I. ii:tkouuctioii. 



A few years ogo experimenttil inbreeding of the al- 

 bino rat, L'us norvegicus albinus, was started at the V/istar 

 Institute of Anatomy and Biology in order to determine the 

 anatomical consequences of such procedure upon successive gen- 

 eration? of progeny, /unong other results obtained was a dis- 

 tinct and progressive decrease in actual and relative brain 

 weight (relative, that is, in reference to body length) for 

 four generations of close inbreeding. From the fourth to the 

 tenth generations the relative brain v/eight remained, on the 

 average, constant at six and one half percent less than that 

 of the average normal rat. 



Vfhen, early in October, 1911, V)t, Donaldson suggest- 

 ed to Professor \7atson that the deterioration in brain weight 

 might be accompanied by a similar deterioration in the abili- 

 ty to form habits a nev,- line of investigation in comparative 

 psychology was opened up. The problem was offered to the v/rit- 

 er and gladly accepted. 



In regard to the question as to whether inbreeding, 

 per se, has deteriorating effects upon progeny it is unsafe 

 to be arbitrary, and authoritative testimony must await the 

 results of further investigations. ^7e know, upon the author- 

 ity of historii^ns, that the Incas of Peru for many generations 

 married their oldest sisters and were, until their extinction 

 by the Spaniards, physically and mentally superior to their 

 subjects. Breeders of domestic animals frequently resort to 

 inbreeding in order to perfect desirable qualities in the strain. 

 It may be, as many claim, that inbreeding io deteriorating 

 only in cases where an hereditary taint, appearing, in the com- 



