Danger to the Race
Radiation may hurt the individual. It may also be harmful for our
children and hurt the race. We have seen that the danger from the
radiation due to testing is small compared to many risks which we
habitually take and almost always ignore, which in fact we have to
ignore to continue to live in this civilized world. In addition we are
not even quite sure that the danger to the individual is real.
There can be little doubt, however, that radiation does produce some
harmful changes in our children. What seems even more frightening, is
that these changes may not show up in our children but only in their
children or further progeny. A danger which may lie hidden for
generations might seem more terrifying, especially as it has often been
repeated that all such radiation effects are harmful.
We transmit our properties to coming generations in a most curious and
concentrated fashion. From the mother and the father a child inherits a
number of chromosomes, twenty-four from each.[14] These are structures
along which the actual carriers of the properties—the genes—are strung
up.
We are beginning to understand something about the nature of the genes.
They seem to be very big spiral molecules. They carry the master plan of
our body and even of our character in a strange chemical code.
The laws of heredity are complicated because of the fact that the same
property is influenced by a gene from each parent. Frequently these two
genes dictate different behavior and then the result is a compromise,
sometimes evenhanded, sometimes unbalanced. But of the two genes only
one will find its way to the child of the next generation. The
compromise is temporary and original properties may emerge again. Which
one of any pair of chromosomes (or of the two assemblies of genes)
carries on is a matter of chance. In the world of the cells as in the
world of atoms it is chance that determines the future—not fate.
Of all these facts we need be particularly interested in one. The units
of inheritance are rather constant but not quite immutable. There is a
small possibility that any gene may suffer a mutation. That is, it may
turn into a new chemical, carrying a new code and new properties.
A gene is an extremely finely and precisely constituted object. It must
be so in order to carry all the racial past in so little material. A
mutation due to chance will spoil this order in almost every instance.
The great majority of mutations are detrimental. Many are lethal.
It is an incredible fact that these random mutations, almost always
harmful and never proceeding according to any plan, should have been
responsible in the very long run for all the many beautiful and perfect
living creatures that nature has produced (and this includes the human
race). The thread leading from single cells to cell colonies, worms,
fishes, vertebrates, mammals and human beings does certainly not seem to
be the work of chance. Much less does it seem to be the work of a gamble
taking one chance of a small improvement against a thousand chances of
deformity or death. Nevertheless it is such a terrible game of chance
which has produced both the human body and in some manner also the human
spirit.
Big numbers are strange things and when each member of a huge assembly
must be given individual attention then the numbers are even harder to
appreciate. Billions of contemporary lives in billions of distinct
generations have led to the incredible outcome: the harmony of life
produced by gambling.
Radiation is surely disruptive. It does cause mutations. Since the genes
appear to be single molecules, a single process of ionization or
excitation is likely to result in a change. As has been said before
there is doubt whether or not cancer and leukemia can be caused by
exceedingly little radiation. There is little doubt, however, that
mutations can be caused by any small amount of radiation. The less
radiation the less the chance. But the chance will always be there.
A very great increase in the natural rate of mutations could indeed have
terrifying effects. We can be quite certain, however, that radiation
from atomic tests will increase the chance of mutations by only a very
small amount.
The argument is essentially the same as the one concerning the danger to
the individual. The tests are responsible for 0.001 or 0.002 roentgens
per year to the human reproductive cells. This is equivalent to
approximately 0.05 roentgen per generation. Most of this radiation is
due to gamma rays from Cs¹³⁷ which has been deposited on the ground or
absorbed in the body. The number of mutations caused by this radiation
is to be compared with the number of natural mutations.
Some of the natural mutations are caused by heat and chemicals. Some are
due to background radiation, to cosmic rays or to gamma and beta rays
emitted by natural radioactive substances in or near our bodies. Our
best estimate is that 10 per cent of the natural mutations are due to
the background radiation.
Over a period of one generation the background radiation dosage to the
human reproductive cells is approximately five roentgens. Assuming a
simple proportionality between dosage and the number of mutations, it
follows that fifty roentgens would be required to induce a number of
mutations equal to the total number of natural mutations (from
background radiation and all other causes). That is, fifty roentgens is
a “doubling dose.”
