GREAT STEPS IN ORGANIC EVOLUTION 403 



has had its outcome in personalities, who have discerned 

 something of its magnificent sweep, who are seeking to 

 understand its factors, who are learning some of its lessons, 

 who cannot rest until they interpret it even though it be 

 mistakenly. 



SUMMARY. 



The biggest fact of science is that the Systema Naturae in all its 

 complexity, intricacy, multitudinousness, and working harmony has 

 come to be as it is from relatively simple beginnings and by suc- 

 cessive achievements. By ' simple ' is meant * unevolved ' a nebula 

 or a group of planetesimals, a zoogloea or a bunch of biococci. 



Of the origin of the first organisms upon the earth we know noth- 

 ing, whether they came from elsewhere or were evolved from some 

 not-living carbonaceous slime activated by ferments. Difficulties 

 beset all the hypotheses of abiogenesis that have been as yet sug- 

 gested; yet, on general grounds, it seems likely that abiogenesis 

 occurred. 



Of the nature of the first organisms we know nothing directly, 

 but it is probable that they were of very minute size and much 

 simpler than most of the Protozoa within the ordinary range of 

 microscopic visibility. Minchin's suggestions leave us convinced that 

 a long journey had to be travelled before the first cell appeared. 



The next great step was the establishment of many distinct types 

 of cellular organisation. Perhaps this was the time of the funda- 

 mental initiatives. 



One of the early events was the emergence and the divergence of 

 Green Plants, a fundamentally important cleavage, without which 

 the evolution of animals would not have been possible. The vegeta- 

 tive line of evolution is obviously off the main track. 



An epoch-making step was the making of ' bodies ', the transition 

 from the unicellular or non-cellular grade of organisation to the 

 multicellular. It opened the way for specialisation of function, for 

 great increase in momentum, for storing energy, and so on, but it 

 soon brought with it the nemesis of natural death. 



Another step of far-reaching importance was the evolution of 

 male and female multicellular individuals, differing in constitution, 

 and complementary in the continuance of the race. This sex- 



