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Whale of a Tale

Return of Tuberculosis

Howler Monkeys Tell All

Wheelchair Design

Smarter Food Processing Techniques
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SHOW 302: Howler Monkeys Tell All

Howler monkeys have fascinated anthropologist Ken Glander for two decades. Working with these primates in a living lab -- a few acres near the Pacific coast of Costa Rica -- Glander has made a significant discovery that challenges previously held beliefs. Anthropologists have traditionally assumed that tooth wear is an obvious clue to an individual's age, but Glander is finding that teeth wear down differently, even in monkeys of the same age. The question is, why? Many years of careful observation reveal a possible answer.

Curriculum Links
Activity: What Happened Here?
Notes & Discussion
Report From the Field: Leslie Reinherz, Television Producer and Museum Consultant



social groups

animal behavior,




Anthropologists, paleontologists, forensic scientists and detectives have much in common: they all try to figure out what happened on the basis of clues left behind. But clues can be misleading. It's very easy to misinterpret the data. Things are not always what they seem, and physical evidence often leads investigators on a wild goose chase.

In this activity, each of six groups will have five minutes to rearrange a box of materials according to directions on an instruction sheet. Follow the instructions in order, exactly as they are written. Do not let another group see what you are doing. If your task takes less than five minutes, continue to look busy, since other groups may have longer tasks. When you have completed the task, put the end product back in the box and exchange boxes with another group, being sure to keep your own instructions.

When you get another group's box, brainstorm with your group to deduce the sequence of events told by the object(s). Your objective is to list the sequence of events in the order that they happened, to create the evidence left behind in the box. Do not touch the objects in the box. List the steps in order on a sheet of paper and list all materials you think were used. Continue to exchange boxes until each group has seen all six.

  • sheet of notebook paper
  • pen

  1. Tear the sheet of paper down the middle and keep the left side. Write the following on the half sheet of paper so that the last letter of each line is on the right, torn edge of the paper:

    • Line 1: My Dearest Ea
    • Line 2: will give 2 thou
    • Line 3: in an effort
    • Line 4: you get out of ja
    • Line 5: be waiting f
    • Line 6: all my everlastin
    • Line 7: Your only lo
    • Line 8: P.S. The fil

  2. Now write this note at the bottom in small print: OK, hotshots! What did this letter say?

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  • styrofoam cup
  • coffee stirrers

Remove the bottom from a styrofoam cup. Bite off a piece of the cup rim. Use a coffee stirrer to carefully notch the perimeter of the bottom of the cup (make it look as though it was removed by poking holes in the bottom). Poke as many holes in the cup as you can without completely destroying the cup. Poke holes in the bitten piece. Place the cup parts and punchouts in the box. Keep and hide the stirrers.
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  • tape
  • paper clips
  • craft sticks
  • index cards
  • pen

Have each person in your group pick a number and write it in the center of an index card. Bend the paper clip into a "C" shape. Tape one paper clip over the number. Cut two small slits near two edges of the card. Insert a craft stick through one slit and down through the other. Place the completed items in the box. Write "THIS WAS LAST" on the box top. Keep the pen and tape.
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  • 5 marbles
  • small block of modeling clay

Form the clay into a rectangle in the bottom of the box. Press the marbles into the clay to create indentations, then remove and hide them.

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  • scissors
  • 5 or 6 old, used or defective 5-1/4" floppy disks with sleeves

Slide the disks into their sleeves. Cut the bottom corners off so that you make a triangle about 2cm per side. Remove the disk triangles from the sleeve triangles. Slit the sleeve triangles on an edge and open them. Place the disk and paper sleeve triangles in the box. Keep and hide the rest of the materials.
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  • toothpicks
  • 10 cm piece of burlap or denim
  • red marking pens

Use the marking pens to write your names on the cloth square. Pick apart the cloth square with the toothpicks and place the torn pieces in the box. At the end of the allotted time, place the unpicked portions in the box. Do not place the toothpicks in the box.

