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cannot afford the biological cost of this intensity of chronic radiation exposure,
and that there should be extreme caution at this time against increasing the
radiation exposure to all people by ten times over its natural level.
Evolutionary Benefits ?
it seems possible that human evolution is occurring in some optimal
balance between mutation tendency and genetic stability. Fertility, length of
life, death rate, and individual usefulness may be highly affected by the number
of accumulated new genes, * which both add to favorable evolutionary drift in
average human vigor and add to the pool of undesirable genes to be selected
against. At low radiation levels, such as 10% or 1% above the natural radiation
background (the range of fallout effect), it seems unlikely that long-range
genetic disturbances can become an appreciable problem, since the natural
radiation background appears to account for only 10%of the change in genetic
structure per generation. One may speculate further that, in the long run,
‘man may be beneficially affected by good genes yet to be formed, so that increasing radiation exposure and the mutation rate may operate to human advantage. Such an argument is unlikely to convince men who understand some
of the dangers of too great a burden of undesirable mutants; it is analogous
to an attempt to convince the experienced cook that the baking of her prize
cake would be accomplished in half the time at higher oven temperature.
Penrose has evidence of indirect beneficial effect of some recessive
lethal genes, which appear to enhance the effect of the functioning gene with
which they are matched in individual combinations. This effect is one in which
mutation may beneficially add some variance to genetic functional characteristics. On the whole, however, there is a strikingly large mass of information
indicating that any genes that can disturb function should be kept to an absolute
minimum.
Unfortunately, there are still many unanswered questions facing
geneticists on the topic, "What is the effect of undesirable genetic burden on
the quality of humans?' Fully satisfactory experimental measures have yet
to be applied to this problem. One approach that has led to considerable
speculation is through estimations of the numbers of undesirable mutations
carried by the average person. Estimations of this burden place it within
the small range of 5 to 15 undesirable genes per average individual. 4,f This
value is the equilibrium resulting from approximately one such gene gained
*Transformed genes are, with rare exception, nonfunctional, lethal, or
undesirable.
Tsome individuals may have none. The fraction having none or very few
diminishes steeply with increasing average numbers of undesirable mutations.
Thus, doubling the burden of mutations may reduce the numbers of individuals
having desirable genetic combinations to rare events.