The atomic tests are therefore increasing the number of mutations by
about 0.05 ÷ 50, which is 0.1 per cent. This kind of increase in the
rate of mutations would certainly not seem to be a serious reason for
worry.
Actually the number of mutations from the tests is very small even
compared to geographical and altitude variations in the natural
radioactivity. The Inca empire existed for many generations in the high
country of Peru. The people of Tibet have been exposed for generation
after generation to the greater cosmic ray intensity which bombards them
through a thinner layer of atmosphere. These people have been exposed to
much greater additional radiation than anything which is caused by
atomic tests. Yet genetic differences have not been noticed in the human
race or for that matter in any other living species in Peru or Tibet. We
are certainly talking here about questions which may strike hard on some
individuals but which from the point of view of the community or race
are not serious.
It has been often repeated that all mutations due to radiation are
harmful. There is every reason to believe that mutations due to
radiation are not different in kind from other mutations. Should we then
seriously believe that all mutations are harmful? That most of them are
is admitted. If all of them were indeed always harmful, we must deny the
simplest facts of evolution.
There will be some who maintain that the human race is not capable of
improvement. Such an argument is irrefutable. It is also unreasonable.
What cannot be further improved is perfect, and not many people will
maintain that our species can claim perfection.
Another and much more plausible argument has been advanced: In the wild
state living species do perfect themselves by means of natural
selection. Human society by caring for the imperfect and defective
individual has eliminated natural selection. Therefore further mutations
will not improve mankind.
It is very hard to discuss this question for the simple reason that the
argument involves the interaction of two processes extremely different
in magnitude and in fact different in kind. On the one hand it concerns
itself with evolution which proceeds in the slow deliberate way of a
glacier. On the other hand it focuses attention upon the process of
human civilization with its technical and social changes which has
gained momentum like an avalanche. The momentum is still there and it is
still increasing and where we shall land we do not know. To consider the
motion of the glacier while being carried along by the avalanche puts
things completely out of proportion. Long before the present rates of
mutation could have any effect upon the human species we shall live in a
very different world and we shall have started to influence our own
behavior including those of selection, natural or otherwise, in ways
which today we cannot foresee.
If we discuss the question how civilization will influence natural
selection, we shall not do it with the hope of arriving at a firm
answer. We shall do it rather in order to illustrate how doubtful all
the arguments are which concern the interplay of two processes which
cannot be measured in the same scale.
It is true that we can and do preserve the lives of children who,
because of inherited weaknesses, would perish under natural conditions.
It is true too that we do this for reasons and for feelings concerning
the individual and we do it without regard to the consequences to the
race. However, under our present condition of civilization a disease
which can be corrected by administering chemicals or using the surgeon’s
knife is no longer effectively a disease. In our present condition such
a life can be as valuable to society and to the race as a life which
does not have these superficial shortcomings. That we can and do
preserve more life in this manner only emphasizes that under present
conditions biological differences which used to be important no longer
matter.
On the other hand, in social living many properties which used to be
indifferent for a wild being have become of great significance. Ability
to communicate and to get along with our fellows is not the only one,
but is perhaps the most obvious one of such properties. The struggle for
existence has become more gentle, and the chance of any individual to
live on in his children is governed by new ways of behavior.
Nevertheless the difference between the individual adapted to civilized
living and the one who is not adapted is of great importance and will
become of greater importance. It is likely that civilization will not
eliminate evolution of the race. Rather it will direct it into new
paths.
But the greatest change might be expected from an entirely different
direction. We are going to understand in real detail the intricacies of
human inheritance. Then we shall be faced with problems and shall find
possibilities of an entirely new and different kind. The interest of a
person in his children is not a superficial one. It is one of the most
strong and lasting forces in biology, sociology and history. A clear
understanding of the details of inheritance may bring about some grave
difficulties because a new situation is never fitted easily into
existing patterns of living. In the end more understanding may bring
about improvements of a kind beside which all the worthwhile things that
have been so far accomplished, might look unimportant.
The real importance of radioactivity for heredity does not lie in the
fact that we may speed up the glacier by one inch in a millennium. The
real importance of nuclear radiation is rather that it is helping us to
understand the strange processes of life and the curious substances
which connect one generation to the next.