TWINS 



Their Importance as Furnishing Evidence of the^Limitations of Environment 



David Fairchild 



IDENTICAL twins are the only 

 human beings in the world who 

 have exactly the same heredity. If 

 we can find out the characteristic 

 ways in which they remain the same 

 throughout life, the qualities and habits 

 and mannerisms which persist un- 

 changed in them both, in spite of their 

 living in entirely different surroundings, 

 we shall know much more than we do 

 at present about what attributes are 

 hereditary and fixed and what are those 

 which we can hope to modify by en- 

 vironment and education. 



THE INFLUENCE OF HEREDITY AND 

 ENVIRONMENT 



In all our experiments in education 

 and civic improvements and in our 

 dealings with different races we are 

 always hampered by our ignorance of 

 that great unknown quantity, heredity, 

 and its influence on the people with 

 whom we are dealing. 



Any exact knowledge we can gain 

 by a study of two identical twins who 

 were separated from each other as 

 babies and brought up in different 

 towns under entirely different circum- 

 stances, scarcely knowing each other, 

 will give us a clearer idea than we 

 appear to have now, of what changes 

 in our bodies, and perhaps, too, in some 

 of our mental and moral characters, 

 are clearly due to the things we eat, the 

 exercise we take, the associations we 

 make, and the work we do — to our 

 environment, as it is called — and what 

 changes, or failures to change, can be 

 correctly traced to our very beginnings 

 in that momentous meeting of the two 

 parent cells which began our earthly 

 lives. 



WHAT DETERMINES OUR CHAR- 

 ACTERISTICS 



It is strange to think of the way our 

 inheritance comes to us, to realize that 



all we are to inherit from our mother 

 and from her entire family is contained 

 in a single tiny cell, while all that we 

 are to inherit from our father and his 

 family is contained in another tiny cell. 

 When these two cells meet they become 

 one larger cell and form the beginning 

 of a new individual. _ 



It is wonderful and almost passing 

 belief to realize that a single micro- 

 scopic cell holds so much of our destiny 

 within itself and that it contains the 

 mechanism which will determine the 

 color of our eyes, the shape of our nose, 

 the love of music, the taste for litera- 

 ture, for law or for science, the quick- 

 ness of temper or sullenness of disposi- 

 tion which will go so far in deciding 

 what our future is to be. All that the 

 generations of ancestors behind us can 

 give us of themselves, they give us 

 through this tiny cell. 



This cell grows and divides into twa 

 cells ; each of these grows and divides 

 into two more cells, and so the process 

 goes on, controlled by the mechanism 

 contained in the original cell — that 

 mechanism, the so-called chromosomes 

 which are easily visible through the 

 microscope. 



No two mother cells are alike, nor 

 any two father cells ; each contains a 

 different arrangement of the hereditary 

 characteristics, and so it is that every 

 individual produced by the union of a 

 father and mother cell is different from 

 one produced by any other union. 

 Although they are brothers and sisters, 

 with the same heredity characteristics 

 behind them to draw from, they have 

 inherited these characteristics in such 

 varying arrangement that they may vary 

 as much as did the hundreds of people 

 who were their ancestors on either side 

 of the family. 



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