12. Diversity Within Species and Population Genetics


12.8. Ethics and Human Population Genetics


Misunderstanding the principles of heredity and population genetics has resulted in bad public policy. Often, when there is misunderstanding there is mistrust. Even today, many prejudices against certain genetic conditions persist.

Modern genetics had its start in 1900, with the rediscovery of the fundamental laws of inheritance proposed by Mendel. For the next 40 or 50 years, this rather simple understanding of genetics resulted in unreasonable expectations on the part of both scientists and laypeople. People generally assumed that much of what a person was in terms of structure, intelligence, and behavior was inherited. This led to the passage of eugenics laws, whose basic purpose was to eliminate “bad genes” from the human gene pool and encourage “good genes.” These laws often prevented the marriage or permitted the sterilization of people who were “known” to have “bad genes” (figure 12.16). Often, these laws were promoted as a way to save money, because sterilization would prevent the birth of future “defectives” and, therefore, would reduce the need for expensive mental institutions and prisons. Some people used these laws to legitimize racism and promote prejudice.




FIGURE 12.16. A Eugenics Law 720.301 Sterilization of mental defectives; statement of policy

Sec. 1. It is hereby declared to be the policy of the state to prevent the procreation and increase in number of feebleminded and insane persons, idiots, imbeciles, moral degenerates and sexual perverts, likely to become a menace to society or wards of the state. The provisions of this act are to be liberally construed to accomplish this purpose. As amended 1962, No. 160, § 1, Eff. March 28, 1963.

This state law was enacted in 1929 and is typical of many such laws passed during the 1920s and 1930s. A basic assumption of this law is that the conditions listed are inheritable; therefore, the sterilization of affected persons would decrease the frequency of these conditions. Prior to 1962, the law also included epileptics. It was repealed in 1974.


The writers of eugenics laws (How Science Works 12.2) overestimated the importance of genetics and underestimated the significance of environmental factors such as disease and poor nutrition. They also overlooked the fact that many genetic abnormalities are caused by recessive alleles. In most cases, the negative effects of recessive alleles can be recognized only in homozygous individuals. Removing only the homozygous individuals from the gene pool would have little influence on the frequency of the “bad genes” in the population. Many recessive alleles would be masked by dominant alleles in heterozygous individuals and would continue to show up in future generations. In addition, we now know that most characteristics are not inherited in a simple dominant/recessive fashion; and that often many alleles at different loci cooperate in the production of a phenotypic characteristic. Furthermore, mutations occur constantly, adding new alleles to the mix. Usually, these new alleles are recessive and deleterious. Thus, essentially all individuals are carrying “bad genes.”

Today, genetic diseases and the degree to which behavioral characteristics and intelligence are inherited are still important social and political issues. The emphasis, however, is on determining the specific method of inheritance and the specific biochemical pathways that result in what is currently labeled as insanity, lack of intelligence, or antisocial behavior. Although progress is slow, several genetic abnormalities have been “cured,” or at least made tolerable, by medicines and control of the diet. For example, phenylketonuria (PKU) is a genetic disease caused by an abnormal biochemical pathway. If children with this condition are allowed to eat foods containing the amino acid phenylalanine, they will become mentally retarded. However, if phenylalanine is excluded from the diet, and certain other dietary adjustments are made, the children will develop normally. NutraSweet is a phenylalanine-based sweetener, so people with PKU must use caution when buying products that contain it. This abnormality can be diagnosed very easily by testing the urine of newborn infants.

Effective genetic counseling is the preferred method of dealing with genetic abnormalities. A person known to be a carrier of a “bad gene” can be told the likelihood of passing on that characteristic to the next generation before deciding whether or not to have children. In addition, amniocentesis (a medical procedure that samples amniotic fluid) and other tests make it possible to diagnose some genetic abnormalities early in pregnancy. If an abnormality is diagnosed, an abortion can be performed. Because abortion is unacceptable to some people, the counseling process must include a discussion of the facts about an abortion and the alternatives. Although at one time counselors often pushed people toward specific decisions, today it is considered inappropriate for counselors to be advocates; their role is to provide information that allows individuals to make the best decisions possible for them.





