Also changes due to climate may be brought about at once in a second generation, though no appreciable modification is shown by the first.

Thus "Sir Charles Lyell mentions that some Englishmen, engaged in conducting the operations of the Real del Monte Company in Mexico, carried out with them some greyhounds of the best breed to hunt the hares which abound in that country.

It was found that the greyhounds could not support the fatigues of a long chase in this attenuated atmosphere, and before they could come up with their prey they lay down gasping for breath; but these same animals have produced whelps, which have grown up, and are not in the least degree incommoded by the want of density in the air, but run down the hares with as much ease as do the fleetest of their race in this country."[80] We have here no action of "Natural Selection;" it was not that certain puppies happened accidentally to be capable of enduring more rarefied air, and so survived, but the offspring were directly modified by the action of surrounding conditions.

Neither was the change elaborated by minute modifications in many successive generations, but appeared at once in the second.
With regard once more to sudden alterations of form, Nathusius is said to state positively as to pigs,[81] that the result of common experience and of his experiments was that rich and abundant food, given during youth, tends by some direct action to make the head broader and shorter.

Curious jaw appendages often characterize Normandy pigs, according to M.Eudes Deslongchamps.