ACQUIRED CHARACTERS 39 



black background, their black areas become more extensive. 

 Thus there is an automatic control of the color-pattern 

 adapted for concealment, such as is known to occur in many 

 fishes. Now Kammerer bred from animals, thus rendered 

 extremely yellow, and reared part of the young on a yellow 

 background, part of them on a black background. Both lots 

 developed yellow spots but these were more extensive in those 

 animals kept on a yellow background. In some of them the 

 yellow was more extensive than in the parents. This result 

 Kammerer ascribes to inheritance of the acquired yellow 

 coloration added to the direct effect of the yellow background 

 on the young. This conclusion is a fallacious one. Spotted 

 animals are extremely variable in pattern, even when the 

 environment does not change. If a particular kind or degree 

 of spotting is selected in the parent animals, it may be ex- 

 pected that offspring will be obtained both darker and lighter 

 than the parents. In this way the race can by selection be 

 made either darker or lighter, quite irrespective of any change 

 in the environment. Kammerer has obtained nothing be- 

 yond such effects as these. There is no reason to think that 

 a change of illumination induced them to any greater extent 

 in the second generation than it did in the first. 



Another light experiment carried out by Kammerer seems 

 to me to have more weight. This was concerned with the 

 degeneration of the eyes in cave animals. It is a well-known 

 fact that cave animals have bodies nearly or quite colorless 

 and possess degenerate eyes. In animals pigment formation 

 is an oxidation process, which frequently does not take place 

 in the absence of light. Therefore many animals which de- 

 velop in complete darkness are unpigmented. The human 

 skin, to be sure, develops pigment even in darkness, but it 

 develops much more of it in direct sunlight. The skin of a 

 European is fair if he stays indoors, but darkens quickly if he 

 spends much time outdoors in the direct sunlight. The dark- 

 est races of mankind are those which live where the sunlight 

 is strongest and the skies are clear; the fairest races live 

 where the sun's rays are less intense and the skies are often 



