II02 LIFE : OUTLINES OF GENERAL BIOLOGY 



If a normal mouse is paired with a waltzing mouse, all the off- 

 spring are normal; and we say that normal locomotion is dominant 

 over the waltzing pecuUarity. If the hybrid offspring (F^) are inbred, 

 their offspring will show 25 per cent, pure normals, 50 per cent, 

 apparent normals, and 25 per cent, pure recessives. One of the last 

 might be certificated as a pure waltzer although both its parents 

 seemed normal, and one of its grandparents was normal through and 

 through. An extracted recessive will breed true to waltzing as long 

 as it is paired with others like itself. 



23. Of far-reaching importance is the idea that an inheritance is 

 (in part at least) a congeries of unit characters which illustrate 

 Mendelian inheritance, and the fact that mutations have this non- 

 blending, non-fractionating quality. It may be pointed out that an 

 apparent blending, as in a mulatto's skin, may arise when the 

 character in question is due to several minor characters which may 

 be dominant in one parent, recessive in another. Similarly, if human 

 stature be determined by factors for the lengths of different parts, 

 which are hereditarily independent, the illusion of blending may be 

 produced by a mingling of various items from the two parents. 

 Or again, there are said to be eight factors determining the colour 

 of a wild rabbit's fur; according to the number that drop out in 

 domesticated breeds, various colours result; a subsequent re-com- 

 bination of these in uncontrolled pairing results in a wild rabbit 

 pattern, which is no longer a mysterious "reversion". 



24. In aU cases, whether we are dealing with variation, heredity, 

 selection, or isolation, we must keep in mind the commonplace that the 

 central fact is the living organism, an agent, often obviously psycho- 

 biological, often certainly able to share, to good purpose, in its own 

 evolution. 



DIFFERENT KINDS OF EVOLUTION 



Evolution is one of the badly over- worked words, like "force", 

 "instinct", or "value". It means a process of Becoming, but it is 

 applied to various orders of facts which have very little in common, 

 either as regards the material evolving or the way in which the 

 evolution comes about. We hear of the evolution of a solar system, 

 the evolution of matter, the evolution of religion, the evolution of 

 the chemical elements, the evolution of man, the evolution of 

 language, the evolution of scenery, the evolution of the horse, the 

 evolution of mind, the evolution of plants, the evolution of sex, 

 the evolution of society, the evolution of species, the evolution of 

 evolution theories, and so on. When processes that are different are 

 called by the same name, there is bound to be confusion; and it 

 is more than verbal. We venture to make some simple suggestions 

 which, if accepted, would lessen the confusion. 



