298 Group Discussion 



what I was trying to say before, that just as in growth we talk about 

 developmental age, so we can talk about the probability of death in 

 any given situation as developmental age further down the scale. 

 If that is really true, if these analogies can be made the same in 

 animals and man, then we can use the results of both field workers 

 and the experimentalists much more usefully to shed light on the 

 human situation. 



Comfort : The figures we get for small mammals have often misled 

 people into thinking that all mammals behave in this way. We have 

 only very few figures for the larger ones but there is some evidence 

 that many larger mammals in the wild achieve high ages quite 

 often. I would be very surprised if some of the larger wild ungulates 

 didn't live long enough to senesce. Wild horses, if one had the chance 

 of observing them, may perhaps live to a fair proportion of the age 

 reached by tame horses. 



Sacher: Porcupines can survive until they are so arthritic they can 

 hardly climb trees — nobody comes up against them except mountain 

 lions. 



Verzdr: Dr. Chitty, did you imply that the time of survival for a 

 certain species depends on the number of individuals living at the 

 time? If you put a pair of fish in a pond, they will have certain 

 survival characteristics for their age. When the pond becomes full 

 with fish the population will become constant. Then the individual 

 survival curve will probably be different, otherwise the number of 

 fish would continue to increase, which is impossible because there is 

 not enough food. 



Chitty: The number alive has a very great influence on the survival 

 rate but the survival time can certainly not be predicted from the 

 numbers of the animals alone. One must also take into account the 

 behaviour of the population ; experimentally you can have a family 

 group of 50 animals which is perfectly amicable and has a good 

 survival rate, yet with two animals in a similar space who are 

 strangers, the survival time of one of them will be about half a day. 

 The presence of other hostile animals of the same sort is, I think, one 

 of the strongest environmental factors which does affect survi^^al, 

 regardless of the amount of food available. 



Danielli: I shall not attempt in any way to summarize this meet- 

 ing. I have been considerably refreshed by it in many ways. We 

 have learned, for example, that man, skunks and porcupines are 

 amongst the few animals who know how to survive into the period of 



