Thumbs Up, Thumbs Down



Thumbs Up, Thumbs Down

Grasping the Idea of Evolution

Introduction Apes and primates have hands capable of grasping objects. The grasp is made possible by the opposable thumb, so called because it moves opposite to the rest of the fingers. In humans, the thumb can move farther across the hand than in any other primate. In this experiment, you will compare your performance of a series of tasks using your thumb and fingers together with your performance of the same tasks without the aid of your thumb.

Materials and Equipment:

For each pair or group of students:

Tape dispenser

Time collection device (stop or wrist watch)

pencil and paper

clothing with buttons

clothing with zipper

shoes with laces

straight back chair

coins of various sizes

door with doorknob

Procedure:

Working in groups of three (timer, data collector, task performer):

1. Observe your hand. Notice especially the relationship of your thumb to the rest of your fingers and the rest of your hand. Note that your thumb can move in a number of directions and angles. Record a description of the range of motion of your thumb in your lab notebook or data sheet.

2. Perform the following list of tasks as you normally would, using your thumb and fingers. Pay special attention to your thumb and its involvement in these tasks. Enter your time needed to complete each task.

1. Write your name with a pencil or pen on a small piece of paper.

2. Unbutton and rebutton an article of clothing that has buttons.

3. Use a zipper on an article that of clothing that has a zipper.

4. Put on a pair of shoes and tie the laces.

5. Pick up a straight-backed chair.

6. Pick up three coins on a flat surface.

7. Open and close a door using the doorknob.

Data Table

| |Hands Untaped |Hands Taped |

|Task |Time needed to complete (sec.) |Time needed to complete (sec.) |

|1) name with pencil | | |

|2) buttons | | |

|3) zipper | | |

|4) tie shoe | | |

|5) pick up chair | | |

|6) pick up coins | | |

|7) open and close door | | |

|8) ___________ | | |

|9) ___________ | | |

|10) __________ | | |

3. Working with your team, have each partner tape the other person's thumbs to their index finger. Be careful not to wrap the tape too tightly and cut off the blood circulation to your hand!

4. Repeat the tasks listed in step two under Procedure with your taped hands. Pay particular attention to any difference in the performance of the tasks. Enter your observations in the data table as before.

Explanation: The goal of this exercise is to point out that the concepts of natural selection and environmental adaptation by a species applies to humans along with other organisms. Oftentimes, I can get across the concepts using examples from predator/prey relationships but when it comes to humans, students often lack the ability to see how we are subject to change. This activity points out the necessity for the opposable thumb, which is so often taken for granted.

Analysis and discussion:

1. Which tasks required the least "thumb involvement"? Which tasks required the most? Explain your answer.

A: The use of clothing features like buttons, zippers and laces seem to be toughest for students because they require the use of fine motor manipulation.

2. Of the tasks you performed, which required fine motor skills (those requiring small subtle hand movements) and which required gross motor skills (those involving larger movements using arm and back muscles)? Is there a correlation between thumb use and the type of motor skills involved? Explain your answer giving evidence from your data and that of others in your class.

A: As mentioned previously, fine motor manipulation of objects is efficiently possible with the opposable thumb. Actions that use gross motor skills can be accomplished effectively without the use of the thumb. This allows for writing opening doors and picking up chairs to be accomplished rather easily in either condition (thumb vs. no thumb).

3. Many scientists believe that the opposable thumb has helped humans adapt to their environment and survive. Using your data as a guide, explain some of the ways in which the use of the thumb enables humans to better survive in their environment.

A: Students should discuss the advantages in terms of tool use for easing the burden of tasks that now seem mundane.

4. Speculate on how the well developed human brain may have helped our species make creative use of its fine motor skills.

A: The human ability to reason and be creative enables a greater variety of uses and innovations that can lead to the development of novel skill use.

Reference

Plati, Susan. How Important is Your Thumb? More Science Experiments on File. New York: Facts on File, 1991.

Link to information about the evolution of the Panda’s thumb.

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