to themselves Stepparent Conflict over Investment in Children  The logic of this conflict is identical to the problem of paternal uncertainty with one important difference: women and men can become step parents  Human stepparents disagree with the child’s natural parent over the optimal investment in children  In a study done, 57% of stepchildren were abused while 0% of biological children were abused o Each family consisted of 2 parents who had a biological child and was a stepparent to the spouse’s child o Example: dad was father to son, stepfather to daughte
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