b. Amniocentesis: its history, power, and limitation: Nora and Fraser.
c. Know your Ps and Qs: the futility of negative eugenics: C.C. Li.
The word Eugenics was first used by Francis Galton, an English geneticist from the Greek word eugenia meaning well-born. In practical terms eugenics means our intervention to modify the natural given by enhancing what is good (positive eugenics), and by decreasing or preventing what is bad (negative eugenics). It is important to realize that the two aspects of eugenics, the positive and the negative are not two sides of the same coin. They are totally different in both, methods and results.
Positive eugenics is a success story. Here we attempt to breed out certain traits judged to be useful for us. A speedy horse, a cow that gives more milk, a drought resistant agricultural plant, a fruit tree with larger and sweeter fruit are the dreams of farmers. To achieve a better agricultural product through proper breeding is beneficial for all concerned. This is positive eugenics. What happens is that we select artificially for a given trait from a large natural population with a great deal of genetic variation. The method of positive eugenics is selective breeding. Once the trait is well defined and is fairly stable it is maintained by inbreeding practices to safeguard a pure line. The original population is not altered in this process, and it retains its natural, rich variation, provided it is not replaced by the selected lines. It is essential to retain the original genetic variation in order to have a base to fall back on in case of any mishaps with the inbred lines in which genetic variation has been reduced. It is customary to maintain large seed banks preserving the variation of the original, natural populations.
Ever since agriculture has been practiced, starting about 10,000 years ago, positive eugenics has been with us. In the Origin of Species Charles Darwin describes in the very first chapter of the book the results of positive eugenics in terms of variation under domestication. The various breeds of pigeons, dogs, horsed, cows, sheep, and so on, are all the products of positive eugenics. In the 1960s the miracle rice, miracle wheat and corn were produced this way. Most flowers on the market are specially bred for size, color, and scent. Every fruit we eat are the results of many centuries old breeding practices.
Positive eugenics is truly a success story. The only discord we encounter in
positive eugenics are breeding practices imposed on human beings. There have
been some sporadic attempts of positive eugenics in people, ranging from such
atrocities as certain slave breeding practices (B.A. Botkin, Slave Narratives.
Volumes 1-17. Washington. The Library of Congress, 1941. Also N. Lewis, Brazil's
dead Indians: The killing of an unwanted race. Atlas, January, p. 22. 1970.)
to attempts to breed "quality" people with superior intellects or
some rare talents. For more details on this subject see the essay on Negative
Amniocentesis is one of the favorite diagnostic methods of negative eugenics. In the book, Medical Genetics, by James Nora and Clarke Fraser (Lea & Febiger, 1974), there is a chapter on Antenatal Diagnosis of Genetic Disorders through amniocentesis. The technique consists of the removal of a small volume of amniotic fluid for analysis. The fluid contains metabolites in solution and also desquamated cells of the fetus. The former can be analyzed chemically for metabolic disorders, the latter cultivated in tissue cultures for chemical analysis and for identifying chromosome aberrations as well as the sex of the fetus by karyotyping. The chapter is most informative and well written, but at the same time it is also sobering as the authors present amniocentesis in practical terms pointing out both, the powers and limitations of the method. Some popular magazines may give the impression that amniocentesis is an easy, simple, and completely harmless procedure. This is far from the truth.
The viability of desquamated cells is greater early in pregnancy, it is for practical reasons better to perform amniocentesis as early as possible, certainly before the 20 weeks gestation. The amniotic fluid is adequate by the 14 weeks, which leaves us a 6 weeks window for culturing the desquamated cells and providing diagnosis. It is necessary to locate the placenta using ultrasound to find the prospective rout of access. An anteriorly placed placenta is a contraindication.
When amniocentesis is performed there is always some risk to the mother and the baby. Leakage of amniotic fluid resulting in abortion do occur sometime. The probability of such mishap is increased by the fact that, more often than the literature seem to lead one to conclude, the first attempt at amniocentesis fails and second and even third attempts become necessary. As to cell cultures the success rate is about 80%, which places even more stress on the tight schedule of 6 weeks available for diagnosis. In rare cases somatic mutation of the cells in the culture may occur leading to false results.
