110 The Outline of Science 



practically dates from the publication of The Origin of Species 



in 1859. 



Heritable novelties or variations often crop up in living crea- 

 tures, and these form the raw material of evolution. These varia- 

 tions are the outcome of expression of changes in the germ-cells 

 that develop into organisms. But why should there be changes 

 in the constitution of the germ-cells? Perhaps because the living 

 material is very complex and inherently liable to change; perhaps 

 because it is the vehicle of a multitude of hereditary items among 

 which there are very likely to be reshufflings or rearrangements; 

 perhaps because the germ-cells have very changeful surroundings 

 (the blood, the body-cavity fluid, the sea-water) ; perhaps because 

 deeply saturating outside influences, such as change of climate 

 and habitat, penetrate through the body to its germ-cells and 

 provoke them to vary. But we must be patient with the weari- 

 some reiteration of "perhaps." Moreover, every many-celled 

 organism reproduced in the usual way, arises from an egg-cell 

 fertilised by a sperm-cell, and the changes involved in and pre- 

 paratory to this fertilisation may make new permutations and 

 combinations of the living items and hereditary qualities not only 

 possible but necessary. It is something like shuffling a pack of 

 cards, but the cards are living. As to the changes wrought on the 

 body during its lifetime by peculiarities in nurture, habits, and 

 surroundings, these dents or modifications are often very impor- 

 tant for the individual, but it does not follow that they are 

 directly important for the race, since it is not certain that they 

 are transmissible. 



Given a crop of variations or new departures or mutations, 

 whatever the inborn novelties may be called, we have then to 

 inquire how these are sifted. The sifting, which means the elimi- 

 nation of the relatively less fit variations and the selection of the 

 relatively more fit, effected in many different ways in the 

 course of the struggle for existence. The organism plays its new 

 card in the game of life, and the consequences may determine 



