EVOLUTION BY DEGENERATION. 



19 



EVOLUTION BY DEGENERATION 



OR Adaptive Degradations, the Cause of many Cases of Evolu- 

 tion AMONG Plants. 



By Rev. Prof. G. Henslow, M.A., V.M.H, 

 [Read March 10, 1914 ; Mr. C. R. Fielder, V.M.H., in the Chair.] > 



Evolution, wrongly implying " Advance " only. — ^The popular idea 

 of evolution would seem to be that it implies a general advance and 

 improvement towards some unknown, perfect ideals in the structure 

 of plants and animals. The converse, however, is often lost sight of ; 

 but the fact is that no animal or plant, which has altered its structure 

 in some way, did so without incurring certain degrees of degradation 

 or loss in another at the same time. It may not be always prominent, 

 but in all cases the organism, in whatever degree its structure may 

 be degraded, is always thereby more in harmony or adaptation to 

 the conditions of hfe which brought about the degradations. Thus, 

 the whale-bone whale, derived, no doubt, from some ancestral 

 terrestrial quadruped, has now no teeth, except as rudiments in 

 the embryonic condition of the animal. It, in all probability, had 

 four legs and feet, but, in changing its habit of life in adaptation to 

 water, the hind ones disappeared, leaving rudiments of the legs only 

 below the surface of the body, while the forefeet are now represented 

 by paddles adapted for swimming ; and the " whale-bone " is a 

 substitute for the teeth, for it is the best means of securing the 

 minute organisms upon which the whale feeds. 



So is it in plants. When stamens became altered, they lost the 

 structure and function of anthers with pollen, and became attractive 

 as honey-secreting organs. 



The idea of progress associated with evolution is correct so far 

 as fossil animals obeyed the law that the most ancient members of 

 any particular group, when in the adult stage, more nearly resembled 

 the embryonic or young stage of their later or modern representatives 

 of the same group. 



Thus the early amphibia were, like our newt, transitional forms 

 between fishes with gills and land reptiles with lungs only ; by their 

 possessing both these organs they v/ere the highest known animals 

 of the Coal period. Their descendants in one line were frogs and 

 toads, which are fish-like only when in the tadpole stage ; but no 

 true frogs and toads are known till a much later epoch. 



The Meaning of Degradation and its Causes. — One speaks of 

 degradations and degenerations in plants, but there is nothing 



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