Madsen et al (2007)

PPS

- A group of Oxford (Western) university students - Two Zulu populations (males only) from South Africa (Non-Western) - Both communities were characterised by extreme poverty

Strengths

- Cross-cultural = multiple cultures display the same behaviours, that are predicted by the kin selection hypothesis, giving it more validity and making the study more inclusive - The experimental method was used, rather than self-reports or correlational studies - Well operationalised variables (cost and genetic relation are both objectively measurable)

Limitations

- Ethical issue = deception was used - While both genders were included in the Western-based study, the Zulu population trials only had males - Confounding variable = parents and siblings were both included in the same category (according to evolutionary psychobiology, youth is what is more important when passing on one's genes)

Aim

- To investigate the hypothesis that an individual will bear more pain for those more closely related to them - To investigate to what extent kin-biased altruism is a culturally-specific phenomenon

Procedure

PPS were asked to provide a list of individuals with varying genetic closeness to them (eg. siblings, parents, cousins, grandparents etc) PPS were told that they would perform a costly (pain) task in order to gain a reward to give to a relative of theirs. Which relative was told the PPS in advance. PPS were asked to to a wall sit, where their backs leaned against a wall and their thighs were parallel to the ground. After some time this position becomes increasingly painful. The PPS were asked to hold this position as long as possible, but they could stop at any time. The recipients of the reward (food baskets for the Zulu populations and food for the London pps) were randomly chosen from a list of 4 categories: 1. the PP themselves (a genetic relatedness value of 1) 2. Their sibling or parent (value of 0.5 - amounts to the degree of genetic relatedness) 3. a grandparent, uncle, aunt, niece, nephew (0.25) 4. cousin (0.125) The PPS did the experiment for each of the categories, but counterbalancing was used to allocate the order of conditions. All trials took place on the same day for the Zulu pps. The London trials lasted over the course of 4 days After the trial, the reward for the receiver was sent or given to the PP, based on the time spent in the wall sit.

Linking back

Study demonstrates support for the kin selection hypothesis: - The more closely one is related to someone, the more cost one will endure for that person - Biological kinship therefore plays a role in behaviour

Background

The Kin Selection Hypothesis: Proposed by Hamilton in 1964. The Kin Selection Hypothesis is an evolutionary explanation for the occurrence of prosocial behaviour. It characterizes helping behaviour as directed at increasing the reproductive chances of genetically related individuals. Evolution is the process by which the individuals with characteristics most suited to the environment are more likely to survive to reproduce to pass on their genes. As these individuals produce, their traits survive as outlined by the process of natural selection. There are two types of fitness when discussing natural selection: Direct fitness: An individual's ability of survival / An individual's survival chances Indirect fitness: An individual's relatives' chances of survival The theory states that natural selection works on the level of the gene, not the organism. Survival of one's genes is the most important aspect to an organism's life, and it can do this by reproducing, but also as the theory states, by protecting and acting prosocially towards those that share parts of its genetic makeup. So that even if the individual dies, especially in sacrifice for the group, it's genes still survive and are carried onto the next generation. Inclusive fitness is the total surviving genes of the organism, both offspring and relatives (sum of the direct and indirect fitness) Therefore, organisms are most likely to help those with whom they share the most genes, namely their offspring and relatives. Organisms will also take more costly actions for their relatives.

Results

The cost PP imposed on themselves (how long they sat in the wall sit position) was proportional to the degree of genetic relatedness of the receiver. - The closer the relationship, the longer they held the position. - The Zulu population helped their cousins to the same degree as their brothers.