Chap 8: Problems of Kinship

What is the difference between reproductive fitness (Darwin) and Inclusive fitness (Hamilton)?

• RF: measures an individual's success in passing down genes to their own offspring

• IF: expands this to include the reproductive success of relatives sharing the same genes

According to Hamilton’s rule, what is the condition for an altruism gene to spread/evolve??

rb > c

• r: genetic relatedness

• b: benefit to recipient

• c: cost to the actor

What is genetic explanation as to why altruism at the individual level (sacrificing oneself to help others) occurs?

Genes are ‘selfish’ (to ensure and promote the survival of its own replicas in other individuals, not just in the individual organism)

What 2 aspects does kin selection include? (PA)

1. Parental care

2. Altruism towards non-descendant kin

What is another way to identify positive relatedness (i.e., r>0) other than kinship?

The green beard effect

How does the green beard effect act as an alternative to kinship?

If you have the genes of a green beard, and you see another person with a green beard, you are more likely to be altruistic towards them, even if they are non-relatives

What is the green beard an example of?

An arbitrary trait that provides no survival or reproductive benefits that can propagate if there are specific genes

What are the 3 requirements for such genes to make this happen?

1. Produces a visually perceptible trait (or feature)

2. Induce the host organism to identify this trait in others

3. Induce the host organism to help those with that feature

What is one assumption for the arbitrary traits?

They do not have any intrinsic survival or reproductive costs

Eg. (of a possible cost) potential mates finding green beard to be unattractive and reducing mating chances

What are the 4 different types of kinship r/s?

1. Parenting

2. Sibship

3. Half sibship

4. Grandparenthood

What is parenting considered as?

A “special” case of evolved kinship mechanisms (i.e., Hamilton's Rule in action)

What does sibship focus on?

Cooperation (support system) and competition (for attention, affection, inheritance etc)

Recap: what is the genetic relatedness of siblings?

0.5

According to Sulloway’s theory of birth order, what are the different “niches”/characteristics of 1st born and later born children?

• 1st borns: conservative

• Later borns (esp middle borns): rebellious

What are 2 characteristic of middle born children?

• They regard their family the least positively

• Less likely to help family member in need

What is the difference between the dynamic between half-sibs vs full-sibs?

Greater conflict between half-sibs (r = 0.25) than full subs (r = 0.5)

What is an example of inclusive fitness implications in animals?

Alarm calling in ground squirrels

What are the consequences of alarm calling?

Squirrels that call alarms are twice as likely to be killed by predators than those who stay quiet

What are 3 reasons that motivate an individual to warn others even though doing so makes it MORE vulnerable to predation? (PPI)

1. Predator confusion - gets squirrels to scatter everywhere, which helps all squirrels, including the alarm caller

2. Parental investment - saving children

3. Inclusive fitness - benefits of saving relatives outweighs cost to oneself

What is the gender difference in the frequency of alarm calling?

Higher among females than males at every age group (from juveniles to adults)

Why is that so?

Males disperse (leave home) when they become sexually mature (~2 y/o), but females remain in where they were born in → become more close to e/o (eg. mothers, sisters) → alarm call more as she would be saving her surrounding relatives

What is the trend of alarm calling like among JUST females?

It is not uniform

What is the 3 sources of evidence for that?

• Females with daughters in a group = 80% rate

• Females with mother & sisters in group, but no daughters = 80% rate

• Females with no kin or offspring in group = 20% rate

Based on this, what is the required condition for high frequency of alarm calling among females?

The presence of individuals who simply share your genes; kins, AND it doesn’t matter who (same effect for daughters/mothers/sisters)

How do primates go through kin recognition?

Use cues of early association (during infancy)

How do parents, grandparents, and aunts identify a newborn kin?

By their odour

Who is better at this?

Women is better than men

What do breastfed newborns prefer in their own mothers compared to other women?

The odour of their own mothers

Who can pre-adolescent children identify based on odour?

Their full siblings (but NOT half- or step-sibs)

What is a characteristic of kin classification systems?

They are universal

Between B & C, which condition led to the lesser and greater decline in accuracy in predicting siblings r/s?

• B (covering lower half of face): lesser decline (5%)

• C (covering upper half of face): greater decline (65%)

What does this imply?

• Upper face (eyes, eyebrows, forehead) provides the vast majority of kinship information

• Lower face contributes very little to kin recognition

In Los Angeles, who are the people more inclined to help?

Close and younger kin

How would human’s tendency to help change based on closeness & age, and how would that change for life or death (burning building) vs everyday conditions?

• Closeness: Close kin > distant kin or strangers

• Age: Young > older (*exception: >45y/o for everyday conditions)

• Both tendencies increase as the gravity of the situation increases (increases for life or death)

What is the general trend of helping toward friends vs siblings?

People gave as much as or more help to friends than to siblings

But as costs escalate, how would that change?

