Biological Approach in Study of Ageing 3 



animals in all those respects where it would be more conven- 

 ient if they were uniform. I want to discuss two subjects 

 connected with the methodology of age studies. One is the 

 kind of information which we can expect to obtain from 

 comparative studies, and the other the special problem of 

 devising means by which to relate age changes in vigour to the 

 life cycle of animals, particularly vertebrates — both in onto- 

 geny and in phylogeny. 



From the biological point of view, comparative age studies, 

 like other comparative studies, could be expected to give two 

 kinds of information, according to the way in which we 

 conduct them — evidence of the existence of fundamental, or 

 at least widespread, processes which make for senescence in 

 organisms, and evidence of the relationship of the human life 

 cycle to that of non-human vertebrates, especially other 

 mammals. The second of these has had curiously little appeal 

 to biologists, possibly because it appears superficially less 

 likely than the first to give rise to large-scale discoveries, but I 

 would like to suggest that it is at present the more promising, 

 if not the more important undertaking ; it is also quite essential 

 to work of the first kind, since it is required to give us an 

 indication of the type of unity in age processes which we are 

 entitled to take as our working hypothesis. 



The special problems of comparative age studies are of two 

 quite distinct kinds. Some are purely observational problems, 

 due to the fact that the lifespans of the animals we wish 

 to examine may be appreciable fractions of our own, that old 

 organisms when they exhibit senescence are inherently 

 variable, that relatively few animals can be accurately aged by 

 inspection, and that the changes we wish to observe may 

 appear only in circumstances remote from the normal wild 

 environment of the organism we are studying. Others depend 

 on the nature of the definitions we use, and the analogy 

 which we draw between age phenomena in different species. 

 These phenomena may be similar, or analogous, or convergent, 

 and we have no initial means of distinguishing between 

 them. 



