Longevity of Man and his Tissues 
ALEX COMFORT 
prospect: we can think of what undirected primate 
evolution has done to longevity in the past in producing 
our present lifespan, and try to extrapolate what it may do in 
the future; or we can try to predict how we ourselves may 
influence human lifespan, either by our wish or by our negli- 
gence. Of these two approaches I think I prefer the second. 
Natural selection is bound to affect us: but Sir Julian Huxley 
has given us reasons for doubting whether pure first-order 
effects of selection pressures can ever again be separated from 
the mass of second-order and social effects on human biology; 
and in any case the principles upon which lifespans have evolved 
are still far from clear. No doubt they have been fixed by 
selection; but we have the very anomalous case of small birds, 
which have a standing wild mortality in the region of 60-75 per 
cent per annum, and a potential longevity of 20 to 30 years. 
This is a figure which is almost certainly never reached in the 
wild. We have in primates, including man, the added compli- 
cations which spring from the steady prolongation of childhood 
and parental dependence. About this I shall have more to say 
when I refer to purposive attempts to alter our longevity—but 
for the moment it is one more reason for not offering any 
sweeping evolutionary predictions as to what, if anything, will 
happen next. Finally and most practically, if further changes 
take place in lifespan with further primate evolution, neither we, 
nor our students, nor our children, will be there to see them, 
whereas man-made changes, deliberate and accidental, seem 
very likely within the next century, and not impossible within 
the lifetime of some of us here present. 
Toe are two ways of considering individual longevity in 
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