My Touchstone Puzzles. W.D. Hamilton’s Work on Social Wasps in the 1960s
Detailed data without concepts have little significance; and concepts without information can become vacuous fantasies.
So, there has to be a continuous interweaving of fact and theory, both within a discipline and in the mind of individual scientists
W.D. Hamilton, one of the most influential evolutionary biologists of the twentieth century, was fascinated and puzzled by social wasps. Towards the end of his academic career, Hamilton openly admitted that: “... it was to social life that wasps were providing my touchstone puzzles” (Hamilton 1996, vi). This article deals with Hamilton’s attempts to understand social life in wasps mostly in the 1960s. First, it provides an overview of the reasons why Hamilton thought social wasps constituted a puzzle. Second, it shows how Hamilton tried to deal with this puzzle, by performing experiments, conducting observations and eventually modifying his theory by including factors, most notably inbreeding, that he had not clearly considered in its first formulation.
In The Genetical Evolution of Social Behavior I & II, Hamilton presented his theory of inclusive fitness addressing how genetic relatedness of individuals in a population affects the evolution of social behaviors (Hamilton 1964a, b). According to Hamilton, inclusive fitness theory was “applicable to social behavior under relatedness for any group in the living world” (Hamilton 1996, 20). The 1964 article is divided in two main parts. In Part I, Hamilton presented the “genetical mathematical model” of inclusive fitness theory (Hamilton 1964b, 2), which “allows for interactions between relatives on one another’s fitness” (Hamilton 1964a, 1). Part II shows how the model applies to concrete biological cases and presents a wide variety of behaviors ranging from warning behaviors to parental care and parasitism
G. Caniglia (*)
© Springer International Publishing AG 2017
F. Stadler (ed.), Integrated History and Philosophy of Science, Vienna Circle Institute Yearbook 20, DOI 10.1007/978-3-319-53258-5_3
(Hamilton 1964b). With these examples, Hamilton attempted to discuss “whether there is evidence that it [the theory] does work effectively in nature” (1964b, 17).
Altruistic behaviors, say those behaviors that are costly to the individuals performing them and beneficial to the ones receiving them, do not give the actor of the behavior advantages in terms of fitness. On the contrary, they lower their fitness. Therefore, altruistic behaviors pose a special challenge for evolutionary explanations of social life (Hamilton 1963). Hamilton asked under what conditions can the genes underpinning such behaviors spread in a population (Hamilton 1963, 1964a). The theory of inclusive fitness, if applied to the evolution of biological altruism, describes the conditions favoring the increase in frequency of a gene with altruistic effects in a population. According to this theory, altruistic behaviors can actually spread, if the benefits of such behaviors fall on individuals who are genetically related to the actor of the behavior rather than on random members of a population (Hamilton 1963).
An important case of biological altruism is represented by the self-sacrificing behaviors of workers in colonies of social insects of the order Hymenoptera, wasps, ants and bees (Hamilton 1963). In Hymenoptera, workers give up their reproductive capacities in favor of one or few individuals that are able to reproduce (Hamilton 1963). In Part II, Hamilton famously presented a hypothesis about how inclusive fitness might apply to the special case of social Hymenoptera, characterized by the unusual sex determination mechanism called haplodiploidy. This hypothesis became famously known as the haploidiploidy hypothesis In dealing with altruism in Hymenoptera, Hamilton paid special attention to “cases which appear anomalous” (Hamilton 1964b, 17) and are not easily explained by the haplodiploidy hypothesis. Both primitively and highly social species of wasps showed two kinds of anomalous and puzzling behaviors (Hamilton 1964b). First, they contain multiple egg-laying queens. This phenomenon is usually known as polygyny, or pleometrosis. Second, they mate multiple times with different males. This phenomenon is usually known as polyandry. Both polyandry and polygyny tend to lower the relatedness of the individuals in a colony and, in doing so, pose serious challenges to explanations in terms of inclusive fitness (Hamilton 1964b).
Already in 1964, Hamilton surmised that inbreeding might play a central role in explaining wasps puzzling behaviors. He also hypothesized that inbreeding depends on the high viscosity of wasp populations in temperate climates, but above all in the tropics (Hamilton 1964b). Yet, only in the paper Altruism and Related Phenomena mostly in Social Insects (Hamilton 1972), after observing and experimenting on many wasp colonies during two trips to South America in 1963-1964 and in 1968-1969 and many conversations with scholars of wasps and evolutionary biologists, Hamilton updated the mathematical model of inclusive fitness presented in 1964, reassessed the value of his haplodiploidy hypothesis and newly discussed the puzzling behavior of wasp societies in the light of these ideas (Hamilton 1972; Segerstrale 2013). Yet, even with these adjustments, Hamilton was not able to solve the puzzle posed to his theory by polygyny and polyandry (Hamilton 1972).
This paper, first, briefly presents Hamilton’s inclusive fitness theory as well as how it applies to the case of Hymenoptera with their special sex determination mechanisms. After focusing on the reasons and context of Hamilton’s trip to South America, it explains why polygyny and polyandry make wasp societies a puzzle, or even an anomaly, for Hamilton’s haplodiploidy hypothesis. Then, it gives an overview of how Hamilton addressed this puzzle both in his observations and experiments during his trips to Brazil as well as by reassessing his mathematical model of inclusive fitness theory in the 1972 paper. Finally, it concludes by presenting Hamilton’s reflections about the puzzle again in 1972.