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.
2.
3.
4.
5.
6.
7.
Write your name with a pencil or pen on a small piece of paper.
Unbutton and rebutton an article of clothing that has buttons.
Use a zipper on an article that of clothing that has a zipper.
Put on a pair of shoes and tie the laces.
Pick up a straight-backed chair.
Pick up three coins on a flat surface.
Open and close a door using the doorknob.
Task
Data Table
Hands Untaped
Time needed to complete
(sec.)
Hands Taped
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.
http://www.athro.com/evo/pthumb.html
Link to information about the evolution of the Panda’s thumb.