183 



varieties of the same species, and much more so between dif- 

 ferent species. If it were not so, varieties and species would 

 after a time become incTistinguishably blended so as to lose 

 their specific characters. This infertility in crossing varies 

 greatly in different races. The English are said to be less 

 fertile in crossing with the Negro than are the French and 

 the Spanish, and also with certain aboriginal inhabitants of 

 America. It cannot be said that there is any appreciable 

 element of aboriginal half-breeds in any part of Australia, 

 nor have the Malays left any special impress on the shores 

 of the Northern parts. It is stated that there are some evi- 

 dences of a superior race having left an impress on a portion 

 of the Australian aborigines, probably towards the eastern 

 littoral portions of Australia, a part that, according to Prof. 

 Tate in his above quoted paper, since the Pluvial Epoch, 

 has gained accessions to its flora from the Indo-Malay pro- 

 vince. 



The above observations respecting a few of the conditions 

 of life and customs of the Australian aborigines seem to 

 show that these have not been favorable to evolution to- 

 wards divergent types. For it must be remembered that, 

 although a collection of organisms has not shown any evolu- 

 tionary progress, it does not at all follow that it was because 

 it had no evolutionary power. Such a condition jnay be con- 

 sidered as non-existent in biology. Where no progress exists 

 it is because the forces at work are mutually antagonistic, 

 and thus bring about a condition of equilibrium. It is as 

 true in biology as in physics that a body set in motion by 

 a force will continue in motion until stopped by a force equal 

 to that which set it in motion. The tendency to individual 

 variability which is always existent is the initial propelling 

 power in organic Nature, and isolation and heredity are the 

 extraneous forces which may, according to circumstances, 

 accelerate, retard, or bring to a condition of rest the body 

 affected. The direction of evolutionary progress will also be 

 the resultant of the respective strengths of these two latter 

 forces, whilst the rapidity or momentum of the changes will 

 depend on the power of the initial force ; that is, the tendency 

 to variability. The familiar diagram of the parrallelogram 

 of forces will make clear what is meant. Let A be a body 

 of intergenerants set in motion by a force BA (variability) 

 in the direction of X (evolution). If two other forces CA 

 (isolation) and DA (heredity) of equal influence act on the 

 body A, there will be no disturbing element as to direction, but 

 they may have an accelerating or a retarding effect on motion 

 according as to whether their line of action is the same as, or 



