LIXXEAN SOCIETY OF LOXDOX. 2$ 



the scientific jSTatural System, which was beinjs; slowly evolved as the 

 result of more close and accurate study of living things, whereby 

 those characters that are permanent and essential came to be dis- 

 tinguislied from those that are transitory and adaptive ; so that 

 the Idea of Likeness, upon which the Natural System was 

 originally based, grew into the Idea of Affinity. 



But is there nothing more for the naturalist to learn when he 

 has collected his material and classified it ? Most assuredly there 

 is. Since the advent of the evolutionai-y epoch, a new idea has 

 become dominant in Biology, the Idea of Phylogeny, which has 

 superseded the Idea of Affinity of earlier days. It is not enough 

 for us to know what is ; we seek to discover how it has come to be 

 what it is : we perceive that the perfect JS^atural System must be a 

 genealogy expressing true blood-relationships. This study inay be 

 said to be still in its infancy, in spite of the extraordinary activity 

 of reseai'ch, especially in Embryology and Palaeontology, that the 

 phylogenetic idea has inspired. Though here and there fragments 

 of the mosaic seem to have been successfully pieced together, the 

 main outlines even of the great picture are as yet but dimly 

 discernible. 



There is yet a further height to be explored. Supposing, for a 

 moment, that we were now in possession of a complete genealogy 

 of animals and plants, we should only be able to answer the 

 question how their evolution had come about, but not the question 

 tvhy. AVe shoidd still have to seek for the causes of evolution, 

 whether efficient or final. The search after the efficient causes o£ 

 organic evolution is, I am glad to say, engaging more and more 

 attention at the present time. The facts of heredity, of variation, 

 of distribution in space and time, are being closely scrutinized with 

 the object of eliciting the laws by which they are governed, and of 

 determining the factors by which they are produced. If it has 

 become clear that Natural Selection is potent in determining the 

 survival of new forms, it is equally clear that it does not give rise 

 to them. And here we come face to face with the most difficult 

 problem of all — namely, that organic evolution should have pro- 

 ceeded from the lower to the higher, from the simple to the complex. 

 Why should the first and simplest organisms have given rise to 

 others more highly organized, and these in tiu-n to others, until 

 all tlie forms that we know were evolved ? If we endeavour to 

 account for progressive development by arguing that highly 

 organized animals and plants are at an advantage in the struggle 

 for existence as compared with the lower, Ave are confronted with 

 the old questions — Why then have not the lower forms all perished 

 under the operation of natural selection ? — Why are so many 

 stages of organization still represented ? To these it may be 

 replied, that many of the higher forms differ so widely from many 

 of the lower, that they do not compete with each other, and so 

 may continue to exist side by side. It must not, however^, be 

 overlooked that ^ide differences of position in the scale of life do 

 not necessarily prevent competition. For instance, the lowly 



