of Heredity 3 



essential nature, "the causes,' as they are sometimes 

 called, of heredity: but we want also to know the laws 

 which the outward and visible phenomena obey. 



Let us recognise from the outset that as to the essential 

 nature of these phenomena we still know absolutely 

 nothing. We have no glimmering of an idea as to what 

 constitutes the essential process by which the likeness 

 of the parent is transmitted to the offspring. We can 

 study the processes of fertilisation and development in 

 the finest detail which the microscope manifests to us, 

 and we may fairly say that we have now a considerable 

 grasp of the visible phenomena ; but of the nature of 

 the physical basis of heredity we have no conception 

 at all. No one has yet any suggestion, working hypo- 

 thesis, or mental picture that has thus far helped in 

 the slightest degree to penetrate beyond what we see. 

 The process is as utterly mysterious to us as a flash of 

 lightning is to a savage. We do not know what is the 

 essential agent in the transmission of parental characters, 

 not even whether it is a material agent or not. Not only 

 is our ignorance complete, but no one has the remotest 

 idea how to set to work on that part of the problem. 

 We are in the state in which the students of physical 

 science were, in the period when it was open to anyone 

 to believe that heat was a material substance or not, as 

 he chose. 



But apart from any conception of the essential modes 

 of transmission of characters, we can study the outward 

 facts of the transmission. Here, if our knowledge is 

 still very vague, we are at least beginning to see how 

 we ought to go to work. Formerly naturalists were 

 content with the collection of numbers of isolated instances 

 of transmission more especially, striking and peculiar 



12 