Once diagnosis has been reached, the next phase in the process is decision
making. Knowing the problem, some people want to prepare for it by providing
the child to be born the best possible environment from the start. Others may
decide to abort the fetus. These are ethical decisions. For more information
see the section on Ethical Considerations.
KNOW YOUR Ps AND Qs.
In negative Eugenics the aim is to lessen the genetic load of the human population, that is to substantially reduce and even eliminate the harmful genes from the general and establish a genetically purified humanity free of genetic disorders. The basic method of negative eugenics is sterilization of those who have genetic disorders to prevent their bad genes to be reintroduced into the general. Therapeutic abortion is the strongest form of this sterilization program. The word therapeutic refers, of course, to the health of the human population, and not to the health of the individual with the disorder. Negative eugenicists often play on the idea of common good.
The probability of the appearance of a genetic disorder is relatively low in an out breeding population where an incest code prevents marriages between relatives closer than first cousins. (The relatedness between first cousins is 1/8, between parent and child is 1/2, between brother and sister is 1/2, and between aunt and nephew or uncle and niece is 1/4.) On the other hand, the probability of accumulation of bad genes under such system of out breeding is quite high. Such accumulation of bad genes is called the genetic load. The aim of the negative eugenics programs is to lessen this genetic load. The question is whether the methods used in negative eugenics are in any way adequate to achieve this goal.
To assess this adequacy we are to measure whatever is being achieved through negative eugenics in terms of realistic probabilities.
Considering the various modes of inheritance we can describe well specified
scenarios. A genetic disorder may be inherited from a recessive gene, or a dominant
gene, or in multiple factor and polygenic systems. The most common form of inheritance
of a disorder is from a recessive gene. On the average, the frequency of a deleterious
recessive gene in the human general is q = 0.02. This means that the disorder
to be manifested must be supported by two such recessive genes in the genotype
of the effected individual. The probability of such event is then 0.02 x 0.02
= 0.0004, that is four in 10.000. According to the negative eugenics program
we sterilize those 4 out of 10.000 everywhere in the world. This would, however,
not eliminate the recessive bad gene from the general, because many of them
remain in heterozygous condition in the carriers who have only one of the bad
genes masked by the normal, dominant allele. Could we include the carriers into
the sterilization program? Not likely. They would represent about 4% of a population
of 6 billion people. Any sterilization program of that magnitude would be prohibitive.
By the way, the number of heterozygotes in a population is given by the value
2pq where p is the frequency of the dominant allele and q is that of the recessive
allele. Since p + q = 1, and q = 0.02, then p = 1 - q = 0.98, and 2pq = 2 x
0.98 x 0.02 = 0.0392, close to 4%.
Another way to assess the efficiency of negative eugenics is to see how long it would take to halve the present 0.02 frequency of a defective gene to a value of 0.01. Disregarding new mutations, the answer in number of generations is given by the reciprocal value of the original frequency, that is 1/0.02, which is equal to 50. If we allow 30 years for a generation, then it would take 1,500 years of sterilization of each and every individual worldwide to reduce the frequency of the deleterious recessive gene from 0.02 to 0.01. The task would be impossible, and the result would be negligible. If the sterilization program would not include everyone having the recessive trait, the elimination process would become slower. Similarly if not just a single gene pair of genes were involved but the system were polygenic, then again the same slight result would be reached much more slowly.
The above calculations would be enough for most rational people, but somehow
negative eugenicists are not that easily dissuaded from sterilizing people.
They might say: OK! We leave the recessive and the polygenic situations alone,
but we should handle the disorders, which come from a dominant gene. After all,
if all those who show a dominant genetic disorder would be sterilized, the frequency
of the dominant gene in the general would be reduced to zero in one generation.
To their surprise, they would find the same number of dominant disorders in
the next generation because natural selection already reduced those to mutation
rate and the appearance of the disorder in the next generation after sterilization
are all new mutations.
Negative eugenics simply does not work. I believe, those who support it should know better their Ps and Qs.
Population Genetics by Ching Chun Li. The University of Chicago press, 1968.
The Harper Encyclopedia of Science, edited by James R. Newman, 1967.
Medical Genetics. Principles and Practice by James J. Nora, and F. Clarke Fraser. Lea & Febiger, 1974. On antenatal diagnosis of genetic diseases. Chapter 16.
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