Families and Development Flashcards
What are families?
Families are collections of individuals who share many genes by common descent
Why does Evolutionary theory predict a certain amount of conflict within families?
Each individual’s fitness inevitably conflicts to some degree with others in the family
Each individual is related more closely to himself or herself than anyone else
Because family members are not identical, they are bound to disagree to some extent
How is relatedness the basis of conflict within families?
100% to self
50% to immediate family members (assuming no step-parents)
Mother and father
Siblings (on average)
Each family member sees him/herself as more valuable than another
Parents are sources of investment and resources
This can be distributed equally or unequally
Parent-Offspring conflict revolves around the distribution of this investment
Even though parents and offspring are closely related, they are not genetically identical
There will be one distribution that maximizes mom’s genes
There will be a different distribution that maximizes each offspring’s genes
Simple case: Parental Investment
The distribution of investment between two sequential offspring of one mother
For any maternal investment, the mother has a choice
Invest in the current offspring
Ex. Weaning
Prepare her body for another pregnancy
All of the mother’s offspring will carry 50% of her genes
She will favor an equal distribution among offspring
Anytime the benefits of giving investment to a present child do not outweigh the costs of withholding for future offspring, a mother should invest in future offspring
Parent-Offspring Conflict: Offspring View
The offspring’s viewpoint is different from the mother’s
When the mother compares a child to a future child, she sees two equally valuable genetic entities
When the child makes this comparison, he/she reaches a different conclusion
100% related to himself
50% related to his siblings
In terms of spreading his genes, he is twice as good as any sibling he could ever have
Offspring should have been shaped by natural selection to devalue the costs his/her own rearing inflicts on his siblings
Sibling devaluation
Sibling devaluation is not fixed at 0.5, it is variable.
Full siblings are related 50%
Half siblings are related 25%
Half siblings will devalue each other more steeply than full siblings
Parent-offspring conflict will be more intense in mating systems that produce lots of half siblings
Parent-Offspring Conflict / universal
This conflict is universal among mammals
Babies of all species will demand nursing long after mother becomes reluctant
There is no “mutually beneficial” time for weaning to take place
Each party sees the situation differently
The offspring is active in eliciting the investment from the mother
This helps explain the regression to less mature behavior when a new baby appears
This manipulates the mother’s impression of where the offspring might be on the developmental curve
Parent-Offspring Conflict begins before birth
The mother is designed to weigh the value of investing in this particular fetus against the value of potential future fetuses
Negative maternal evaluation
Believed to explain why nearly half of all fetuses are spontaneously aborted
The fetus is more interested in its own survival than the mother
The fetus has evolved hormonal means of manipulating the mother
This provides the fetus with more resources than are in the mother’s best interests
This causes a number of different problems during pregnancy
Maternal diabetes, maternal high blood pressure
Sharing
A parent’s fitness is served by getting as many of her genes as possible into future generations
A parent is equally related to all of her children, so she should invest equally in them
Thus, parents should want their children to share more often than their children would want to
Sibling Rivalry
Children share some genes
Thus, we would expect that children would show concern for the welfare of their siblings.
Children do not share all of their genes. There will inevitably be some conflict
Sibling Rivalry: Twins
Identical twins share 100% of their genes.
One might expect that they are completely unselfish towards each other.
The occurrence of identical twins may have been too rare in human history for this unselfishness to have evolved.
There does exist some evidence that identical twins are less selfish towards each other
Neglect and Infanticide: Mother’s Evaluation
Begins in the womb and continues into childhood. The mother has a motive to evaluate each child as a vehicle for her fitness
A younger child needs more care than an older child
A sick child needs more care than a well child
Should a mother invest in a child that is so sick that it has little chance of making her a grandmother?
Should a mother invest highly in a child during a period of famine, or withhold resource until a better time?
Discriminative parental solicitude
investment in offspring that is conditional on parental resources and offspring’s relatedness, need, health, etc.
Daly and Wilson (1988)
Propose that post-partum blues and post-partum depression are mechanisms to give the mother an objective frame of mind
If the mother were euphoric at birth, she would not be able to ask herself difficult, but adaptive questions
Should I invest in this baby at this time?
