124 Heredity and Environment 



there are no "qualities" or "characteristics" which are "trans- 

 mitted" as such from one generation to the next. Such terms 

 are not without fault when used merely as figures of speech, but 

 when interpreted literally, as they frequently are, they are alto- 

 gether misleading; they are the result of reasoning about names 

 rather than facts, of getting far from phenomena and philosophiz- 

 ing about them. The comparison of heredity to the transmission 

 of property from parents to children has produced confusion in 

 the scientific as well as in the popular mind. It is only necessary 

 to recall the most elementary facts about development to recog- 

 nize that in a literal sense developed characteristics of parents are 

 never transmitted to children. 



2. The Transmission Hypothesis. — And yet the idea that the 

 characteristics of adult persons are transmitted from one genera- 

 tion to the next is a very ancient one and was universally held 

 until the most recent times. Before the details of development 

 were known it was natural to suppose, as Hippocrates did, that 

 white-flowered plants gave rise to white-flowered seeds and that 

 blue-eyed parents produced blue-eyed germs, without attempt- 

 ing to define what was meant by white-flowered seeds or blue- 

 eyed germs. And even after the facts of development were fairly 

 well known it was generally held that the germ cells were made 

 by the adult animal or plant and that the characteristics of the 

 adult were in some way carried over to the germ cells; but the 

 manner in which this supposed transmission took place remained 

 undefined until Darwin attempted to explain it by his "provisional 

 hypothesis of pangenesis." Darwin assumed that minute parti- 

 cles or "gemmules" were given off by every cell of the body, at 

 every stage of development, and that these gemmules then col- 

 lected in the germ cells which thus became storehouses of little 

 germs from all parts of the body. Afterward, in the develop- 

 ment of the embryo, the gemmules, or little germs, developed 

 into cells and organs similar to those from which they originally 

 came. 



