One class period
Students will understand the following:
- Identical twins are genetically identical.
- For this reason, twins separated at birth and later reunited have been subjects for scientific researchers investigating the influence of heredity and environment on human personality.
For this lesson, you will need:
- Research materials on genetics, particularly on twins
- Computer with Internet access
- Initiate a class discussion about the heredity-versus-environment issue. Do your students think that heredity is the primary influence over human personality development, or do they think that a child's experiences and associations are more influential?
- Continue the discussion by asking students to come up with ways the question could be scientifically investigated.
- If your students have not brought up twin studies, ask them why a pair of identical twins who had been separated at birth, raised in different environments, and reunited as adults could be excellent subjects for a study of the effects of heredity versus environment on personality development. (Make sure students understand that identical twins are genetically identical.)
- Ask the class how they would interpret the following sets of data: (a) each identical twin in the pair has a very different personality and lifestyle; (b) the twins are unbelievably similar, not only in physical appearance but also in personality and lifestyle.
- Divide your class into groups, and challenge each group to devise a questionnaire with at least 10 questions they would ask each of the twins in a study designed to weigh the effects of heredity and those of environment on personality development.
- Have students do research on the Internet to find the results of actual studies that have been done using separated identical twins as subjects.
- Have students play the roles of the separated identical twins and fill in their own questionnaires based on findings from their research.
Adaptations for Older Students:
Have students contact a twin registry such as the Gregor Mendel Institute of Medical Genetics and Twin Studies (located in Rome) or the Minnesota Center for Twin and Adoption Research to find out about actual research being conducted. What methods are being employed to collect data? How is this research being used to benefit society?
- Explain what steps should be taken by scientists studying twins to avoid possible invasion of privacy.
- What might explain the extraordinary similarities between identical twins separated soon after birth, reared in different environments, and reunited for the first time as adults?
- What do twin studies indicate about the influence of the environment and the complex interaction of genes on our personality, intellectual ability and emotions such as happiness?
- Although telepathic communication has not been proven to exist among twins, describe what consequences might arise if such communication were possible. Could telepathy be used responsibly? What are the ethical considerations associated with telepathic communication?
- The environment before birth is critical to the development of the unborn child. Prenatal influences may lead to differences in size, appearance and psychological development. Describe the function of the following structures: chorion, amniotic sac, placenta and umbilical cord. How might the functioning of these structures be compromised if there is more than one embryo developing?
- Describe the four possible mechanisms in which identical twins could form. Why is there a point during pregnancy after which the developing twins' health may be in jeopardy?
You can evaluate your students on their questionnaires using the following three-point rubric:
Three points: all questions thoughtfully designed; questions well phrased and unambiguous; at least 10 questions
Two points: most questions thoughtfully designed; phrasing of some questions awkward or unclear; at least 10 questions
One point: questions reflect little thought; phrasing of many questions awkward or unclear; fewer than 10 questions
You can ask your students to contribute to the assessment rubric by determining what kinds of questions would advance the study.
Imagine Your Twin
Suggest the following scenario to your students: "You have just learned that you have an identical twin you have never met. You are about to meet for the first time, and you have so many questions. Will my twin be like me or different? Will we get along?
Will we like each other?" Have students, keeping this scenario in mind, make a list of physical traits they think they and their twins might have in common. Next, have them compile a list of behavioral traits they think they would share with their twins. The list should include habits, mannerisms, ways of expressing emotions, likes, dislikes, and so on. Finally, students could write short stories about their meetings with their long-lost twins.
Writers and anthropologists have noted the religious beliefs, rituals, myths, and legends that have revolved around twins throughout time. Art, statuary, literature, and temples have been inspired by twins. With your class, delve into the world of twin folklore, and have groups of students prepare presentations for the class on particular legends about twins.
"Annual Twins Day Festival More Than Just Fun and Games"
National Public Radio, weekend edition, Aug 6, 1995; program number 1135
The transcript of this radio program discusses the "Twins Day Festival" in Twinsburg, Ohio, which annually attracts 3,000 sets of twins and the researchers who wish to study them.
"Worldwide: U.S. Twin Births Rose 42%"
Wall Street Journal, February 14, 1997
How might society be different if there were as many twins as everyone else? That may soon be a reality, given the trend of increasing twin births. This article tells why that trend is occurring.
Access this resource at:
This site includes discussions and numerous links to support and inform parents of monoamniotic twins.
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Credit: Lisa Lyle Wu, science teacher, Thomas Jefferson High School for Science and Technology, Alexandria, Virginia.
Definition: A technique involving the formation of a two-dimensional image used for the examination and measurement of internal body structures and the detection of bodily abnormalities--also known as sonography.
Context: These pictures are captured with ultrasound.
Definition: A specific sequence of nucleotides in DNA or RNA that is the functional unit of inheritance controlling the transmission and expression of one or more traits.
Context: Identical twins are a miracle of nature: two people with the same set of genes.
Definition: Two persons closely resembling each other who share the same set of genes.
Context: Most identical twins have identical backgrounds.
Definition: Communication from one mind to another by extrasensory means.
Context: It has been suggested that twins have the ability to communicate telepathically.
Definition: A school of psychology that takes the objective evidence of behavior (as measured responses to stimuli) as the only concern of its research and the only basis of its theory, without reference to conscious experience.
Context: American psychology went through a reign of behaviorism.