Discussion 37 



Lorge: That may be so; it may be working both ways. 



Kallmann: Dr. Comfort, you said that the ability of many animal 

 species to reach old age is largely a function of domestication. Do you 

 believe that domestication has a favourable or an unfavourable effect 

 upon the ability to have an extended lifespan? Are corroborative data 

 available ? 



Comfort: The animals we observed in the wild may, in some cases, 

 reach old age; there are some species that appear to do so, but a great 

 many do not. If we take, say, robins or rats, the proportion that live 

 to old age is relatively small; in the case of rats it is virtually nil, in the 

 case' of robins, surprisingly enough, ringing studies show that you do 

 occasionally get an 11-year-old or even 14-year-old robin in the wild. 

 Now, when you wish to study these creatures and to have a statistically 

 significant proportion reaching old age, you have to bring them more or 

 less under your control in the laboratory, and in doing so you auto- 

 matically produce what is effectively a different organism. It is almost 

 impossible to avoid doing this, particularly if you are breeding over a 

 number of generations : you find that you are exerting various unrecog- 

 nized forms of selection. This is true in the case of Drosophila, the fruit 

 fly, which breeds rapidly. If you bring in the progeny of wild animals, 

 you yourself will change as you learn better and better ways of keeping 

 them, and they tend to change due to selection and to the influence of 

 the various new factors to which they were not exposed in the wild. 

 If you prevent the less vigorous of them being eaten by wolves or caught 

 by ferrets in early life, you may find that those less vigorous individuals 

 will live on and develop diseases or die at another stage in their develop- 

 ment ; the animal that has been in domestication for any length of time 

 is really a rather different organism from the animal which exists in the 

 wild. In order to produce circumstances in which many of these small 

 rodents and birds can age at all or can age with any frequency, it is 

 necessary to deal with the domestic forms. That is why I say that if you 

 talk about the ageing of them in the wild, you are in general talking 

 about a hypothetical state which neither evolution nor the actual facts 

 of the matter have ever envisaged, and which we are not warranted in 

 assuming. 



Kallmann: I am just wondering why we still have so many non- 

 domesticated rats. 



Comfort: I think you will find that there are very few non- domesticated 

 older rats. It would be interesting to know that; there may be evidence. 

 I cannot say for rats, but certainly we have a great many non-domesti- 

 cated mice and voles. 



Kallmann: But the principle would be a negative selective factor, 

 wouldn't it? Rate of reproductivity is somehow related to length of life. 



Comfort: In terms of reproduction the effect of postponing senescence 

 is surprisingly small when you have an animal which has this enormous 

 random mortality. That was one of the points I was making from the 

 evolutionary point of view, that you score much more by producing a 

 lot of offspring young. The evolutionary score of high early reproductivity 

 is going to be a good deal higher than that of potential longevity. 



