PART IV. THE THEORY AND EVIDENCE OF 

 ORGANIC EVOLUTION: ADAPTATION 



CHAPTER XV 



Organic evolution versus special creation Spontaneous generation and 

 biogenesis The origin of living things. 



AT the present day we see the surface of the earth teeming with 

 hosts of living things, incalculable in number and of endless 

 diversity in form and structure. Every situation where life is 

 possible is occupied by plants or animals of some kind or other, 

 all specially adapted in bodily organization to the conditions 

 under which they have to maintain their existence. From the 

 bleak and inhospitable summits of high mountain ranges to ocean 

 depths which can be measured in miles ; from the perpetually 

 frozen circumpolar regions to the torrid zone on either side of 

 the equator, living things abound. Seas, rivers, lakes, dry land 

 and air have all alike been taken possession of by representatives 

 of the animal and vegetable kingdoms. A single drop of water 

 may contain thousands of organisms, and every chalk-cliff, coal- 

 seam or peat-bog testifies to the countless myriads which have 

 lived in past times and whose remains have contributed in no 

 small measure to the formation of the earth's crust. 



In the animal kingdom alone it is probable that at least a 

 million different kinds or species are living on the earth at the 

 present day. Some half million or so have already been dis- 

 covered, named and more or less imperfectly described, while 

 every exploring expedition brings back many which have never 

 before been seen. 



Nevertheless there must have been a time when no living 

 things whatever existed on the earth. According to the 

 nebular hypothesis our planet is still gradually cooling from a 

 molten state, preceded probably by an incandescent gaseous 

 condition, which must have rendered the existence of any proto- 

 plasmic organism a physical impossibility. Protoplasm becomes 



p 2 



