loio LIFE : OUTLINES OF GENERAL BIOLOGY 



disturbances and re-arrangements). It is only when we can definitely 

 subtract from the observed differences all the "modifications" 

 (probably non-transmissible) that we get at the germinal variations 

 which certainly form the greater part, if not the whole, of the raw 

 materials of possible evolution. 



Suppose we have registered the occurrence of variations and 

 obtained curves like those in Figs. 171 and 172, a glance at the 

 curve shows the range of variation of the particular species as regards 

 the character measured. A more or less stationary species would show 

 a very symmetrical curve, as many below as above the central mean. 

 A low curve would indicate that there was no very striking difference 

 between the great majority and those at either end, but a curve 

 rising very high at its climax would indicate that there were on either 

 hand numerous individuals diverging from mediocrity. 



If the curve that results from registering the measured quantities 

 is very lop-sided, its skewness will show at once that the stock or 

 community measured is evolving in one direction as regards the 

 measured character; and if the same shape of curve is yielded in 

 different places and among different stocks, the inference would be 

 that the species as a whole is moving in a particular direction. 

 Similarly a very marked double-peaked or double-humped curve 

 might serve a useful biological purpose in its statistical registration 

 of the fact that the species was spHtting into two species. But we 

 cannot do more than give this faint indication of the value of this 

 very important method. 



ARE ACQUIRED GAINS ENTAILED? 



All biologists, of whatever school, are agreed that peculiarities 

 of nurture, for better or for worse, may mean much for the in- 

 dividual. Nurture includes all the environmental, nutritional and 

 habitudinal influences, and the individual organism is often pro- 

 foundly influenced by their generosity or niggardliness, adequacy 

 or inadequacy, normality or abnormaUty. The degree of develop- 

 ment attained by what we may call the hereditary "buds", depends, 

 so to speak, on the soil and the sunshine, the wind and the rain. 

 Recall the Dalmatian newt called Proteus, which remains wan-white 

 in the dark caves, but soon puts on pigment in the well-Hghted 

 laboratory. Its buried and arrested eye may develop a little further 

 than usual, if it is illumined. 



The red Chinese primrose, familiar in greenhouses, has red flowers 

 when it is reared at I5°-20°C.; but the same plant, reared at 

 30°-35° C, with moisture and shade, has pure white flowers. There 

 is a Mendelian race of American fruit-flies (Drosophila) with a 

 peculiar abnormality which is exhibited generation after generation 



