402 EVOLUTION AND ANIMAL LIFE 



most of them at least, believe that this kind of usefulness is 

 real, and that it is the principal clew to the chief significance 

 of color and pattern and this not alone in the case of in- 

 sects, but of most other animals as well. 



From this point of view, namely, that color patterns may 

 be of advantage in the struggle for existence, just as strength, 

 swiftness, and other capacities and conditions are, the speciali- 

 zation and refinement, all the wide modification and variety 

 of colors and patterns are explicable by the hypothesis of 

 their gradual development in time through the natural selec- 

 tion of fortuitous advantageous variations. On this basis, 

 such special instances of resemblance to particular parts of 

 the environment, as that shown by Kallima in its likeness 

 to a dead leaf, and Diapheromera in its simulation of a dry, 

 leafless twig, are simply the logical extremes of such a line of 

 specialization. 



But the nature observer may be inclined to ask how such 

 brilliant and bizarre colors as those of the swallowtail butter- 

 flies and the tiger-banded caterpillars of Anosia can be included 

 in any category of "protective resemblance" patterns. They 

 are not so included, but are explained ingeniously by an added 

 hypothesis called that of "warning colors/' while for the strik- 

 ing similarities of pattern often noted between two unrelated 

 conspicuously colored species still another hypothesis is pro- 

 posed. In these cases it is not concealment that the color 

 pattern effects, but indeed just the opposite. Since the pioneer 

 studies of Bates and Wallace and Belt, naturalists have been 

 observing and experimenting and pondering these exposing, 

 as well as these concealing, conditions of color and pattern, 

 and they have proposed several theories or hypotheses ex- 

 planatory of the various conditions. These hypotheses are 

 plausible; but they are much more than that: they are each 

 more or less well backed up by observation and experiment, 

 and some of them have gained a large acceptance among 

 naturalists. Both the reasoning and observed facts on which 

 these hypotheses rest are based on the usefulness of the colors 

 and patterns to the animals in their relation to the outside world. 

 And the influence of advantage and natural selection is given 

 the chief credit for determining the present-day conditions of 

 these colors and patterns. 



Before, however, we take up these hypotheses, defining 



