Active Causes of Organic Evolution 177 



When a review is made of the general assemblage of organic 

 bodies, it can truly be said that botanists and zoologists have 

 been profoundly impressed by the apparently unerring manner 

 in which the minutest details of plant and animal structure 

 were handed down for each species. Unquestionably also, 

 it was this impression wliich caused the early cosmologists 

 to propound the view of special creation They were fre- 

 quently also medicine men, astrologers, and priests to their 

 nations. So, as vdW be more fully traced later, special creation 

 became a part of international religious belief. Though now 

 we give to heredity its appropriate place as one factor amongst 

 several in evolutionary history, that place deserves to be first. 



But the marvelous exactness with which even the most 

 microscopic parental details of both parents are handed dowTi, 

 in sexual heredity, from generation to generation in plants, 

 was first demonstrated by the writer from a study of plant 

 hybrids and their parents (63 passim). Thus as sho^^^l there 

 in Plates I- VII the forms, the sizes, the numbers, the degree 

 of wall thickening of cells; the number, size, and shape of hairs 

 and of their cells; the stomata over a given area; the size 

 and shape of starch grains; and every other detail of cell life 

 were a blended and faithfully reproduced picture of parental 

 details, except that these were each reduced either exactly 

 or approximately by one-half. Though some observers have 

 tried to obscure or cover over such exact results as applicable 

 to parental heredity between two species, the evidence is over- 

 whelmingly in favor of the correctness of such a conclusion. 

 Some years previously Galton had reached a like conclusion 

 for man, by statistical study of many naked-eye details (72: 12). 



But, as the writer clearly and frequently emphasized through- 

 out his work, the hereditary details are by no means always 

 evenly and equally blended, but show at times a marked ten- 

 dency to swaying more in the direction of one parent than of 

 another. And here the subject of variation in individuals of 

 common parents, and in individuals of a common species, 

 at once arises in connection with evolutionary descent. It 

 can be accepted fully, however, that in organisms, as in iiior- 



