The third and fourth books give evidence of acuteness in psychological analysis; the fourth and sixth of the most active and varied observation of natural phenomena; the fifth of original insight and strong common sense in conceiving the origin of society and the progressive advance of man to civilization.
This has been criticized both from the biological and from the psychological standpoint.
27, has become a psychological symbol.
On the psychological reasons for this see W.
Whether it was physiological or psychological didn't matter at this point.