A number of studies have attempted to test the significance of kinship and Hamilton's rule using classic social psychology vignette or questionnaire designs (Burnstein, Crandall, & Kitayama, 1994; Kruger, 2003; Park & Schaller, 2005; Webster, 2004).
While these may not be sufficient to affect reproductive success, the fact that the costs and benefits are not merely hypothetical can be used to test the prediction that altruistic behaviour is mediated by Hamilton's rule.
If participants follow Hamilton's rule, investment (time for which the position was held) should increase with the recipient's relatedness to the participant.
Second, evolutionary theory does not consider relatedness as the only criterion for investment under Hamilton's rule.
In other words, Hamilton's rule is not limited to the peculiar cultural environment now characteristic of the post-industrialized West.
As such, they provide the first compelling experimental evidence that humans abide by Hamilton's rule when making judgments about how to behave towards others.
The first type of Hamilton's rule arises in social groups in which participants have correlated phenotypes.
The second type of Hamilton's rule arises when the fitness consequences of a phenotype can be divided into distinct components.
The two types of Hamilton's rule have coefficients described by statistical regressions.
I show that the direct fitness form of Hamilton's rule has the same logical status as FTNS: it is an exact, partial condition for change ascribed to social selection.
Queller (1992a,b) developed a framework for analyzing Hamilton's rule and comparing it with standard approaches of quantitative genetics.
This form of Hamilton's rule is an exact, partial result that applies to all selective systems, just as the partial frequency fundamental theorem is an exact, partial result with universal scope.