THE EVOLUTION OF LIFE 355 



fragments belong to a creature called Pithecanthropus 

 erectus which was, so far as its fragmentary skeleton in- 

 dicates, a human being decidedly nearer the apes than 

 are any existing races of men. Much later we find remains 

 of a more human type along with skeletons of the extinct 

 cave bear, cave lion and mammoth. We find also the 

 stone implements of primitive man, such as arrow heads 

 and axes; at first these were crude but later they were 

 more accurately made. These were made by men of the 

 stone age, but later there are found implements of bronze 

 and still later those of iron. Although man is of recent 

 origin, geologically speaking, he has been on the earth 

 several hundred thousand years, although we cannot 

 measure this time with a great degree of exactness. 



Taken as a whole, and despite the gaps and imperfec- 

 tions of the record, the history of fossil forms shows us a 

 gradual advance from lower to higher types of life. In 

 some cases where the record is unusually complete, as in 

 the series of fossil horses and elephants, it enables us to 

 follow, step by step, the evolution of our modern forms. 

 The science of geology reveals to us an almost immeasur- 

 able past during which the seas, the continents, the moun- 

 tains and the valleys of our earth were gradually being 

 formed, and the earth's wealth of plant and animal life 

 was gradually being evolved. 



From a variety of sources, such as morphology, or the 

 science of structure, embryology, geology, the geograph- 

 ical distribution of life and the observed facts of variation 

 there is an overwhelming mass of evidence for the con- 

 clusion that plants and animals including man have arisen 

 by a gradual process of evolution. It is a problem of 

 great importance to ascertain by what method this great 

 change has been effected in organic life. Ordinarily 

 plants and animals give rise to progeny closely resembling 



