Heritability III

This lesson is a puzzle. Begin by imagining a trait associated with cognitive skills. Intelligence is one example, but you could just as well consider specific skills such as mathematics, verbal ability, spatial ability, or memory. Your task is to think of a society, give it certain numerical values on attributes that contribute to the cognitive skill, and then examine the heritability of the cognitive skill in the society.

Above there are four attributes that are associated with the cognitive skill-Education, Attitude to Education, Skill Encouragement, and Literacy. To the right of each skill there are two anchor points with a text field in between. To fashion your society, enter a numerical value between 0 and 100 into the text box to reflect the degree to which the society as a whole emphasizes the choice. The closer the number is to 0, the more the society resembles the left anchor point and the closer to 100, the more the society resembles the right anchor point. For example, if you enter a 0 into the text field for Education, then the society has no formal educational system as happens in certain preliterate hunter-gatherer cultures. If you enter 100 into the same field, then the society demands and has compulsory formal education as most industrialized countries have today. A value of 50 might reflect a society like Western Europe several hundred years ago in which some people were well educated but many never went to school at all.

It is crucial to understand that the number that you enter reflects the valence or the strength to which a society holds certain views. For example, a 0 in the text fields for Skill Encouragement means that everyone in the society rewards and encourages manual skills. Values that are close to 0, but not actually equal to 0, signify that the majority in the society prefers and encourages the development of manual over intellectual skills but not everyone in the society shares this opinion. A value of 50 would mean that the society is evenly split--half of the population encourages the development of manual skills while the other half supports the development of intellectual ability.


  1. It is thought that we humans have spent most of our time on this planet organized in small, nonliterate, hunter gatherer societies. Even today, some of these cultures do not teach simple arithmetic to their children. Some have a rudimentary numbering system that goes "one", "two", and "many" instead of the numbering system of "one", "two" "three", etc. that we industrialized cultures learn before kindergarten. Spend some time thinking about such a culture and enter numeric values for it into the Applet text boxes. Write down the heritability of the cognitive trait.
  2. Now think of the United States at the turn of the millennium. How much does the average person in this culture value compulsory formal education? What does the average person want with respect to the literacy of the society? Put suitable numbers in the text boxes and record the heritability.
  3. Now imagine the majority of world cultures which are intermediate between the preliterate, hunter-gatherer society and modern America. Try to think of three such cultures--making certain that they are not identical--and enter values for them in the text fields. Record the heritabilities within these cultures.
  4. From the preceding exercises, you will probably notice two important facts. First, there is a systematic change in heritability as you went from the preliterate, hunter gatherer society through intermediate societies and ended with modern industrialized cultures. (If you did not notice any regularity, then fix any three of the text fields to 50 and vary the fourth text field from 0 to 100). The second fact is that the spread of the curve for ability differs among some of the cultures. The major thought question--and it is not an easy one--is to explain why such systematic change in heritability should occur. The change in the variance of the curve from one culture to the next is a major hint. You may also want to try Heritability-IV--which plots two different curves, one for each culture-before trying to answer the question. If you have trouble arriving at an answer, please do not despair. This is really a very hard question. We will discuss the problem in class and you will get the answer there.


Heritability: Introduction
Heritability I: Scatterplots
Heritability II: Environmental variation around a genotypic value.
Heritability IV: Between-group Heritability.