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If we accept hamilton's rule then what would we expect?

If we accept Hamilton’s rule (1964) then we would expect humans to behave more altruistically to related relatives than to unrelated individuals.


what is Hamilton's rule?

rB>C where r is relatedness B is benefit and c is cost

You should offer to help someone when the cost to own reproductive success is less than the benefit to the other persons RS multiplied by their relatedness to you


what year is Hamilton's rule?



give examples of Hamilton's rule being shown in experiments but what are the issues with these?

• Fire at vacation complex, search for family before friends (Sime1983)

• This is biased towards younger relatives (Want, 1996; risk all family vs 2 older/ younger relatives)- tell people can absolutely save to relatives or 50/50 and save all- if you offer people two younger relatives they will take the guaranteed- if you offer grandparents they wont take the guarantee. Children have greater Reproductive potential so more inclusive fitness for the individual.

• Live organ donation (kidney, bone marrow) higher to kin (Borgida et al., 1992)

Problems with these three studies:
• Fire vignette lacks ecological validity- would people acc walk away from grandparents in fire
• All three deal with major, life-threatening situations


past life and death situs how to we need to consider Kinship

In daily cooperation- we are a very cooperative pro-social species so why are humans like this


farming and kinship study

Berte (1988) K’ekchi’ of Belize - Subsistence farmers Planting and harvest require cooperative labour- can’t run a farm on own- so have to get other people to help you out and in exchange you may help them back -69.3% of labour exchanges took place between related households
Men most closely related to other villages had sig higher RS- is not just that can see


food sharing and kinship study

Betzig and Turke (1986) found that on the Pacific atoll, food sharing was most common between close relatives.


Relatives care for children kinship study

Among Ye’kwana (smith et al., 1987), and Black communities in the USA (Burton 1990) amongst others e..g Efe pygmies and Hungarian Gypsies- relatives are sig more willing to provide care for another woman’s child than are unrelated individuals if they had no children themselves.


help for women and kinship study

McGuire et al (1985) 300 LA women found that close relatives were more likely to be sources of help during times of need than unrelated individuals and, in addition such help was more likely to be on a strictly reciprocal basis if it was between friends.


families staying together and kinship

Effects extend to grouping patterns e.g. study of fission in Amish church Hurd (1985) showed that closely related individuals tend to stay toether and Morgan (1979) showed that Inuit whaling crews have very high coefficients of relatedness.


e.g.s of kinship in more day to day and what do these tell us?

-labour services
-food sharing
-help to women
-family grouping patterns
-axe fighting

So.. very clear patterns across number of small scale societies that people are more willing to put themselves out and even take life and death risks for those who are more closely related to them.


axe fighting and kinship study

• Yanomamȍ
o Quite a violent society- women snatching to be an extra wife is quite common
o When violence erupts- side taking in axe fight predicted by relatedness- who you are willing to risk life on a semi-day to day basis for (Chagnon & Bugos, 1979)


what is the flaw with the range of kin cooperation studies?

as impressive as this range of examples may be, however, they offer only circumstantial evidence for kin-bias because they are all based on observational data… need experimental data


experimental data for kin selection

Fieldman et al., 2007
Subjects were asked to perform an isometric skiing exercise in return for a cash reward. The length of time a participant maintained the position on a given trial was transformed into a material benefit for a recipient, who varied in biological relatedness to the participant.
The length of time subjects were prepared to sustain the pain was directly related to the recipient’s relatedness to the subject.
These effects were shown to be independent of the order of the trials, the subject’s assessment of the recipient’s financial need, the subject’s perceived affection for the recipient and the amount of time they had spend together during the previous year. Thus, research seemed to be driven only by the recipient’s relatedness.


what is the issue with Hamilton's rule in real life situs?

kin selection is not always what we see- this is the case with reproductive value and kin selection and then again with adoption (and fostering), step-siblings. These have caused us to somewhat reconsider the assertions of Hamilton's rule.


Introduction to reproductive value and kin selection

Despite the central importance of kinship, simple genetic relatedness will not be the sole determinant of behaviour. For one thing, Hamilton’s rule quite explicitly implies that organisms should be altruistic towards non-relatives (and unhelpful towards relatives) whenever they gain higher inclusive fitness by doing so


what has been pointed out and by who about value and kin selection

Hughes (1988) has pointed out that conventional arguments about relatedness invariably assume that all individuals of the same degree of relatedness are equally valuable from an evolutionary point of view. In fact, when the point of the exercise is to maximise fitness (one’s genetic contribution to the next generation) they are not all equally valuable.
Parents who are post-reproductive may be less valuable than children who are in their prime reproductive years.


