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Page:Popular Science Monthly Volume 73.djvu/127

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merely to the science of myrmecology, but to wider biological theories as well. It is, indeed, through the examination of myriads of specimens representing particular periods in the history of the world, that we may expect to solve some of the most difficult questions of evolution. Scudder noticed that among certain of the groups of fossil insects there were particular tendencies observable throughout, notwithstanding the 'fact that the species belonged to different groups. Legs had grown longer, or wing-cells had shortened, since the Miocene, and different series, already at that time quite separate and free from crossing, had been affected in the same manner. The same sort of thing was later remarked by Professor Osborn in the teeth of extinct animals, and he became convinced that there were fundamental predispositions to vary in particular directions. Theories of this sort, if completely verified,

PSM V73 D127 Fossil chestnut leaf castanea dolichophylla.png

Fossil Chestnut Leaf (Castanea dolichophylla). Close to the leaf is also seen a small freshwater shell (Planorbis florissantensis).

would greatly affect our ideas of the process of evolution; but the chief need at present is for more light, derived from more and more diverse groups of animals. Hence the study of the fossil insects, at first seeming of purely entomological interest, is likely to lead to results of the first importance.

While we thus search for trends of evolution, we note also the great conservatism of insect types. It is well known that warm-blooded animals have undergone great changes since the Miocene, one of them being the evolution of man himself. In the case of the insects, however, the modifications have been slight indeed, even where these have been driven far and wide by adverse changes of climate.

We find, it is true, a fair number of extinct genera; types which no longer persist in the modern world; but these appear to be merely those which have died out, not the ancestors of any modern kinds. None of