Are there any known traits (in any organisms) that serve exclusively one purpose? (Counterexample: Giraffes long neck help them reach less available food AND communicate sub-sonically).
If so is that the exception rather than the rule?
This will be used for a human evolution paper, in which I would suggest that the descended hyoids in hominins and modern Homo sapiens could have serve multiple purposes, such as size exaggeration and language. I want to debate an argument that a similar descension in deer evolved, or was selected for, for only one use (i.e. size exaggeration) and that this correlates to human larynx evolution, by citing literature (if available) that demonstrates that organisms use features for multiple purposes more often than not.