People would give more help to siblings than to friends, even when they report being emotionally closer to friends

What is the difference in investment received from full vs half siblings?

People received more investment from full siblings, even when half-sib were raised together and treated as full-sib by parents

What is the r/s between genetic relatedness and emotional closeness?

Positive: the more genetically related, the more emotionally close people feel

What are the 2 factors that are accounted for in the r/s above? (“regardless of…”)

• Residential proximity

• Frequency of contact

How did the cortisol levels of children living in a Caribbean village vary when they lived with:

• Both biological parents

• Single mother

• Stepfather and half-sibs or distant relative

• Both biological parents: lowest

• Single mother: higher

• Stepfather and half-sibs or distant relative: highest

Patterns of inheritance: What are the 3 categories of people we are more likely to leave wealth to?

We leave wealth to

• Kin > non-kin

• Close kin > distant kin

• Children > siblings

Why do we leave our wealth to our children instead of our siblings?

Children have higher reproductive value

What is the gender difference in distribution of inheritance/wealth?

Women distribute more widely than men

What is the gender difference in trusting the other party with their wealth?

Men trust their wives, but women don’t trust their husband

What is one possible reason for women not trusting their husband?

In the case where the woman dies, the husband is more likely to remarry and thus, divert resources away from her family

What conditions make men more likely to trust/leave money with their wives?

If she was relatively old and post-reproductive

What is grandparental uncertainty?

Grandparents differ in their certainty whether a grandchild is actually their genetic relative

How does certainty differ through the maternal vs paternal line?

• Maternal: perfect certainty

• Paternal: uncertainty compounds

Why is there perfect certainty through the maternal line?

The maternal grandmother is 100% certain her daughter is her child (she gave birth to her), and her daughter is 100% certain the baby is hers, so maternal grandmothers have 100% certainty

Why is there compounded uncertainty through the paternity line?

Paternal grandfathers cannot be 100% certain whether his son is really his, and his son also has uncertainties about his child, hence producing double uncertainty

What is the correlated investment grandkids receive from and closeness with their respective grandparents?

Grandkids receive more resources, time, knowledge (and grief) from, and feel closest to maternal grandmother, compared to paternal grandfather

What is the ranking of grandparental investment (& certainty) from most to least?

1. Maternal grandmother (MoMo)

2. Maternal grandfather (MoFa)

3. Paternal grandmother (FaMo)

4. Paternal grandfather (FaFa)

What does the results stay true regardless of?

Distance

What does maternal grandmother’s investment contribute to?

Improved survival of both the mother and grandchildren

Why do paternal grandmothers invest less than maternal grandfather?

There are higher rates of infidelity in the younger generation, which leads to paternity uncertainty on the dad side (the paternal grandmother will be more uncertain of the grandchild)

What is the investment difference by aunts & uncles?

• Matrilateral aunt > Patrilateral aunt

• Matrilateral uncle > Patrilateral uncle

What is the altruism ranking toward cousins from most to least?

1. Mother’s sister’s children

2. Mother’s brother’s children = Father’s sister’s children

3. Father’s brother’s children

What is the concrete definition of ‘family’?

Where offspring continue to live with parents into adulthood

How common is the formation of families across all bird and mammal species?

Only 3% form families

What are the 2 costs of having a family?

1. Delayed and sometimes suppressed reproduction

2. Concentrated competition for resources (eg. food, shelter, territory, mates)

According to Emlen’s theory of evolution of families, what are the 3 conditions for families to form?

1. More offspring are birthed than available (ST) reproductive vacancies

2. Offspring do not initially compete with parents for reproductive vacancies

3. Benefits of staying at home outweigh the costs (eg. resource access, skills acquisition > resource competition)

5 predictions based on this theory (no definition)

1. Under what condition will families form and break up?

• Form: when there is a shortage of reproductive vacancies

• Break up: when vacancies become available

2. What do families that control many resources end up becoming?

More stable and enduring

3. What will families help out more on with e/o as compared to groups without kin?

Rearing the young (due to kin selection)

4. What happens when a breeder (parent) is lost due to death or departure?

Family members will get into a conflict over who will fill the breeding vacancy

5. What happens if it is replaced by a breeder who is NOT genetically related to family members?

It will increase sexual aggression

What are the 3 critiques of this theory? (that are not just based on kin selection)

1. Human families stay together to win group competition (larger groups outcompete rival groups for territory, resources, and power)

2. Humans also engage in social exchange with non-kin based on reciprocal altruism

3. Postmenopausal women gain higher inclusive fitness by staying and helping grandchildren than seeking reproductive opportunities elsewhere

What are the 3 major forms of conflict within families?

1. Parental conflict (between mum & dad)

2. Parental-offspring conflict (between parents & offspring)

3. Sibling conflict (between siblings)