Some researchers, particularly advocates of the extended evolutionary synthesis, promote the view that causation in biological systems is inherently reciprocal.
Ultimate causes (e.g. natural selection) were seen as (i) providing historical accounts for the existence of an organism's features, and (ii) explaining the function or ‘goal-directedness’ of living beings.
However, many biologists, psychologists and philosophers have taken issue with Mayr's corollary that the proximate-ultimate distinction implies that development is irrelevant to evolution.
[2][4][6] (see also [3][10][11][12]) It emphasizes how causation cycles through biological systems recursively, allowing proximate causes to feed back and thereby feature in ultimate explanations.
The ‘ultimate explanation’ for the male trait is the prior existence of female preferences, proximately manifest in differential peahen mate choice decisions, whilst the ‘ultimate explanation’ for the peahens’ mating preferences is the prior existence of variation in the peacock's tail associated with fitness.
On one side are researchers who consider that interaction and feedback processes traditionally characterized as ‘proximate’ have explanatory value for ‘ultimate’ evolutionary questions.