The purpose of this series of commentaries is to celebrate long-forgotten or underappreciated articles from the archive. So it feels a little odd to be providing an appreciation of W. D. Hamilton’s 1963 work “The Evolution of Altruistic Behavior,” which the Web of Knowledge suggests has been cited more than 700 times. By Hamilton’s standards, however, that does constitute obscurity. And, in particular, these citations are dwarfed by those of his monumental article “The Genetical Evolution of Social Behaviour” (Journal of Theoretical Biology 7:1–52), published a year later, by nearly 20 to 1. Some of this imbalance is warranted, as the latter article covers much of the same ground in more detail and makes a number of additional contributions. But Hamilton’s “little-read first paper” (W. D. Hamilton, 1996, Narrow Roads of Gene Land, Volume 1: Evolution of Social Behaviour, Oxford University Press, Oxford, p. 5) manages, in barely more than two pages of text, to cover the core principles of inclusive fitness theory. So I believe it deserves a second look.

Intragenomic conflict may arise when social partners are more related through one parent than the other—for example, owing to individuals or gametes of one sex dispersing further prior to fertilization. In particular, genes originating from the former parent are favored to promote selflessness, and those originating from the latter parent are favored to promote selfishness. While the impact of patterns of dispersal on the evolution of intragenomic conflict has received recent attention, the consequences of intragenomic conflict for the evolution of dispersal remain to be explored. We suggest that if the evolution of dispersal is driven at least in part by kin selection, differential relatedness of social partners via their mothers versus their fathers may lead to an intragenomic conflict, with maternal-origin genes and paternal-origin genes favoring different rates of dispersal. As an illustration, we extend a classic model of the evolution of dispersal to explore how intragenomic conflict may arise between an individual’s maternal-origin and paternal-origin genes over whether that individual should disperse in order to ease kin competition. Our analysis reveals extensive potential for intragenomic conflict over dispersal and predicts that genes underpinning dispersal phenotypes may exhibit parent-of-origin-specific expression, which may facilitate their discovery.

Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.