What motivates animals: indeed what motivates humans? There is no shortage of ideas either for higher animals or humans, nor are there insufficient observations to test them. What is often missing is the filtering of those ideas to exclude hypotheses that do not fit the data.
Why kin selection misses its mark. This theory accounts for altruistic donation of benefits from one individual to another by arguing that it must be confined to relatives in such a way that it does not diminish the transmission of the genes of the donor to subsequent generations. This has been further generalised, although by what reasoning I do not know, to extend the requirement for kinship to all colonies, even in species in which no altruistic exchanges occur.
Theorists of animal behavior segregate explanations into the two categories of proximate (mechanistic) causes versus ultimate effects. The latter must adhere to the Darwinian prescription for survival of the fittest. A unique feature of kin selection is that it addresses animal behavior directly in the terms of fitness without an intervening proximate mechanism so that both components are subsumed within a single doctrine. While this may be acceptable, it opens the opportunity for the insertion of a separate mechanistic cause into the hypothesis. Kin selection complies poorly with experimental observations, though the failures are often obscured by the tendency of proponents to introduce ad hoc variations into the theory.
Why social animals like each other. Maybe the reason that kin selection has retained its luster is because alternative mechanisms have proved even less tractable. In “The Social Gene” I present the case that there is another explanation, of the greatest simplicity, for how animals, including humans, interact – that social animals have a social gene. This takes the form of a pleasurable response of one animal to being close to another. Although pleasure is part of the makeup of social vertebrates, I prefer to use the term ‘reward’, which I have defined as any sensation that an animal experiences that causes it to retain or extend it; the converse is a ‘penalty’.
This gene of a ‘proximity reward’ may be expected to have properties that vary between different species. One of these is a tendency to increase with the degree of familiarity between the two animals which can explain, without invoking the hypothesis of kin selection, why they frequently give preference to relatives whom they have known throughout their lives. Familiarity may likewise reveal an incompatibility with individuals who detest each other.
Why primates groom each other. A second parameter of the reward of proximity is that it may be exchanged for other rewards, which allow animals to parlay the pleasure of company for other gifts. Humans in particular regularly rely on friends both for help and for camaraderie. I will use the example of grooming to illustrate how ‘selfish’ compares with ‘social’ in accounting for this activity.
Primates routinely undertake the chore of removing harmful ticks and lice from the inaccessible back and neck of an associate. John Maynard Smith analyzed the kind of decisions that would allow it by first postulating a population of altruists who were willing to donate time for the activity. However, animals with a gene for selfishness would refuse the chore, overwhelm the group and cause a plague of the parasites. This in turn would be opposed by a gene for reciprocators who would only groom altruistic individuals so that a new equilibrium would be reached that allowed a renewed degree of grooming. This is a complex idea that seems to justify the stability of self interest in animal interactions.
The social gene version simply removes the description of the word ‘chore’ from the evaluation of this activity on the grounds that the donor of the service is also enjoying the reward of extreme proximity and anecdotal evidence exists that the animals do indeed continue it beyond the time when most parasites have been removed. This property can account for many other activities of animals including dispersal and adoption that are inadequately discussed in the context of kin selection.
Why the genders segregate outside the mating season. I will now explore another potential facet of sociality, that it may be influenced by hormones. Most social animals that only mate once a year, also separate into two herds outside the rut. These are the female nursery group and the bachelor group of males. Studies have shown that animals separate spontaneously without any coercion and so we may identify among males a variant of the proximity reward that I describe as a ‘homosociality reward’.
The most likely contributors to this are the gonadal hormones that mediate all other aspects of sexual function. There is a large literature on seasonal hormonal variation among male annual breeders, and testosterone is the only one that rises synchronously with the mating season and drops radically outside it. Although a correlation does not necessarily identify a cause, there is plenty of evidence from studies of other animals in other situations that testosterone mediates both gender determination and gender preference.
Why homosexuality? The discussion of the role of sex hormones in sociality can be extended to humans. The details of the effects are complicated so I will confine my discussion to the observation that our brain gender is much less definitive than our physical gender; this allows us to experience a proximity reward to the same sex which at its extreme is expressed as homosexuality. It is a short step to conclude that the quality which allows us to collaborate in all our endeavors and is the very essence of civilization, takes the form of a high degree of homosociality. Homosexuality itself is not genetically sustainable, but it may be replenished continuously by the fitness benefits of a strong homosociality.
Means and ends. A principal conclusion from these analyses is that nature is gentler than the expression of “nature red in tooth and claw” would suggest. There is some comfort in sensing that primates in the African forest may be working devotedly to pick at a mate’s fur in order to alleviate it from pests or that a pack of wolves may rest contentedly together, nuzzling and licking each other in the aftermath of a successful kill. In humans the reward of sociality modifies our tendency to make harsh judgments or pursue hard bargains. It also has the less salubrious effect of encouraging us to import our opinions from associates who may be no more perceptive than we are.
About the Author
Anthony Caswell is a retired professor of Molecular and Cellular Pharmacology at the University of Miami. His contribution to the discourse on humans and nature began initially with a desire to understand the paradox of homosexuality, but eventually reached far beyond this goal to include the sociality of all higher animals as well as humans. He has proposed a hypothesis of sociality, which puts the personalities of the animals at its center and their Darwinian fitness as its ultimate effect, in the place of the minimalist doctrine currently favored.
Publication: Caswell, A: (2016): The Social Gene. FriesenPress.
Published on 16 February 2018
 Caswell, A. (2016). The Social Gene. FriesenPress.
 Smith, J. M., & Price, G. R. (1973). The Logic of Animal Conflict. Nature, 246, 15.
 Hines, M. (2010). Sex-related variation in human behavior and the brain. Trends in Cognitive Sciences, 14, 448-456.
 Bekoff, M. (2000). Animal Emotions: Exploring Passionate Natures, BioScience 50: 861-870;.Balcombe, J. (2009). Animal pleasure and its moral significance. Applied Animal Behavior Science, 118, 208-216.