Among ourselves this is well known.The simplest physical peculiarity is mostly reproduced.I know a case of a man whose wife has the lobe of one of her ears a little flattened.An ordinary observer might scarcely notice it, and yet every one of her children has an approximation to the same peculiarity to some extent.If you look at the other extreme, too, the gravest diseases, such as gout, scrofula, and consumption, may be handed down with just the same certainty and persistence as we noticed in the perpetuation of the bandy legs of the Ancon sheep.
However, these facts are best illustrated in animals, and the extent of the variation, as is well known, is very remarkable in dogs.For example, there are some dogs very much smaller than others; indeed, the variation is so enormous that probably the smallest dog would be about the size of the head of the largest; there are very great variations in the structural forms not only of the skeleton but also in the shape of the skull, and in the proportions of the face and the disposition of the teeth.
The Pointer, the Retriever, Bulldog, and the Terrier, differ very greatly, and yet there is every reason to believe that every one of these races has arisen from the same source,--that all the most important races have arisen by this selective breeding from accidental variation.
A still more striking case of what may be done by selective breeding, and it is a better case, because there is no chance of that partial infusion of error to which I alluded, has been studied very carefully by Mr.Darwin,--the case of the domestic pigeons.I dare say there may be some among you who may be pigeon 'fanciers', and I wish you to understand that in approaching the subject, I would speak with all humility and hesitation, as I regret to say that I am not a pigeon fancier.I know it is a great art and mystery, and a thing upon which a man must not speak lightly; but I shall endeavour, as far as my understanding goes, to give you a summary of the published and unpublished information which I have gained from Mr.Darwin.
Among the enormous variety,--I believe there are somewhere about a hundred and fifty kinds of pigeons,--there are four kinds which may be selected as representing the extremest divergences of one kind from another.Their names are the Carrier, the Pouter, the Fantail, and the Tumbler.In the large diagrams they are each represented in their relative sizes to each other.This first one is the Carrier; you will notice this large excrescence on its beak; it has a comparatively small head; there is a bare space round the eyes; it has a long neck, a very long beak, very strong legs, large feet, long wings, and so on.The second one is the Pouter, a very large bird, with very long legs and beak.It is called the Pouter because it is in the habit of causing its gullet to swell up by inflating it with air.I should tell you that all pigeons have a tendency to do this at times, but in the Pouter it is carried to an enormous extent.The birds appear to be quite proud of their power of swelling and puffing themselves out in this way; and I think it is about as droll a sight as you can well see to look at a cage full of these pigeons puffing and blowing themselves out in this ridiculous manner.
The third kind I mentioned--the Fantail--is a small bird, with exceedingly small legs and a very small beak.It is most curiously distinguished by the size and extent of its tail, which, instead of containing twelve feathers, may have many more,--say thirty, or even more--I believe there are some with as many as forty-two.This bird has a curious habit of spreading out the feathers of its tail in such a way that they reach forward, and touch its head; and if this can be accomplished, I believe it is looked upon as a point of great beauty.
