THE EFFECT UPON HUMAN EVOLUTION 281 



An unstable pituitocentric marrying another unstable pituito- 

 centric will have children either exceptionally small or tall, or 

 abnormally bright or stupid. The instability tends to right itself 

 in the next generation, or that following. Genius as a sport, 

 as well as sudden degeneration of family stock, the whole prob- 

 lem of mutation, may be closely connected with this tendency. 



It has been noted that the extinction of species has been pre- 

 ceded by a great increase in their size, for example, the case 

 of the great reptilia of prehistoric time. That possibly represented 

 pituitary stabilization, and so an abeyance of the ability to vary, 

 necessary for fresh adaptation to a changing environment. In- 

 deed, endocrine instability appears the fundamental condition of 

 the tendency to vary, endocrine stability the opposite. 



Certain endocrine facts in relation to heredity should be men- 

 tioned. The daughters of mothers who menstruated early, them- 

 selves menstruate early. Animals fed upon thyroid during preg- 

 nancy, comparable to the thyrocentric, give birth to offspring with 

 a very large thymus, comparable to the thymocentric. Women 

 with partial thyroid deficiency, or myxedema, bear cretins. 

 These are suggestive of what the internal secretions may do to 

 an individual in inheritance and development. Inherited en- 

 docrine potential is the maximum reaction of which a gland is 

 capable. This matter of potential is comparable to the factor 

 of reserve power or margin of safety demonstrated up to the hilt 

 for such organs as the heart and kidney as varying from indi- 

 vidual to individual. A low potential, like instability of an 

 internal secretion gland, may be latent, and not made manifest 

 until the proper stimulus, the maximum amount of stress and 

 strain, like accident, disease, shock or war, arrives. 



When the individual is tested the effects may be purely local 

 because there is always in the organism a point of least re- 

 sistance. Physical changes alone may be prominent. Or because 

 somatic changes are minor, the psychic will dominate the pic- 

 ture. An attack of the "blues/' unaccompanied by any demon- 

 strable transformation of the bodily processes, may be the sole 

 symptom of an endocrine failure somewhere in the chain due to 

 hereditary weakness or low potential. 



So we may account for family trends and streaks, for varieties 

 and strains among individuals, upon more precise lines based 

 upon endocrine analysis. Family disturbances of the internal se- 

 cretions of the extreme sort denominated disease are well known. 

 Indeed, a number of family diseases or predispositions to diseases. 



