THE TROBLEMS OF HP:REDITY AND THKIK SOLUTION. 5(U 



but it has lKM't)in(' likely that o('noral oxpivssions will tx^ t'ouiKl capable 

 of sulHciently wide application to be justly called "laws'' of heredity. 

 That this is so was till recently due almost entirely to the work of 

 Mr. F. (Talton. to whom we nvo indebti^d for th(^ tirst systematic 

 attem})t to enunciate such a law. 



All laws of heredity so far propounded ai'e of a statistical character 

 and have been obtained by statistical methods. If we consider for a 

 moment what is actually meant by a "law of heredity" we shall see 

 at once w hy these investigations nuist follow statistical methods. For 

 a "law" of heredity is simply an attempt to declare the course of 

 heredity under given conditions. But if we attempt to pnxlicate the 

 course of heredity w(^ have to deal with conditions and groups of causes 

 wholly unknown to us, whose presence we can not recognize, and 

 whose magnitude we can not estimate in any particular case. The 

 course of hei'edity in particular cases therefore can not be foreseen. 



Of the many factors which determine the degree to which a given 

 character shall be present in a given individual only one is usually 

 known to us, namely, the degree to which that character is present in 

 the parents. It is connnon knowdedge that thiu'e is not that close cor- 

 respondence between parent and oti'spring which would r(\sult were 

 this factor the only one operating; but that, on the contrary, the 

 resemblance between the two is oidy an uncertain one. 



Ill dealing with phenomena of this class the stud\' of single instances 

 r(>\ cals no regularity. It is only by collection of facts in great num- 

 bei-s, and by statistical treatment of the mass, tliat an}' order or law 

 can be percei\'ed. In the case of a chemical reaction, for instance, l)y 

 suitable means the conditions can be accurately reproduced, so that in 

 every individual case we can predict with centainty that the same 

 result will occur. But with heredity it is somewhat as it is in the case 

 of the rainfall. No one can say how nmch rain will fall to-morrow in 

 a given place, but we can jiredict with moderate accuracy how much 

 will fall next year, and for a period of yeai's a prediction can Ix^ made 

 which accords v(>ry closely with the truth. 



Similar predictions can from statistical data be made as to the dura- 

 tion of life and a great variidy of events, the conditioning causes of 

 which are very imperfectly undei'stood. It is predictions of this kind 

 that th(^ study of heredity is beginning to make possilile, and in that 

 sense hiws of hcu'edity can be perceived. 



We are as far as ever from knowing w liy some characters are trans- 

 mitted, while others are not; nor can anyone yet foretell which indi- 

 vidual parent will transmit characters to the oflspring and Avhich will 

 not; nevertheless the progress made is distinct. 



As yet investigations of this kind ha\(^ Ikhmi made in Only a fc^v 

 instances, the most notable being those of Galton on human stature 



SM l'J02' 3«) 



