8. Problems of Kinship

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

• RF: measures an individual's success in passing on genes through their own offspring

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

Hamilton’s rule: What are the conditions for the spread of an altruism gene?

Altruism could evolve if:

rb > c

• r: genetic relatedness

• b: benefit to recipient

• c: cost to the actor

What is altruism at the individual level (sacrificing oneself to help others) equivalent to?

Selfishness at the gene level (promotes shared genes and not the individual organism)

What 2 things does kin selection include?

1. Parental care

2. Altruism towards non-descendant kin

Is kinship the only way of identifying positive relatedness? (i.e., r>0)

No — 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 a 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 distinctive trait

2. Induce people to notice this trait in others

3. Cause the organism to behave altruistically towards those others

What is one assumption for the arbitrary traits?

They do not have any intrinsic survival or reproductive costs

Eg. 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

Sulloway’s theory of birth order: What are the different “niches”/characteristics of children based on birth order?

• 1st borns: conservative

• Later borns (esp middle borns): rebellious

What is specific characteristic of middle borns?

They regard their family the least positively and are 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)

Example of Inclusive Fitness implications

Alarm calling in ground squirrels

What are the consequences of alarm calling?

Squirrels that call alarms are twice as likely to be killed by the predator than squirrels that stay quiet

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

1. Predator confusion - getting 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?

Females call far more 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 → therefore usually more closely related to e/o (eg. mothers, sisters), so females alarm call more as she would be saving her surrounding relatives

What is the trend of alarm calling among JUST females?

It is not uniform

What is the 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?

Have individuals in the populations who simply share your genes; kins, AND 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 the odour of the newborn kin

Who is better at this?

Women is better at this 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

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

Close and younger kin