this disease; or when the havoc caused by insect pests has become so disastrous as to cause a careful study of such forms of life in order to eradicate them. These influences, so clearly at work now, have, however, been in operation in greater or less degree since the sixteenth century. They were at work also during the later period of Greek civilization and had it not been for the persistence of religious superstition they would have been effective in the Arabian civilization.
Turning now to the effects of the biological sciences, three important influences may be mentioned: First, biological knowledge, through the prevention and cure of disease, has greatly decreased the rates of mortality; secondly, through the destruction of injurious pests and through the selection and cultivation of vegetable and animal life, it has multiplied and improved the food supply, and incidentally it has increased other forms of wealth. In these two ways then the sciences of life have made possible an increase in population at least as great as that made possible by the physical sciences. But it should be noted that the biological sciences are supplementary to the physical sciences. Both stimulate the growth of population, but the biological sciences do so without the suffering and waste prevalent before their development. Neither group can do its proper work without the other and each group has been a stimulus to the growth of the other. Sanitary measures could not be carried out without engineering knowledge, the present concentration of population would be impossible without sanitary precautions, and a large food supply would be useless without rapid means of transportation and communication. Finally, biological sciences have to some extent, and will to a greater degree, improve individuals and the race through selection and education. Medical science has been severely criticized because it has counteracted the effects of natural selection by making it possible for the unfit to live and propagate their kind. Without doubt a partial knowledge of the laws of life has produced some temporary evil effects along with the good. But the remedy lies not in a return to former conditions, but in the adoption of new methods through the perfection of our knowledge. Psychology has already enabled us to make rapid strides in our system of education and in our treatment of mental diseases; and a better knowledge of the laws of heredity and improved methods of social control will enable us consciously to improve the human species in ways most advantageous. And they will accomplish this more quickly and effectively than by the blind process of natural selection.
The past century may be regarded as preeminently a period of biological discovery, not because the physical sciences have not advanced also in a marked degree, but because biological discovery is the new factor which has been added to science to influence social progress. This new factor is destined to further in a wonderful degree individual
