248 The Mechanism of Evolution in Leptinotarsa 



way a typical group of individuals of like gametic constitution — a biotype. 

 This character of the pronotum is composed of many elements, each capable of 

 independent expression, and each to a greater or less extent independently capa- 

 ble of modification. In figure 41 are shown certain true-breeding races, homo- 

 zygous in action, with patterns that are capable of having their elements modified 

 greatly, without changing the homozygous nature of the pattern as a whole. Are 

 there biotypes within biotypes? If so, where is the limit? Would it not be 

 possible to go on indefinitely, as skill and methods become acute and refined, 

 more and more to get ad infinitum smaller and smaller genes and geno-differ- 

 ences, until a stage is reached in the distant future where the only difference was 

 one of presence or absence of one electron or other minute material unit ? 



(2) Do these groups — biotypes or aggregations of genotypically like individ- 

 uals — exist in nature as isolated realities in the population, or are they merely 

 individual momentary conditions present in members of the population which 

 can be separated and when isolated breed true as long as the isolation is main- 

 tained? What is the position and meaning of these experimentally isolated 

 groups in populations from nature. 



There is no doubt that from beans, grains, etc., it is possible to isolate geno- 

 types as Johannsen and others have done, or to isolate clones from organisms 

 like Paramcecium, as has been accomplished by Jennings; but were all of the 

 genotypes isolated, and how many other genotypes based upon different char- 

 acters could have been secured ? Are we not still thinking and talking of these 

 matters in terms of the morphologist and anatomist ? Are not genes and geno- 

 typical constitutions at base purely morphological concepts in that they involve 

 identity of parts or constitution ? The key to the whole situation lies, I believe, 

 in the determination of what homozygous and heterozygous conditions of the 

 germinal material really signify, 



Neo-Mendelians, descriptively at least if not in fact, adhere to the anatomical 

 picture, and homozygous gametes are those of like factorial constitution, and 

 heterozygous gametes those of unlike composition. This is not true. Homozy- 

 gous as well as heterozygous are descriptive of uniformity of reaction in the ger- 

 minal material and not of the conditions of constitution per se. That is, homo- 

 zygous gametes are those in which a state of physico-chemical adjustment has 

 been attained, such that, regardless of the active potentialities present, the action 

 of the gamete is always the same in normal development and in combinations. 

 Genotypical gametes are the same in character and action, in that a genotypical 

 gamete or group may be different in their potentiality constitution, but they 

 react alike, behave alike in ordinary breeding, and hence are descriptively stated 

 to be alike. It is a singleness or uniformity of action that determines the 

 behavior, and this is dependent upon the stability of the physico-chemical com- 

 plex in the germinal material, and not at all upon the nature or array of poten- 

 tialities present. 



The first problem with any natural population is to discover if there are pres- 

 ent minor stable groups which can exist without selection to maintain them, 

 but which, nevertheless, interbreed to a greater or less extent in the population. 

 With a species like L. midtitceniata it is, as has been shown, easy to isolate many 

 true-breeding strains. How many of these will remain without " selection " 

 when carried as group cultures ? To what extent can these be modified by cumu- 

 lative " selection " ? 



