Note 45 — Chapter III · Characters as Hereditary and Acquired (continued).

We meet with a closely analogous reflex mechanism in brainless vertebrata of other kinds; but these do not furnish such good test cases, because the possibility of natural selection cannot be so efficiently attenuated. The perching of brainless birds, for instance, at once refers us to the roosting of sleeping birds, where the reflex mechanism concerned is clearly of high adaptive value. Therefore such a case is not available as a test, although the probability is that birds have inherited their balancing mechanisms from their sauropsidian ancestors, where it would have been of no such adaptive importance.