Granted that instinctive modes of behaviour are hereditary and definite within the limits of congenital variation, the question of their manner of genesis is narrowed to a clear issue.
He was educated at the village school until the age of twelve, and owing to congenital lameness had to walk with crutches.
In the case of diagnosis of congenital anomaly, there is no upper limit.
In the condition known as albinism there is a congenital deficiency or entire absence of pigment.
Since on the average only two of the young survive in the struggle for existence to take the place of their two parents, there is a selection out of the ten million young, none of which are exactly alike, and the selection is determined in nature by the survival of the congenital variety which is fittest to the conditions of life.
In a congenital condition known as haemophylia (q.v.) it is difficult to stop the flow of blood.
The area of biological knowledge which Darwin was the first to subject to scientific method and to render, as it were, contributory to the great stream formed by the union of the various branches, is that which relates to the breeding of animals and plants, their congenital variations, and the transmission and perpetuation of those variations.
It is held 1 that the Darwinian doctrine of selection of fortuitous congenital variations is sufficient to account for all cases, that the Lamarckian hypothesis of transmission cf acquired characters is not supported by experimental evidence, and that the latter should therefore be dismissed.
On the other hand, congenital defect amounting to absence of one cerebellar hemisphere has been found to occasion practically no symptoms whatsoever.
But this instance is really fully explained (as the present writer has shown) by the theory of natural selection acting on congenital fortuitous variations.