314 PRESENT PROBLEMS IN EVOLUTION AND HEREDITY. 



t)ie iHiblicatioii of the theory of Darwin, in 1S58, and, after subsiding, 

 has again been aroused by Weismann's theory of heredity, published 

 in 1883. 



This is the situation I have ventured to present to you as Cartwright 

 lecturer, not, of course, without introducing some conclusions of my 

 own, which have been derived livmi vertebrate pahcontology, but which 

 I shall direct mainly upon human evolution. 



So far as theories need come before us now, remember that Lamarck 

 (1792) attributed evolution to the hereditary transmission to ottspring 

 of changes (acquired variations) caused by environment and habit in 

 the parent. Darwin's latest view was that evolution is due to the 

 natural selection of such congenital vai'iations as favored survival, sup- 

 j)lemented by the transmission of acquired variations. Weismann 

 denies the transmission of acquired variations, or characters, entirely, 

 and attributes evolution solely to the natural selection of the indi- 

 viduals which bear the most favorable variations of the geim or repro- 

 ductive cells. We nuist therefore clearly distinguish between "con- 

 genital variations" which are part of our inheritance and "acquired 

 variations" which are due to our life liabits; the question is, are the 

 latter transmitted':! 



At the outset I would emphasize the extreme complexity of evolution 

 by a few words upon variation, or in terms of medical science, upon 

 anomalies. 



Wlien we sjieak of a part as "anomalous" we mean that it varies at 

 birth from the ordinary or typical form; it may be minute, as the small 

 slip of a tendon, or large, as the addition of a complete vertebra to the 

 spinal cohimn. Wood has found that in tlie muscular system alone 

 there are nine anomalies in the average individual. It is clear that 

 the evolution of a new type, so far as the muscular system is concerned, 

 must consist in the accumulation of anomalies in a certain definite 

 direction by heredity. Thus the anomalous condition of one generation 

 may become the typicial condition of a very much later generation, and 

 we observe the paradox of a. typi(;al structure becoming an anomaly 

 and an anomalous structure becoming typi(;al: for example, the supra- 

 condylar foramen of the liumerus was once typical, it is now anom- 

 ahms; the retardation in development of the wisdom tooth was once 

 anoaialous, it is now typical. 



The same principle applies to races which are in different stages of 

 evolution; an anomaly in the white, such as the early closure of the 

 cranial sutures, is normal in the black. Now the deductions of the 

 Weismann school of evolutionists seem to be founded ui)on the prin- 

 ciple "■de minimis non curat /e.r;" that we need only regard such major 

 variations as can, ex hypothesis weigh in the scale of survival. Against 

 this 1 urge tluxt we must regard the evolution of particular structures, 

 the components of larger organs, the separate muscles and bones for 

 example, for the very reason that while iu some cases they play a most 



