600 



COLLEGE ZOOLOGY 



Figure 425. How the law of differential birth rate 

 works. If a competent couple multiplies at a 3-child 

 rate, and a hereditary feeble-minded couple at a 

 9-child rate, their great grandchildren, provided they 

 all live, will be as the above white sector is to the 

 black area. 



persons to avoid transmitting the poten- 

 tialities of serious genetic disability to their 

 offspring insofar as such measures are con- 

 sistent with their own interests and welfare. 

 However, much of the hope for man's im- 

 provement does not lie in genetic improve- 

 ment, but in cultural, social, and scientific 

 advance. 



Therefore, the best chances of immediate 

 progress are to be secured by euthenics, the 

 science of improving man by providing the 

 best possible environment. Euthenics, while 

 not improving the genetic quality of the 

 race, is a program of great value for human 

 betterment. An organism develops from a 

 fertilized egg in which the genetic poten- 

 tialities of the individual are predetermined 

 by the genes, but what the fertilized egg de- 

 velops into is determined by the interac- 

 tion of two powerful forces, the genes and 

 the environment (Fig. 424). This makes ob- 

 vious the importance of a favorable environ- 

 ment so as to give opportunity for the best 

 possible expression of the genetic constitu- 

 tion. 



What the environment may do for us is 

 illustrated by the condition known as cre- 

 tinism. The cretin is a feeble-minded dwarf 

 who possesses a defective thyroid gland, 

 which is unable to secrete sufficient hor- 

 mones for the proper development of the 

 body. If thyroid secretion is artificially sup- 



plied to a young cretin, his condition may 

 be improved or completely alleviated. 



SELECTED COLLATERAL 

 READINGS 



Altenburg, Edgar. Genetics. Holt, New York, 



1957. 

 Braun, W. Bacterial Genetics. Saunders, Phila- 

 delphia, 1953. 

 Colin, E.G. Elements of Genetics. McGraw- 

 Hill, New York, 1956. 

 Grow, James F. Effects of Radiation and Fall- 

 out. Public Affairs Pamphlet No. 256, Public 



Affairs Gommittee, New York, 1957. 

 Dunn, L.G. Genetics in the 20th Century. 



Macmillan, New York, 1951. 

 Gates, R.R. Human Genetics, Vols. I and II. 



Macmillan, New York, 1946. 

 Lush, Jay L. Animal Breeding Plans. Iowa 



State College Press, Ames, Iowa, 1945. 

 Osborn, Frederick. Preface to Eugenics. Harper, 



New York, 1951. 

 Penrose, L.S. The Biology of Mental Defect. 



Grune and Stratton, New York, 1949. 

 Reed, S.G. Counseling in Medical Genetics. 



Saunders, Philadelphia, 1955. 

 Scheinfeld, A. The New You and Heredity. 



Lippincott, Philadelphia, 1950. 

 Schubert, J., and Lapp, R.E. Radiation: What 



Is It and How It Affects You. Viking, New 



York, 1957. 

 Sinnott, E.W., Dunn, L.G., and Dobzhansky, 



T. Principles of Genetics. McGraw-Hill, 



New York, 1958. 

 Snyder, L.H., and Da\id, P.R. The Principles 



of Heredity. Heath, Boston, 1957. 

 Srb, A.M., and Owen, R.D. General Genetics. 



Freeman, San Francisco, 1952. 

 Stern, Curt. Principles of Human Genetics. 



Freeman, San Francisco, 1949. 

 Swanson, C.P. Cytology and Cytogenetics. 



Prentice-Hall, Englewood Cliffs, N.J., 1957. 

 Waddington, C.H. The Strategy of the Genes. 



Macmillan, New York, 1958. 

 Wagner, R.P., and Mitchell, H.K. Genetics 



and Metabolism. Wiley, New York, 1955. 



