On Tue, May 13, 2008 at 7:52 AM, L&L Knight <> wrote:
> As far as I can see, the rule of thumb for evolution is that organisms that
> are better suited to the environment they exist within are more likely to
> survive to sexual maturity and hence tend to produce more offspring. The
> rub is that in the case of species with sexual dimorphism, the gender making
> the decision doesn't always make its decision on the basis of
> characteristics that enhance an individual's survivability [eg excessively
> long tails, predator-attracting colours etc].
For what it's worth, Darwin described sexual selection [selection by
mate] as a different mechanism from natural selection [seletion by
arbitrary local conditions]. This lets you explain the difference
between the Peacock and the Peafowl (for example) without having to
resort to some kind of elaborate story that would conjure up a
selective constraint favoring both forms simultaneously. Put another
way, sexual selection may produce forms that are not otherwise better
adapted to their environment. At the same time, sexual favoritism
can't lead to males or females that are killed off too easily. "Land
of Parrots" had some interesting material on parrots that have color
patches that are visible to members of their species without being
within the color range of their predators. A lot of birds with sexual
color patches seem to have them in places where they can be
hidden/revealed very selectively. For example, male hummingbirds often
have fantastical gorgets that look black in anything other than good
light from exactly the right angle (only a few degrees, I'd guess.)
Closer to home, some of the bowerbirds have pink marks on the backs of
their heads that are very clear in the field guides and pretty nearly
invisible (to me anyway) in the field under most conditions.
Anyway, that's my layman's understanding of it.
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