Re: Pubic bones and Anal fins

drosen0000@xxxxxxxxx wrote:

Questions on pubic bones, an item common in the male members of most
tetrapod species. Humans and bonobos don't have any, but this makes
pubic bones even more interesting.
1) How did pubic bones evolve in tetrapods?
2) Are pubic bones in tetrapods homologous to anal fins in fish?
3) Are there any plausible theories on how pubic bones are used in
extant animals?

I presume that you mean the "baculum" (or "os penis") when you say
"pubic bone" (which is actually part of the hip, not part of the
penis).

Most mammals possess bacula, although it is the most morphologically
variable bone in the body. That variation has led to two general
hypotheses for its existence and morphology. The first is that really
serves no purpose other than structural reinforcement in the erect
penis, but because it is polygenic in its encoding, it is also
inherently pleiotropic. As the organism evolves to new environments,
the baculum changes its morphology concommittantly, but with little
selective constraint, thus the variability.

The second hypothesis is that the variation seen in bacula serves a
primary role as a pre-zygotic species isolating mechanism. The shape of
the baculum is part of a lock-and-key mechanism that species have
evolved to insure proper species recognition, and thus the minimization
of outbreeding depressions. The os penis is differently constructed in
each species because it is in each species's best interest to be
different. I personally tend to favor this explanation.

Wirt Atmar


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Relevant Pages

  • Re: Pubic bones and Anal fins
    ... How did pubic bones evolve in tetrapods? ... Are pubic bones in tetrapods homologous to anal fins in fish? ... primary role as a pre-zygotic species isolating mechanism. ...
    (sci.bio.evolution)
  • Pubic bones and Anal fins
    ... Questions on pubic bones, an item common in the male members of most ... Humans and bonobos don't have any, ... Are pubic bones in tetrapods homologous to anal fins in fish? ...
    (sci.bio.evolution)