In many societies, babies are not named until they are several days old. When it become certain that the are viable
Infanticide is condemned in our society, but has vestigial remains
Women who kill their babies are mostly young, poor, and unmarried
These are the exact conditions in the EEA that would predict low success in raising a child
Scheper-Hughes (1992)
Similar practices occur today, and not just in tribal societies.
Documented parental solicitude in a Brazilian shanytown.
Poverty is so high that 46% of all children die before age 5
Children seen as “little winged angel, fragile bird…”
Conflict Between Father and Mother
The degree of conflict between the father and mother depends on the father’s confidence that his mate’s children are his
Conflict Between Father and Mother: Lions
In some species it is common for the male that has taken a new female to kill all her existing dependent offspring
And sometimes all those born before the required gestation time
The incentive is to get the female to stop investing in another male’s offspring and to become pregnant with his offspring as soon as possible
Step-parent Conflict Over Investment in Children
Provides a clear case of conflict of interest
The stepparent knows for certain that the stepchild is unrelated
Different than in cases of paternal uncertainty because both women and men can become stepparents
Much research exists showing that stepparents disagree with the child’s natural parent over the optimal investment of children
Cinderella has a clear evolutionary basis
Child abuse
The standard explanation of child abuse is that child abusers learned bad parenting skills from their own parents.
This does not explain why stepchildren are at much greater risk than biological children.
Lightcap et al. (1982)
Studied families with 2 parents who each had a biological child and a stepchild.
If bad parenting was the explanation, both children should be equally abused.
Found that adults abused 12 of 21 stepchildren (57%), but 0 of 20 (0%) biological children
Daly and Wilson (1988)
Studied homicides of children.
Extreme cases of abuse.
A child living with one natural and one stepparent is as much as 100 times more likely to be killed than a child living with two natural parents!
This is an extremely strong finding
The results cannot be explained by poverty or other social factors
Perception of Paternity
Evolutionary considerations suggests that
A father should be interested in determining whether the baby is his before investing in its care
A mother should be interested in convincing a potentially investing male that the child is indeed his
Handicapped Children / Lightcap et al. (1982)
Handicapped children are abused more often than non-handicapped children.
Children with physical handicaps would have had a difficult time competing in the EEA.
Handicapped children were less likely to convert maternal investment into grandchildren.
Another example of discriminative parental solicitude that may have been adaptive for our ancestors.
Divorce
Bertzig (1989)
Looked at cross cultural data on divorce from 186 societies
Found that in every region, infidelity and infertility were the most common bases for divorce
These led by a high margin over personality differences, economic problems, problems with in-laws, etc.
These two major causes of divorce involve threats to the reproductive fitness of one or both partners
What is Childhood for?
Why do humans take such a long time to develop?
It isn’t just a matter of growing, many other animals grow to similar adult sizes very rapidly
It has been suggested that childhood allows for time to learn the many skills necessary to function in society
Linguistic skills, social skills, practical skills, etc.
Play
Children’s play changes with age
Infants’ play consists largely of manipulating single objects
Shaking rattles, banging blocks, mouthing dolls, etc.
During the second year, children begin pretend play
Feeding dolls, resting dolls with naps, driving model cars around, etc.
Suggested that play serves the purpose of giving the child practice at skills that would be necessary as an adult
For the infant, this means learning the nature of physical objects. What happens when I bang this?
Older children are learning about social relations
Immaturity
Bjorklund (1997)
Suggests that immaturity may play an adaptive role in a child’s life and development.
Some aspects of childhood are designed by evolution to adapt the child to its current environment, not its future one.
Chicks have temporary structures on their beaks called an “egg tooth” that helps it break out of its shell. It disappears soon afterwards.
Children are oblivious to how poor they are at tasks
A lack of awareness of limitations may prevent them from being discouraged
Allows children to keep attempting to learn necessary life skills
This contributes to a child’s optimism and willingness to compete
This also may be related to children’s failure to detect sarcasm
Reproductive value
the number of future children a person can be expected to produce
Reproductive value is not the same as fertility
A child has zero fertility, but high prospects for producing children in the future.
Reproductive value increases until puberty, when it then begins to decrease with age.
The older you are the fewer children you can expect in the future.