what did Hughes argue about relatedness and whose concept did he use

Hughes argued that he coefficient of relatedness should be adjusted for the individual’s reproductive value. A concept developed by Fischer 1930 it is a measure of an individual’s age specific future likelihood of producing offspring, relative to the average for a population as a whole. E.g. in women this peaks in early 20s and then declines.


fieldwork study supporting the idea of reproductive value and kin selection

• Hughes (1988)
o Reviewed case-study literature on fissioning in family/ social groups- human groups will grow to a certain size and then becomes unwieldly so splits – can happen in families or communities.
o Would expect people to go with those most related to them but there were frequent examples of groupings not being explained entirely by r..
o E.g Rapan household (Hanson, 1970)- one female much more closely related to household B but moved with household A- Hughes asked why she would do that as opposed to close relatives. Hughes argued had to think about focal offspring, i.e. children in which the reproductive interest of a number of individuals is concentrated. If look at total relatedness then ‘wrong group’ but if limit relatedness to children she was more related to children in household A.
o Focal offspring – children in whom a number of less related adults all share reproductive interest.

o East Tennessee mountain communities (Bryant, 1981) split more logically by focal offspring than by patriline and surname.
o Garia of New Guinea conflict side taking- worked better thinking about children rather than patriline/ matriline (Lawrence, 1984)


what is an affine

Affines- people related by marriage but not those directly related


who tried to quantify reproductive potential and what did they propose?

Dyble et al. 2018
Essentially tried to quantify this- coefficient of shared reproductive interest – about trying to quantify the degree to which someone is important to your inclusive fitness.
Sb> C i.e. should cooperate where the benefit to the other person x their shared reproductive interest to you is greater than the cost to you.
Shared reproductive interest=calculated based on your relatedness to target individuals children based on your relatedness to them and your relatedness to their partner divided by your relatedness to your children (modulated by how related you are to spouse) but generally 0.5.


what would the cooperation coefficient be for a niece?

cooperating with a niece- relatedness is 0.25 as is siblings child relatedness to own child is 0.5 so S (shared reproductive interest)= 0.25/0.5= .5


what should be noted about affines?

Affinal benefit is asymmetrical- e.g. can have an interest in offspring of a brothers wife as these share relatedness with self- but she in return has no shared relatedness to your own children- so it doesn’t work vice versa.


aside from affines where else can reproductive value be seen?

In kinship and age of individuals


experimental support for age and reproductive value of kinship

• Wang (1996)- subjects were asked which of two alterative medical treatments they would prefer to treat six members of their family who had (hypothetically) fatal diseases. One possible treatment was deterministic and ensured the survival of 1/3rd of patients (either two youngest or two oldest) the alternative was probabilistic in nature with a 1/3 prob that all would be saved.
• Young teenagers preferred the probabilistic outcome over deterministic
• Middle-aged preferred the deterministic but only when it saved two youngest not two oldest
• Wang explained this by pointing out that the inclusive fitness of individuals who are themselves middle-aged is unlikely to be enhanced by the activity of relatives who are even older, whereas their younger relatives would be expected to contribute substantially with their reproductive lives ahead of them. Teenage subjects on the other hand can expect their inclusive fitness to be enhanced by all their relatives at that particular stage in their lives, and they need show no particular preference for one generation over the other.


real world support for age and reproductive value of kinship

McGuire et al., (1985) showed that investment tended to flow from older to younger kin in their study of 300 LA women.


who suggested what about grandparents in terms of reproductive fitness and kin selection?

Hames (1988) and Hill and Hurtado (1997) suggested that grandparents should vary the level of solicitude toward grandchildren according to the sex of the offspring they were helping. Thus, since females put more effort into rearing rather than mating, one should expect maternal grandparents to be more solicitous than paternal grandparents, since this is the best way to enhance their daughter’s RS. This tendency will then be exacerbated by considerations of paternity certainty. In humans maternity is always certain, but paternity is not. Consequently, the degree of parental solicitude towards a son’s offspring is expected to vary with the degree of paternity certainty a man has.


evidence about grandparents aiding daughters more

Euler and Wietzel (1996) found that paternal grandparents provided less care than maternal grandparents, and that paternal grandfathers showed the least care of all (perhaps because not only could the grandchild not be a relation but neither may be the child). Maternal grandmothers provided the most care, the mother has the highest related degree of genetic certainty to the child in question.


what is it important to remember about studies where reproductive success is added

Important to remember that this is still just inclusive fitness just looking at cooperation at the parent level as opposed to the offspring level. Tells us interesting thing but is just a re-evaluation of relatedness- people act as a proxy (ie. sister in law) to relatedness with nieces and nephews. Still overall looks at relatedness


what acts against Dyble's theory (aka reproductive ability) of kin

Adoption and step siblings Glaringly against even Dyble’s theory because is not own children