But greater general vigour would
almost certainly lead to greater volume or persistence of sound, and so
the same view will apply to both cases on my theory.
Thanks for the references you give me. My ignorance of German prevents
me supporting my views by the mass of observations continually being
made abroad, so I can only advance my own ideas for what they are worth.
I like Dorking much, but can find no house to suit me, so fear I shall
have to move again.
With best wishes, believe me yours very faithfully,
ALFRED R. WALLACE.
* * * * *
_Down, Beckenham, Kent. September 5, [1877]._
My dear Wallace,--"Conscious" seems to me much better than "voluntary."
Conscious action, I presume, comes into play when two males fight for a
female; but I do not know whether you admit that, for instance, the
spur of the cock is due to sexual selection.
I am quite willing to admit that the sounds and vocal organs of some
males are used only for challenging, but I doubt whether this applies to
the musical notes of Hylobates or to the howling (I judge chiefly from
Rengger) of the American monkeys.
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