32. THE ORIGIN OF LIFE 



Stanley L. Miller 



1. Early Considerations of the Problem 



The problem of the origin of life has occupied man's mind since history began. 

 The problem was not as troublesome for the ancients as it is for us today, since 

 it was quite clear to them that life arose by spontaneous generation. Thus when 

 the Egyptians saw snakes arise from the muds of the Nile and when the Greeks 

 saw rats arise from piles of garbage on exposure to warmth, they interpreted 

 this to mean that such animals arose spontaneously. 



That organisms could arise spontaneously, as well as by sexual and 

 asexual reproduction, was not seriously questioned until the middle of the 17th 

 century. In 1688 the Tuscan physician, Francesco Redi, showed that worms 

 did not develop in meat if the flask was covered with muslin so that flies could 

 not lay their eggs on the meat. 



The demonstration that micro-organisms, which had been discovered in 1676, 

 did not develop spontaneously was much more diflicult. In 1765 Lazzaro Spal- 

 lanzani showed that micro-organisms did not appear in various nutrient 

 broths if the vessels were sealed and boiled. Objections were raised that the 

 heating had destroyed the "vital force" in the broth and air. This "vital force" 

 was postulated as necessary for life to develop. By readmitting air it was 

 possible to show that the broth could still support the growth of micro- 

 organisms. But Spallanzani could not demonstrate that the air in the sealed 

 flask had not been altered, and the doctrine of spontaneous generation persisted 

 widely. 



This problem was finally solved by Pasteur in 1862. He used a flask with 

 broth, but instead of sealing the flask he drew out a long S -shaped tube with its 

 end open to the air. The air was free to pass in and out of the flask, but the 

 particles of dust, bacteria and molds in the air were caught on the sides of the 

 long S-shaped tube. When the broth in the flask was boiled and allowed to 

 cool, no micro-organisms developed. When the S-shaped tube was broken off at 

 the neck of the flask, micro-organisms developed. These experiments were 

 extended by Pasteur and by Tyndall to answer all the numerous objections 

 that were raised. Thus, after two centuries of experimentation and many 

 more centuries of belief, the doctrine of spontaneous generation was disproved. 

 (For an extension of this history, see Oparin, 1938.) 



Shortly before 1858, Darwin and Wallace had published, simultaneously and 

 independently, the theory of evolution by natural selection. This theory could 

 account for the evolution from the simplest single-celled organism to the most 

 complex plants and animals, including man. Therefore, the problem of the 

 origin of life no longer involved how each species developed, but only how the 

 flrst living organism arose. 



To answer this question it has been proposed that life was created by a 

 supernatural event. This is not a scientific theory, since by its very nature it is 



[MS received December, 1960] 845 



