[2] He has a particular interest in behavioural ecology and evolutionary biology, and is most noted for introducing the concept of sperm competition in 1970.
[5] His Ph.D. was on The reproductive behaviour and the nature of sexual selection in Scatophaga stercoraria L. (yellow dung fly), and provided a detailed quantitative test of Darwin's theory of sexual selection, and an early application of optimality theory in biology.
However, the paradigm shift of the gene-centric view of evolution (popularised by Richard Dawkins in The Selfish Gene) shortly afterwards overturned this idea: mainstream views in behavioural ecology and sociobiology saw natural selection restored to Darwinian principles in terms of survival value to the individual (and its kin).
Parker's work played a part in this shift and in the early development of behavioural ecology.
In 2008, he won the Darwin Medal: for his lifetime contribution to the foundations and development of behavioural ecology, in particular for understanding evolutionary adaptations and their consequences for natural populations.He has been awarded the degrees of Doctor of Science, honoris causa by the University of Bristol.