98 SECTIONAL ADDRESSES 



forms are restricted by their tracheal respiration to very small size and 

 therefore to cold-bloodedness and to a reliance on instinctive behaviour. 

 Thus lungs were one needful precursor of intelligence. 



Warm blood was another, since only with a constant internal environ- 

 ment could the brain achieve stability and regularity for its finer functions. 

 This limits us to birds and mammals. Birds were ruled out by their 

 depriving themselves of possible hands in favour of actual wings. 



Remain the mammals. Most mammalian lines cut themselves off from 

 ultimate progress by concentrating on immediate specialisation of limbs, 

 teeth, and sense of smell. As Elliot Smith has set forth, the penultimate 

 steps in human development could never have been taken except in the 

 trees, where the forelimb could be converted into a hand, and sight 

 inevitably ousted smell as the dominant sense. But for the ultimate step 

 it was necessary for the anthropoid to descend from the trees before he 

 could become man. This meant the final liberation of the hand, and 

 placed a higher premium upon intelligence. Further, the fcetalisation 

 necessary for a prolonged period of learning could only have occurred in 

 a monotocous species. 



The final step taken in evolutionary progress to date is that to con- 

 ceptual thought. We see, however, that this could only arise in a 

 monotocous mammal of terrestrial habit, but arboreal for most of its 

 mammalian ancestry. All other known groups of animals are ruled 

 out. Conceptual thought is not merely found exclusively in man : it 

 could not have been evolved on earth except in man. 



Evolution is thus seen as a series of blind alleys. Some are extremely 

 short — those leading to new genera and species that either remain stable 

 or become extinct. Others are longer — the lines of adaptive radiation 

 which run for tens of millions of years before coming up against their 

 terminal blank wall. Others are still longer — the lines that have led to 

 the development and advance of the major phyla ; their course is to 

 be reckoned in hundreds of millions of years. But all save one have 

 terminated blindly. 



Only along one single line is progress and its future possibility being 

 continued — the line of man. If man were wiped out, it is in the highest 

 degree improbable that the step to conceptual thought would again be 

 taken, even by his nearest relatives. In the ten or twenty million years 

 since his ancestral stock branched off, these relatives have been forced into 

 their own lines of specialisation, and have quite left behind them that 

 more generalised stage from which a conscious thinking creature could 

 naturally develop. 



The Evolutionary Future. 



What of the future ? In the past, every major step in evolutionary 

 progress has been followed by an outburst of change, whether by exploiting 

 anew the familiar possibilities of adaptive radiation, or by peopling new 

 environmental realms, or by improving the fundamental progressive 

 mechanism itself. 



Conscious and conceptual thought is the latest step in life's progress. 

 It is, in the perspective of evolution, a very recent one. Its main effects 

 are indubitably still to come. What will they be ? Prophetic phantasy is 

 a dangerous pastime. But at least we can exclude certain possibilities. 



