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(Chairs should be arranged in audience formation leaving ample playing space area. One student is selected to stand down-center. Instructions will proceed as follows:)
This person was born of two parents. (Two more students are selected and instructed to enter stage left and stand on either side -- down-center -- a half-step in back of the first.
His/Her parents had parents, which are his/her grandparents. (Four students are selected and instructed to enter stage right and stand a half-step in back of the grandparents; with each generation addition, the formation should spread like an inverted triangle. Stage areas are also included in the instruction, i.e., up-right, down-left, etc.)
His/Her grandparents had parents, which are his/her great-grandparents. (Add eight more students.)
(If you have a combined class grouping and have enough students, add this last.) His/Her great-grandparents had parents, his/her great-great grandparents. (Add sixteen students.)
Everyone standing in back of (First student) is his/her ancestor, a family member who was born before he/she was. If anyone of you did not ever exist, he/she would not exist. (First person) as well as each group of parents represents a generation.
How many generations are represented here? (Four or five if you included the last grouping.)
How many ancestors does (First student) have? (14/30.)
(Students are instructed to take notice of where they are standing and then to take their seats. The organization of generations is repeated with the teacher calling each generational grouping.) (First students name), parents, grandparents, great-grandparents, great-great grandparents.
(To the students) What happens to the number of members in the group with each additional generation? (It doubles; it increases exponentially.)
If we could continue going backwards in time, say about 64 times -- or 64 generations ago, (First student) would have about 18 and a half quintillion ancestors. A quintillion is the number one followed by 18 zeros. If we tried to count it by seconds, it would take 32 billion years, which is older than the age of the universe! (Students are instructed to be seated.)
Each of us has this kind of ancestry. If we go back in time to year 400 -- 1600 years ago or 64 generations -- each of us winds up with about 18 and a half quintillion ancestors. But theres a problem here. One quintillion equals one billion billion. Whats the problem? (There are a lot more ancestors than there are or ever were people on Earth.)
READING: From Billions & Billions, by Carl Sagan, p. 23.
Something is wrong with our calculation. What? Well, we have assumed all those lineal ancestors to be different people. But this, of course, is not the case. The same ancestor is related to us by many different routes. We are repeatedly, multiply connected with each of our relatives . . . Something like this is true of the whole human population. If we go far enough back, any two people on Earth have a common ancestor . . . We are all cousins -- everyone on Earth.
