50 READINGS IN BIOLOGICAL SCIENCE 



HOW LIFE BECOMES COMPLEX * 

 S. J. HOLMES 



Lest the reader be led to expect a discussion of the distractions of living 

 in our modern society, I may explain at the outset that this is a purely bi- 

 ological article. It deals with the complexities of the life processes in plants 

 and, especially, in animals, and how these complexities came about. 



Life presents an enormous range in complexity from that of the human 

 body down to the bacteria or organisms even simpler, such as the filter- 

 able viruses, if they are organisms at all. An amoeba carries on the same 

 fundamental Hfe processes as a man, with almost no organs. It moves with- 

 out muscles, transmits stimuli without nerves, digests without stomach 

 or intestine, respires without lungs or gills, and reproduces its kind by 

 pinching itself in two. An amoeba, which is by no means the simplest form 

 of life, is the product of long series of evolutionary changes. It occupies 

 a niche in nature in which it has persisted with little change for millions 

 of years, during which other animals have forged ahead and acquired 

 structural organizations of great complexity and almost endless variety. 

 If we compare the structure of a frog, an insect, a clam, a starfish or an 

 earthworm, we find remarkable differences of form and internal organiza- 

 tion but the diverse organs of these animals are devoted to the discharge of 

 the same essential functions. All of them have organs of digestion, ab- 

 sorption, respiration, excretion and reproduction. The varied structures 

 of these animals represent so many different w^ays of solving essentially 

 the same physiological problems. Why all this bewildering variety of 

 structure and pattern? 



Obviously, life as it has become more complex has followed many dif- 

 ferent paths. For the most part we can not say that one animal solves its 

 problems better than another. The amoeba gets along very well in its way, 

 and so does the starfish, the spider, the squid, the porpoise and all the rest 

 of our animal relatives. They persist and perpetuate their kind, and pos- 

 sibly enjoy life after their fashion, and this is about all a hving creature can 

 reasonably expect. As Aristotle observed, the activities of all organisms 

 center about two ends — the preservation of the individual and the perpetua- 

 tion of its kind. These are the two great problems that face every living 

 creature. Death to the individual or its kind is the penalty for failure to 

 discover the correct solution. Organisms have tried different ways — mil- 

 lions of different ways — of finding an answer to these Sphinx riddles, and 

 the number of right answers that have been hit upon is indicated by the 

 multitudinous diverse types of plant and animal life. A higher type of 

 organization would be of no advantage to a creature in certain situations. 



* Reprinted by permission of the Scientific Mo7ithly, American Association for the 

 Advancement of Science. Copyright 1941. 



