A long tail of truth and beauty: a simple rule of pattern formation explains symmetry, complexity and beauty in the peacock’s tail

Darwin’s theory of sexual selection by female choice has become a standard
explanation for exaggerated sexually dimorphic traits, such as the
peacock’s (Pavo cristatus) long tail. Eyespot beauty-based female choice
requires genetic variation in female preference and the number of
eyespots, as well as a genetic correlation between the two. However,
little genetic variation has been documented in either of these traits in
natural and feral peacock populations. We examined the anatomical plan
underlying feather development and discovered that eyespot feather
follicles originate in alternating rows of 10/11, which uniquely
determines the train’s feather complexity, bilateral symmetry, and eyespot
arrangement and beauty. This pattern precludes intrinsic variation in
eyespot number, resulting in a fixed number of total eyespots in fully
mature individuals. Since number of eyespots and tail length are
independent traits and function of the age of the animal, the only
variation available in these trats is also function of age. We propose an
alternate, male drive, hypothesis in which females choose males based on
their overall dominance (size, vigour, call, courting), and beauty of the
train may (or may not) be a factor in female choice but it cannot affect
the train length.  This hypothesis can explain all known results.