I. Haeckel and His Opponents

It was rightly recognised that with this conclusion must fall a conception belonging to the most treasured among the collection of older human prejudices: the conception that the “soul of man” is a special being all to itself, having quite another, a different, “higher origin” from all other things in Nature. The doctrine of descent must naturally lead to the view that man's soul-activities are only a special form of those physiological functions which are found in his vertebrate ancestors, and that these activities have evolved themselves with the same necessity from the mental activities of the animals, as the brain of man, which is the material condition of his intellect, has evolved out of the vertebrate brain.