Define Altruism

Any act that confers a benefit on the recipient of the act at some

cost to the donor

Hamilton's rule

(equation)

r B > C

where:

 B = the benefit to the recipient of the altruistic act

 C = the cost to the donor

 r = the coefficient of relatedness

Conditions for Altruism to be 

satisfied

1. altruistic behaviour should evolve only if inequality is satisfied

2. if individuals are not related (i.e. r = 0), then altruistic behaviour should not occur

3. reproductive value of the beneficiary

Define:

'reproductive value of beneficiary'

(for altruism)

age specific value of a woman having a baby at any given age.

e.g. value much less for woman after menopause than Harri 

examples of  

STUDIES of human kin-directed altruism

1. Food sharing/labour exchange

2. Inheritance bequests

(Canadian wills (Smith et al 1987))

3. Child Care Assistance

Study of inheritance bequests

- wealth increases the reproductive prospects

- Canadian wills study (Smith et al 1987)

- individuals leave more of their estate to kin and spouses than to unrelated individuals

- individuals leave more of their estate to close kin (high r) than to distant kin

- individuals leave more of their estate to their offspring than to their siblings

- male bias in bequests to children of wealthy individuals and a female bias in those to children of poorer individuals

Marshall Sahlins findings:

Kin selection and Adoption

-adoption is a human behaviour that contradicts the logic of evoluationary theory

- Pacific Islands: majority of households have at least one adopted child

'such widespread altruism towards non-kin means that evolutionary reasoning doesn't apply to contemporary humans'

Silk (1980) findings:

Kin selection and adoption

-adoptive parents are usually close kin (grandparents, aunts and uncles)

- parents give up children when they can't afford to raise them (and rarely give up 1st born)

- adoptive parents usually have no dependent children, and are sometimes wealthy

- natural parents are:

often reluctant

maintain contact, terminate aggreement if necessary

prefer wealthy adoptive parents

General pattern:

- natural parents act in way that enhances the health, security + welfare of children.

- care preferentially delegated to close kin

therefore:

consistent with evolutionary predictions:

adoption = regulate family size + enhance quality of care.

observations on discriminative parental solicitude

(Daly & Wilson, 1988)

-adoptive children discriminated against within the family in the distribution of parental wealth

- adoptive children receive less resources than natural children

- risk of infanticide as a function of living with two biological parents vs step parents