In hunter gatherer societies, reproductive value increases markedly up to about age 15
Grief for LOST Children Depends on Their Age
Maximum grief was reported for children who died at an age corresponding to the peak of reproductive value for hunter-gatherers
This pattern is consistent with conditions in the EEA, not today
The Grandmother Hypothesis
proposes that a time comes when women can further their fitness more by investing in existing kin (i.e. grandchildren) than in trying to produce more of their own children
Menopause may have evolved to switch women from investing in producing children of their own to investing in kin
This hypothesis still needs further evidence
Life History Theory (LHT)
A framework that addresses how (in the face of trade-offs) organisms should allocate time and energy to tasks and traits in ways that maximize their fitness
Optimal allocations vary across the life course
LHT concerns the evolutionary forces shaping the timing of life events involved in
Development
Growth
Reproduction
Aging- SENSES-
Individuals can enhance fitness in two primary ways
Invest in traits that affect the age/schedule of mortality
Invest in traits that affect the age/schedule of fertility
Fundamental Tradeoffs in Life History Theory- Example
A trait that
Increases fertility by increasing mating frequency (e.g. a mating display)
Reduces survival by compromising immune function or predation risk
Energy allocations to growth
Reduce fertility at younger ages
Increase fertility at older ages
Allocation to offspring viability (e.g. feeding)
Reduce one’s own survival or fertility
Increase the survival and/or fertility of offspring
Fundamental Tradeoffs in Life History Theory: 3 Broad Examples
The tradeoff between present and future reproduction
The tradeoff between quantity and quality of offspring
The tradeoff between mating effort and parenting effort
The problem of senescence / deterioration
Trade of Between Present and Future Reproduction: This tradeoff is primarily applied to understanding why we die
Antagonistic pleiotropy
genes with opposing effects on fitness at two different ages- Ex: Testosterone
e.g. a positive effect on fertility at a younger age and a negative effect on fertility at an older age
Such genes should accumulate in populations
Senescence is an inevitable byproduct of optimal allocation design
As risk of death due to difficult-to-avoid causes such as predation, accidents, and so on increases, the benefit of allocating energy and resources to the future diminishes
That energy would be wasted
Death is the price we pay to reproduce. If we spent all energy to stay alive, we would have no energy to reproduce.
Tradeoff Between Quantity and Quality of Offspring
Limited resources to invest in reproduction
A such, additional offspring must reduce average investment per offspring
Division of resources allocated to current reproduction
Increase offspring quantity, or…
Increase offspring quality
Selection should shape investment to maximize
Offspring Number x Rate of survival
Note: the optimal amount of investment per offspring is less than that required for maximal survival
Tradeoff Between Mating and Parenting Effort
As we’ve discussed, males and females differ in parental investment
Sex differences in investment are due to the differences in payoffs
Parenting (increasing offspring quality)
Mating (increasing offspring number)
When females are highly selective about mates due to greater investment in offspring
Those males who are eligible for mating can expect high future reproductive rate
This leads them to engage in mating rather than parental effort
Males who might benefit by parenting don’t get the chance because females don’t select them
children are like “public goods”
Each parent profits from any investment
Each parent has a temptation to divert resources elsewhere
This results in (an additional) conflict between the sexes
How Do People Coordinate Their Actions?
Public rituals: as social practices that generate common knowledge
Public ceremonies
Help maintain social integration and existing systems of authority
Public rallies and demonstrations
It is also about letting audience members know what other audience members know
Ritual language is often patterned and repetitive
When a person hears something repeated
Not only does he or she get the message
He or she knows it is repeated and hence knows that it is more likely that others have heard it
Group dance rituals
Allows individuals to convey meaning to each other through movement
Also, an excellent common knowledge generator
When dancing, each person knows that everyone else is paying attention
If a person were not, the pattern of movement would be immediately disrupted
coordination problems
each person wants to participate in a joint action only if others participate also
One way to coordinate is simply to communicate a message, such as “Let’s all participate.”
