Purpose: The purpose of this assignment is to investigate how genes relate to behavior. Outlined below is a thought experiment, followed by some questions. Please read the thought experiment and answer the relevant questions.

Thought experiment: Suppose that a single egg is taken from a mother and fertilized in a petri dish with sperm taken from the father. When the fertilized egg divides into two cells, the cells are mechanically separated. One cell is left alone. The sex of the second cell is engineered in the following way. If the first cell is XX (female), the father's X in the second cell is removed and the father's Y is inserted; if the first cell is XY (male), then the father's Y is replaced with the father's X. Both cells--the original and the engineered cell--are allowed to divide on their own and at the proper time are implanted into the mother's uterus. They will develop, be born, and be raised as twins--but a very special type of twin. They will be genetically identical in every respect except for their sex determining chromosomes, so one will be female and the other will be male.

Suppose this procedure is done with an exceptionally large number of parents, randomly selected from all types of life--migrant worker to corporate president, urbanite to farmer, criminal to cleric--with no other interventions into the twin's lives. That is, the parent's raise them as they see fit, the children are free to form their own friendships, develop their own interests, etc. Because we have not selected any particular genes (the initial fertilization was, after all, random) or any particular environments from the population, the outcomes of these twins should mirror the outcomes for people in general. Some will be real estate millionaires, others homeless; some will be illiterate, others world famous scholars; some will be persistent criminals with life sentences, others will be the judges who do the sentencing.

The design of this thought exercise is a true experiment as opposed to a nonexperimental or observational design. In genetic terms it is called a cotwin control design. Individuals were randomly assigned to the control groups and experimental groups in the sense that the initial fertilization was allowed to proceed on its own, and the experimenter directly manipulated the treatment. However, each individual in the control group has its own "match" in the experimental group. Those of you who have had courses in statistics or experimental design will recognize that this matching strategy is an exceptionally powerful research design.

Questions: Assume (again, in thought experiment mode) that we examine how all these twins turn out when they reach age 50. Please state your predictions about the following outcomes:

(1) Which of the twins (i.e., the female or the male) would be more likely to have entered a convent as a Catholic nun?

(2) Which of the twins (i.e., the female or the male) would be more likely to have played professional football as a lineman (OOPS, a lineperson)?

(3) Which of the twins would have been more likely to have been arrested or convicted of prostitution?

(4) Which of the twins would have been more likely to have been accused of, arrested for, or convicted of rape?

Now answer the following:

(5) What does a true experiment say about cause and effect?

(6) Write a one page essay on how you view the causal effect of the X and Y chromosome on the predictions you made. Think of the following questions: Does the X or Y chromosome have any causal influence on the professions of being a Catholic nun or a football lineperson? What about on being a rapist or a prostitute? Does the meaning of "cause" differ in the nun example from the prostitute example? What about the meaning of "cause" in the lineman versus the rape example? How do the potential effects of environment (e.g., being raised in a Catholic family) and socialization (e.g., being in an adolescent male peer group with demeaning, sexist attitudes toward women) fit into your interpretation of causality in terms of the X and Y chromosome?

(My weary eyeballs would appreciate it if your essay is double spaced and typewritten; if you want to write more than a single page, please feel free to do so.)