Re: Breast Size (Was: Re: Homosexuality and genetic determinism)

Paul Bernhardt (
5 Jun 1995 13:24:29 GMT

Eric Bohlman ( wrote:
: Bryant ( wrote:

: : You don't evolve. Lineages and populations evolve. Because fitness
: : advantages shape many traits (adaptations), it's fair to say that those
: : traits evolved TO provide those fitness advantages. Our opposable thumbs
: : evolved TO grasp (Gil, leave that one alone, eh?)...

: Nope, it's not fair to say that. It implies that the "purpose" of a
: trait existed in advance of the trait's appearance. If a trait makes
: something useful (like grasping) possible, then the trait is likely to
: stick around; that's what natural selection means. But until something
: resembling the opposable thumb appeared, grasping didn't exist, so it
: could not have been a cause of the trait.

: Evolution is *not* a directed process by which species converge to some a
: priori Platonic ideal; it's the process by which species become able to
: survive their current environments. What's adaptive in one environment
: may be maladaptive in another environment (and environments are
: constantly changing). Unless some a priori Platonic ideals for
: environments can be found, the concept of "purposive" evolution is
: meaningless.

This whole chicken and egg thing has been wonderfully discussed by Gould.
Basically, he used the example of the flying insect. The wing of the
insect serves two puposes, temperature control and flying.
The size necessary for effective temperature
control is way to small for true flight. Increases in temperature control
wings past this necessary size should not happen because there is no
advantage gained. However, these wing 'buds' are large enough to cause
the insect to drift on air currents a little farther when falling. It is
not gliding, merely a little more time aloft, softer landing, more
random falling pattern, and drift farther from a spot directly below the
falling insect. That means prey animals would have more difficulty
catching an insect with these wing 'buds'. With that said, after the
development of temperature control wing buds, selection pressure for the
wing that gives greater time aloft occurs. Eventually, true gliding
wings, without much control have evolved. They are much bigger than the
wings needed for temperature control, possibly to the point of being a
disadvantage. So, the musculature needed to close and open so that
temperature control is optimized develops. This musculature also can
allow a little control over gliding. The pressure, and minimal physical
characteristics, towards flapping of wings for directed propelled flight is
therefore in place.

Evolution is a dynamic interplay between the demands of environment
(sometimes including members of the same species, sometimes not), the
individual's characteristics and normal random fluctuations in
charactertistics of the life form. There is no compelling need for
'mutation'. The thumb doesn't have to appear all at once. It can start as
a normal variation in the range of motion of one finger/toe. At the
extremes of the variation in range of motion, some individuals have
extraordinary range of motion and live in an environment that rewards an
individual with that range of motion. They reproduce more efficiently.
The genetic advantage is spread to other subgroups or the other subgroups
are crowded out. The range of motion might be refined by normal
variations from the new normal finger arangement, etc. etc. etc. The
dance continues today, re: moths that adapted to living in the vicinity of