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A Mini-Lesson

 

FOOTSTEPS IN TIME

Analysis of the Laetoli Footprints

Steve Randak

EVOLUTION

Human Evolution Patterns

 SYNOPSIS

The 3.6 million year old tracks of an early hominin (formerly "hominid") in Laetoli provide a tantalizing opportunity to explore how scientists use patterns of the present to understand the past. What do those footprints tell us? How can we find out? Students measure and correlate their foot lengths and body heights, then use these data to estimate the height of the Laetoli hominin.

 CONCEPTS

Observations of present life can provide clues to life in the past.

Transitional forms are generally a mosaic; that is, some traits (e.g. bipedalism) evolve more rapidly than other traits (e.g., brain size).

Bipedalism appeared very early in human evolution.

The Laetoli footprints provide evidence confirming early hominin bipedalism, suggested earlier from leg and foot bones of early hominins.

 MATERIALS

Transparency of deductions in "Science as a Way of Knowing - Evolution"

Student Handouts (detailed below)

The sharpness of these images may be less than desired, due to the limitations of digital rendering required by this medium. They ARE usable, but if you would prefer sharper hard copies (from the originals), just email the webmaster with your request and address, and they will be mailed to you ASAP.

OR, CLICK HERE. for a shorter but more informative "topographic" version of the Southern trackway. See photo of students using the full scale trackway of this version, how to get the TOPO trackway (now in digital format), and see an additional activity: "The Laetoli Puzzle" using sample topo tracks.

LAETOLI TOPO TRACKWAY
in SOUTH AFRICA

See how this Topo Trackway is being used in South Africa by Dr. Terry Hutter, to help teach South Africans about their origins.
CLICK HERE for more details and pictures.

 

STUDENT HANDOUTS
(For each team of 4-5):

For each of the following items, click on its name to see the best (sharpest) modified version on this site to copy (in jpeg format), or click here to access the PDF page for PDF versions of these items). To return to this lesson page, click the "Back" button on your browser.

1. Copy of the Total Trackway illustration. With the kind permission of the Scientific American artist, Laurie Grace, we make this figure available to you on this site to copy (only for non-profit classroom use). Enlarged versions of the Southern and Northern Trackways are also available, more suitable for further enlarging to full scale. Both sets of trackways have had their 1 meter scale bars corrected (since the original scale bars were not accurate). [OR, see reference to "TOPO Trackway" under Materials.]

2. Full scale photo of cast of sample footprint (G1-37), and photogrammetric diagram of the same footprint (showing depth profile topographically), are now available. [Photo was formerly available on this site, reversed and mislabeled as "G1-33"].
G1-37 Photo and Diagram (HTML; may not print to scale directly)
G1-37 Photogrammetric Diagram (PDF: 3.7MB) from Leakey & Harris
G1-37 Photo (PDF: 6.7MB) from S. Randak. [This is a big file...long download time. If you would like this one, contact the webmaster).

3. Metric ruler and/or meter stick

4&5. Stem and Leaf Graphs sheet & Scatter Plot sheet
(These forms, along wth a Raw Data recording table, and sample forms with data recorded and processed, are also available on the PDF page).

6&7. Information Processing & Experimental Write-up sheets. Also available in PDF format.

TEACHING STRATEGY


Laetoli Trackway from Scientific American, Sept. 1998, pp. 47,49
"Preserving the Laetoli Footprints" by
Neville Agnew and Martha Demas.
Permission kindly granted by artist Laurie Grace, to use illustration for non-profit classroom purposes only.

BACKGROUND: The Laetoli trackway was discovered in volcanic ash sediments dated at about 3.6 mya. Fossils of about the same age have also been found in that vicinity, and they have been identified as Australopithecus afarensis - the same species as the "Lucy" fossils found in Ethiopia by Don Johanson and colleagues. For these reasons, it has been generally assumed that the tracks were those of Lucy's species - A. afarensis - though Mary Leakey has been hesitant to say this conclusively.

1. Prepare copies of the trackway from Laetoli (for sharpest copy, use the Scientific American article, 1998, cited at the end of this lesson, or copy from the figure accessed above in "Student Handouts", or from the PDF files. If possible (it's most impressive), enlarge the total trackway to full scale (so the 1 meter scale is actually one meter), using the services of a blueprint maker or a copy service. This would make a nice demo trackway about 9 meters long. Plastic lamination would make it more durable.

For a picture of students at work on a full-scale trackway, and some details on how one teacher did this very effectively, CLICK HERE.

