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Human Evolution Patterns
|Students describe, measure and compare cranial casts from contemporary apes (chimpanzees and gorillas, typically), modern humans and fossil "hominins" (erect and bipedal forms evolutionarily separated from apes). ("Hominid" is the new collective term for African apes and humans.) The purpose of the activity is for students to discover for themselves what some of the similarities and differences are that exist between these forms, and to see the pattern of the gradual accumulation of traits over time, leading to modern humans.|
|Documenting similarities and differences between species is fundamental to understanding their biological and evolutionary relationships.|
1. When used in conjunction with certain other lessons (see extensions below), illustrates the compelling power of multiple independent lines of evidence as a tool for selecting the "best explanation" in the process of science.
2. Transitional forms in an evolutionary sequence are generally mosaic; some traits evolve more rapidly than others.
3. Modern humans have not evolved from modern apes: both have evolved from a common ancestor
1. handle and read the measuring instruments.
2. identify the appropriate skeletal and dental features and
3. describe features of a given specimen as either similar to, different from or the same as those present in another specimen.
4. recognize the sequence pattern in which several human skull features appeared over time.
5. (Optional) summarize and graph measurement data of the cranial specimens.
6. (Optional) construct and justify a taxonomic classification of the specimens.
1. Plastic casts of modern apes, humans and fossil hominins. Preferably two chimpanzee or gorilla specimens, male and female are ideal. A modern human skull may be available from the skeleton standing in the corner of your lab, but, if not, the 25,000 year old Predmost fossil cast will serve, as well.
2. Plastic casts of a Neandertal (50-60,000 year old La Chapelle is commonly available), 450,000 year old Homo erectus ("Peking" is the most widely available and least expensive) and an australopithecine (preferably the "robust" 1.8 million year old Olduvai number 5 or "Zinjanthropus") as an example of an early hominin form that shows a "mosaic" mixture of ape- like and human-like features).
These casts are commercially available, primarily from Carolina Biological Supply and Ward's although you may find other sources, as well. Check our SKULLS: PRICE COMPARISON chart for online addresses and prices for recommended skulls. There is also a recommended "PREFERENCE" column on the table, indicating 5 skulls for a basic set, then a prioritizing of additional skulls for future enhancement if/when funds are available. Drawings of specimens may also be used but are not nearly as good as the actual skull replicas. A set of 7 drawings of hominid profiles can be downloaded from this site. Just click here for hominid drawings.
In order to accommodate a greater number of measurements, we have added a collection of 28 HOMINID PHOTOS: 4 views each of 7 skulls: front, top, right side, and an under-view of each skull. In fact, an excellent craniometry-focused version of this exercise can be found in an online article in the NABT journal The American Biology Teacher for March 2007: Investigating Human Evolution Using Digital Imiaging & Craniometry by John C. Robertson. This is a 5-page pdf article, providing the index (ratio) formulas to use for various dimensions, thereby eliminating the need for the skulls all being the same scale. The digital photos provided on the ENSI site (HOMINID PHOTOS) would be excellent ready-to-go material to use for this work.
3. Sliding calipers or hinge calipers and rulers with metric
scales. Extremely inexpensive plastic sliding calipers may be
purchased at hardware or arts & crafts stores. Hinge calipers
can be made out of cut-out cardboard (hinged with snap clips;
worn tips can be strengthened with white glue), or plastic or
masonite (hinged with small bolt & nut). Click here for a
template for cardboard
or plastic calipers.
4. Carpet squares, foam pads, or similar table padding on which to set the casts for each student group or "Skull Station".
|One to two 45-55 minute periods, depending on the amount of analysis you want to have the students engage in. (Some or all of the student analysis can be done outside of the classroom as homework.)|
See attached Hominid Cranium Comparison Checklist. Worksheets are ruled notebook paper with hand-drawn columns corresponding to each specimen.