Bad Science: A Brief History of the Eugenics Movement

• 1885: Francis Galton, cousin to Charles Darwin, proposes that human society could be improved "through better breeding." The term eugenics is coined; it is "the systematic elimination of undesirables to improve humanity." This would be accomplished by breeding those with "desirable" traits and preventing reproduction of those with "undesirable" traits. John Humphrey Noyes, an American sexual libertarian, molds the eugenics concept to justify polygamy: "While the good man will be limited by his conscience to what the law allows, the bad man, free from moral check, will distribute his seed beyond the legal limit."

• 1907: Indiana is the first state to pass an involuntary sterilization law.

• 1919: Charles B. Davenport, founder of Cold Springs Harbor Laboratory and of the Eugenics Record Office, "proves" that "pauperism" is inherited and "that being a naval officer is an inherited trait." He notes that the lack of women in the navy also "proves" that the gene is unique to males.

• 1920: Davenport founds the American Eugenics Society. He sponsors "Fitter Families Contests," held at many state fairs around the country. The society persuades 20 state governments to authorize the sterilization of men and women in prisons and mental hospitals. The society also puts pressure on the federal government to restrict the immigration of "undesirable" races into the United States.

• 1927: Oliver Wendel Holmes argues for the involuntary sterilization of Carrie S. Buck, an 18-year-old resident of the Virginia State Colony for Epileptics and Feeble-Minded. Buck is the first person to be selected for sterilization under the law. Buck is sterilized, even though it is later revealed that neither she nor her illegitimate daughter, Vivian, is feebleminded.

• 1931: Involuntary sterilization measures are passed by 30 states.

• 1933-1941: Nazi death camps, with the mass murder of Jews, Gypsies, Poles, and Russians, are established and run, resulting in the extermination of millions of people. According to the New York Times (August 29, 1935), "Adolf Hitler, ... guided by the nation's anthropologists, eugenists and social philosophers, has been able to construct a comprehensive racial policy of population development and improvement. ... It sets a pattern. ... These ideas have met stout opposition in the Rousseauian social philosophy, ... which bases ... its whole social and political theory upon the patent fallacy of human equality. ... Racial consanguinity occurs only through endogamous mating or interbreeding within racial stock ... conditions under which racial groups of distinctly superior hereditary qualities ... have emerged."

• 1972-1973: Up to 4,000 sterilizations are still performed in Virginia alone, and the federal government estimates that 25,000 adults are sterilized nationwide.

• 1973: Since March 1973, the American Eugenics Society has called itself The Society for the Study of Social Biology.

• 1987: Eugenic sterilization of institutionalized retarded persons is still permissible in 19 states, but the laws are rarely carried out. Some states enact laws that forbid the sterilization of people in state institutions.

• Present: Some groups and individuals still hold to the concepts of eugenics, claiming that recent evidence "proves" that traits such as alcoholism, homosexuality, and schizophrenia are genetic and, therefore, should be eliminated from the population to "improve humanity." However, the movement lacks the organization and legal basis it held in the past. Modern genetic advances, such as genetic engineering techniques and the mapping of the human genome, allow the identification of individuals with specific genetic defects. Questions about who should have access to such information and how it may be used causes renewed interest in the eugenics debate.




1919 Charles B. Davenport, founder of Cold Springs Harbor Laboratory and of the Eugenics Record Office, “proved” that “pauperism” was inherited. Also “proved that being a naval officer is an inherited trait.” He noted that the lack of women in the navy also “proved” that the gene was unique to males.



20. What is amniocentesis?

21. What were eugenics laws? List two facts about human genetics that the advocates of eugenics failed to consider.



All organisms with similar genetic information and the potential to reproduce are members of the same species. A species usually consists of several local groups of individuals, known as populations. Groups of interbreeding organisms are members of a gene pool. Although individuals are limited in the number of alleles they can contain, within the population there may be many different kinds of alleles for a trait. Subpopulations may have different allele frequencies from one another.

