Pace Six 



EVOLUTION 



July, 1928 



Why Amoeba Behaves 



By Clkveland Sylvester Simkins 



THOSE minute organisms that live on the border line 

 of naked vision as independent rells have within 

 their structure a reaction system which at first blush 

 seems purposeful, but which is seen to be controlled en- 

 tirely by the known laws of biochemistry when examined 

 more closely in the light of present advanced knowl- 

 edge. 



It was natural enough that early students of these 

 simple life forms should have imputed to them a sort 

 of intelligence similar to that of man, a sort of primitive 

 soul, and insisted that they are controlled by sensations 

 of pleasure and pain such as determine human behavior. 



The amoeba is a naked bit of protoplasm. Protoplasm 

 is complex in chemical make-up, varies in physical 

 consistency from instant to instant, and possesses vari- 

 ous substances whose specific gravity differs in different 

 parts of the same cell. The surface of the protoplasm 

 is a jelly-like membrane, while the inner material is 

 more of a liquid. Yet this inner material may take on 

 the same character as the surface membrane; it may be- 

 come jelly-like under appropriate conditions. Within the 

 cell the jelly and fluid states alternate. Neither is constant. 



When any part of the interior protoplasm jells it 

 shrinks, thereby producing pressure and heat, tending 

 to convert the jelly into fluid again. These two re- 

 versible processes, known as gelation and solation, are 

 self-regulative and unstably balanced as long as the 

 animal remains alive. A little shove one way or the 

 other upsets the balance, and solation goes on until it 

 checks itself and gelation begins. 



Is This Behaving? 



The outer surface of the amoeba will not mix with 

 water. Thus there exists an interface between the ani- 

 mal's body and the medium in which it lives. This is 

 controlled by surfa(;e tension, not only on the outer sur- 

 face but also inside the protoplasmic mass, since surface 

 tension develops wherever media of different densities 

 come in contact with each other. Hence, the interior of 

 the cell is subjected to interfacial forces that are changed 

 by every activity, — digestion, absorption, assimilation. 



Both jelly and fluid are made up of mole.-ules that 

 have their own interfacial forces and surface films, 

 which when distorted or influenced by any disturbance 

 whatever, start a series of changes that effect a reaction 

 in the organism as a whole. Any change in one part of 

 the system will make itself felt in the more remote parts. 

 Thus the very process of life and the succession of events 

 supplies its own stimulus to behavior. 



The series of cause and effect leads unmistakably 

 into a reaction which the organism can not escape. It is 

 forced to react by the very nature of its chemical and 

 physical constitution. For example, if ultra-violet light 

 is thrown upon one side of an amoeba, the protoplasm 

 on that side is jelled, shrinkage occurs, the internal 

 fields of force are distorted, the increased pressure in- 

 duces solation on the other side, the softening substance 



flows outward and the remainder of the organism flows 

 after it, thus moving away from the stimulus. 



The forces underlying these changes reside in the sur- 

 face films of the colloidal particles, the stimulus of the 

 radiation disrupts them. This in turn disrupts the bal- 

 ance of the interfacial forces of so large an area that a 

 shifting of positions, substances and forces takes place 

 to attain a new stability. The various phases of form 

 and motion are caused by changes in the surface ten- 

 sion. They constantly vary as affected by environment. 

 She Learns Little 



The length of time any given phase endures depends 

 on the intensity of the stimulus which threw the colloids 

 into that pliase. A very strong reaction caused by ac- 

 tual contact with some noxious chemical will throw the 

 surface into a jelly state that persists for some time. 

 During this time everything encountered by the amoeba, 

 even food particles, will be rejected. If, on the other 

 hand, the previous experience of the organism has 

 caused a fluid or receptive phase in the surface jell the 

 formerly rejected particles will now be engulfed. This 

 behavior has been cited as proof that the organism 

 exercises a power of discrimination between two par- 

 ticles and chooses one or the other. 



But these reactions of the amoeba to its environment 

 do not indicate choice on the basis of pleasure or pain, 

 nor of a primitive intelligence that chooses between 

 two particles as an incipient sense of taste, any 

 more than a drop of water placed upon a particle of 

 glass and salt would choose the salt in preference to the 

 glass. When we consider the behavior of amoeba in 

 the light of modern colloidal chemistry, the ability to 

 select becomes less significant as a criterion of living 

 things. Selection does depend upon the previous ex- 

 perience of the organism. A series of reactions that 

 set up a certain phase endures for a time, during which 

 the attitude of the organism toward all things is the 

 same, regardless of their food value. This phase soon 

 changes, due to the instability of the protoplasm. This 

 duration of a certain phase may be the germ of reten- 

 tion, which by repetition becomes established as a basic 

 property of protoplasm and serves as the commencement 

 of that higher, psychic process known as memory. 

 Lacks Will Power 



The ability to react upon the experience of the past 

 is a fleeting one at its highest development. In man it 

 endures for varying lengths of time, in amoeba it en- 

 dures but a moment. There is no scientific evidence 

 available that puts us under the least obligation to ex- 

 plain the behavior of the amoeba as manifestations of 

 taste, will, choice or skill, nor should we think of it as H 

 capable of forming habits. Its reactions are forced 

 movements, determined by the intensity, character and 

 continuation of the stimuli to which it is subject at the 

 moment. Any so-called selective ability in the amoeba 

 cannot fairly be called "microscopic mentality" or psy- 

 chic ability", nor can isolated instances in its activity. 



