NATURAL SELECTION: II 497 



words must be made entirely from letters used in preceding words. How 

 many English words can be made from the twenty-six letters of the alpha- 

 bet? The weight of paper required for manufacture of an unabridged dic- 

 tionary gives graphic evidence of their vast number. Let us now pick one 

 of the longer words from this dictionary: "disestablishmentarian." How 

 many other words can be made from the letters in this one? The number is 

 large but is much smaller than the number of words we can make from the 

 letters of the entire alphabet. By picking the word "disestablishmentarian" 

 we have eliminated the future possibility of constructing words that include 

 the letters c, j, g, j, k, o, p, q, u, v, \v, x, y, z. 



From the letters remaining to us we now elect to construct the word "mis- 

 administrate." In doing so we have lost the letters b, h, and /; they can no 

 longer be used in our game. The next word we make, from the letters in 

 "misadministrate," is "semianimate." In doing this we have lost d and r 

 from our stock of letters. From the letters remaining we now make the 

 word "stamina," losing e in the process. Our next word may be "main- 

 tain"; if so, we have lost s. Next, perhaps, we construct "taint," losing m by 

 doing so. Next may come "tint," with loss of a from our stock of letters. 

 The number of words we can construct from the three letters remaining to 

 us is extremely limited. The point we wish to make is that this limitation is 

 imposed by past events — by the decisions made each time we chose to con- 

 struct a certain word rather than some other one possible to us at the time. 

 If we had chosen differently the letters remaining for use at the end of the 

 game would have been different ones from the /, n, and / of our example. 

 Looking over the course of our game as a whole we might be impressed by 

 the fact that our example exhibits a progressive tendency to emphasize the 

 importance of /, n, and t. But this emphasis is only a product of decisions 

 made during the course of the game, not of any innate importance or 

 superiority of /, n, and t themselves. Thus we see that past events exercise 

 a directive or channeling action upon subsequent events. 



How does this fact apply to the evolution of Ufe? Here also past events 

 influence the course of subsequent history. On page 90 we noted the funda- 

 mental importance of the element phosphorus (in phosphates of adenylic 

 acid) in mobilizing and transporting the free energy needed for all living 

 processes. Why do living organisms concentrate on phosphorus for this 

 function? "Does the unique behavior of phosphorus in this case depend 

 upon very special properties, such that even quite similar elements could 

 not serve as substitutes; or is this unique function to be attributed to events 

 in evolutionary history which caused the accidental 'selection' of phos- 

 phorus for this role?" (Blum, 1955). Blum suggested that the phosphorus- 