As an alternative, consider using formatted handouts created by other teachers. See item #7 under the Extensions & Variations section of this lesson.
|This lab activity may be done in conjunction with units on either taxonomic classification, interpreting the fossil record, comparative anatomy of skeletal features, or human biological attributes. It may be desirable, but it is certainly not necessary, to have dealt with basic ape and human biological and behavioral attributes. The teacher's emphasis should be on how well humans can be used as evidence to support the idea that modern species are evolutionarily related to one another and descended from now-extinct non-modern forms. (See sample Human Evolution Unit Outline, offering one workable sequence of topics which includes a lesson like this one, and has worked well as an early introduction to a unit on evolution).|
1. Have students work in groups of 3-5 since there are typically fewer cranial casts than students available.
2. Students may either work in stationary groups (in which case the specimens are passed from one group to another) or in groups that move from one "Skull Station" to another.
3. Each student should have a copy of the Hominid Cranium Comparison Checklist because the details of each measurement and observation are spelled out on it. Each student should also have her/his own data worksheet for recording descriptions and measurements.
4. Have all students label the columns on their data worksheets with the names of each specimen. Have them simply number the left hand edge of the worksheet 1 through 18 to correspond to the 18 items on the checklist. (This will put all entries for a single checklist item on the same line across the page to facilitate comparisons.)
5. Have students take turns being responsible for the 18 items on the Checklist in order to keep everyone involved as much as possible.
6. Remind students to record all measurements in millimeters (not inches).
7. Ask students to support each specimen in the palms of their hands and not like bowling balls with their fingers stuck into the eye orbits and nasal cavity!
8. After the students have measured and described the specimens, have them determine and describe the patterns represented by their findings. This can be done in a variety of ways:
- a) simply list those features that all of the specimens have in common;
- b) identify those features which are most useful for distinguishing between the specimens;
- c) describe the changes that occur in only the hominin crania over time;
- d) plot their data on graphs using the geological dates listed above (in Materials). Consider doing the Chronology Lab, where a more complete plotting of hominin ages can be done (see link under Extensions and Variations below.)
9. Following their efforts to summarily describe the patterns
they perceive in the specimens, engage the students in a discussion
and/or consideration of the evolutionary significance and adaptive
benefits of the changes they have just described in the hominin
- a. Why do you think the canine tooth reduced in size so much from earlier to later hominins? (Ans.: grasping function of long canines replaced by easy use of hands, associated with bipedalism).
- b. Why do you think the face flattens over time in hominins? (Ans.: similar reason as for item a.)
- c. How does the position of the foramen magnum relate to the body posture and locomotor pattern of the animal? (Ans.: more forward and under the skull, associated with erect posture of bipedalism; skull balances on top of spinal column. With semi-erect posture of apes, foramen magnum is located more to the rear of the skull.)
- d. What areas or portions of the braincase enlarge first and which ones enlarge later in the hominins? (Ans.: Rear portion enlarges first; top and forward portions enlarge later.)
- e. What behavioral and cognitive functions are associated with these cerebral areas? (Ans.: associated with "higher" rational beahvior)
- f. Have we really lost the browridge? (Ans.: not really; forehead rises directly above the browridge, enclosing the much enlarged frontal lobes.)
1. Teacher observation: are the assessable objectives being met?
2. Teacher-constructed test, based on the observations made and pointed out, and on the discussion which follows.
3. Do students recognize some of the patterns revealed? Do they see how hominins have changed over time
1. Have students plot a chronology of hominin existence, based
on the age-ranges of the different hominin species (see the mini-lesson
on this site:
2. Arrange the skull casts in a row, oldest on the left (as viewed by students). Be sure to put the modern ape skulls on the class' far right, at the same end as modern humans, since they are both modern. This is an excellent time to get students to see that humans did NOT evolve from apes, but rather apes and humans evolved from some common ancestor which was neither ape nor human, but probably more apelike, due to its more likely primitive semi-erect posture. Ask students to point out any general changes or trends they see, from left to right. Ask which skulls look most "primitive", and which most modern. Point out (or get students to express) how the sequence of skulls relates to the chronology which they built (or which you can reveal to them).
