to strong assortative mating.Finally,music is functionally analogous to
sexually selected acoustic displays in other species.Sexual Selection Theory:The Basics
Darwin (1871) identified two different kinds of sexual selection:aggres-
sive rivalry and mate choice.Rivalry,especially between males,tends to
produce weapons,such as sharp teeth,large horns,and strong muscles.
Mate choice,especially by females,tends to produce ornaments,such as
colorful tails,innovative sounds,and musky smells.Although Darwin
provided overwhelming evidence for the importance of female mate
choice in producing male ornaments,biologists after him focused almost
exclusively on male rivalry,rejecting the possibility of female choice
(Cronin 1991).For a century,sexual selection was seen as a process
where active,competitive males struggled for “possession”of passive
females by acquiring territories and status,and repelling rivals.Orna-
ments were usually interpreted as species-recognition signals for helping
animals avoid mating with the wrong species.Only in the last couple of
decades did the picture change,with astounding vindication of Darwin’s
mate choice idea in hundreds of experimental and theoretical studies
(Ridley 1993;Andersson 1994).Research on sexual selection through
mate choice is currently one of the most active areas of behavioral
science,with papers saturating major animal behavior journals.The
sophistication and complexity of mate choice theory have grown enor-
mously in recent years.But for our purposes,we need to understand only
two key ideas:mate choice for indicators,and mate choice for aesthetic
displays.Music as a Set of Sexually Selected Indicators
The idea of indicators is that sexual selection shapes animals to adver-
tise reproductively important things like age,health,fertility,status,and
general fitness (see Andersson 1994).For example,the peacock’s tail may
function as an indicator,because unhealthy,weak,peacocks cannot grow
very large tails,and even if they could,they could not escape from preda-
tors that easily notice large tails.The result is that the size of a peacock’s
tail statistically correlates with the bird’s age,health,and heritable fitness.
Peahens thus have a strong incentive for paying attention to tail size,
because by mating with a large-tailed peacock,they are getting good
genes that will give their offspring survival and reproductive advantages.
Whereas some indicators reveal good genes, others reveal good
resources,good parenting skills,or good fertility.338 Geoffrey Miller