No. 544] ORIGIN OF UNIT CHARACTERS 



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strong indeed, further, that some of these characters, 

 while apparently continuous in origin, certainly become 

 discontinuous in heredity; from which it follows that 

 discontinuity in heredity constitutes no proof of discon- 

 tinuity in origin. 



The question is, how do these manifold characters of 

 which the body is made up arise, continuously or discon- 

 tinuously? A conservative opinion from what may be 

 gathered in the whole field of observation at the present 

 time is that while the greater part of evolution is continu- 

 ous, especially in the origins of certain parts and in the 

 development of certain proportions, there must also be 

 a discontinuity, especially in numerical or meristic struc- 

 tures, such as vertebrae and teeth, and in chemical com- 

 ponents and reactions which are essentially antithetic 

 or discontinuous. In other words, there is both continu- 

 ity and discontinuity, and one problem is to show what 

 is continuous and what is discontinuous. 



The history of "characters" is our quest, and now 

 that attention is concentrated all along the line of obser- 

 vation in plants and animals, living and fossil, on the 

 genesis and behavior of single characters, we have laid 

 the train for substantial progress. A vast gain is that 

 which relegates the problem of species to a side issue, or 

 rather to an incidental result of the accumulation of a 

 greater or less number of units. 



A 1 ' character" may be racial shape of head or length 

 of limb, it may be a cusplet on a grinding tooth, color of 

 hair, or a sportive white lock of hair, it may be the brown 

 or blue color of the eye, it may be the speed of a horse, 

 or the obstinacy of a mule, in short, any structure or 

 function, simple or extremely complex, which is stable 

 and distinct in heredity. A "new character" is some- 

 thing which is unknown before, it may be a new unit, 

 like the horns of cattle, it may be a new form or propor- 

 tion of such a unit. "I understand by the term unit char- 

 acter," observes Morgan, "any particular structure or 

 function that mav appear in heredity independent of 