Genetically distinct populations exist because local conditions may demand certain characteristics, founding populations may have had unrepresentative allele frequencies, and barriers may prevent the free flow of genetic information from one locality to another. Distinguishable subpopulations are known as subspecies, varieties, strains, breeds, or races.

Genetic diversity is generated by mutations, which can introduce new alleles; sexual reproduction, which can generate new genetic combinations; and migration, which can subtract genetic information from, or add genetic information to, a local population. The size of the population is also important, because small populations have reduced genetic diversity.

A knowledge of population genetics is useful for plant and animal breeders and for people who specialize in genetic counseling. The genetic diversity of domesticated plants and animals has been reduced as a result of striving to produce high frequencies of valuable alleles. Clones and intraspecific hybrids are examples. Understanding allele frequencies and how they differ in various populations sheds light on why certain alleles are common in some human populations. Such understanding is also valuable in counseling members of populations with high frequencies of alleles that are relatively rare in the general population.


Basic Review

1. A(n) _____ is all the individuals of the same kind of organism found within a specified geographic region and time.

2. A(n) _____ is all the alleles of all the individuals in a population.

a. gene pool

b. population

c. allele pool

d. clone

3. Which of the following does not belong?

a. subspecies

b. breed

c. variety

d. culture

4. Which of the following is a reason that genetically distinct populations exits?

a. adaptation

b. the founder effect

c. cloning

d. All of the above are correct.

5. Genetic diversity in domesticated plants and animals is affected by

a. selective breeding.

b. genetic engineering.

c. cloning.

d. All of the above are correct.

6. Morphological, behavioral, metabolic, and genetic differences are all important

a. standards used to identify species.

b. ways of generating genetic diversity in a population.

c. reasons for the existence of gene pools.

d. sources of mutation.

7. A(n) _____ is a form of genetic drift in which there is a sharp reduction in population size due to a chance event that results in a reduction in genetic diversity in subsequent generations.

8. The organisms that are produced by the controlled breeding of separate varieties of the same species are often referred to as

a. intraspecific hybrids.

b. interspecific hybrids.

c. mutants.

d. clones.

9. Which of the following causes degeneration of the nervous system and the early death of children?

a. sickle-cell anemia

b. Tay-Sachs disease

c. PKU

d. eugenics

10. _____ is the term used to describe genetic differences among members of a population.

11. The basic purpose of _____ _____ is to eliminate “bad genes” from the human gene pool and encourage “good genes.”

12. If two organisms look different, it means that they are members of different species. (T/F)

13. A “zorse” is the result of breeding between a zebra and a horse and

a. is an example of an interspecies hybrid.

b. will no doubt be the beginning of a whole new species.

c. only happens in zoos.

d. is an example of intraspecies breeding.

14. Grape plants are grafted onto the stems of already-existing plants to generate more grape plants. This is also known as _____.

15. As a population decreases in size, it is most likely that

a. genetic diversity will decrease.

b. extinction is more likely.

c. the gene pool also decreases in size.

d. All of the above are true.



1. population 2. a 3. d 4. d 5. d 6. a 7. genetic bottleneck 8. a 9. b 10. genetic diversity 11. eugenics laws 12. F 13. a 14. cloning 15. D


Thinking Critically

Is GINA on Your Side?

“The Genetic Information Nondiscrimination Act of 2008 (Pub.L. 110-233, 122 Stat. 881, enacted May 21, 2008, GINA), is an Act of Congress in the United States designed to prohibit the improper use of genetic information in health insurance and employment. The Act prohibits group health plans and health insurers from denying coverage to a healthy individual or charging that person higher premiums based solely on a genetic predisposition to developing a disease in the future. The legislation also bars employers from using individuals’ genetic information when making hiring, firing, job placement, or promotion decisions.”

Did you know about his law? What biological information led to the introduction of this bill? On what basis might a person have voted no on this bill? From your perspective, under what kinds of circumstances might a person file suit under this law?