Table 1.

Summary of the four scenarios for the origin of male sexual traits and female preferences discussed here.

assumptions and predictions	Fisherian origin	Darwinian origin	adaptive sensory bias	hidden preferences
relies on	pre-existing indicator of male genetic quality	pre-existing indicator of direct benefits to females	pre-existing sensory bias shaped by selection	pre-existing incidental sensory bias
type of selection at the time of origin	indirect (among females)	direct (among females)	direct (among males)	direct (among males)
historical pattern	male trait pre-dates female preference	male trait pre-dates female preference	female preference pre-dates male trait	female preference pre-dates male trait
male traits preferred	reliable indicators of genetic quality (armament, dominance rank, etc.)	indicators of paternal investment (overall body size, territory, health and vigour, etc.)	traits that exploit female sensory capabilities used in other contexts (see table 2)	arbitrary traits that do not match female sensory capabilities used in other contexts (tail length in birds, symmetry, etc.)
number of male traits preferred in any one taxa	one or a few	one or a few	few or many	few or many
type of coevolution likely to follow after origin	good genes processes, Fisher's runaway process	direct benefits processes, Fisher's runaway process	sexually antagonistic coevolution, direct benefits processes, Fisher's runaway process	none, sexually antagonistic coevolution, Fisher's runaway process