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NOVA scienceNOW: First Primates
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Viewing Ideas
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Before Watching
Identify the
characteristics of a primate. Present the
following list of animals to your students. Have them identify those that are
primates and explain their reasoning. Consider displaying pictures of some of
the less familiar animals.
- Dogs
(No)
- Human
beings (Yes)
- Dolphins
(No)
- Lemurs
(Yes)
- Lions
(No)
- Rabbits
(No)
- Orangutans
(Yes)
- Deer
(No)
- Tree
shrews (No, though they are close relatives)
Next,
explain that primates have the following characteristics: (1) forward-facing
eyes with binocular vision allowing for depth perception; (2) thumb mobility
for holding on; (3) precision grip
for picking up small objects; (4) grasping hands (which aid in power grip) with
nails rather than claws. With these characteristics in mind, have your students
revisit their list and change answers if necessary, again explaining their
reasoning. Where are they in agreement? Can any of the maybes be switched over to a yes or a no?
Conclude the activity by watching the program segment, which details the
characteristics of primates.
Examine
the advantages of stereoscopic vision.
A key primate
characteristic that will be described in the segment is stereoscopic vision. It involves using two eyes located
so both aid depth perception and the ability to see things three-dimensionally.
Each eye takes in slightly different information about 3-D objects, which aids
the brain in approximating distance.
To
help students understand the importance of stereoscopic vision, have them
experience what the world is like without it. Before class, gather cups and
small items, such as paper clips, coins, or buttons. Provide a ruler, four
cups, and four items per team.
Setup:
Student
one: Sit in a chair several meters away from a desk or table with the surface
just below eye level. Close both eyes. Student
two: Hold the paper clips or similar items and stand near the desk or table. Student
three: Place paper on the surface and set the four cups on top of the paper.
Prepare to record data in a data table like the one below.
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Student Name
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Number of Items Using One Eye
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Number of Items Using Two Eyes
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Notes
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Task:
Student
one: Opening only one eye, direct student two to move his or her hand right/left
and forward/back until you think it is directly over one of the cups. At that
point, tell student two to drop the item. Mark on the paper where the item
first dropped. Students
one and two: Repeat with the remaining items and cups. Student
three: Record how many items landed in the cups and measure how far off any
misses were. Student
two: Pick up all the items that were dropped. All
three students: Repeat the above steps. This time, however, student one should
use both eyes. All
three students: Switch roles and repeat the experiment, shifting the position
of the cups on the desk.
As a
class, discuss stereoscopic vision, why it is important, and the difference in
depth perception when we see with one eye vs. two eyes. (Seeing with two
eyes improves depth perception and therefore should result in a higher success
rate. However, 10–20 trials per team is a small sample, which may skew
the data. Take a class average, if necessary.) What might be the evolutionary advantages of stereoscopic vision? (As
will be mentioned in the program segment, stereoscopic vision "allows us
to judge the world around us in three dimensions," meaning it provides
greater depth perception. This trait could help primates judge leaps between
branches, distance to prey, or position of fruit on a branch. The ability to
focus on objects in three dimensions increases efficiency and success.)
Examine the
advantages of hands with thumb mobility: A
distinguishing primate characteristic is hands with thumb mobility. To understand
one advantage of this, have your students experience what it's like
without thumb mobility. Before class, gather masking tape, stopwatches, small
items (e.g., paper clips, toothpicks, coins, marbles, or buttons), and cups.
Supply about 20 items, one stopwatch, and one cup per pair. Calculators are
optional.
Have
each student pair:
Spread the items
out on a desktop and set the cup about six inches away. Student one:
Using just your dominant hand (the hand you write with), pick up all the items
one at a time and drop them into the cup. Student two:
Time and record how long it takes Student one to pick up and drop all the items
into the cup.
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Student Name
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Trial
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Dominant Hand and Free Thumb
(time in seconds)
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Dominant Hand and Taped Thumb
(time in seconds)
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1.
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2.
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Average Time
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Repeat Steps
a–c for a second trial. Calculate the
average time: Average Time = (Time 1 + Time 2) / 2 Student
two: Using masking tape, bind Student one's thumb to the side of her/his
hand, being careful not to impair circulation. Repeat Steps
a–e with a taped thumb. Switch
roles and repeat the experiment.
Lead
a class discussion on the differences between picking up small items using a
free thumb and attempting the task with one's thumb taped. What was the
average time for picking up the items with the dominant hand and a free thumb?
With the dominant hand and a taped thumb?
What do students think contributed to the time differences? (A
movable thumb aids in precision gripping or picking up small objects.) Why are movable thumbs important?
After Watching
Safety
Warning: Wear goggles, and have students
wear goggles, when performing the activities and handling the materials below.
Dissolve limestone
with acid. In the program segment,
Jonathan Bloch and his graduate student, Doug Boyer, extract delicate bones
from limestone. Limestone (e.g., calcium carbonate—CaCO3)
reacts chemically with acid, forming carbon dioxide (CO2) and lime
(e.g., calcium hydroxide—Ca(OH)2). By using a strong acid to
remove the limestone, Bloch and Boyer are able to expose the trapped, ancient
bones little by little. Your students also can use acid to remove limestone.
