THE UNITY OF ECOLOGY — DARLING 463 



of biological communities was tacit in the phenomena of plant suc- 

 cessions elucidated by the Clementian school of ecologists in America. 

 Adams saw that the orderly thread of developmental succession could 

 easily be broken or influenced by all manner of factors, but there was 

 still the unbreakable thread of process or, in fact, history. There 

 is at present some reaction against the idea of orderly succession to 

 a climax state which is stable and continuing, because so many ex- 

 amples can be brought forward to show how natural phenomena such 

 as hurricane, fire, and frost-heave — each at certain moments of bio- 

 logical significance such as a seed year or not — can make nonsense 

 of orderly progression within the community under investigation. 

 But they do not make nonsense of the idea and the trend, and the plain 

 record of process of history brings us to a perspective of reality. It 

 is part of the thesis of this essay that man was able to civilize by 

 being a breaker of climaxes, giving him the stored wealth of the ages 

 in plants, animals, and soil fertility with which to buttress himself 

 against the environment and to enjoy the immense capacity for social 

 evolution provided by the new ability to be pennanently gregarious. 

 The concept of the dynamic biological community took a long time 

 to mature — if we admit that it is even now much advanced beyond 

 adolescence. Its development shows all the signs of what most of us 

 detect some time or other in our personal investigations, inability 

 to see much more than what we are looking for, or seeing without 

 apprehending significance. Edward Forbes saw the concept of com- 

 munity clearly in his classic marine work of 1843-45, but his early 

 death robbed Scotland and ecology of a luminous mind. The plant 

 ecologists of the late 19th century, headed by Warming, made the 

 concept of community a cornerstone of a growing science, and Tansley's 

 famous paper of 1920 codified it and gave it greater significance. 

 Tansley emphasized in this paper that conceptual arguments and 

 hypotheses must be firmly based on observation of the vegetation itself 

 and that one must constantly go back to the field. It was a necessary 

 admonition in that laboratory era. Tansley developed then the idea 

 of the community as a quasi-organism or organic entity, of the whole 

 being greater than the sum of its parts. He made comparisons of 

 plant communities with human communities, and remarked that lack- 

 ing psychical awareness, instinctive cooperation did not develop — only 

 symbioses of varying degrees — and that competition was the law of 

 relationship. It was later, in Vegetation of tlie British Islands, that 

 Tansley gave lengthy consideration to the biotic or animal factor in 

 the expression of communities, realizing for example that a landscape 

 of chalk downland, so old and English and accepted as natural, de- 

 pends completely on the continued grazing of sheep. The very habitat 

 of chalk grassland is man-produced by way of the sheep, yet it is 



