Page:Popular Science Monthly Volume 33.djvu/140

130 associated primitive ideas of the divine mind and will—crude cosmogonies current at the beginning of recorded human observation. Conceptions, transient in character, have had alliance with religious sentiments, essentially permanent. When a traditional cosmogony, such as the Mosaic, is transmitted as of equal sacredness with religion, there is grave danger that science, in discrediting the cosmogony, may do hurt to religion. This danger is avoided when we discriminate between the transient and permanent elements in theology. There is not, and never was, any necessary connection between any theory of Nature's history and the kernel of religion—the sense of a supreme mystery behind Nature, the sense of, moral obligation transcending utility, and the hope of everlasting life. The conflict which so many suppose to be between religion and science is more and more seen to be really between new science and old—if by stretch of courtesy primitive observation and theorizing can be called science at all. Timidity, half informed and careless in discrimination, imagines science to be intent on destroying the temple of religion, whereas its chief est mission is to broaden and heighten it. The more intelligible Nature becomes to the student, the profounder his reverence for the Intelligence manifested in Nature, Evolution, as a philosophy, deals only with the history of Nature, not its origin; with its transformations, not its essence,

That evolution is truth, and axiomatic truth, Prof. Le Conte firmly maintains. His presentation of its proofs, though rapid, is masterly, and brought down to date. lie sets forth the important and little appreciated work of Agassiz in this connection—his proof that the laws of embryonic development are also the laws of geological succession. Agassiz, however, holding as he did the doctrine of permanency of specific types, rejected the theory of the derivative origin of species. Prof. Le Conte then presents the factors of evolution tersely and concisely—the effects of physical environment, of the use and disuse of organs, of natural, sexual, and physiological selection. He brings forward evidence for evolution from the general laws of animal structure, incidentally discriminating between analogies and homologies. He compares the forelimbs of mammals, birds, reptiles, and fishes, part for part, in a specially able manner. Embryology is next summarized in proof of the derivative origin of specific forms, and the parallel between the development of an individual and of the species to which the individual belongs is brought out very forcibly. The significance of rudimentary organs—teeth in whales, the cæcum in man—is shown to depend solely on descent from forms wherein such organs were useful. Unexercised, they have dwindled, and tend to disappear. Evolution is next shown to be supported by the facts of geographical distribution. Isolation of the Australian continent at a remote geological era explains the primitive characteristics of its fauna and flora. The peculiarities of island-life, the rapid changes in organic forms during the last glacial epoch, and the recession of arctic species to the snow-line of the Alps and the high mountains of Colorado and California, are shown to be intelligible on no other hypothesis but that of evolution. Prof. Le Conte next surveys the testimony drawn from the artificial production of varieties, and presents with graphic illustration the law of cross-breeding.

While maintaining that the fact of evolution is certain, our author points out that all its laws are not yet fully understood. Among the difficulties which he considers are those of the uselessness in incipient stages of organs afterward developing into usefulness. In such stages, for example, fins probably commenced as buds from a trunk; it is difficult to see how as buds they could be of any use, and therefore how they could be improved by natural selection until they grew to efficient size, and especially until muscles were developed to move them. Again, in the case of a variety in a new and useful direction making its appearance, what has prevented its obliteration by cross-breeding with the parental form? Thus, while he holds the law of evolution to be even more surely demonstrated than the law of gravitation, Prof, Le Conte points out problems to which students may most profitably direct their powers of observation and generalization.

Because our author is thoroughly a man of science, he finds his knowledge in