48 The Nature of Biological Diversity 



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win, 1937) whose only claim to lasting distinction was prohahly the 

 foreword contrihuted to it hy Sir Frederick Gowland Hopkins. In 

 that foreword he gave the following text: "I venture to think that 

 productive thought in hiochemistry . . . calls for the widest possible 

 survey of life's manifestations. One of its ultimate tasks is to decide 

 on what, from the chemical standpoint, is essential for these manifes- 

 tations as distinct from what is secondary and specific." Comparative 

 hiochemistry is indeed concerned as much with resemblances as it is 

 with differences, and the further biochemical research progresses, the 

 more does it appear that living organisms closely resemble each other 

 at the molecular level, no matter what their structure, mode of life, 

 or environment. It is as though there is some fundamental structural 

 and metabolic ground plan to which all kinds of living things conform. 

 If we could but strip away everything that is secondary and specific 

 and leave this ground plan revealed and naked, we should very prob- 

 ably have a fair idea of the structural and metabolic make-up of the 

 earliest forms of anything that would be called "alive" by present-day 

 standards. Further back than this, perhaps, we could not go; but that 

 is a problem for the future rather than for this time and place. In 

 writing here about evolutionary diversity the existence of a funda- 

 mental ground plan is taken for granted. It is assumed, moreover, 

 that the features of this fundamental plan were laid down very early 

 in the evolution of modern living forms and that they correspond to 

 a common starting point for evolutionary divergence and differen- 

 tiation. 



J. B. S. Haldane (1937) once wrote that: "Our final theory of 

 evolution will see it largely as a biochemical process." Now if, as 

 seems generally to be believed, evolution has proceeded by a long 

 series of individual mutations, and if, as there is every reason to 

 think, individual mutations, or at any rate their consequences, are 

 open to investigation along biochemical lines, we are also bound to 

 believe, again with Haldane, that "future interpretations of genetics 

 will be largely expressed in biochemical terms." Biochemical genetics 

 is now a large and important branch of biochemical inquiry. More- 

 over, it is well documented (see, for example, Haldane, 1954). 



If we accept the notion of a fundamental ground plan — and all 

 modern biochemistry seems to point in this direction — and if we sup- 

 pose that this ground plan was laid down early in the course of 

 biological time, it would seem probable that mutant forms could only 

 be viable if the underlying mutations were consistent with the mainte- 

 nance of the primary, basic, and fundamental pattern. Moreover, when 

 at a later stage a number of consistent and specific adaptational super- 



