242 



SCIENCE 



[N. S. Vol. XXXIV. No. 869 



other independent of it in heredity, and how 

 in other cases the joint action of two or more 

 independent factors may he necessary to pro- 

 duce a single visible result. The cognate sub- 

 ject of reversion next comes in for discussion, 

 and is finely illustrated by examples from the 

 breeding of rabbits, sweet-peas and pigeons. 

 Dominance is the subject of the next chapter, 

 and is shown to be imperfect in heterozygous 

 forms like the Andalusian fowl, or, in other 

 cases, of reversed character in the two sexes, 

 as in horns in sheep. 



The origin of domesticated varieties from 

 wild forms is next discussed. It is believed 

 to occur by unit-character variation (muta- 

 tion) but in several different ways as (1) by 

 loss of factors, a method clearly illustrated in 

 the case of sweet-peas both with historical 

 data and data derived from breeding experi- 

 ments; (2) by the reduplication of factors; 

 (3) by the interpolation of new factors, in 

 some cases unrelated in character, in others 

 inhibiting in action. " Repulsion and coupling 

 of factors " are hypothecated to explain pe- 

 culiar ratios or the sex-limitation of charac- 

 ters in heredity. In discussing this subject 

 Punnett follows Bateson closely, assuming 

 that each sex possesses a factor not found in 

 the other, and which repels certain sex-limited 

 characters in gametogenesis. 



The production of " intermediates " ob- 

 served in many experimental studies of in- 

 heritance is explained with the help of (hypo- 

 thetical) supplementary and inhibiting fac- 

 tors. 



A finely written chapter on " variation and 

 evolution " contrasts with the older views of 

 the Darwinian period the newer views derived 

 from the study of genetics, and shows how the 

 theory of natural selection has been relieved 

 of the burden of explaining the origin of new 

 characters, and required only to explain their 

 perpetuation. Protective mimicry is ex- 

 plained as due to parallel mutation rather 

 than to actual imitation. 



Another chapter discusses the economic as- 

 pects of genetics in the breeding of animals 

 and plants, and the last one is devoted to 

 " man." This delightful chapter is a literary 



gem, in which the author's power of keen 

 analysis, of vivid imagination, and of clear 

 exposition show to best advantage, not with- 

 out a spark of genuine humor and a lot of 

 good sense. He reviews the classic cases of 

 Mendelian inheritance in man, of brachydac- 

 tyly, night blindness, hemophilia, eye-color, 

 etc. He considers the possible interrelations 

 of physical and mental traits and the scientific 

 basis of eugenics in the following passage: 



A discussion of eye-color suggests reflections of 

 another kind. It is difficult to believe that the 

 marlcedly different states of pigmentation which 

 occur in the same species are not associated with 

 deep-seated chemical differences influencing the 

 character and bent of the individual. May not 

 these difi:erences in pigmentation be coupled with 

 and so become in some measure a guide to mental 

 and temperamental characteristics? In the Na- 

 tional Portrait Gallery in London the pictures of 

 celebrated men and women are largely grouped 

 according to the vocations in which they have suc- 

 ceeded. The observant will probably have noticed 

 that there is a tendency for a given type of eye- 

 color to predominate in some of the larger groups. 

 It is rare to find anything but a blue among the 

 soldiers and sailors, while among the actors, 

 preachers and orators the dark eye is predominant, 

 although for the population as a whole it is far 

 scarcer than the light. The facts are suggestive, 

 and it is not impossible that future research may 

 reveal an intimate connection between peculiarities 

 of pigmentation and peculiarities of mind. 



The inheritance of mental characters is often 

 elusive, for it is frequently difficult to appraise 

 the effects of early environment in determining a 

 man 's bent. That ability can be transmitted there 

 is no doubt, for this is borne out by general ex- 

 perience, as well as by the numerous cases of able 

 families brought together by Galton and others. 

 But when we come to inquire more precisely what 

 it is that is transmitted we are bafBed. A distin- 

 guished son follows in the footsteps of a distin- 

 guished father. Is this due to the inheritance of 

 a particular mental aptitude, or is it an instance 

 of general mental ability displayed in a field 

 rendered attractive by early association. We have 

 at present very little definite evidence for sup- 

 posing that what appear to be special forms of 

 ability may be due to specific factors. Hurst, 

 indeed, has brought forward some facts which 

 suggest that musical sense sometimes behaves as a 

 recessive character, and it is likely that the study 



