The human species

by A. de Quatrefages

Science has in reality done nothing more than define the idea of which the public had merely a vague consciousness, and it was not till very lately, and after a very curious oscillation, that she succeeded in doing so. In 1686, Jean Ray, in his Historia Plantarum, considered that those plants which had a common origin and could be reproduced by seed belonged to the same species, whatever their apparent differences might be. He only took filiation into account. Tournefort, on the contrary, who in 1700 was the first to make a clear statement of the question, termed the collection of plants a species which were distinguished by some particular character. He relied only on resemblance.

Ray and Tournefort have had from time to time a few imitators, who, in their definition of species, have clung to one of the two ideas. But the immense majority of zoologists have been aware of the impossibility of separating them. To convince ourselves of this fact it is only necessary to read the definitions which they have given. Each one of them, from Buffon and Cuvier to MM. Chevreul and C. Vogt has, so to speak, proposed his own. Now, however they may differ in other respects, they all agree in this. The terms of the definitions vary, each endeavours to represent in the best manner possible the complex idea of species; some extend it still further, and connect with it the ideas of cycle and variation: but in all the fundamental idea is the same.

In a case of such difficulty as that of finding a good definition for a combination of ideas, the latest comer always hopes to improve upon his predecessors. For this reason I have also given my formula: “Species is a collection of individuals more or less resembling each other, which may be regarded as having descended from a single primitive pair by an uninterrupted and natural succession of families.”

In this definition, as also in that of some of my colleagues, among others of M. Chevreul, the idea of resemblance is made of less importance and subordinate to that of filiation. The fact is that there never is an identity of characters between one individual and another. Putting aside the variations resulting from age and sex, it is at once evident that all representatives of the same specific type differ in some points. Although these differences are very slight, they constitute individual traits, shades as Isidore Geoffroy said, which enable us to distinguish between two of the same species.

But the differences are not confined within these limits. The specific types are variable, that is to say, every kind of physical character is modified in their derivatives and, under the influence of certain conditions, to such an extent as to make it often very difficult to recognise their unity of origin. This, again, is a fact upon which all naturalists agree. Blainville even, who, defined species as “the individual repeated and continued through time and space,” distinctly recognised this variability; for the individual is perpetually undergoing modification, and does not retain its similarity during the various stages of life. He admitted, moreover, the existence of distinct races.

The variability of species has also been the subject of animated discussion among naturalists. The memorable contention which arose upon this subject between Cuvier and Geoffroy is not yet forgotten, a struggle considered by Goethe as more important than the gravest political events. In the present day a school to which many of the most illustrious names in England, Germany and elsewhere belong, has taken up, with certain modifications, the ideas of Lamarck and Geoffroy; it gives support to them from retaining the term variability of species.

There is a grave confusion of words in this formula. Lamarck, Geoffroy, Darwin and his school, consider the species not only as variable but as transmutable. The specific types are not merely modified, they are replaced by new types. Variation is in their estimation only a phase of the very different phenomena of transmutation.

I shall discuss these theories presently. I shall now confine myself to the remark that true variability, admitted even by the defenders of dogmatic invariability, by Blainville, for example, a variability which I fully accept, has nothing in common with the transmutability of Lamarck, Geoffroy and Darwin. Let us briefly determine the limits of this variability.

III. When an individual trait is exaggerated and passes a limit always very loosely defined, it constitutes an exceptional character which clearly distinguishes the individual affected by it from all those most nearly resembling it. This individual constitutes a Variety.

The same term must be applied to all those individuals, which, like certain plants reproduced by slips, grafts, or shoots, derive their origin from the first exceptional individual, without having the power of transmitting their distinctive characters by means of normal generation. I borrow from M. Chevreul a curious example of these multiple varieties. In 1803 or 1805, M. Descemet discovered in his garden at Saint Denis, in the midst of a bed of acacias (Robinia pseudo-acacia) an individual without thorns which he describes under the epithet spectabilis. It is to the multiplication of this individual by the art of the gardener that all the thornless acacias, now distributed over every part of the globe, owe their origin. Now these individuals produce seeds, but if the seeds are sown they only yield thorny acacias. The acacia spectabilis has remained a Variety.