Trivers was one of the most—perhaps the most—influential evolutionary biologists of the 20th century. His work should be much more widely known in social and behavioural sciences, in particular in economics, as Trivers’ intellectual approach is very much in line with a game theoretic understanding of social interactions.
It is hard to overstate the importance of his work. Einstein famously published four groundbreaking papers in 1905, a year often referred to as his “Annus mirabilis”, during which he revolutionised physics. Trivers might be said to have had a “Quinquennium Mirabile” for the five years between 1971 and 1976, during which he produced a series of ideas that revolutionised evolutionary biology.
Reciprocal altruism - 1971:
The human altruistic system is a sensitive, unstable one. Often it will pay to cheat: namely, when the partner will not find out, when he will not discontinue his altruism even if he does find out, or when he is unlikely to survive long enough to reciprocate adequately. And the perception of subtle cheating may be very difficult. Given this unstable character of the system, where a degree of cheating is adaptive, natural selection will rapidly favor a complex psychological system in each individual regulating both his own altruistic and cheating tendencies and his responses to these tendencies in others. As selection favors subtler forms of cheating, it will favor more acute abilities to detect cheating.
Parental investment -1972:
Since the female already invests more than the male, breeding failure for lack of an additional investment selects more strongly against her than against the male. In that sense, her initial very great investment commits her to additional investment more than the male’s initial slight investment commies him.
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Critics of evolutionary theory sometimes argue that it does not make any predictions that can be tested and that it only rationalises what has already been observed. Trivers’ work is one of the best examples disproving this accusation. In his paper on parental investment, Trivers argues that the differences in behaviour between males and females should reflect the degree of asymmetry in their parental investment. As a result, animals with more parental investment asymmetry should show greater asymmetry than those with less, and if we ever find animals with role reversals, we should also observe reversals in strategies. And indeed, we observe that in animals with less asymmetry in parental investment, like swans, the differences between males and females are less noticeable. In the rare cases where male investments are larger, like in seahorses, where the females literally place their eggs in the belly of the male who incubates them, we observe a role reversal, with females courting males and competing for access to them.
Parent Offspring Conflict - 1974:
The offspring can cry not only when it is famished but also when it merely wants more food than the parent is selected to give. Likewise, it can begin to withhold its smile until it has gotten its way. Selection will then of course favor parental ability to discriminate the two uses of the signals, but still subtler mimicry and deception by the offspring are always possible.
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Obviously, overall parents tend to love their children and children tend to love their parents, but Trivers showed—with a theory now largely supported by empirical research— that the whole picture is more complex, because there are always also elements of conflict in parent-offspring relations.
Self-deception - 1976:
In the preface to Dawkins’ The Selfish Gene, Robert Trivers proposed a solution to this problem: our tendency to self-deceive, to think we are better than we are, may serve as a mechanism that enables us to deceive others more effectively. He wrote:
If … deceit is fundamental to animal communication, then there must be strong selection to spot deception and this ought, in turn, to select for a degree of self-deception, rendering some facts and motives unconscious so as not to betray – by the subtle signs of self-knowledge – the deception being practiced. —Trivers (1976)
Commenting on this assertion, psychologist Steven Pinker remarked, “This sentence... might have the highest ratio of profundity to words in the history of the social sciences”
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In a 2011 paper with Bill von Hippel, Trivers developed this idea further, listing how self-deception can help. When trying to deceive, people may face cognitive load (the cognitive work required to make sure a web of lies does not have glaring contradictions). Given that lying is a betrayal of trust and is sanctioned when it is found out, it is risky, and people can get nervous about being found out, possibly showing signs of nervousness. Finally, people might try to mask signs of nervousness, thereby also behaving in a way that indirectly suggests lying. Self-deception, by inducing people to believe in their own lies, so to speak, can eliminate these possible clues while leading others to believe the preferred story of the person self-deceiving.
Trivers’ theory of self-deception has been supported by empirical research (including research I have contributed to). It explains what seems to be one of the most irrational patterns of human behaviour as emerging from strategic incentives.
Trivers has been one of the most influential evolutionary biologists, and his papers are still worth reading today. His insights, published more than 50 years ago, are fascinating. They often align very well with economic theories of behaviour, and it is therefore regrettable that his ideas are not more well-known in economics, and in particular in behavioural economics.
A key feature of Trivers’ take across these contributions was to see that beneath the world of social interactions we observe, there are deep structures in terms of incentives that shape the game we play. Understanding these games and their structures helps us make sense of the seemingly endless complexity of human psychology and social dynamics. In several key contributions, Trivers helped lift the veil on the underlying logic of human behaviour.
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