If we use our general biological evidence in this way, merely to help in clearing up points about human biology, we need not be entirely limited to mammals. Some sex phenomena are quite general, and may be drawn from the sexual species most convenient to study and control in experiments. When we get away from mammalian forms, however, we must be very sure that the cases used for illustrations are of general application, are similar in respect to the points compared, or that any vital differences are understood and conscientiously pointed out.
Too much stress cannot be laid upon the point that such animal data, carefully checked up with the human material, cannot safely be used for any other purpose than to discover what the facts are about the human body. When the discussion of human social institutions is taken up in Part II, the obvious assumption will always be that these rest upon human biology, and that we must not let our minds wander into vague analogies concerning birds, spiders or crustacea.
BIBLIOGRAPHY FOR CHAPTER I
Loeb, Jacques. Artificial Parthenogenesis and Fertilization. Chicago, 1913.
Loeb, Jacques. The Organism as a Whole. N.Y., 1916, p. 125—brief summary of results of [1].