Hamilton's inclusive fitness maintains heritable altruism polymorphism through rb = c

Abstract

How can altruism evolve or be maintained in a selfish world? Hamilton's rule shows that the former process will occur when > -the benefits to the recipients of an altruistic act, weighted by the relatedness between the social partners , exceed the costs to the altruists-drives altruistic genotypes spreading against nonaltruistic ones. From this rule, we infer that altruistic genotypes will persist in a population by forming a stable heritable polymorphism with nonaltruistic genotypes if = makes inclusive fitness of the two morphs equal. We test this prediction using the data of 12 years of study on a cooperatively breeding bird, the Tibetan ground tit , where helping is performed by males only and kin-directed. Individual variation in ever acting as a helper was heritable ( = 0.47), and the resultant altruism polymorphism remained stable as indicated by low-level annual fluctuation of the percentage of helpers among all adult males (24-28%). Helpers' indirect fitness gains from increased lifetime reproductive success of related breeders statistically fully compensated for their lifetime direct fitness losses, suggesting that = holds. While our work provides a fundamental support for Hamilton's idea, it highlights the equivalent inclusive fitness returns to altruists and nonaltruists mediated by = as a theoretically and realistically important mechanism to maintain social polymorphism.

Hamilton's rule is essential but insufficient for understanding monogamy's role in social evolution

“…Consistent with the equation's predictions, phylogenetically controlled comparative analyses implicate monogamy, or at least reduced promiscuity, as the most probable ancestral states across social Hymenoptera, cooperatively breeding birds, and social mammals [3,4,8]. Also, some studies that attempted to measure the inclusive fitness of helpers found that Hamilton's condition for advantageous helping is met [13,14]. Indeed, the apparent necessity that the evolution of both facultative and obligate sterility must pass through a ‘monogamy window' was presented as a clear refutation of NTW [15].…”

Disentangling principled and opportunistic motives for reacting to injustice: A genetically-informed exploration of justice sensitivity

“…This addresses the general theoretical question of whether moral character and values are distinct from the temperament and action tendencies which personality inventories typically tap (Cawley III, Martin, & Johnson, 2000). Also important to analyse is whether any such distinct, heritable strategies for principled versus opportunistic justice sensitivity share common genetic substrates with other psychological traits that serve to sustain cooperation for the greater common good-such as altruism (Rushton et al, 1986;Wang & Lu, 2018) and trust (e.g., Cesarini et al, 2008)-versus serve to maximize adaptive fitness gains over others, such as social dominance and the monopolization of territory and resources (Kleppestø et al, 2019). This possibility can be tested with our genetically informative sample.…”

Can Hamilton’s rule be violated?

“…A study that does look at polymorphisms is Wang and Lu (2018) . In this study, players have one of two different roles; there are breeding pairs, which are the potential recipients of help, and potential helpers.…”