284 Discussion 



the other, it may then be possible to identify the physiological 

 channels through which the gene affects the lifespan. But this is 

 difficult if not impossible if you are dealing with the joint results of a 

 multitude of genes which differentiate two different inbred strains or 

 populations. 



Maynard Smith: It will be easier in the mouse, although it will 

 take longer, because you have more idea of what mice die of than I 

 have of what flies die of. 



Rockstein: Your results do not really agree with Dr. Maurizio's or 

 mine. The honey-bee lives longer when it has a functioning ovary, 

 certainly in the queenless colony. The housefly lives longer when it 

 is well fed and is laying lots of eggs. 



On the other hand, you implied that the effect of temperature in 

 prolonging life was through the destruction of the ovaries. Of 

 course, these occur together and may not necessarily involve cause 

 and effect. Instead, this may be the net effect of temperature 

 through a more important higher level of control, which affects ovary 

 development (as well as other processes) so as to result ultimately in 

 the rapid dying off of the population. 



Sacher: There is also the opposite interpretation, that since the 

 ovary is regenerated it is not the destruction, but rather the regener- 

 ation, that extends life. 



Maynard Smith: You can get the same results with animals which 

 never had and never will have ovaries — these animals will live much 

 longer than their double first cousins who have got ovaries. It is 

 reasonable to take the simple hypothesis that it is the egg-laying that 

 matters. Since, as Prof. Wigglesworth commented earlier, females 

 are liable to suffer from protein-shortage, my results are quite con- 

 sistent with yours. On sugar and water your females may have died 

 young because they were suffering from serious protein shortage. 

 My experiment suggests that if you deprive a female of her ovary or 

 cause it to regress, then she does not suffer from protein shortage as 

 much as she would if she were laying eggs. 



Gerki7ig: Can you give an estimate of the size of the ovary in 

 relation to the body? Is it as much as 50 per cent? 



Maynard Smith: I do not know exactly, but it is certainly not as 

 much as that. 



Gerking: In the fish I talked about the ovary may weigh as much 

 as 20 or 30 per cent of body weight at maturity. Once the eggs are 

 shed then you can hardly find the o^"ary. Its restoration to this 20 

 or 30 per cent level requires a great amount of energy. I wanted to 

 point out that in both the fish and Drosophila a very large proportion 

 of metabolism is devoted to egg production. You have concluded 



