920 LIFE : OUTLINES OF GENERAL BIOLOGY 



synthetic types, and of bridging the gaps between discontinuous 

 species by collecting sports or mutations. 



(d) Embryological. — In many cases the life-history of the 

 individual is a condensed recapitulation of the presumed history of 

 the race. The embryonic development of many an organ, such as 

 brain, heart, and kidney, is a re-treading of the racial evolution. 

 Even the gradual growth of a much-branched nerve-cell in a bird 

 or mammal has its later stages represented by the final forms 

 reached, but not transcended, in reptile, amphibian, and fish. In 

 a very real sense the frogling climbs up its own genealogical tree; 

 and the way in which antique structures, such as gill-slits, outlive 

 their usefulness, leaves one with the alternative — Evolution or 

 Magic? 



{e) Physiological and Actual. — Besides geographical, palaeon- 

 tological, anatomical, and embryological "evidences", there are 

 others which may be grouped as physiological, actual, and experi- 

 mental. Thus the transfusion of blood may be effected harmoniously 

 between organisms which are on other grounds (e.g. anatomical) 

 believed to be near relations. The closeness of the relationship, 

 e.g. among Primates, may be measured by the amount of the 

 precipitate which follows the mixture of the blood of different 

 types. The test-tube shows visibly how near the gorilla is to the 

 orang, but how far from the baboon. 



The whole story of domestication and cultivation is an experi- 

 mental corroboration of the theory of evolution, or rather of the 

 evolutionist way of looking at the present. The past lives on in the 

 present; but, more than that, in many a corner of the world, as we 

 have illustrated in reference to the Foula Mouse, evolution is going 

 on under our eyes. 



To sum up, the general idea of organic evolution is that the 

 present-day living creatures have arisen naturally by gradual 

 change from ancestors on the whole simpler, just as tame pigeons 

 have arisen from wild rock-doves, or races of cabbages from Wild 

 Kale. 



Evolution may be defined as a continuous natural change in a 

 race in a definite direction, in the course of which new departures 

 emerge and may, according to their value and viability, be estab- 

 lished alongside of, or gradually in place of, the originative 

 stock. 



The evidences include all the facts of life, since all admit of 

 evolutionist interpretation, and there are none that contradict this. 

 The evolution idea is a key that fits all the locks into which we are 

 able to insert it. 



Since the "evidences" have been often well stated — ^by Darwin 

 best of all — we have restricted ourselves here to an outline; and to 

 this we now add two or three illustrations in greater detail. 



