lO THE HISTORY OF BIOLOGY 



line of thought which is far more concerned with a close study of nature and 

 makes it the basis of the entire cosmic system — the atomic theory. The 

 founder of this philosophy is said to have been Leucippus, a thinker of whom 

 we know nothing except that he was the teacher of Democritus, one of the 

 foremost natural research-workers and natural philosophers of all time. 

 Democritus was born at Abdera, a Greek colony on the Thracian coast. In 

 his time Abdera was a rich and powerful city, but in the course of subsequent 

 centuries it declined and its citizens became notorious for their stupidity, 

 which gave rise to the epithet "Abderitic" as a universal expression for 

 extreme foolishness. His period of activity is, like that of most of the early 

 Greek philosophers, not known for certain, but it is generally assumed that 

 he was born between the years 470 and 460 b.c. and died at a very advanced 

 age — in fact, not far short of a hundred years. From his father, one of the 

 richest and most eminent citizens of his native town, he received a large 

 inheritance, which he is said to have spent entirely on long journeys under- 

 taken for the purpose of acquiring knowledge from various countries and 

 peoples. On his return home he was supported by a brother until his fellow- 

 countrymen, proud of his scientific fame, granted him a pension sufficient 

 for all his needs. Known for his mild and friendly disposition and surrounded 

 by admiring disciples, he grew old in peace and died without suffering from 

 ill health. He was known as one of the most productive scientific authors of 

 antiquity, and his writings seem to have embraced many and varied subjects. 

 Except for a few fragments, however, they are entirely lost and indeed seem 

 to have already been so as early as the late classical period. Through other 

 ancient authors, however, particularly Aristotle, who always mentions him 

 with respect and seems to a large extent to have made use of his learning, 

 we are able to form a fairly good idea of his scientific point of view. 



Maferialisfic theory of the universe 

 His teacher, Leucippus, seems to have based philosophy on Parmenides' 

 theory of the immutability of matter, and to have come across this in the 

 paradoxical form that it assumed among the later Eleatics. In order to pre- 

 serve the elements of truth in this theory and at the same time to make pos- 

 sible the changes which are incontestably observable in the world, Leucippus 

 conceived the universe as composed of a quantity of particles moving in 

 empty space. Democritus adopted this theory and developed it further. He 

 thus became the founder of the atomic theory, one of the most fruitful ideas 

 in natural science. And on this atomic theory he, as no one else has done 

 either before or since, based the whole of his theory of existence, both 

 spiritual and material. No thinker of antiquity ever produced such a consist- 

 ent and materialistic theory of the nature of the cosmos; none has advanced 

 further in the endeavour to satisfy the demand — upon which Anaximan- 

 der had already insisted — for a natural explanation of the origin of matter. 



