Lesson Plan
Objective: The student will compare two theories of human evolution using microsatellite data.
Materials: The teacher should provide copies of the following articles: (see below for a brief explanation of the ideas in the articles)
"Out of Africa into Asia." Scientific American, January 1999
Piazza, Alberto. "Human Evolution: Towards a Genetic History of China." Nature, October 1998, pp. 391-394
Wood, Bernan. "Human Evolution: Ecce Hommo." Nature, November1997, pp. 395-398.
Procedure:
1. Introduction: The teacher will introduce the concept of microsatellites. Feel free to browse our website for information! Just follow the links below.
c-Evolution of microsatellites.
Information about the articles for the teacher:
General Aspects: Scientists may have pinpointed direct descendants of the first human to migrate out of Africa into Asia, due to their resemblance of features: dark skin and small, gracille forms. A recent DNA study of hair (collected in 1907) from Andamanes individuals by Radcliffe Brown suggests an even closer connection than the physical features imply.
Carlos Fox and Erika Hegelberg extracted DNA from 42 out of 70 hair samples and amplified a short segment of DNA from the mitochondria (mtDNA). This DNA is less related to physical characteristics than chromosomal DNA and is less sensitive to the pressure of natural selection. They found that the sequences of base pairs in the mtDNA fragments clustered closer to the African population --especially Southern African pygmies-- than to the Asian population.
An extensive survey of Chinese DNA conducted by Li Jim, using microsatellites revealed minor genetic variations among the population suggesting that these groups had had little time to diverge from one another .
M. Stone King reported the results of an analysis of 8 alu loci in the nuclear DNA of 1500 people drawn from population around the world . From these results he estimated that the major split between African and non-African population occurred about 140,000 years ago, this date is consistent with evidence from mtDNA
The second theory holds that humans evolved separately in different parts of the world from population of Homo erectus that dispersed also from Africa (one to two millions years ago). These groups of humanoids managed to develop into a single species Homo sapiens by exchanging genes with one another.
Milford Wolpoff has pointed out that interbreeding could have ensured that the descendants of different humanoids ended up being genetically similar. He is skeptical of the Andaman study, which cannot be properly critiqued until it is published. An unfortunate dispute regarding the hair has held up publication. Also the access to blood, hair and other human samples is restricted by many countries for fear that genetics information will be misused.
Activity: Divide the groups in three small groups. Each group will receive a reading, and the following answers should be completed.
Which are the two theories about human evolution?
Which one is the rival theory?
Mention the pros and cons of each theory?
Explain why is so difficult to maintain the 1st theory?
What will you do considering the ethical aspects of the situation?
After 30 minutes, the three groups should return together and discuss readings as a whole group. One method for discussing as a large group would be to create two circles of students; one inner circle and one outer circle. Students begin facing each other discussing one of the questions above, after they have dialogued with each other the inner circle moves to another person. Students can then discuss the articles with a number of different students.