THE MPXHANISM OF ORGANIC EVOLUTION 



By Charles B. Dwknport 

 Dcpurtment r.f Genetics, Cariir;jir Trtxtitutlnn nf Wnsliinpton 



[With 1 pl:it(>| 



As "sve look over the avoiKI (o-tlay wc see, as the ancients did, 

 the marvelous phenomenon of a world populated not only l»y Iniitians 

 but also by many hundi'ed thousand so-called species of animals 

 and plants existing in uncountable individuals whose numbers can 

 no more be expressed by the ordinary system of numbering than 

 astronomical distances can be readily expressed in miles. A cubic 

 millimeter of the blood of a leucaemic mouse nuiy contain over a 

 million white corpuscles, and there may well be 1,000 such cubic 

 millimeters of blood in a mouse. This gives us a billion white cor- 

 puscles in one mouse not to consider the other cells of the mouse's 

 body. These white corpuscles are essentially organisms, with powers 

 of food gathering, assimilation, excretion, locomotion, sensation, 

 etc. And this is but one mouse. Even if we assume so few as 2i/2 

 house mice to a human being on the earth (and mice are ubiquitous), 

 and that each has oidy 10 million leucocytes, we shall have aO mil- 

 lion billion white blood corpuscles in house mice alone. 



•J have sometimes speculated on the number of organisms visible 

 to the low power of the microscope that are in our inner harbor - 

 at the end of xVugust, when it has a creamy, souplike consistency. 

 Assuming one per cubic millimeter, which is certainly far too small, 

 there would be a quadrillion individuals in this space, which would 

 occupy only a square millimeter in the one-millionth map of the 

 world, which has over half a billion square millimeters. 



Pardon me for wearying you with figures. I have wanted to put 

 you in a position to grant my first point that the niunber of ii^li- 

 vidual organisms on the globe is essentially infinite, though the num- 

 ber of kinds that naturalists have been able to count and describe in 

 the past 150 years is still finite. 



Next, I would call to your attention that most of these individuals 

 have a short life and are quickly replaced by others, even if we leave 



' Prespnted before the two hiinflrcd thirty flilrrt mopflnK of thn Wnslilnston Academy of 

 Sciences, as one of the series of papers on Origin and Evolution. Reprinted by permission 

 from the Journal of The WushinKton Academy of Sciences, vol. 20, No. 11, Aug. 10, 1930. 



'Cold Spring Harbor, Long Island Sound. 



417 