This wouldn’t work, though…
For the message to be successful
Each person must know about it
Each person must know that each other person knows about it
Each person must know that each other person knows that each other person knows about it, and so on…
That is, the message must be “common knowledge”
This truism is a fact of everyday life and the central focus of the lecture today
Successful communication
Not simply a matter of whether a given message is received
Also depends on whether people are aware that other people also received it
It’s not just about people’s knowledge of the message
It’s also about people knowing that other people know about it
This is the “metaknowledge” of the message
Common knowledge
Common Knowledge: Precise definition
We say that an event or fact is common knowledge among a group of people if:
Everyone knows it
Everyone knows that everyone knows it
Everyone knows that everyone knows that everyone knows it
And so on…
Situations like the acquaintance example are called “coordination problems”
Each person wants to act only if the others do also
How to create common knowledge
Eye contact
Successful communication does not simply distribute messages, but also lets each person know that other people know, and so on
Common Knowledge as an Everyday Concept
Evite- what does it work, you can see who is coming
Common knowledge is in some sense the opposite of a secret
“I told Peter first… then I told Fred… and told them not to tell anyone else or talk about it with anyone else until I did… After I talked with other people in our circles, then they did, so after a while everyone was talking with everyone else about it instead of having this big secret that everyone bottled up inside”
Signorile (1995)
Social reasons / Advertising for common knowledge
“Pleasure from a good is greater when many people want to consume it, because a person does not want to be out of step with what is popular.” (Becker, 1991)
The Super Bowl
The best common knowledge generator in the United States
Sociality- Define
the tendency for an animal to associate with other members of its species
Sociality / the comparative method
Sociality has a particular distribution across the animal kingdom
Why would an animal be or not be social?
If the costs of being social outweigh the benefits, and animal will evolve solitary habits
This cost/benefit analysis applies to individuals, not the group
The Costs of Sociality
Increased competition
Animals that avoid their fellows never have valuable resources stolen from them
Groups tend to be more conspicuous than solitary animals
The Benefits of Sociality
Groups are often better at finding resources and defending resources than solitary animals
Members of a group may be less vulnerable to predators because there are many sets of eyes and ears
Factors effecting these costs and benefits
Organism Size
Smaller organisms have more potential predators than larger animals
Large size in some species might eliminate any anti-predator benefit they might gain from being social
Patch Size
the size of a typical food patch to the nutritional needs of the species in question.
Patch size is large when it is sufficient to feed several individuals; it is small when it will feed only one
Reciprocity in Social Behavior
Reciprocity is an alternative pathway to adaptive altruistic behavior
Yinon and Dovrat (1987)
“Wrong-number technique”
The experimenter dials a phone number.
When someone answers, he says that he has dialed incorrectly, that he has no more money to make another call, and that he must get a message to his wife.
He tells a brief story of himself and his crisis
Asks the person that he has dialed to call his wife and relay the critical message
Cost, benefit, and reciprocity were systematically varied
Cost – kept the wife’s phone line busy for either 30 or 60 minutes
Benefit – some versions of the story were depicted as more urgent
Reciprocity – the fictitious profession or job the experimenter claimed in the story
Help is more likely when
The cost is low
The need is more urgent
The requestor has a high potential to reciprocate
Cheater detection
the ability to see who has undeservedly taken a benefit
It is argued that we have an evolved specialized mental ability to recognize when someone has cheated by taking a benefit when it is not entitled
Mealey, Daod, & Krage (1996)
Character stories had a significant effect on recall
Subjects remembered more faces that had been paired with the “cheater” label than faces paired with a neutral or positive label
This study demonstrates that reputation affects availability
“Ultimatum” Games
“Divide Ten Dollars”
The proposer suggests a division of the cash to a responder
If the responder accepts, each gets the specified amount
If the responder rejects the offer, both get nothing
Game theory would predict that the best strategy is to offer the minimal unit of currency
The other player should prefer $1.00 to nothing
People typically propose a five-and-five split
Why are people so “nice”?
Proposers might feel that if they offer too little, their offer will be rejected and they will end up with nothing
“dictator” game
Ultimatum” Game without the ability to reject.
