Atlantic Ocean and is bounded by Africa and Europe on one hand and North and South America on the other. Finally the tip of the pyramid projects above the surrounding waters, and forms the continent of Antarctica. It may seem a mere accident that this tip lies near the South Pole, while the center of the opposite face lies near the North Pole. Yet this has been of almost infinite importance in the evolution not only of plants and animals but of men. The reason is that this arrangement gives rise to a vast and almost continuous land mass in comparatively high latitudes. Only in such places does evolution appear to make rapid progress. * * W. D. Matthew, "Climate and Evolution," N. Y. Acad. Sci., 1915. Evolution is especially stimulated by two conditions. The first is that there shall be marked changes in the environment so that the process of natural selection has full opportunity to do its work. The second is that numerous new forms or mutants, as the biologists call them, shall be produced. Both of these conditions are most fully met in large continents in the temperate zone, for in such places climatic variations are most extreme. Such variations may take the form of extreme changes either from day to night, from season to season, or from one century to another. In any case, as Darwin long ago pointed out, they cause some forms of life to perish while others survive. Thus climatic variations are among the most powerful factors in causing natural selection and hence in stimulating evolution. Moreover it has lately been shown that variations in temperature are one of the chief causes of organic variation. Morgan and Plough, * for example, have discovered that when a certain fly, called the drosophila, is subjected to extremes of heat or cold, the offspring show an unusually strong tendency to differ from the parents. Hence the climatic variability of the interior of large continents in temperate latitudes provides new forms of life and then selects some of them for preservation. The fossils found in the rocks of the earth's crust support this view. They indicate that most of the great families of higher animals originated in the central part of the great land mass of Europe and Asia. A second but much smaller area of evolution was situated in the similar part of North America. From these two centers new forms of life spread outward to other continents. Their movements were helped by the fact that the tetrahedral form of the earth causes almost all the continents to be united by bridges of land. * Unpublished manuscript.