406 



THE QUARTERLY REVIEW OF BIOLOGY 



sary to probe deeper into the matter, 

 which has been done by devising experi- 

 ments of such a character that we are 

 enabled to study the organization, the 

 constitutional make-up or pattern, of the 

 organism free from the disturbing in- 

 fluence of the necessity normally present in 

 biological work for the organism to derive 

 its energy from sources external to itself. 

 When this is done it at once appears that 

 the apparent genetic difference between 

 wild and vestigial Drosophila in respect of 

 duration of life, which so clearly manifests 

 itself in Mendelian experiments, is really 

 only a result of the fact that in a normal 

 environment, optimal for wild type flies 

 in respect of food, vestigial flies are not 

 able to bring to complete somatic ex- 

 pression their inherent potential viability. 

 Vestigial and wild type flies are seen, 

 under these conditions, to have the same 

 inherent vitality. Furthermore, under 

 these conditions, altering the density of 

 population does not alter the shape of the 

 life curve or the average absolute lon- 

 gevity. 



With the confusing effects of the inter- 

 relationship of heredity and environment 

 thus experimentally cleared away, we are 

 able to plan experiments which will give 

 us some real insight into the basic bio- 

 logical variables which determine lon- 

 gevity. And parenthetically it may be 

 remarked that in a great deal of standard 

 genetic work with what may be loosely 

 called "physiological" in distinction from 

 "morphological" characters, there per- 



haps inheres the same kind of confusing 

 interrelationship in the effects of heredity 

 and environment which led to the initial 

 paradox in the fly work we have dis- 

 cussed. There is an underlying postulate, 

 usually unrecognized and almost never 

 discussed, implicit in nearly all genetic 

 work. It is that, if in a constant environ- 

 ment A, a difference between two 

 organisms such that one has the character 

 in the condition B and the other in the 

 condition B', segregates in the second filial 

 generation following a cross, the difference 

 between B and B' is to be regarded as 

 genetically determined Or caused. But 

 this postulate is only completely valid if it 

 has first been demonstrated that the en- 

 vironmental condition A is equally favor- 

 able for the development to complete 

 somatic expression of both B and B'. 



To come back now to our own trail, it 

 has been possible to show, by experi- 

 ments with cantaloupe seedlings so devised 

 that we are working solely with inherent 

 vitality, that the duration of life or lon- 

 gevity of the individual varies inversely 

 as the rate of energy expenditure in me- 

 tabolism during life. In short, the faster 

 an organism lives, the sooner it dies. 



This, then, is the conclusion at this 

 stage of a continuing program of experi- 

 mental research on the biology of life 

 duration or longevity. This conclusion 

 may, and doubtless will, be modified, re- 

 fined, and extended as the experimental 

 program continues, but I think it is hardly 

 likely to be reversed. 



LIST OF LITERATURE 



Note: Inasmuch as there is an extensive bibliog- 

 raphy on the subject of this paper in the author's 

 recent book The Kate of Living. Being an Account of 

 Some Experimental Studies on the Biology of Life Duration, 

 New York (Alfred A. Knopf), 1918. Pp. 185; and 

 London (University of London Press), 1918, it seems 

 unnecessary to do more here than to list a few supple- 



mentary titles beyond those covered in the work 

 cited. These are as follows: 



(1) Abrahams, A. On the physiology of violent 

 exercise in relation to the possibility of strain. 

 Lancet, March 3, 192.8, pp. 419-435. 



CO Buxton, P. A., and G. H. E. Hopkins. Re- 