Hoffman et al. (1996)
People may be relatively nice, even in dictator games because others are watching
Isolating the “reputation” influence
Perform the experiment double-blind
Anonymity consistently reduces niceness
It is also clear that many people still fail to keep all the benefits for themselves
Authors conclude that it is difficult for most people to act completely selfishly
Because people are designed to operate in a world of repeated interactions
In the real world, our reputations hang over all choices that we make
Our reputations greatly affect how others will treat us
Garret Hardin (1968)
The Tragedy of the Commons
Cheating
The herder who cheats will receive additional revenue from the sale of animals or animal products
The addition to the cheaters herd increases the total herd on the commons
This contributes to overgrazing and reduces the eventual value of every animal
The proceeds of the sale belong to him alone
The decrease in value is distributed across all of the animals Both his and his neighbors
The benefits to the cheater outweigh the costs to the cheater, so he will be inclined to increase his herd
Every rational herder is inclined to the same conclusion
Just as in the prisoner’s dilemma, when each chooses the rational alternative, each ends up worse off than if they had cooperated
Reciprocity and the Environment
What we have learned
Altruism can spread only if it is withheld from non-reciprocators
When people’s behavior is not obvious to others, cheating increases
The central problem of environmentalism
How to get people to accept initial costs in order to get eventual benefits, when others show no signs of cooperating
The best way is to adjust the costs and benefits
Companionate Love
the emotion behind close friendship and the enduring bond of marriage (the love that is neither romantic or sexual)
Friends and/or spouses feel as if they are in each other’s debt
These debts are not measured
The obligation to pay these debts is not onerous, but deeply satisfying
People feel a spontaneous pleasure in helping a friend or spouse without anticipating repayment
Of course, these favors are tabulated somewhere in the mind
If the ledger has become too lopsided, a person might call in the debt or cut off future credit (i.e. end the relationship)
The line of credit is long, the terms of repayment are forgiving
Companionate love doesn’t contradict the theory of reciprocal altruism
Embodies an elastic version in which emotional guarantors are stretched to the limit
Friends and Acquaintances
examples one delivers a benefit to someone without being altruistic in the biologists sense of incurring cost and thereby needing a repayment to make the act worthwhile
The benefits to others are simply side effects of the benefits to yourself
Symbiosis
a form of helping in nature in which two organisms associate because the side effects of each one’s lifestyle benefit the other one
friendship
The more you value the person, the more the person values you
Friendship Cheaters
Friendship (like other forms of altruism) is vulnerable to cheaters
We call them “fair-weather friends”
Sham Friends
Reap the benefits of associating with the valuable person
Mimic signs of warmth in an effort to become valued by the person
Laughing With
– The pleasure of acceptance – In-group feelings
– Bonding
Two surprising findings
– Most conventional laughter is not a response to jokes or humorous stories
– The average speaker laughs about 46 percent more often than the audience
Sex determines the proportion of speaker and audience laughter
– Women laugh more than men
– Men are the best “laugh getters”
Laughter is sexy
– Women like men who make them laugh
– Men like women who they make laugh
The Strategy of Humor
The perfect quip can give the speaker instant victory, deservedly or not
- We often feel that a clever aphorism captures a truth that would require pages to defend in any other way
Evidence for the Sexual Advertisement Hypothesis
- A woman’s interest in a male partner can be predicted by
– The number of times she joined the man in laughing
– The number of instances she laughed - The presence of a male audience is particularly strong in producing laughter in women speakers
Coordination Problems- Driving Example
“Suppose several of us are driving on the same winding two-lane roads.
– It matters little to anyone whether he drives in the left or the right lane, provided the others do likewise.
* But if some drive in the left lane and some in the right, everyone is in danger of collision.
– So each must choose whether to drive in the left lane or in the right, according to his expectations about others:
* To drive in the left lane if most or all of the others do
* To drive in the right lane if most or all of the others do (and to drive where he pleases if the others are more or less equally divided).”
Analysis of Coordination Problems
Coordination Problem
– Situations
* Of interdependent decision by two or more agents in
which coincidence of interest predominates
* In which two or more agents try to achieve uniformity of action by each doing whatever the other(s) will do
Solving Coordination Problems
People are likely to succeed through a system of concordant mutual expectations
* Examples
– I may call back because I expect you not to, while you do not
because you expect me to
– Each of us may drive on the right because he expects the rest to do so
– Each person may do his/her part because he/she expects the others to do theirs
“Want to just Netflix and chill?”
You can save face with such a statement because of a lack of common knowledge
* Doubtaboutyourtrue intentions multiplies exponentially
– Indirect speech merely provides shared individual knowledge
– Direct speech provides common knowledge
Laughter
Laughter may function as an honest signal of common knowledge
Laughter can increase or decrease cooperation