3. Hopefully, students will see a mix of "ape-like" and modern human features in the skulls. If so, do they see the trend from fewer modern human features in the earlier specimens to more modern human features in the later specimens? This is a good opportunity to point out that such a changing mosaic of traits is typical (and expected) as we trace a group through time, and thereby reflects the gradual accumulation of traits as expected in evolution by natural selection.
4. Can students see that the appearance of human traits was apparently a gradual process, not sudden?
5. This lesson provides a basic experience revealing anatomical indications that we have evolved. It would be highly beneficial for students to also do the lessons which compare CHROMOSOMES, PROTEINS, and DNA, all indicating a similar trend, and collectively showing an excellent example of the power of MULTIPLE INDEPENDENT LINES OF EVIDENCE (or MILEs) all pointing in the same direction: that humans have evolved.
6. An interesting extension of this lab is to explore what we can tell from the bones, such things as likely age, sex, size, race, appearance, health, etc. If possible, have a forensic pathologist from a local crime lab or a physical anthropologist from a local university talk to your students, and point out the clues they look for to answer those questions, and the degrees of confidence they have in those clues. An alternative is to have an enterprising student search the internet for that information, and report to the class.
7. Consider using one of the sets of handout materials developed and used successfully by other ENSI teachers. These may give you a little more "structure", which is often helpful when embarking upon territory which is somewhat new to you. To see and download these materials (in PDF format), just click on one of the following sets:
The first set was developed by Jo Ann Lane, in Cleveland, Ohio. This is the material which she presented at the 1998 NABT convention in Reno.
The second set of materials was developed and used successfully for several years by webmaster Larry Flammer, in San Jose, California.
Two other variations can be found, as presented by Mari Knutson (of Lynden, WA), and Dorothy Reardon (of Carmichael, CA) at the 1999 NABT convention in Ft. Worth, Texas.
8. A very useful extension and/or alternative to the Skulls
Lab is the approach developed by Jeremy DeSilva at the Boston
Museum of Natural History:
HUMAN EVOLUTION: INTERPRETING THE EVIDENCE. This was featured in the American Biology Teacher journal, April 2004. It is structured around the comparison of three different interpretations by 3 different anthropologists in how known hominin fossils are related to each other. Students become involved in reviewing their criteria and assumptions, and defending their own interpretations. An excellent experience in the process of science, including uncertainty, bias, assumptions, and controversy amongst scientists. Website includes full text of article and diagrams (3 full page provisional phylogenies, easily compared as transparencies, or handouts for students.)
9. Be sure to bring in the excellent materials about Ardipithecus ramidus that were published in the AAAS journal Science (2 October 2009). These extensive fossils take human evolution back to 4.4 mya, providing insight into its anatomy, environment and behavior. They show that Ardi was bipedal, yet had a grasping big toe. Raises possibility that common ancestor to apes and humans was perhaps bipedal, and that apes secondarily evolved knuckle-walking while humans became more efficient at bipedalism!
10. For another possible alternative see the article: "Were
Australopithecines Ape-Human Intermediates, or Just Apes?"
by Phil Senter (The American Biology Teacher, vol.72,
no.2, Feb, 2010, pp. 70-76). Students compare skeletal features
of Lucy, chimp, and human (diagrams provided). Results show that
a representative of the Australopithecine grade (Lucy) has too
many anatomical traits in common with humans - and in
contrast with apes - to support a conclusion that the creature
is a mere ape. Instead, Lucy appears to be a clear intermediate.
One caution here is the need to make clear: the evidence
shows that Lucy did not evolve from a modern chimpanzee,
and did not (likely) give rise to modern humans. There is also
the questionable assumption that the common ancestor of chimps
and humans was chimp-like rather than human-like. The analysis
ramidus tends to raise some doubts here. Access to this
article online may be blocked to non-NABT members during 2010.
If you can't get the article, contact the webmaster.
Nickels, Martin. 1987. "Human evolution: a challenge for biology teachers". The American Biology Teacher 49 (3): 143-148. (March, 1987). (This article, by the creator of this activity, provides more detailed information regarding the skeletal features, measurements and observations on the Checklist. Martin Nickels is the anthropologist member of the ENSI directorship).
