SUMMARY OF EVIDENCE 83 



7. The argument from the distribution of organisms 

 in time is corroborated by their distribution in space 

 — their geographical distribution. If the evolution- 

 ary theory is true, we may expect to find that closely 

 related species are frequently located near each other; 

 and that when they are widely separated — for example, 

 by seas or oceans — facts are available which point to 

 the possibility and even the likelihood of their early 

 migration from a common centre. We may also ex- 

 pect to find that when the fauna and flora of two terri- 

 tories have always been effectually isolated from each 

 other, whether by insurmountable mountain ranges or 

 by geologically permanent bodies of water, their species 

 differ widely. The facts agree with this expectation 

 to a marked degree. It is true that apparent excep- 

 tions exist. Closely allied species are found on oppo- 

 site sides of the globe; and the fauna and flora of 

 certain islands — for example, Madagascar and New 

 Zealand — differ widely from those of neighbouring 

 continents and islands. But these anomalies can 

 usually be accounted for by geological investigation. 

 North America and the continent of Europe were in 

 former ages connected by land. The comparative 

 similarity which has been discovered between the 

 species of Great Britain and Japan is accounted for 

 by the absence of any permanent barriers between 

 them, whether of climate or of geological nature. On 

 the other hand the depth of water which now separates 

 Madagascar and New Zealand from the nearest land 

 seems to prove that the present isolation of their fauna 



