Supposing that we had not lost some species, it is evident that they may be destroyed. Lions and rhinoceroses are becoming very scarce, and if the rest of the nations had imitated the English, there would not now have been a wolf left. It is probable that there have been races of men who are no longer to be found. Why should they not have existed as well as the whites, the blacks, the Kaffirs, to whom nature has given an apron of their own skin, hanging from the belly to the middle of the thigh; the Samoyeds, whose women have nipples of a beautiful jet.--Voltaire 'Chain of Created Beings' in Philosophical Dictionary. trans. William F. Fleming.
Even among professional historians of philosophy, Voltaire is rarely read these days. Of his works Candide is familiar, but little else. Among scholars there is a veritable and long-overdue revival of interest in his lover, Du Châtelet, but if French Enlightenment thought receives interest the focus is (not entirely correctly) on Diderot, Buffon, Montesquieu, and, of course, Rousseau. Yet, thanks to the awful Charlie Hebdo massacre, Voltaire's Treatise on Tolerance suddenly became a best-seller. And because there is an ongoing campaign to promote Enlightenment values/project (against creeping Islamification of Europe, the dangers of postmodernism, anti-clericalism, etc.) his name still evokes recognition.
The quoted paragraph gives a nice sense of his strengths and weaknesses. Anticipating Darwin (and presumably relying on Hooke or Buffon), Voltaire clearly discerns that human caused animal extinction is a genuine possibility. This gives his thought an ongoing relevance.* In context he is attacking the (Platonizing) doctrine of the great chain of being. This doctrine is committed to (now quoting the Brittanica) "three general features of the universe: plenitude, continuity, and gradation. The principle of plenitude states that the universe is “full,” exhibiting the maximal diversity of kinds of existences; everything possible (i.e., not self-contradictory) is actual. The principle of continuity asserts that the universe is composed of an infinite series of forms, each of which shares with its neighbour at least one attribute. According to the principle of linear gradation, this series ranges in hierarchical order from the barest type of existence to the ens perfectissimum, or God."
Voltaire's argument against the chain of being is informed by reliance on empirical facts (and probable reasoning about them). For example, gradation is undermined by appeal to the size and orbits of planets.) Voltaire's argument is not resolutely empirical because it also relies on possible extrapolation from the facts. (In so doing it draws on a tendency inspired by Newton to turn metaphysical debates into empirical questions. (For that reason I call the general strategy, "Newton's Challenge to Philosophy.") In the article, Voltaire implicitly relies on Newton's arguments against a plenum. He then explicitly appeals to Newton:
And then, how, in so many empty spaces, do you extend a chain connecting the whole? There can certainly be no other than that which Newton discovered — that which makes all the globes of the planetary world gravitate one towards another in the immense void.
Of course, Voltaire does not explain why there cannot be other universal laws that are such connecting chains. This gives a sense of how frustrating Voltaire can be. (It is especially odd because, as I noted last week, in his article on final causes such universal laws do important work for Voltaire.)
Voltaire's daring is evident in his willingness to entertain the possibility of human extinction. (The main underlying target is clearly the Biblical narrative with its claim of sole descent from Adam.) But he does so by assuming racial diversity. Given that he is entertaining the (possible) extinction of human races this makes sense.
While the essay breathes the atmosphere of progress of Moderns over Ancients, I don't think that in this essay the point is to assert the superiority of whites** -- after all, the whole essay is an attack on the foolishness of Plato -- , and he is silent on the relative status of whites and blacks. That silence is somewhat surprising because he is a terrible racist toward blacks elsewhere, especially in his Traité de métaphysique!** But even in this essay Voltaire does introduce what we may call fetishistic and exotic images of the so-called Kaffirs and Samoyeds (I think the latter are meant to refer to Siberian tribes).+ If one takes rhetoric and aesthetics seriously, one wonders if those that wish to promote Voltaire and his Enlightenment are seduced by such imagery.
*As Spencer Pack first pointed out to me Adam Smith also notes the real possibility of extinction (of the Cori) in the Wealth of Nations., but he blames the "the dogs and cats of the Spaniards."
+I am unsure if Caffre/Kaffir was already always derogatory in the eighteenth century.