Variation and Natural Selection
Objective:
To study how variation within a species is the basis for natural selection.
Process Skills:
Measuring, collecting and analyzing data, inferring
Materials:
Metric rule, graph paper, peanuts in the shell
Background:
1.
Variation has been described as “the raw material of natural selection.” What is variation?
2.
What determines an individual’s phenotype? How might a mutation of a genotype prove to be beneficial to a species?
3.
Explain why it is advantageous for a species to show variation among individuals.
Inquiry:
1.
Crack open the peanut shell and measure the length of 100 peanuts in millimeters. Record your results in a table, giving the lengths and number of peanuts for each length. Why is the fact of different lengths evidence of variation within the species?
2.
Make a bar graph using your data from Step 1. What should you label the vertical axis?
The horizontal axis? Which is the independent variable? Which is the dependent variable?
3.
Combine the class data and graph them in a separate bar graph. Describe any difference between your data and the class data. How can you account for these differences?
4.
Describe the overall shape of your bar graph from step 3. What may have caused the peanut-size variation you observed?
5.
Use the class data to calculate the average peanut length. How do the number of average peanut length compare with the number of very large and very small peanuts.
6.
According to the class data, what size is the largest peanut measured? The smallest? The peanut supplies the seed with energy. What is the relationship of peanut size to the amount of energy available to the seed?
7.
Repeat the steps for a human trait of your choice.
8.
Repeat the steps for 100 leaves collected. Look for patterns in the leaves. Look for opportunities to evolve. Compare using measurements.
Conclusions:
1.
What might have caused the large and small sizes of the peanut measured? If the environment changed so that a very large peanut was an advantageous variation, what would happen over time to the peanut population in response to such a change?
2.
Describe and environmental change that would favor the much larger peanut. Can you think of a change that would favor the much smaller peanut?
3.
Why do you think most peanuts are not the size of the smallest peanut measured?
4.
How might you determine whether a trait (such as very large peanut-size) is a result of genetic or environmental factors?
5.
For each of the other traits that you chose, (the human trait and leaves) give an environmental factor that would affect the selection of each of these qualities.