304 SIGNIFICANCE OF SEXUAL REPRODUCTION [V. 



Physics and Chemistry were done with should we be per- 

 mitted to proceed to the investigation of organic nature. Under 

 these circumstances we ought not to possess now any scientific 

 theory of medicine ; for the study of pathological physiology 

 could not be commenced until normal physiology was com- 

 pletely known and understood. Yet how great a debt is owing 

 by normal to pathological physiology ! This is an example 

 which enforces the conclusion that it is not only permissible, 

 but in the highest degree advantageous, for the difl'erent spheres 

 of phenomena to be attacked simultaneously. 



Furthermore, if we had been compelled to proceed from the 

 simple to the complex, what would have become of the Theory 

 of Descent, the influence of which has advanced our knowledge 

 of Biology to an altogether immeasurable extent } 



But in this often-repeated criticism that we are not yet ready 

 to attack such complicated phenomena as heredity, is hidden 

 still another fallacy, for it is implied that facts become less 

 certain in proportion to the complexity of their causes. But 

 is it less certain that the egg of an eagle developes into an 

 eagle, or that the peculiarities of the father and mother are 

 transmitted to the child, than that a stone falls to the ground 

 when its support is taken away? Again, is it not possible to 

 draw a perfectly distinct and certain conclusion as to the re- 

 lative quantity of the material basis of heredity, present in the 

 germ-cells of either parent, from the fact that the father and 

 mother possess an equal or nearly equal share in heredity ? But 

 it is really unnecessary to argue in this way : why should we do 

 more than re-affirm that such a method of procedure in scien- 

 tific investigation is the only way by which we can gradually 

 penetrate the hidden depths of natural phenomena? 



No ! Biology is not obliged to wait until Physics and Chemistry 

 are completely finished ; nor have we to wait for the investiga- 

 tion of the phenomena of heredity until the physiology of the 

 cell is complete. Instead of comparing the progress of science 

 to a building, I should prefer to compare it to a mining operation, 

 undertaken in order to open up a freely branching lode. Such 

 a lode must not be attacked from one point alone, but from 

 many points simultaneously. From some of these we should 

 quickly reach the deep-seated parts of the lode, from others 

 we should only reach its superficial parts ; but from every point 



