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Re: display structures (was Re: Homo sapiens idaltu)

On Fri, 13 Jun 2003, Colin McHenry wrote:

> There may tend to be a difference in the type of 'display' structure used,
> depending on whether the intra-specific display focuses more on male-male
> interactions, or upon female choice.

There is another "function" of display: species
recognition.  Heritable nesting
behavior, for example, can be very idiosyncratic from hybrid to
hybrid.  Mating with the wrong sort of hybrid could waste parental
investment.  I think this is not strictly female choice but, especially in
cases of paternal investment, mutual choice.

> So, there are structures that are used in display, in living animals.  Does
> this then allow one to state that 'The function of structure X is for
> intraspecific display'.  I have a couple of issues with this sort of
> statement.  The first is semantic - I find that the use of the phraseology
> 'function....for' is very determinate.  It emphasised one aspect of the
> possible use of a structure, and seems almost to swamp any other 'possible
> uses'.  This is one of the reasons I try to avoid using 'function' in this
> context.

Yes, unless you formulate it like this: Giraffe necks function to
enhance access to leaves, to spot predators from a distance, and
to give an edge in male/male aggression, etc.

> Thus it is with fossil species.  The head crests on hadrosaurs probably
> played a role in all aspects of the animal's vocalisation, rather than just
> in sexual display.  Remember that elephants use ultrasonics to keep the
> members of a dispersed herd in contact with each other, even though they may
> not be able to see each other (they also use ultrasonics in sexual display,
> especially between males).

And one other possible function must be considered for
hadrosaurs: that the structures were for species recognition.  That is,
they are the result of selection for character displacement for purpose of
avoiding hybrid matings (and less-than-fit nesting strategies).