• Choose a category
• All
• Classic-Fiction

By Root 480 0

relation of the individual to its species, we must clarify the nature of a species. The textbook that I studied early in this century in my first college course in general biology asserted that "a species is merely a concept of the human mind-the only reality in nature is the individual, and an understanding of the differences between individuals gives us a key to the differences between species." This nonminalist position conforms to the definition of a species as a group of individuals "which differ less among themselves in the sum of their characters than they do from the members of any other group of individuals" (Woodruff 1922). One might make a similar statement about human artifacts; the word chairs, for example, denotes a group of objects that differ less among themselves than they do from other kinds of household furniture. But chairs are related to each other only ideally; they conform to a concept in our minds; one chair does not create another. If all the chairs in the world were to be destroyed tomorrow, furniture makers would be so busy that, after a few months, there would be no lack of chairs. When a biological species is exterminated, it can never be replaced.

The definition of species in my college textbook is close to the original concept of a species as a class of objects that look alike, as, with due regard to age and sex, the members of a biological species mostly do. Early systematists, including Linnaeus, regarding species

Page 22

as unchanging entities, each corresponding to a Platonic form or an idea in the mind of God, depended largely upon their outward aspect, sometimes supplemented by a study of their anatomy, to delimit them. As is evident from the foregoing quotation, widespread acceptance of Darwin's theory of evolution did not immediately change this. More recently, the old morphological concept of species has been superseded by a more realistic, dynamic view. The biological concept of a species, now widely used in classification, regards it as a group of individuals that freely breed together wherever they intermingle, producing fertile progeny. Spontaneous interbreeding is a more dependable indication of specific limits than is the production of fertile offspring by artificial crossing. The former depends upon the appearance and behavior of animals; the latter, upon the compatibility of their genetic complexes, which is a quite different matter.

Extreme forms of a species may differ so conspicuously in appearance as to be placed in separate species, as in the case of Baltimore and Bullock's orioles, variously considered separate or lumped together as Northern Orioles; or that of Yellow-shafted and Red-shafted flickers, now united as Northern Flickers. On the other hand, forms too similar to be readily distinguished may by classified as different species if they fail to interbreed where they are in contact, as is true of a number of American flycatchers. Since we think so much about genes nowadays, we might define a species as a group of individuals who share a common pool of genes, a selection of which is present, in diverse combinations, in each of them. All members of a species are descended from the same ancestral stock; a species is monophyletic. When we view a species in this biological rather than in the formalistic manner, it becomes clear that it is not merely a concept of the human mind but a self-perpetuating natural entity, no less real than the individuals that compose it. Indeed, if reality has degrees, and the longer something exists the more real it is, species have greater reality than individuals, which are to their species as leaves to a tree.

One may ask why animals and plants belong to species that are typically sharply delimited from other species instead of inter-

Page 23

grading so that they might be arranged in series without discontinuities, in which case we might, for example, find every possible gradation between an Ostrich and a hummingbird, or an oak tree and a violet. Probably, if all the organisms that have become extinct