Now, since a child inherits some qualities from its father and some from its mother, it follows that if the father and mother are different from each other, the child must differ from both, and yet resemble both. For he will inherit from the father qualities which the mother has not inherited from her ancestors, and he will inherit from the mother qualities which the father did not inherit from his ancestors. So the child will resemble both parents, without being an exact copy of either. It "varies" from both parents by inheriting from each. The child of a black and a white parent is what we call a half-caste: he is neither a negro nor a white man. The pup of a bulldog and a terrier is neither a bull-dog nor a terrier; he is a bull-terrier terrier. But heredity goes farther than that, and variation is more complex than that. We must not think of a man as inheriting from his father and mother only. He inherits from the parents of both his parents; and from thousands of ancestors before those. He inherits from men and women who died thousands of years before he was born. He inherits from the cave-man, from the tree-man, from the ape-man, from the ape, and from the beast before the ape. The child in the womb begins as a cell, and develops through the stages of evolution, becoming an embryo worm, fish, quadruped, ape, and, finally, a human baby. The child is born with the bodily and mental qualities inherited from many generations of beasts and many generations of men. Any one of the many ancient qualities of mind or body may crop up again in a modern child. Children have been born with tails: children have been born with six nipples, like a dog, instead of with two, like a human being. And now I will explain, simply and briefly, what we mean by the word "Atavism." WHY THE CLOCK OF DESCENT SOMETIMES GOES BACKWARD "Atavism," or "breeding back," or "reversion," may reach back through thousands of generations, and some trait of the cave-man, or the beast, may reappear in a child of Twentieth Century civilisation. Darwin, in _The Descent of Man_, Chapter II, gives many instances of "atavism," or breeding back, by human beings to apish and even quadrupedal characteristics. Alluding to a case cited by Mr. J. Wood, in which a man had seven muscles "proper to certain apes," Darwin says: It is quite incredible that a man should through mere accident abnormally resemble certain apes in no less than seven of his muscles, if there had been no genetic connection between them. On the other hand, if man is descended from some apelike creature, no valid reason can be assigned why certain muscles should not suddenly reappear after an interval of many thousand generations, in the same manner as with horses, asses, and mules, dark-coloured stripes suddenly reappear on the legs and shoulders after an interval of hundreds, or, more probably, of thousands of generations. Dr. Lydston, in The Diseases of Society (Lippincott: 1904) says: