Not so peculiar, really. For one thing, as Courtney points out, pigeons were an easily accessible group of domesticated animal varieties that Darwin could study more or less at his leisure; but this rather begs the question: why start a general argument for a theory of organic origins with the apparently obscure side-show of plant and animal breeding?

The answer, it seems to me, is that domesticated plant and animal varieties can be shown to be the result of descent with modification by means of selection. Darwin knew that he could not literally show descent with modification to be the cause of naturally occurring organic diversity – the process was simply far to slow for that; and he also knew that he could not literally show natural selection in action – again, because the process was far too slow. The closest he could get to demonstrating both principles in action, therefore, was in the (admittedly artificial, or man-made) case of plant and animal domestication.

Starting with the apparently obscure topic of variation under domestication was – like pretty much everything else in the Origin – a carefully calculated move, designed to begin the slow and steady task of persuading skeptical readers that two equally invisible processes (descent with modification and natural selection) were the true causes of organic diversity.

Young earth creationists, on the other hand, make the argument from (uneducated) incredulity that the vast profusion of phenotypes cannot possibly come from the tiny little genomes. Here’s a clear example that shows it can.

Has Darwin’s claim about lineage of the fancy pigeons been confirmed by DNA study?