Tuesday, November 8, 2011

A Misguided Belief to Dispel.2

Genetic Principals of Domestication
By Mark Shipway

The idea that domesticated breeds such as the Bengalese have hybrid histories was shared by domestic animal breeders before Charles Darwin's time. The view probably started with Linnaeus, who named the Bengalese in 1766. We are all familiar with Darwin's work.................or are we? In the chapter entitled "Variation Under Domestication" from "On the Origin of Species" he says:

"One circumstance which has struck me much; namely, that all the breeders of various domestic animals ..... are firmly convinced that the several breeds to which each has attended, are decended from so many aboriginally  distinct species"

He goes on to at length to disprove this conviction and  concludes:

"When in any country several domestic breeds have once been established , their occasional with the aid of selection, has no doubt, largely aided in the formation of new sub breeds [such as the Euro Bengalese]; but this has been greatly exaggerated ...   I am convinced that the accumulative action of selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more effectively, is by far the predominant power."

Put another way, by implication, before Darwin's time it was assumed that because not all the characteristics of a domesticated breed matched those of a wild species, it was assumed the former must be the result of crossing of several  species (this is the basis upon the Bengalese hybrid myth was developed).  Darwin questioned this assumption. According to theory, differences between the  White Rumped Munia and the Bengalese can be better accounted for as being the result of selective breeding of one species by the Chinese or Japanese over a long period rather than hybridisation between two or more species. As you no doubt are aware, Darwin's views largely reshaped those of the evolutionists and geneticists in his time and have formed the basis for for modern evolutionary science.

Of course the fact that a Bengalese may be piebald, fawn, chestnut, chocolate dilute, fawn dilute, chestnut dilute, crested, frill, grey, pearl, ino or white is attributable to a mutation and is a separate issue to the one about the ancestry of the finch. Throughout this article I am referring to the natural chocolate or wild form. The piebald effect is caused by one of two separate mutations, one of which now predominates the breed and has a complex genetic make-up which has been described as "penetrance".  (As a side note, the fact that selfs have traditionally been so uncommon in Australia is that, as far as I am aware, we never benefited from an import of wild White Rumped Munias which Europe received from Asia from the 1950's and 60's).

to be continued....