From: le01167@portal.lasc.lockheed.com (Ron Nadel (x2025))
Subject: Re: sexual selection
News-Software: VAX/VMS VNEWS 1.41    
Keywords: peacock tails
Organization: Lockheed Aeronautical Systems Co. - Rye Canyon
Distribution: usa
Date: Thu, 20 Aug 92 16:52:46 GMT

In article <10437@bonzo.ed.ac.uk>, kate@cogsci.ed.ac.uk (Kate Jeffery) writes...

>In article <1992Aug19.015201.27032@s1.gov> lip@s1.gov (Loren I. Petrich) writes:
>>	The way that features such as brightly colored feathers would
>>do that is by advertising that their owner is in good health; a sick
>>bird would probably not be able to produce lots of shiny and bright
>>feathers.
> 
>Well, so, why don't *all* male birds have long brightly coloured
>ornamental bits to their anatomy if it's such a good indicator of
>health & hence desirability? 

Even if brightly colored _bits_ of bird anatomy are beneficial, why
should ALL birds have them?  These features had to evolve, and organisms
don't just evolve something because it's good and they _should_ have
it.  And look at it this way: flight is beneficial to birds, and essentially
all birds have wings, but some bird's wings aren't good for flying.
Your question above is akin to asking _So why don't all birds have
wings that allow them to fly?_  Your question would be more appropriate
if some Pea cocks did not have the coloration (in other words within
the same species _so if it's so good, why don't all Pea cocks have it?_).
And quite a number of bird species do have males with coloration schemes.

>little analogous to why all clocks run clockwise(!) or nearly all of
>the world's population drive on the right, ....

This is an important point in evolutionary discussions.  Not every
single phenotypic trait has evolved for some benefit.  There is a
strong element of chance in this, considering the genetic mutations 
and drift necessary for any change to come about, and genes can have several 
phenotypic expressions but be selected for one - you simply cannot approach 
it from the _what function or benefit does it have_ direction so much as 
where did the trait come from and how.  Then you can begin to investigate 
IF a trait has function/benefit that falls within the resolution of natural 
selection.

I disagree that most of the world's population drives on the 
right side of the road, when you consider that India, China, and
Japan are left siders (not to mention, of course, Jolly Ol').

>Afetr reading Dawkins' book I started wondering whether sexual
>selection might account for another puzzling ornament - breasts! 

PUZZLING ornament?  Really?

>I know they are not entirely without function 

An UNDERSTATEMENT...  8^>

>but other primates seem to manage perfectly well with very small ones. 
>Anyone know why humans females are thought to posssess them in such 
>relative abundance?... 

>Kate Jeffery

Other primates manage perfectly well with small brains too, but a bigger one
IS better, no?  If you compare humans to other mammals, our penises and breasts
are puny (I'm thining of horses and cattle and pigs especially) - thank evolution
we have this huge brain to brag about.  And our larger brain size is not the 
expression of a particular gene so much as a reflection of our neoteny in general,
so maybe large breast size is regulated by some other genetic sequence.

Boy we can have some fun in light of the above sexual selection considerations 
of such factors as _signs of health_ etc.  Perhaps male humans see large breasts as a 
sign of health and more fitness for child baring (I don't buy it), perhaps males take 
it as a sign of greater sexual activity and promises of pleasures untold (I've heard men
say this who believe it, but they were Neanderthals so their species doesn't count.  I 
also know someone who truly believes that the size of a woman's nipples and aureola 
indicate how much intercourse she has had in her life!).  But whatever the reason, 
if there is some selective advantage to large breasts, you might ask why ALL women
don't have large ones.

While human breasts may be large there may not be an evolutionary/selective explanation 
for their size (although there is one for their existance).  But just as in the Pea fowl, 
if coloration is an attraction for the Pea hen, then the more color the more likely is 
mating; and in humans, if males find breasts an attraction, larger breasts would have 
meant a greater chance of mating.  But things aren't quite so simple with humans, so I
don't think you can point to any one or two features alone.  In humans there is a myriad
of factors that go into the making of our sexual selection process (things like personality,
overall appearances, even success and level of education or religion - and many of these
things don't have genes for them).  Plus we have to be careful to not give a biological 
explanation (excuse) for sexist behaviour. ;^)

I personally am not convinced by Dawkin's arguments, they're too teleological for me.
But I do find this breast thing interesting.

Ron 8^/
Newsgroups: sci.bio