234 THE POPULAR SCIENCE MONTHLY 



tions is possible. It seems probable, as Boveri has shown, that different 

 chromosomes of the fertilized egg differ in hereditary potencies, and 

 where the number of chromosomes is fairly large the number of possible 

 combinations of these chromosomes in the germ cells becomes very great. 

 In woman, where there are probably 48 chromosomes, and, after 

 synapsis, 24 pairs of maternal and paternal ones, the possible number 

 of permutations in the distribution of these chromosomes to the different 

 egg cells would be (2) 24 , or 16,777,036, and the possible number of 

 different types of fertilized eggs or oosperms which could be produced 

 by a single pair of parents would be (16,777,036) 2 , or approximately 

 three hundred thousand billions. But probably other things than 

 chromosomes differ in different germ cells, and it is by no means certain 

 that individual chromosomes are always composed of the same chromo- 

 meres, or units of the next smaller order, and in view of these possi- 

 bilities it may well be that every human germ cell differs morpholog- 

 ically and physiologically from every other one, in short that every 

 oosperm and every individual which develops from it is absolutely 

 unique. 



Indeed, the production of unique individuals seems to be the chief 

 purpose and result of sexual reproduction. In a sexual reproduction 

 the individual variations which occur are chiefly, if not entirely, due 

 to environment, but in sexual reproduction they are also due to new 

 combinations of hereditary elements. The particular germinal organi- 

 zation transmitted from one generation to the next depends upon, (a) 

 The ancestral organization, (b) The particular character of the cell 

 divisions by which the germ cells are formed, (c) The particular kinds 

 of egg and sperm cells which combine in fertilization. The ancestral 

 organization determines all the general characteristics of race, species, 

 genus, order, phylum. It determines the possibilities and limitations of 

 individual variations. Given a certain ancestral organization, the indi- 

 vidual peculiarities of the germ cells are determined by the particular 

 character of cell division by which the germ cells are formed, and the 

 peculiarities of the individuals or persons which develop from these 

 cells are determined in large part by the particular kinds of germ cells 

 which unite in fertilization. 



The behavior of chromosomes in maturation and fertilization is like 

 the shuffle and deal of cards in a game, and apparently with the same 

 object, namely, never to deal the same hand twice. To make this com- 

 parison more complete suppose that kings be discarded from the pack, 

 leaving 48 cards of two colors, red and black, which we will compare 

 to the 48 maternal and paternal chromosomes in the human oocyte ; sup- 

 pose that in the shuffling of these cards corresponding cards of the red 

 and the black suits are temporarily stuck together so that the ace of 

 diamonds is united with the ace of clubs, the queen of hearts with the 

 queen of spades, etc., thus forming 24 red-black pairs of the same 