Before class, gather goggles, vinegar, clear glass cups, and small pieces of
rocks containing calcium carbonate, such as chalk, limestone, or marble. Then,
in class, place the chalk and the rocks in separate cups and pour vinegar into
each. Within a few minutes, students should see tiny bubbles appear. The gas is
carbon dioxide, which is released as the acid reacts chemically with the
calcium carbonate. It may require several acid baths, but students should see
that the smooth surface of the chalk becomes pockmarked and rough as the acid
dissolves it.
Extension: Before class, purchase some plaster of paris,
available at your local craft or hardware store. Prepare a small amount, and
encase a paperclip in a small block of the plaster. Plaster of paris is largely a calcium sulfate hemihydrate and will react with vinegar
the same way limestone does. Place the small block of plaster of paris in a glass, add vinegar, and let it sit for a while. Pour
out the old vinegar and add new. Repeat several times. You will gradually be
removing the plaster of paris from the paperclip, just as Jonathan and Doug
removed the limestone from around the delicate bones of their early primate
fossil.
Document a fossil,
archeological, or forensic site. In the
segment, graduate student Doug Boyer devised a method to "meticulously
document the relationship between each and every bone exposed in the
limestone." Such documentation is a vital part of many scientific
disciplines, including archeology, paleontology, and forensics. Test your
students' ability to document a scene. The activity steps can apply to
individuals or to pairs of students:
Gather small
objects that can form a pile (e.g., pens, pencils, rulers, straws, paper clips,
etc.) Students will need a writing implement separate from any in the
collection. Give each
student or pair eight objects. Have them make a pile where the objects overlap,
cross over, pile on top of, and lean against each other. Have students
draw a map of or otherwise document their pile. (Set a time limit of 5–10
minutes.) NOTE: If a digital camera is available, have students also take a
photograph of their original pile and for sharing at the end of the activity. Then have each
student or pair disassemble their pile and exchange their objects and
map/documentation with another student or pair. Have the second
group try to recreate the original pile based on the objects and documentation
they've received. Compare this to the photograph, if applicable. How accurate
was the documentation? Was the second group able to reconstruct the pile using
the documentation?
Lead
a class discussion on documentation and why it is important. How easy or
difficult was it to document the piles? To recreate the piles? What might have
made the process easier? (More time, agreed-upon notation, graph paper,
photographs, practice documenting items.)
In what situations might documentation be crucial? (Whenever the
relationship between items, and between items and their location, is important,
such as fossil bones in a piece of limestone, fragments of a pot at an
archeological site, or evidence at a crime scene.) Why was it important for Bloch and Boyer to create a map of the
delicate bones, as shown in the segment? (They weren't sure
which bones went with which animal. The careful process of documenting the
bones took months, but it allowed them to recreate the skeletons of the three
separate animals.)
Examine the nature
of evidence. Astronomer Carl Sagan
(1934–1996) popularized the phrase, "Extraordinary claims require
extraordinary evidence." Thus, if someone makes an extraordinary claim,
such as that he has found the earliest primate, then there must be some
extraordinary evidence to back up that claim. The story of identifying the
first primate is an example of evidence that converges from a variety of
sources: Jonathan Bloch found the nail; Mary Silcox found the tiny ear tube;
and Eric Sargis provided anatomy data.
Present your
students with a (not so extraordinary) claim and related pieces of evidence,
and have them consider how convincing they find the evidence, individually and
as a whole. Start by holding up a sealed envelope in front of the class. Make
the claim that there's an ace of spades in the envelope. Tell students
you will supply them with different pieces of evidence, and that their job is
to determine how well your claim—that the envelope contains an ace of spades—is
supported by the evidence. Present the sets of evidence to your class orally,
and have small groups discuss each set.
Evidence Set 1: Look at the
shadow of the envelope's contents. Tell
students that:
When
the envelope is held up to the light, one and only one dark area can be seen. The
dark area appears to be about the size of a playing card. (So a visual
inspection looks roughly correct for the envelope to contain a playing card.) The
dark area is a rectangle with slightly rounded corners. A
set of sample playing cards from various decks all have slightly rounded
corners. (So the shape is right for a playing card.)
Discussion:
Ask, "Based solely on this shadow inspection, can there be a playing card
in the envelope?" (Yes.) Do your
students think that there is a playing card in the envelope? (Possibly.
It at least looks reasonable.) Are your
students convinced that there is an ace of spades in this envelope? (They
definitely should not be convinced that the envelope contains the ace of spades.)
Evidence Set 2: Consider the
weight of the envelope's contents. Tell
students that:
The
weight of this sealed envelope is 7.9 grams. A
similar, empty envelope weighs 4.9 grams. (So this envelope's contents weigh
about 3 grams.) The
sample playing cards each weigh between 1.3 and 2.0 grams. (So, a single
playing card can't account for the weight in the envelope.)
