88 GENETICS [Bot. Absts., Vol. IV, 



571. East, Edwin M., and Donald F. Jones. Inbreeding and outbreeding. 14 X 21 

 cm., 285 p., 46 fig. J. B. Lippincott : Philadelphia. 1919. — Earl}' marriage customs and meth- 

 ods of animal breeding are founded upon conclusion that inbreeding frequently gives unde- 

 sirable results. Inbreeding, however, has been often practiced and has given us our best 

 races of horses, swine, cattle and poultry, while in Ancient Egypt and Greece at height of their 

 power rather close inbreeding was practiced. One purpose of authors is to present critical 

 data as basis of determining application of certain fundamental principles to sociology, agri- 

 culture and evolutionary theory. — In concise, clear manner are presented well known facts 

 of reproduction in plants and animals together with cytological basis upon which mechanism 

 of heredity depends. These facts furnish principles upon which explanation of heterosis 

 has been developed. — It is shown that, in general, sexual reproduction occurs in higher forms 

 of life and asexual in simpler, although many of our most vigorous plants are usually self-fer- 

 tilized. Degeneracy which often occurs in asexually propagated varieties of potato and sugar 

 cane is most logically explained by diseases which are with difficulty eradicated because of 

 the method of propagation. Conclusion reached that Knight-Darwin Law should read "Na- 

 ture discovered a great advantage in occasional cross-fertilization." Adaptations for cross- 

 pollination in plants are briefly discussed. — Well known facts of Mendelism, together with 

 present factor hypotheses, relative stability of factors and analogies between this explanation 

 and the stability of the chemical atom are clearly outlined. Although chemical element 

 radium is breaking down rapidly this does not seriously detract from value of atomic theory. 

 Likewise occasionally demonstrated changes which occur in factors do not seriously mar value 

 of factor hypotheses, for they occur so infrequently that theory of permanent entity is justi- 

 fied. — Mathematical considerations of inbreeding are presented. Formulae for comparative 

 measure of actual number of ancestors compared with possible number are given for different 

 systems of mating. It is stated that these formulae do not tell anything concerning actual 

 germinal constituents of any individual resulting from given system of inbreeding. Formulae 

 for increase of homozygotes in any generation following cross when self-fertilization is prac- 

 ticed are presented. It is demonstrated that decrease in heterozygosity is automatic and varies 

 with closeness of inbreeding. The way in which factor linkage modifies results is illustrated 

 for two factor pairs. That artificial self-fertilization in cross-fertilized species and normal 

 self-fertilization in self-fertilized species following artificial cross, give same results from 

 Mendelian standpoint is clearly proven. — In light of these mathematical considerations results 

 of controlled inbreeding experiments are analyzed. Results from animal and plant field are 

 presented with special emphasis upon long-continued experiments of self-fertilization with 

 maize as obtained at the Connecticut Experiment Station. All experiments show that "in- 

 breeding has but one demonstrable effect on organism subjected to its action — the isolation 

 of homozygous types." Inbreeding is not injurious "merely by reason of consanguinity." 

 Facts of hybrid vigor or heterosis are next reviewed and cause of heterosis discussed. Review 

 of theories of hybrid vigor given and present conception of combined action of dominant linked 

 factors shown to be closely related to former physiological stimulus idea. Conclusion reached 

 that "Homozygosity when obtained with the combination of all the most favorable characters 

 is the most effective condition for the purpose of growth and reproduction." — Sterility is dis- 

 cussed and conclusion reached that sterility often accompanying inbreeding is not same thing 



Bterility resulting from hybridization. First case is phenomenon of Mendelian heredity 

 because certain segregations have occurred which accomplish certain end results. In other 

 case individuals are sterile because they cannot go through this same process because of lack 

 of compatibility of uniting cells. — It is pointed out that the vital feature of cross-fertilization 

 from standpoint of evolution "is to be explained solely on the ground of offering selective 

 agencies the greatest amount of raw material." — As applied to plant and animal improve- 

 ment, effects of inbreeding and outbreeding are discussed. Inbreeding is shown to be import- 

 ant agency in bringing about uniformity and concentrating desirable qualities in particular 

 race while crossing induces variability as basis for origin of new and valuable types of plants 

 and animals. As the l'i is often more vigorous than its parents, it is logical to maintain pure 



es which are used as parents, the I'\ cross being grown as commercial product. — Application 

 of the truths so ably developed, to science of eugenics is interestingly discussed. Racial mix- 



