Heredity, then, must be assumed to apply to both equally.

In proportion as there is plastic mind there will be plastic body.
Unfortunately, the most plastic part of body is likewise the hardest to observe, at any rate whilst it is alive, namely, the brain.

No certain criterion of heredity, then, is likely to be available from this quarter.

You will see it stated, for instance, that the size of the brain cavity will serve to mark off one race from another.

This is extremely doubtful, to put it mildly.