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Introduction to Environmental Geoscience
Homework #1 for Fall 2008

Due 2 September 2008

Late homework will cost 15 points per week or part of a week it is late.


Has your family contributed to global population growth?

Please complete the following work to determine if your family has contributed to global population growth.

We have all heard the statement "Think globally, act locally." Let's apply it to our own families. Take a piece of paper and draw a large square somewhat like the one in the image below. Then lightly draw three horizontal lines on which you will enter symbols for your grandparents on the top line, symbols for their children on the middle line, and symbols for their grandchildren on the bottom line.

Enter the following symbols:

  1. On the first line enter small round open circles to indicate your four grandparents. You may use step grandparents if applicable.
  2. On second line enter small filled circles, one for each child of your grandparents. This line includes all your aunts, uncles, and parents. Also enter small round open circles for their husbands or wives. Note one child may have have been married more than once, and that child will have more than one open circle.
  3. On the third line, enter small filled circles of all the children of families on the second row. If any of your brothers/sisters married, do not show their spouse or children. Those children would go on a fourth line and should not be counted for this homework assignment.
  4. To help you remember who is related to who, draw horizontal lines to show marriage, vertical lines lead to children from the marriage.
  5. Now calculate growth rate: Divide the number of filled circles by the number of open circles. Values less than one lead to a smaller population over time, values greater than one lead to increasing population.
  6. Write the value for your family on the separate piece of paper and hand in on the due date. I do not need your diagram, but you may hand it in if you like. Some may not wish to reveal too much about their family, and I respect their wish. That's why I don't require the diagram.

In writing out this assignment, I soon realized it could get complicated. Everyone denoted by a closed circle should have some of the DNA of the grandparents (related by blood was the old phrase). Everyone denoted by an open circle should not have some of the DNA of the grandparents (for example, daughters-in-law of the grandparents). But, what about adopted children and step children? Theoretically, everyone on the third line should have some of the DNA of the grandparents on the first line. To keep it simple, treat adopted children the same as all other children. But don't include step children unless they are blood relatives of the grandparents.

An Example

Here is a diagram of a hypothetical family. If it were your's, you would be one of the children on the left on the third line because these children (you and your brothers and/or sisters) have one parent from each of the four grandparents. They have no parent with an open circle. Your cousins are the other children on the third line. Your aunts and uncles are on the second line. Notice I drew the diagram with one person on the second line with two spouses. This indicates that person married twice, one marriage produced one child, one produced two children. Also notice some children never married.

This diagram has 10 open circles and 16 closed circles. The ratio is 1.6 for the two generations. The ratio for the first generation is 8/4=2. The ratio for the second generation is 8/14=0.57. Thus the first generation produced two children per person of that generation, increasing the world's population. Each person in the second generation produced 0.57 children on average, reducing population. This is fairly typical, many families now have fewer children than their parents had.

family growth tree

Revised on: 20 August, 2008

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