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The Fundamentals tion, and Darwin rarely used the word. The title of Darwin’s great work was, “The Origin of Species by Means of Natural Selection.” The problem which he set out to solve touched but a small part of the field of evolution. His proposition was simply that species may reasonably be supposed to be nothing more than enlarged of accentuated varieties, which all admit are descendants from a common ancestry. For example, there are a great many varieties of oak trees. But it is supposed by all botanists that these have originated from a common ancestor. Some chestnut trees, however, differ less from some oak trees than the extreme varieties of both do from each other. Nevertheless, the oak and the chestnut are reckoned not as varieties, but as different species. But the dividing line between them is so uncertain that it is im- possible to define it in language; hence, some botanists have set up an independent species between the two, which they call “chestnut oak.” WHAT IS A “SPECIES”? This, however, is but a single illustration of the great difficulty which scientific men have had in getting a satis- factory definition of species. That most generally accepted is “a collection of individual plants and animals which re- semble each other so closely that they can reasonably be sup- posed to have descended from a common ancestor.” I t is easy to see, however, that this definition begs the whole ques- tion at issue. For we have no certain means of knowing how widely the progeny may in some cases differ from the parent; and we do not know but that resemblances may result from the action of other causes than that of parental connection. The definition is far from being one that would be accepted in the exact sciences. I t may be “reasonably supposed” that such small differ- ences as separate species have resulted through variations of individuals descended from a common ancestry, yet it is a long
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