In Egypt, all the conditions of existence, and, consequently, the actions of the conditions of life, are the same in our days as they were in those distant times, the history of which is preserved by the monuments. Far from tending to modify a race which is already fixed, they have only helped to fix it more and more. In the order of ideas which I support, a change in the Egyptian type would be inconceivable. The persistence of a type, far from being an objection to the manner in which I understand the conditions of life to act, viz.: the formation and maintenance of races, is a confirmation of it. XIV. In conclusion; like all animal and vegetable species, the human species can vary within certain limits; like plants and animals, man has his _varieties_ and _races_, which have appeared and been formed by the action of the same causes. In the human kingdom, as in the two other organic kingdoms, the first causes of variation are, _conditions of life_ and _heredity_. In phenomena of this kind, conditions of life act as the supreme ruler. If they vary, they become modifying agents, if they remain constant, agents of stabilisation. In both cases their result is to harmonise organisms with the conditions of their existence. Heredity, which is essentially a preserving agent, becomes an agent of variation, when it transmits and accumulates the modifying actions of the conditions of life. XV. It is now easy to understand, in the general sense, the formation of human races. Man at first doubtless peopled his centre of appearance and the countries immediately adjoining. He then commenced the immense and varied dispersion which dates from tertiary times and continues to the present day. He has passed through two geological epochs, and is now in his third. He has seen the mammoth and rhinoceros flourishing in Siberia in the midst of a rich fauna; he has at least seen them driven by the cold into the midst of Europe; and he has assisted in their extinction. Later on, he has retaken possession of the _barren-lands_ himself; he has pushed his colonies as far as the neighbourhood of the pole, perhaps to the very pole itself, while at the same time he has invaded the forests and deserts of the tropics, reached the extremity of two great continents, and peopled all the archipelagoes. For many thousands of years, man has therefore been subject to the action of all the external conditions of life with which we are acquainted, to that of the conditions of life of which we can at the utmost only form an idea. The various kinds of life to which he has been subjected, and the different degrees of civilisation at which he stopped or to which he has reached, have all diversified still more his conditions of existence. Was it possible that he should retain everywhere and for all time his original characters?