He states, however, that the presence of callosities on the legs of the camel and llama "are the unmistakable results of rubbing or friction; so also with the callosities of baboons and the pouched monkeys, and the double soles of man's feet."[133] In this point he anticipates Erasmus Darwin and Lamarck. As we shall see, however, his notions were much less firmly grounded than those of Erasmus Darwin, who was a close observer as well as a profound thinker. In his chapter on the _Dégénération des Animaux_, or, as it is translated, "modification of animals," Buffon insists that the three causes are climate, food, and domestication. The examples he gives are the sheep, which having originated, as he thought, from the mufflon, shows marked changes. The ox varies under the influence of food; reared where the pasturage is rich it is twice the size of those living in a dry country. The races of the torrid zones bear a hump on their shoulders; "the zebu, the buffalo, is, in short, only a variety, only a race of our domestic ox." He attributed the camel's hump to domesticity. He refers the changes of color in the northern hare to the simple change of seasons. He is most explicit in referring to the agency of climate, and also to time and to the uniformity of nature's processes in causing variation. Writing in 1756 he says: "If we consider each species in the different climates which it inhabits we shall find perceptible varieties as regards size and form; they all derive an impress to a greater or less extent from the climate in which they live. These changes are only made slowly and imperceptibly. Nature's great workman is time. He marches ever with an even pace and does nothing by leaps and bounds, but by degrees, gradations, and succession he does all things; and the changes which he works--at first imperceptible--become little by little perceptible, and show themselves eventually in results about which there can be no mistake. Nevertheless, animals in a free, wild state are perhaps less subject than any other living beings, man not excepted, to alterations, changes, and variations of all kinds. Being free to choose their own food and climate, they vary less than domestic animals vary."[134] The Buffonian factor of the direct influence of climate is not in general of so thoroughgoing a character as usually supposed by the commentators of Buffon. He generally applies it to the superficial changes, such as the increase or decrease in the amount of hair, or similar modifications not usually regarded as specific characters. The modifications due to the direct influence of climate may be effected, he says, within even a few generations.