Chapter 36 



LIVING ORGANISMS— THEIR ORIGIN, CONTINUITY, 

 DEVELOPMENT, AND DESCENT WITH CHANGE 



I. ORIGIN OF LIFE 



A. Abiogenesis (Spontaneous Generation) 



A majority of scientists up to the seventeenth century beHeved in 

 abiogenesis, which stated that Hving things, especially the lower types, 

 arose spontaneously from nonliving substances. Such beliefs as the fol- 

 lowing were common: Field mice were thought to arise spontaneously 

 from the mud of the Nile River. Aristotle (384-322 b.c.) believed that 

 eels (fishes) arose spontaneously from nonliving materials. Kircher 

 stated that he actually saw animals arise through the action of water 

 on the stems of plants. Von Helmont (1577-1644), a Flemish physician, 

 believed that house mice were generated from pieces of cheese placed in 

 bundles of rags. Flies were thought to arise spontaneously from dirt, 

 manure, and decaying meats. Anaximander (611-547 B.C.) thought that 

 air imparted life to all living things. 



Reasons Why Abiogenesis Was Believed. — Abiogenesis, or sponta- 

 neous generation of things, was believed because the complex life cycles 

 of many of the animals and plants were not understood at that time. 

 Many microscopic stages of certain living organisms were not seen or 

 escaped methods of observation, because the microscope had not been 

 sufficiently perfected to observe accurately. This lack of accurate knowl- 

 edge formed a natural setting for such a theory as abiogenesis. Experi- 

 mental methods of attacking such problems were not yet developed. 

 Scientists attempted to prove by hearsay, supposition, or discussion rather 

 than by experimental investigation. Rather than prove by exact evi- 

 dence, they would attempt to prove by more or less logical reasoning. 



Needham, in 1749, believed he had demonstrated the spontaneous 

 origin of minute living organisms in infusions which he had boiled and 

 sealed in flasks. By boiling he thought he had killed all living matter 



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