In chapter 14, discussing hummingbird feathers
Originally Posted by Darwin
The Duke of Argyll, in commenting on this case,* passes over sexual selection, and asks, "What explanation does the law of natural selection give of such specific varieties as these?" He answers "none whatever"; and I quite agree with him. But can this be so confidently said of sexual selection?

This is a fine example of "sexual selection" being employed as a catch-all.

He continues:
Quote
Seeing in how many ways the tail-feathers of humming-birds differ, why should not the four central feathers have varied in this one species alone, so as to have acquired white tips? The variations may have been gradual, or somewhat abrupt as in the case recently given of the humming-birds near Bogota, in which certain individuals alone have the "central tail-feathers tipped with beautiful green." In the female of the Urosticte I noticed extremely minute or rudimental white tips to the two outer of the four central black tail-feathers; so that here we have an indication of change of some kind in the plumage of this species. If we grant the possibility of the central tail-feathers of the male varying in whiteness, there is nothing strange in such variations having been sexually selected.

Shifting the burden of proof. Why should Argyll be compelled to prove the tastes of an hummingbird? He is not the one making the claim.

Note that Darwin does not propose an experiment, like whitening feather tips & seeing which is preferred - you know, science. No no no. He employs his catch-all, and submits no evidence to support his claim. He implies his opposition is obliged to prove him wrong, when the burden is unquestionably his.

And keep in mind what he said about 'natural selection'. If the colours make the creature too conspicuous... But I'm kidding. That was just double-talk - he didn't really mean it.

Dark Matter + Dark Energy = Dark Truth

"We find that such evidence demonstrates that the ID argument is dependent upon setting a scientifically unreasonable burden of proof for the theory of evolution." - Judge Jones Kitzmiller case
http://www.talkreason.org/articles/Falsify.cfm

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