When sexual selection runs away
The concept of runaway sexual selection illustrates one of the ways
that sexual selection is hypothesized to work.
The quandary of female choice
This leads to an interesting question: how did female choice for
traits like a long, colorful tail evolve? After all, if a female
chooses a male with a long, awkward tail, her sons will probably
have a similar tail and that tail might hurt their chances
of survival by attracting predators. How could natural
selection act to produce a preference for a disadvantageous
It makes sense for a female to choose a mate based on traits that help him survive. For example, a female bird would do well to choose
a strong-looking, disease-free mate. That male likely carries "good" genes
that allow him to resist disease and get sufficient food and he will
pass those genes on to his offspring.
However, there are many examples of females choosing mates based on less useful
traits (e.g., song complexity) or even traits detrimental
to survival (e.g., brightly colored plumage, as in the case of the
peacock). These cases present evolutionary biologists with a bit
of a puzzle. How did these preferences arise in the first place? If a
female chooses a male with bright
feathers, her sons will have bright feathers, which are likely to
attract predators. A gene for choosing brightly colored males would
seem to be disadvantageous. How do such genes spread through a population?