6o READINGS IN BIOLOGICAL SCIENCE 



wonderfully suggestive of the possible future realization of the ancient 

 dream of man-made Hfe. These studies have led some biologists to surren- 

 der the idea of natural death and to reach instead the daring conclusion that 

 death is "accidental." 



,Most biologists today prefer the definition given by G. H. Lewes, that 

 "life is a series of definite and successive changes both in structure and in 

 composition, which take place in an individual without destroying its 

 identity." 



In his eager desire to find the key that will unlock the mystery of the 

 life process, the scientist has speculated about the awe-inspiring theme 

 of the origin of life. Tracing backward the history of man's evolution, we 

 come to a point beyond which we can go no farther. Through mammals 

 we go back to the age of reptiles; from reptiles to mollusks; from mollusks 

 to seaworms, and from seaworms to slime and single-celled creatures. 

 Beyond that there seems to be a "No Trespassing" sign over a gate which 

 hides from us the greatest mystery of all. 



Where did life come from? How did it start? Why has it ascended the 

 evolutionary ladder that it has and where is it going next? 



For thousands of years mankind adhered to the notion known as spon- 

 taneous generation, according to which hving creatures arose spontane- 

 ously out of the air or the sea, or out of the mud. There are various schools 

 of thought today which differ sharply in their speculations about life's 

 beginning. There are some scientists who support the theory of Panspermia, 

 according to which hfe is as old and as fundamental as inanimate matter. 

 Its sperms or spores, according to this view, are supposed to be scattered 

 through the vast universe and to have reached our planet quite acciden- 

 tally. Lord Kelvin has suggested that they were carried here via those 

 brilliantly illuminated meteorites which constantly bombard our earth 

 from outer space. 



The image of Aphrodite rising from the sea has a scientific justification 

 in the view of those biologists who believe that the living has risen on this 

 planet from what we regard as the non-living. These men of science pro- 

 claim that it is fairly certain that life originated in the primeval ocean, 

 since the inorganic salts present in the circulating fluids of animals corres- 

 pond in nature and relative amounts to what we have good reason to 

 believe was the composition of the ocean hundreds of millions of years ago. 

 A new approach to the problem of the origin of life on earth was recently 

 suggested by Dr. Assar Hadding, the noted Swedish geologist, who con- 

 tends the hfe began here in warm water puddles after the world's first 

 rains. 



Life, according to Dr. Hadding, was impossible until our globe had 

 cooled sufficiently to allow the condensation of water. This first happened, 

 he believes, in the Winter seasons of the two poles. Before that, the sur- 

 face of the globe must have been covered with loose, hot volcanic ash. 



