5 1 2 Organisms Are Products of 



Josiah 

 Wedgwood 



-o 



a 



Cousin Mary 



3rd degree Howard 



a- 



JT^^^ 



Erasmus 

 Darwin 



Josiah 

 Jr. 



i7> 



Robert Charles Erasmus 

 d. 20 



Emma 

 Wedgwood 



r^ 



Charles 

 Darwin 

 (1809-1882) 



^ di Ik ^ 6 



William Sir Sir Major Horace 



George Francis Leonard 



6 6 



i"^ 



C. G. 

 Darwin 



Fig. 461 A part of the pedigree of five genera- 

 tions of an illustrious faviily. Note the cousin 

 marriages. What kinds of factors viight explain 

 the large nianber of famous descendants? 



soldier, had a son by a feeble-minded 

 girl. Four hundred eighty descendants 

 of this union have been traced through 

 five generations. About many of these 

 nothing could be learned, but one hun- 

 dred forty-three are said to have been 

 feeble-minded and forty-six normal. 

 Later in his life Martin Kallikak married 

 a normal wife and started a second line 

 of descendants. Four hundred ninety-six 

 of these have been reported on; as far as 

 the records show all Mere nomial. It 

 looks as though at least some types of 

 feeble-mindcdness might be inherited. 



Other pedigrees you may read about 

 are those of the Jukes and the Edwards 

 families. 1 lie Jukes (a fictitious name) 

 are described as a line of shiftless good- 

 for-nothings, poor, and a burden to the 

 community. From Jonathan Edwards, a 

 New England clergyman of colonial 

 times, who married a brilliant wife, have 

 been traced almost one thousand four 



Heredity and Environ?nent unit ix 



hundred descendants. Many of these 

 were professional men who became suc- 

 cessful in one way or another. Do these 

 family histories give evidence of the in- 

 heritance of mental traits? 



Criticism of the evidence. In all these 

 cases we depend on records written 

 many years ago. These cannot be veri- 

 fied. They were written by people, who, 

 in general, were not trained to be ac- 

 curate. Frequently they were written by 

 people who allowed their prejudices to 

 color their reports. Can you rely on such 

 as evidence? 



But a far more important criticism is 

 that the effect of the environment has 

 not been taken into account. Certainly 

 in the case of the Jukes and Edwards 

 families we know that a large part must 

 have been played by the environment. 

 In short we are forced to admit that we 

 have little definite information about the 

 inheritance of mental traits. 



Improving germ plasm in man. With 

 so few facts at our command there is lit- 

 tle we can say about breeding better 

 men. We do know, however, that defec- 

 tive germ plasm ^^'hich shows as feeble- 

 mindedness tends to be transmitted to 

 the offspring. For this reason it has been 

 argued that the feeble-minded, wher- 

 ev^er possible, should be segregated in in- 

 stitutions where they will be unable to 

 pass on their defective germ plasm. More 

 than half the states have followed the ex- 

 ample of Wisconsin in issuing marriage 

 licenses only to those who have been ex- 

 amined by a physician for certain com- 

 municable diseases. In some states, but 

 not in all, the license to marry is refused 

 to those who have these diseases. It has 

 been suggested that the examinatio/i 



