Two hands holding a straw without using thier thumbs
Written by: 
Amy Peterson
Illustrated by: 
Megan Joyce

show/hide words to know

Ancestor: an organism from which others have evolved. In humans, a relative from whom one is descended, who lived at least several generations ago.

Descendants: people that come from a previous generation. You are the descendant of your parents and grandparents, but also the descendant of species that evolved and lived in Africa millions of years ago.

Digit: digits are the parts at the very end of the arms or legs of a creature. Our fingers and toes are all digits.

Trait: any distinguishing factor or quality that can vary in a group. Eye color and height are examples of traits that we can easily see.

Before you begin

This experiment will demonstrate the importance of opposable thumbs.

Our opposable thumbs let us grasp and manipulate objects. When you tape down your thumb, you’ll get a sense of how hard it would be to do many things if our hands were shaped differently. Even a simple task like placing a straw in a bottle becomes difficult! Why do you think human hands are shaped the way that they are?

What you will need

  • Painter’s tape
  • Drinking straw
  • Empty plastic bottle with cap
  • Trash container
  • Info sheet [PDF]


Hands being taped for the experiment, with the tape holding the thumb down flat so it cannot be used.

Have someone help you apply the tape to your hands so you cannot bend or move your thumbs.

A person trying to complete the experiment with taped hands

Try to do some simple things, like picking up the straw. Try to put the straw into the bottle. Now, remove the straw and try to place the cap onto the bottle.

Learn more

Our closest living relatives, chimpanzees, have hands that are similar to ours. Their hands allow them to use some simple tools, like using a stick to get ants out of anthills. But they don’t have a brain like ours, so they can’t plan out making complex tools, and they don’t improve on the design of their tools over time.

baby Colobus monkeyAll living things have evolved through time in response to their environment. Many millions of years ago, the ancestor to all living primates developed an opposable digit on its hands and feet, which allowed it to cling to branches in the trees where it lived. This trait became beneficial to survival and was passed to all the descendants of that ancestor species.

The opposable digit has evolved differently for different species. For example, like most primates, chimps retained their “thumbs” on both their hands and feet. Colobus monkeys have greatly reduced the thumbs on their hands, because these monkeys no longer needed an opposable digit for how they move. Humans have a thumb on our hands, but we no longer have an opposable big toe.

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Bibliographic Details

  • Article: Thumbs Up
  • Author(s): Amy Peterson
  • Publisher: Arizona State University Institute of Human Origins Ask An Anthropologist
  • Site name: ASU - Ask An Anthropologist
  • Date published: February 6, 2019
  • Date modified: September 14, 2020
  • Date accessed: May 24, 2024
  • Link:

APA Style

Amy Peterson. (2019, Feb 06). Thumbs Up. Retrieved May 24, 2024, from

American Psychological Association, 6th ed., 2nd printing, 2009.
For more info, see the APA citation guide.

Chicago Manual of Style

Amy Peterson. "Thumbs Up." ASU - Ask An Anthropologist. Published February 6, 2019. Last modified September 14, 2020.

Chicago Manual of Style, 17th ed., 2017.
For more info, see the Chicago Manual citation guide.

MLA Style

Amy Peterson. Thumbs Up. ASU - Ask An Anthropologist. February 6, 2019, Accessed 2024 May 24.

Modern Language Association, 8th ed., 2016.
For more info, see the MLA citation guide.

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Experiment Packet

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