IN THE THEORY OF NATURAL SELECTION. 297 



cedure in scientific 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 investigation 

 of the phenomena of heredity until the physiology of the cell is 

 complete. Instead of comparing the progress of science to a build- 

 ing, 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 some knowledge of the 

 complex tout ensemble of the lode would be gained. And the more 

 numerous the points of attack, the more complete would be the 

 knowledge acquired, for valuable insight will be obtained in every 

 place where the work is carried on with discretion and perseverance. 



But discretion is indispensable for a fruitful result ; or, leaving 

 our metaphor, facts must be connected together by theories, if 

 science is to advance. Just as theories are valueless without a firm 

 basis of facts, so the mere collection of facts, without relation and 

 without coherence, is utterly valueless. Science is impossible with- 

 out hypotheses and theories: they are the plummets with which 

 we test the depth of the ocean of unknown phenomena, and thus 

 determine the future course to be pursued on our voyage of dis- 

 covery. They do not give us absolute knowledge, but they afford 

 us as much insight as it is possible for us to gain at the present 

 time. To go on investigating without the guidance of theories, 

 is like attempting to walk in a thick mist without a track and 

 without a compass. We should get somewhere under these circum- 

 stances, but chance alone would determine whether we should reach 

 a stony desert of unintelligible facts or a system of roads leading in 

 some useful direction ; and in most cases chance would decide 

 against us. 



In this sense I trust that the sign-post or compass which I offer 

 may be accepted. Even though it should be its fate to be replaced 

 by a better one at a later period, it will have fulfilled its object if 

 it enables science to advance for even a short distance. 