Discussion:
Ask, "Can there be a playing card in the envelope?" (Yes, but
not just one.) Based only on the weight
evidence, do students think that there is a playing card in the envelope? (Probably
not.) Based on both the shadow and weight
evidence together, do they think that there is a playing card in the envelope? (Possibly.
The contents could be a playing card plus something else.) Are your students convinced that there is an ace of
spades in this envelope? (They definitely should not be convinced.)
Evidence Set 3: Consider the
dimensions of the envelope's contents.
Tell students that:
Discussion:
Based strictly on this evidence, can students say that the envelope contains a
playing card? (Opinion will probably be split; the dimensions are close but
not a perfect match.) Based on all the
evidence, do they think that there is a playing card in the envelope? (Possibly.) Are your students convinced that there is an ace of
spades in this envelope? (Again, they definitely should not be convinced
that the envelope contains the ace of spades.)
Evidence Set 4: Shake the
envelope's contents. Tell students that:
When
the envelope is shaken, the dark area moves around. After
several shakes, the shape of the dark area changes. With
some manipulation, the dark area can be separated into two dark areas, both 8.8
by 6.3 centimeters with rounded corners.
Discussion:
Based on all the evidence, do students think there is a playing card in the
envelope? (Probably yes; the dimensions and shape of the dark areas are
exactly those of a playing card, and two playing cards weighing 1.5 grams each
could combine to weigh the 3 grams difference between the empty envelope and
its contents.) Are your students convinced
that there is an ace of spades in this envelope? (Again, they
definitely should not be convinced that the envelope contains the ace of
spades, though with the strong evidence that the envelope contains playing
cards, they are justified in turning their attention to this part of the claim.
Evidence Set 5: Closely inspect
the contents of the envelope. Tell
students that:
A
close visual inspection of the dark areas reveals patterns faintly visible
through the envelope. Under
inspection through one side of the envelope, one of the dark areas appears to
be largely covered by a slightly reddish pattern; the other appears to have a
series of red diamonds, in two rows of three each, plus indistinct patterns in
two opposite corners. Under
inspection through the other side of the envelope, one of the dark areas again
appears to be largely covered by a slightly reddish pattern; the other appears
to have a large spade shape in its middle, plus indistinct patterns in two
opposite corners.
Discussion:
Based on all the evidence, are your students convinced that there is an ace of
spades in this envelope? (Probably yes. The evidence is very strong (though
not necessarily absolutely conclusive) that the envelope contains two playing
cards, one of which is the ace of spades.
This
activity modeled one of the primary characteristics of science—the use of
evidence to support or counter a claim or hypothesis . Researchers gather
evidence, bit by bit, from different locations, sources, and lines of inquiry
until a strong case can be made for a claim or until something is found that
contradicts a claim and requires a new, different hypothesis. So far, Bloch and
his colleagues have found evidence that the plesiadapiforms are indeed the earliest primates. Yet who knows what
the next piece of evidence or line of inquiry will bring?
Web Sites
NOVA scienceNOW
www.pbs.org/nova/sciencenow/0303/02.html
Offers resources related to the
earliest primates, including additional activities, streamed video, and reports
by experts.
Florida
Museum of Natural Science: Article
www.flmnh.ufl.edu/sciencestories/2007/bloch_primate.htm
Reports
on the early primate discoveries of Jonathan Bloch and his colleagues.
NetVet:
Primates
netvet.wustl.edu/primates.htm
Provides
links to many Web sites on primates and primatology.
NOVA: The
Last Great Ape
www.pbs.org/wgbh/nova/bonobos
Offers a
variety of interesting readings, slide shows, and tools for learning about
bonobos—one of the five great apes, along with humans.
PBS
Evolution
www.pbs.org/wgbh/evolution
Presents
the PBS miniseries on evolutionary science and related Web-based materials,
including an interactive timeline (Deep Time).
Paleontologists
discover most primitive primate skeleton
www.eurekalert.org/pub_releases/2007-01/yu-pdm012307.php
Reports
on the study led by University of Florida paleontologist Jonathan Bloch, who is
featured in the video, about the earliest known primates.
Scientific
American Frontiers: Chimps R Us
www.pbs.org/saf/1108
Presents
a Scientific American Frontiers episode and related Web-based materials on
chimps.
Books
Our
Inner Ape: A Leading Primatologist Explains Why We Are Who We Are
by Frans
De Waal.
Riverhead Hardcover, October 2005.
Explores
and compares three primates: chimps, bonobos, and human beings.
The
Pictorial Guide to the Living Primates
by Noel
Rowe.
Pogonias Press, 1996.
Offers a
photographic field guide of primates.
Primate
Adaptation and Evolution, 2nd edition
by John
G. Fleagle.
San Diego: Academic Press, 1999.
Presents
a detailed survey of living primates and a current synopsis of the primate
fossil record.
Activity Author
Teon
Edwards is a curriculum developer with a background in astrophysics,
mathematics, and the use of technology and multimedia in teaching and learning.
Since 1996, she has developed numerous science and mathematics education
materials for school, home, and informal learning environments.
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