Page:Popular Science Monthly Volume 28.djvu/227

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217
NEUTER INSECTS.

NEUTER INSECTS.
By CHARLES MORRIS.

IN the later editions of Darwin's "Origin of Species" he has answered with remarkable ability nearly all of the several weighty arguments brought against his theory. Some seemingly insuperable objections have been met with an array of facts before which they quite break down. Thus, several instances of extraordinary organs in certain species or types of animals, which it was claimed could not possibly have originated through natural selection, he has shown to be connected by intermediate variations with ordinary organs, which variations are useful at every point of their development, so that the strange appendages might easily have arisen through minute gradations of change.

There is one objection, however, which he can scarcely be said to have answered so happily. This is that in reference to neuter insects—the specially developed working-ants, for instance. As he himself acknowledges, the phenomenon of neuter insects appeared to him at first insuperable, and actually fatal to the whole theory, since these neuters often differ widely in instinct and structure from the males and females, yet, being sterile, they are incapable of hereditarily reproducing their characteristics. In working-ants the difference from the sexual forms is often very great, as in the shape of the thorax, the lack of wings and sometimes of eyes, and in instinct. The difference in instinct is still greater in the hive-bee. Nor is this the whole of the difficulty. In some species of ants there are two and even three distinct castes, well defined, and each with specialities of structure.

Yet, as it is quite impossible that these sterile females could transmit their peculiarities to descendants, and as no such peculiarities exist in the structure of the males and developed females, hereditary influence would seem to vigorously oppose their reproduction, and it seems quite extraordinary that the sexual forms should produce offspring so markedly unlike them. The case is as remarkable as if the offspring of a lion and lioness should be a cat or a leopard, or if a sheep should produce an antelope.

Darwin seeks to explain this difficulty by considering that selection may apply to the family as well as to the individual, and that chance peculiarities of structure, which proved useful to the community, may have been preserved by selection, the tribes in which such useful aberrant forms appeared surviving, while tribes more normal in reproductive power perished. Illustrative facts tending in the same direction are given, and there is certainly a degree of force in this argument, though it can scarcely be accepted as wholly satisfactory.

It is probable that Darwin did not give to this question as full a