Natural Selection of the Opposable Thumb

Introduction: The opposable thumb was caused by a beneficial mutation, which gave some primates an advantage in their environment. This thumb became a successful characteristic that was passed to subsequent generations. This activity is designed for you to appreciate the importance and benefit of having an opposable thumb.

Procedure: Work with a partner, you will need help. Tape your thumbs to the side of your hands. Do this so that you are unable to use your thumbs, but allow the blood to circulate! Several activities are listed. Try to complete each with your thumbs taped. Have your partner record your response. Then switch and have your partner complete the activities while you record their responses.

Activities: For each activity, check the box with the appropriate rating:

Activity / very difficult / difficult / easy / very easy
pick up a piece of paper
pick up a pen or pencil
write your name on a piece of paper
use scissors to cut circles from paper
use a paper clip to clip papers together
crumple up a piece of paper
unbutton one button on your shirt
button your shirt
untie shoelaces
tie shoelaces
unzip a zipper
zip the zipper
pick up a drinking cup and pretend to drink

Choose one activity that you felt was extremely difficult. Repeat the activity, having your partner time you (count or use a watch). Then remove the tape and use your thumbs to perform the task again, having your partner record the time:

Task:______

Time with thumb: ______

Time withoutthumb: ______

Post Activity Questions:

  1. How did the opposable thumb evolve (where did the first opposable thumb come from)?
  1. Would you be able to do these simple tasks on a daily basis without opposable thumbs? Why or why not?
  1. In order for us to have opposable thumbs, when the mutation first occurred millions of years ago, it must have helped our ancestors become more "fit" in their environment. Imagine that you are "Lucy" (the oldest human ancestor ever found) living 4 million years ago. How would the opposable thumb be beneficial to you?
  1. BONUS!!: How did eyelashes evolve? How did eyelashes make our ancestors more fit in their environment?