<^"-^i] B. MORPHOLOGICAL 129 



TEST CASE XIX. CORRELATED CHARACTERS 



The difficulty of imagining that evolution worked in the direction 

 Irom species towards genus is vastly increased when we come to 

 deal with the correlations that exist in the characters of the 

 various flowering plants. Though there is usually no conceivable 

 adaptational reason behind them, the characters of whole families, 

 for example, usually go together in groups, for whose connection 

 we can see no reason at all, unless it be simplv that the common 

 ancestor happened to possess this combination. In the grasses 

 there go together alternate leaves, in two ranks, a split sheath, a 

 ligule, jointed stems, a spikelet inflorescence with glumes and 

 paleae, and so on. How did natural selection pick out all these 

 characters to go together, even if by any stretch of the imagina- 

 tion one could imagine it picking out a split sheath in a grass, 

 and a closed one in the allied sedges, or in fact any of the other 

 characters? They must have been derived from a common an- 

 cestor, and if so, where did selection and adaptation come in? If 

 all the structural characters of a family, those characters in fact 

 that mark it out as a family, are hereditarv characters, there is 

 comparatively little room left for any adaptive characters at all 

 and once again it is clear that morphological characters override 

 selection. Even if there be no specially adaptive characters in 

 the grasses or the sedges, there must have been some disadvan- 

 tageous ones in the plants that were suppressed in the struggle for 

 existence which made the wide gap that now separates these two 

 allied families. But is it conceivable that a series of intermediate 

 forms with, for example, a sheath partiallv split should have been 

 so inferior that they were killed out? Still more difficult is it to 

 imagine intermediates which showed intermediate characters 

 m all the characters of diff^erence, if one suppose for an instant 

 that such a thing were possible; there can be no intermediates 

 between 2-ranked and 3-ranked leaves, or between the two types 

 of inflorescence, etc. Direct mutation must have occurred in 

 many cases; and gradual adaptation is hardly conceivable, 

 especially when so many characters have to go together, and each 

 has to be brought to the point of perfection (cf. p. 114). 



The larger the family, the greater on the average is the variety 

 of conditions that it occupies, as may be seen in the grasses. Yet 

 natural selection is supposed to form a family by gradual adapta- 

 tion, and it is therefore clear that, as indeed the^ geological record 

 shows, families must have come verij early in evolution, and the 



WED 



