We are a bit late, but here is the announcement from the Royal Swedish Academy of Sciences,
… Robert Trivers, is one of the small group of pioneering scientists who began to ponder on the social behaviour patterns of animals and how they might have arisen through evolution. Between 1971 and 1976, he launched five ideas that have been of the greatest importance for the development of sociobiology. They have inspired many behavioural ecologists, who have to a large extent confirmed Trivers’s ideas.
The first problem he focused on was how evolutionary theory could explain cooperation between individuals that are not related. Trivers concluded that cooperation of this kind can only develop if the animals cooperate over a long period of time and if they are able to recognise each other. This idea had an immediate and great impact and Trivers’s thoughts have later been developed by game theoreticians, among others.
Trivers’s second bid idea deals with the way in which the traits of male and female animals are influenced by their investment in their offspring. In a species where the female is responsible for most of the care, the male will develop traits that the female likes, for example, colourful plumage, attractive song or an impressive body size. If the females do not like the male, he will have poorer chances of passing his genes on to the next generation.
A third hypothesis presented by Trivers is the explanation of why certain species sometimes give birth to more young of the same sex. He argued that it could be advantageous, for example, for a female to give birth to sons when she was in good condition, since the sons usually grown bigger than the daughters and therefore demand more energy.
Trivers also explained why conflicts often arise between older young and their parents. This is not something that only occurs in teenage families. His interpretation is that when the young are old enough to take care of themselves, the parents gain by saving their care for younger or future young. The older young, on the other hand, want to benefit from their parents’ care as long as possible.
The fifth idea for which Trivers has been awarded the Crafoord Prize concerns social hymenoptera: ants, bees and wasps. He predicted that the workers in an ant community, which are always female, may be expected to invest three times the amount of resources in bringing up their sisters than their brothers. When Trivers later investigated the situation in reality, the results indicated that he had been right, which later research also confirmed.
Thus, together with the previous Crafoord Laureates William D. Hamilton, George C. Williams, Edward O. Wilson and John Maynard Smith, Robert Trivers has laid the theoretical foundations for research on the evolution of social behavioural patterns in animals, a field that is known today as sociobiology and which is a part of the larger field of behavioural ecology.