In any case, at least try to enlarge the total trackway so that the 1 meter scale is a convenient fraction of a full meter (e.g. 10 cm), in order to make it easier for students to convert their measurements to real size and distances. Make enough copies so that there is one for each group of 4-5 in your class. Plastic lamination would make these easily re-usable year after year.

2. Have materials ready to go (metric rulers, and/or meter sticks, copies of enlarged footprint pictures, full scale copy of sample footprint, and the "processing" handouts (graphs and information sheets).

PRESENTATION:
3. Display on the overhead some of the "deductions" listed in "Science as a Way of Knowing - Evolutionary Biology" by John A. Moore (see materials list). These deductions are generally stated as: "if the hypothesis of evolution is true, then...". Let students have time to read a few of them, perhaps you could read a few...then go to #16:

- "Deduction 16: If the idea (hypothesis) of evolution is to be established as true, we must be able to obtain information on organisms that lived in the past."

4. Hand out (or display) the Laetoli footprints (the full trackway, as it is actually found in Laetoli, is shown in the frame on the left. (A high resolution copy is accessible from the list of materials above). Ask what questions the footprints might answer about the hominins who made them?

NOTE: NEW TAXONOMY: "Hominin" replaces the earlier "hominid" due to revised taxonomy based on new molecular and genetic evidence. Click here for more details.

STUDENT RESPONSES (some possibilities):
- How old are the footprints?
- Were all the hominin prints formed at the same time?
- How heavy were the hominins who made them?
- How tall were they?
- What sex or age were they?
- What interaction (if any) occurred between the hominins and other animals?
- In what direction were they walking?
- Why did they stop or break stride?

TEACHER DIALOGUE:
5. Take one of these...."How tall were they?", and ask your students to DESIGN A STUDY which would do that. If they are new at this, or if they have difficulty getting started, ask what physical properties of the prints might help answer that question. (Depth of prints, length of each print, stride distance...). Elicit from students (or point out) that print depths could vary depending on their weight, softness and wetness of soil, etc. Likewise, establish that stride could vary due to pace (how fast), tilt of path, etc. So ask "How could we determine if there is a correlation between footprint length and a person's height?" If students don't suggest measuring their own feet and heights, give some clues that should bring them to suggest this. For example, you could suggest that, since they look like human footprints, we could assume that such a correlation in us might reasonably apply to the hominins who made the prints.

6. Ultimately, get students working in teams to measure the heights and corresponding foot lengths of each other (all in cm). Have students report their data (personal or team) to you as it is obtained, so you (or an assigned student) can record these data on a Raw Data form (on overhead or board). Once there are twenty or more sets of data, plot them (or display the data, and have students plot them) on a scatter plot, with (say) height for the vertical axis, and foot length on the horizontal axis. (See Student Handouts list for the Scatter Plot sheet). This should give a clustering of points through which a straight "best-fit" line could be drawn, indicating a direct relationship (larger feet are correlated with taller people). See Samples in PDF forms. You can then plot the data on the Stem & Leaf Graphs, and add Box Plots to the sides of the Scatter Plot Graph. This will facilitate an easy discussion of the statistical qualities of the data, and the possible relationship of the Laetoli prints when one of them is added. See Extension #1 (below) for the source of instructions for doing the Stem & Leaf and Box Plots.

7. Returning to the original question "How tall were the hominins who made the prints?", hand out copies of the photo of the cast of print G1-37 (and/or its photogrammetric diagram (see "Student Handouts") . Have students measure the length, from heel to end of big toe, to the nearest cm (should get about 18-20 cm). Even better, have someone make a print in firm mud or wet sand, and find out how the print should be measured to give the actual size of that foot, then apply that strategy to the rubbing.

8. You will need to extend the "best-fit" line on your graph so that it intersects that foot size, then note the corresponding height that individual would probably be. If interested, figure the height in feet (divide height in cm by 30.5). Try this technique on other footprints in the same (G1) series (same individual, so should get about the same height). [See PROBLEM Below]. Now repeat the technique for the footprints in the other series (G2/3) These are larger, so should give a greater height. The general consensus now about the G2/3 series is that a second, slightly smaller individual was walking behind and in the same footsteps made by the first individual making those tracks, so some steps might be a bit distorted). According to the article by Neville Agnew in Scientific American (1998), G1-36 is about 20 cm long (p.47), and G1-25 measures about 19 cm long (p.48). The height of the smaller individual was about 4 feet, and the larger individual was about 5 feet (sidebar, p.49). The trackway, made in volcanic ash, is dated at 3.4 - 3.8 million years ago.

