The late British biologist John Maynard Smith (1920-2004) is famous for applying game theory to the study of natural selection. At Eton College, inspired by the work of old Etonian JBS Haldane, Maynard Smith developed an interest in Darwinian evolutionary theory and mathematics. Then he entered University College London (UCL) to study fruit fly genetics under Haldane. In 1973 Maynard Smith formalised a central concept in game theory called the evolutionarily stable strategy (ESS). His ideas, presented in books such as 'Evolution and the Theory of Games', were enormously influential and led to a more rigorous scientific analysis and understanding of interactions between living things.
I think the world of animal behaviour, and of human behaviour, for that matter, is full of situations in which signals are cost-free because there's no conflict of interest between signaller and receiver. I'd like to give you an example, this is going back to my fruit fly days. In Drosophila Subobscura, females do not mate twice. If they've been mated, they will not mate again, and there's no way a male can force a copulation on them or, he can mate... he can court till the cows come home, she won't mate. If you put a mated female with a male, the male approaches her and starts doing his stuff, and she turns... bends her abdomen towards him and extrudes the ovipositor, and that is a signal saying, 'Look, mate, I'm mated.' And he stops at once. Now, I think this is a cost-free signal. It doesn't pay the male to ignore it, because, you know, he's not getting anywhere. It costs the female practically nothing to extrude her ovipositor. She gains by it because she's not continuously harassed when she's trying to feed, and so on, he's not getting in her way. This is just an example of a context in which I think, if there's no conflict of interest between male and female or between signaller and receiver, then signals can be cost-free.
Title: An example of a cost-free signal in "Drosophila Subobscura"
Richard Dawkins was educated at Oxford University and has taught zoology at the universities of California and Oxford. He is a fellow of New College, Oxford and the Charles Simonyi Professor of the Public Understanding of Science at Oxford University. Dawkins is one of the leading thinkers in modern evolutionary biology. He is also one of the best read and most popular writers on the subject: his books about evolution and science include "The Selfish Gene", "The Extended Phenotype", "The Blind Watchmaker", "River Out of Eden", "Climbing Mount Improbable", and most recently, "Unweaving the Rainbow".