Biological Possibilities in the Next Ten Thousand Years 
possible successors with their own abilities, and youth to boot. 
Possibly a movie star at the age of forty might have similar 
feelings. 
Assuming that cloning is possible, I expect that most clones 
would be made from people aged at least fifty, except for athletes 
and dancers, who would be cloned younger. They would be 
made from people who were held to have excelled in a socially 
acceptable accomplishment. Sometimes this would be found 
to be due to accident. The clonal progeny of Arthur Rimbaud, 
if given favourable conditions, might have shown no propensity 
for poetry, and become second-rate empire builders. Presum- 
ably such a clone would not be further grown. Other clones 
would be the asexual progeny of people with very rare capaci- 
ties, whose value was problematic, for example permanent dark 
adaptation, lack of the pain sense, and special capacities for 
visceral perception and control. Centenarians, if reasonably 
healthy, would generally be cloned, if this is possible; not that 
longevity is necessarily desirable, but that data on its desirability 
are needed. Centenarians who could continue to learn systema- 
tically up to the age of thirty would almost certainly be useful, 
and probably happy members of society. 
There are several other possibilities of altering human geneti- 
cal make-up besides selection. One is the deliberate provocation 
of mutations, probably by chemical agents, which seem more 
specific than X-rays and the like. This will first be attempted 
in tissue cultures. And if tissue culture becomes a frequent 
stage in the human life cycle, it may be practicable to do it on 
a large scale. It may also be possible to synthesize new genes 
and introduce them into human chromosomes. It will be still 
easier to duplicate existing genes, thus in some cases perpetuat- 
ing the advantage of heterozygosity. There is still another 
possibility. No doubt, in our evolutionary past, we lost capa- 
cities which we should value, for example olfactory capacities, 
and the capacity for healing with little scarring which is asso- 
ciated with a loose skin. Hybridization with animals possessing 
these capacities is probably impossible, certainly undesirable by 
present human standards. But Muller and Pontecorvo were 
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