9. Have your students do an "Experiment Write-Up" (see items 6&7 in the list of Student Handouts). This provides a useful structure, applicable to many such lessons, getting students to "meta-think" the process of learning which they have just been doing. In addition, completing an "Info Processing Sheet" provides an opportunity to summarize and capsulize, and focus on the key elements of the study. This is also in the Student Handouts.

 

EXTENSIONS AND VARIATIONS

1. A useful extension of this lesson is to do (or have your students do) Stem & Leaf & Box Plots on the class' height and foot size data, to quickly show means, medians, and quartiles (see Exploring Data, by Landwehr and Watkins, 1987, in references below). Use these to show how the height and foot length of this hominin lie outside the range for modern humans, suggesting that we are dealing with a different species (or younger individuals?). A form for this can be accessed from the list of Student Handouts; this form plus a completed sample are available on the PDF page.

2. An easy extension of the Laetoli trackway analysis is to ask students to discuss the break in strides seen in the northern section of the trackways, especially tracks G2/ 3-3, 3-5, 3-6, and G1/ 6,7,8,9. What kinds of stepping appears to be taking place here? What could they be doing? Why? This could be so much more intriguing than similar trackway analyses of dinosaur prints you may have seen. These were very early hominins... perhaps our ancestors??? That event (whatever it was) really happened!

3. New Suggestion (5/2006): Teacher Patti Carothers at Monte Vista HS in Danville, CA offers this:
Students had commented how big the feet in the trackway seemed to be, so she had one member of each lab group take a walking step into a plastic shoe box with wet sand. The average "sand print" was 3.4 cm longer than the actual foot! They had a great week using the [topo] trackway.

4. Try "The Laetoli Trackway Puzzle" lesson, a more detailed inquiry and analysis of the trackways, using a portion of the "topographic" (photogrammetric) version of the Laetoli trackway (from the Mary Leakey source). Worksheet and diagrams are available on that there.

5. The UC Berkeley Museum of Paleontology (UCMP) has an excellent collection of lessons, many of which could be adapted to use in high school biology. One of them is similar to the present lesson, but geared toward grades 2-4. Its title is "Tennis Shoe Detectives" by Sharon K. Heindel. You can find it by clicking on the title (which will take you out of the ENSIweb site; click on "Back" in the menu bar of your browser to return to this page).

6. Another related activity is called "Lengthy Relationships". It deals with finding the mathematical relationships between: foot length and leg length, foot length and height, leg length and height, stride and leg length, stride and speed. Its original source is uncertain; it was contributed by Jennifer Johnson (SENSI 1996, Hillsborough, CA, now with the UCMP). We have it on site; you can get it by clicking on its title.

7. To see another, more recent ancient trackway, take a look at this report of Stone Age Human Tracks, 350,000 years old, discovered near Naples, Italy. If you click on the two figures, they will enlarge, and would be suitable for display digitally or on an overhead projector.

 

RESOURCES

Agnew, Neville, and Martha Demas. "Preserving the Laetoli Footprints". Scientific American, Sept. 1998, pp.44-55. (Source of the trackway used in this lesson)

Leakey, Mary D. & J.M. Harris (Ed). 1987. Laetoli: a Pliocene Site in Northern Tanzania. Clarendon Press, Oxford.

Some students might want to know the footprint lengths and estimated heights of those individuals as published by professional paleontologists. Those Laetoli Data have been compiled from the two sources listed above, along with some further suggestions for student follow-up.

Hay, Richard L., and Mary D. Leakey. "Fossil Footprints of Laetoli". Scientific American, February, 1982, pp.50-57. This is an excellent source of detailed information, and the source of photogrammetric diagrams of many of the footprints.

Tattersall, Ian. "Evolution Comes to Life". Scientific American, August, 1992

Gore, Rick. "Tracking the First of Our Kind". National Geographic, September, 1997, pp.92-99.

Landwehr, James M., and Ann E. Watkins. Exploring Data. 1987. Dale Seymour Publications (technique for doing stem & leaf and box plots). Be sure to get the Teacher's Edition. A 1994 edition is available from Amazon.com for $10.75

Moore, John. Science as a Way of Knowing - Evolutionary Biology. Reprint from American Zoologist, vol.24, no.2, 1984, page 485. Also in The Foundations of Modern Biology. 1993.

 ATTRIBUTION

Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.

1. Original Source: Steve Randak, NABT Convention, Reno, 11/98;
additional material presented at the NABT in Ft. Worth TX, 10/99.

2. Adapted for website by L. Flammer 4/99
Major revisions 1/17/00, 3/2/00, and 5/5/03


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