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In order to decide if in any particular case it will be worth while eugenically to sterilize,
it must first be clear how the abnormality in question is inherited. A single dominant
character which is usually transmitted to fifty percent of the offspring will easily be
eliminated in this way in the course of a generation or two. Lobster claw is a case in
point.
Again, there is a case for sterilization where a sex linked recessive is involved. Women
who do not show the character themselves may transmit the gene to fifty percent of their
sons and to fifty percent of their daughters who, being heterozygous, will behave as
carriers. Hemophilia is an instance of this.
Yet with hemophilia the case for sterilization is not quite so clear cut. For where there is
no sterilization, the fertility of heamophiles is only one quarter of that of normal persons.
This is chiefly because many heamophiles die before they reach maturity, while with
those who survive their disability lowers their fertility. Thus it would seem that the gene
should disappear in a fairly short time.
This is not the case. From time to time in a small minority of people the gene for normal
clotting of blood is changed and a gene for non clotting takes its place. In this way new
cases are always arising, hence, while heamophilia could be slightly reduced, it could
not be stamped out by sterilization. Census figures relating to the disease show that the
proportion of heamophiles in the population has remained at roughly the same level
during the past hundred years.
A new spontaneous case arising which has not been transmitted and which is then spoken
of as a mutation appears in about one in one hundred thousand gametes. In this particular
ovum or sperm arises the altered gene for non-clotting and only the one person will
be afflicted with the disease, his brothers and sisters escaping. In diseases where the
mutation rate is lower, sterilization might possibly reduce the number of people afflicted
with a disease transmitted by the same mechanism namely where the factor is a sex
linked recessive.
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