  • This activity is a thought-provoking exercise in reconstruction that demonstrates how difficult it is to interpret data in scientific investigation. Students discover that the sequence of events doesn't always follow the most obvious path.

  • You will need six shoeboxes. Each will contain materials that students use to set up a puzzle for their classmates to solve (refer to the materials listed in the activity). Students examine the material clues in the box and try to reconstruct a sequence of events.

  • Download and print the activity, then cut apart the six puzzles. Give one set of puzzle instructions and the corresponding box of materials to each of six groups of five to six students. Tell students they will have exactly five minutes to complete the first part of the activity. The time limit on the deduction process is open-ended. If you want to set up a scoring system, have groups give themselves 1 point for each step they correctly identify and 10 extra points (per box) if they correctly identify all steps in the exact sequence in which they occurred.

  • Some of the scenarios are very simple; others are complex. The idea is to determine what happened and in what order. With box No. 1, for example, students looking at the clues will probably assume that the letter was written first, and then the sheet of paper was torn in half; actually, the letter is never written out. Both researchers and detectives must learn to question the obvious.

  • Science is a process of continually challenging previously held assumptions. Many theories have been overturned when scientists review the evidence again or look at the data in a new way. Consider, for example, how beliefs about dinosaurs have been radically questioned in recent years.

  • Bones offer clues to the mysteries of the past. As an individual ages, bone size and appearance change. For example, arthritis causes noticeable scarring on bone ends. As the disease progresses, more bone scars are formed. Evidence gleaned from the ages and scarring progression of arthritic patients of today leads to some interesting speculation about skeletons from the past. Though bone scars do not tell scientists the geologic age of the bone, they may indicate the age range of the individual whose skeleton has been found.

  • Similarly, observations of present-day howler monkeys tell us something about monkeys in ancient times. Glander's twenty-year study points to the critical role diet plays in affecting teeth. What implications might that conclusion have for the dating of human fossils?

  • We know that diet and use can markedly influence the appearance of the teeth in similarly aged organisms of the same species. In humans, tooth wear can vary by culture. For instance, some teeth of Eskimo individuals may show severe wear from years of combined uses as a tool and a digestive organ. Teeth of a city dweller of the same age as the Eskimo are likely to look as though they belonged to a much younger individual.

  • The monkey studies have led to other surprises. Glander had assumed that those monkeys in the river colony lived a life of ease; but since much of the river growth is toxic, life for those monkeys proved equally as difficult as for the inland monkeys. In scientific investigation, it pays to stay open to possibilities.


Being on assignment can be a harrowing experience occasionally, as producer Reinherz discovered last spring on production in Costa Rica to make the howler monkey segment. Reinherz, with the Chedd-Angier Production Company in Watertown, Massachusetts, for ten years, worked on this and many other segments of FRONTIERS during that time.

Reinherz faced some unusual and exciting challenges working on productions for Chedd-Angier. She has waited patiently for ants to emerge from their nests and iguanas to appear within range of a camera. Here, she describes what happened on one of her final shoots with the production company. "We had been filming the howlers in the forest and broke for lunch. After we ate, we began to smell smoke, looked around and found that slash-and-burn agriculture was going on in our back yard."

She continued. "We just happened to be filming in the driest part of the forest, where the worst burning was taking place. Fire engines appeared, but they couldn't pump a lot of water; a bucket brigade eventually put out the fire. It very nearly burned the entire hotel down to the ground and would've destroyed the monkey colony had it spread. The experience really brought home the whole issue of razing the forest."

En route to becoming a producer, Reinherz earned a Ph.D. in zoology from Duke University. A fellowship from the AAAS took her to a job at a television station. She fell in love with the business and decided to become a science educator using the medium of film. Reinherz has now taken her interest in science and science education to another realm. She is a consultant to the Museum of Science, Environment and Technology in Cleveland, Ohio, scheduled to open in 1996. There she is working on yet another kind of graphic display, developing exhibits for the museum.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.