The Human Evolution Coloring Book by Adrienne Zihlman (1981) is a good source for illustrations to help students learn anatomical terms and see comparisons. It's available currently for a nominal cost from Amazon.com, Barnes & Noble or Borders Books. A sample of two pages (99 and 100), modified to clarify certain dimensions, can be downloaded (in PDF format) from this ENSIweb site. They can be accessed from the bottom of the sample Human Evolution Unit offered by Larry Flammer. Just click on this to get them.
Go to the RESOURCES section on this site, click on HUMAN EVOLUTION for additional links to excellent photos, descriptions and analyses for students to use.
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.
Original source: "This cranium comparison lab activity is the most recent version of one I began using at least as early as 1985. I have presented various versions and modifications of it at several workshops for high school biology teachers at regional and district meetings, national meetings of the National Association of Biology Teachers, every Evolution and Nature of Science (ENSI) summer institute (1989-1994) and some Satellite Evolution and Nature of Science (SENSI) sessions." M. Nickels.
Modifications: "I know many teachers I have worked with over the years have adopted and modified different earlier versions of this activity for their own purposes, but I think this version is more applicable by more teachers than any of my earlier ones. It is simpler because it does not include the mandible (lower jaw) as part of the activity and restricts the use of hinge calipers (which are less readily available than sliding calipers and rulers with metric scales)." M. Nickels.
Content of "Associated Concepts", "Assessment", and "Extensions & Variations" was added by Larry Flammer, 7/98. Updated 11/99; again 2/03.
The following is a useful worksheet for students to complete while doing the lab, to help focus and direct their study. A pdf version follows, for easier printout (requires Adobe Reader...free download).
1. Work in groups of 3-4 students so that everyone can be involved in the activity.
2. BE SURE (!) TO TAKE TURNS doing different measurements and observations.
3. When taking a measurement, use the SLIDING CALIPERS (except for #11 & #12 which may require the HINGE calipers) and remember to...
4. ALWAYS MEASURE IN MILLIMETERS [mm] and round off to whole numbers.
5. PLEASE DO NOT ADD ANY PENCIL OR PEN MARK "TATTOOS" TO THESE CRANIA, OR STICK YOUR FINGERS IN THEIR EYE ORBITS OR NOSES!
1. Does the FOREHEAD (frontal bone) look more vertical OR flatter when the skull is held in normal anatomical position [NAP] (i.e., with the eyes oriented forward)?
2. Is a SUPRAORBITAL BROWRIDGE present?
3. If present, is the BROWRIDGE DIVIDED in the middle, or CONTINUOUS?
4. What is the SHAPE OF THE BRAINCASE (front to back) when viewed from above?
5. Is a SAGITTAL CREST present?
6. In NAP, is the FORAMEN MAGNUM oriented more downward OR more to the rear?
7. Is the MASTOID process relatively flat OR does it noticeably protrude (project)?
8. Are the NASAL BONES raised (arched) OR flat?
9. Measure the MAXIMUM BREADTH (width) of the NASAL OPENING [mm].
10. Measure the MAXIMUM HEIGHT of the NASAL OPENING [mm].
11. Measure the LENGTH of the MAXILLA (the upper jaw) [mm]. (Measure down the middle of the palate from the front edge of the foramen magnum to either between or just in front of the two central incisors to determine how much the face projects forward.)
12. Measure the BIZYGOMATIC BREADTH using the hinge caliper if necessary [mm]. (This is the width or breadth of the face from the widest part of one zygomatic arch to the widest part of the other zygomatic arch.)
13. SHAPE OF THE DENTAL ARCADE: Do the tooth rows diverge towards the back OR are they more straight-sided and parallel to one another?
14. When viewed from the side, are the INCISORS angled out OR are they vertical?
15. Measure the COMBINED WIDTH or BREADTH of the 4 INCISORS together.
16. Does the CANINE tooth project above the chewing surfaces of the other teeth?
17. Is a CANINE DIASTEMA present?
18. Measure the COMBINED LENGTH of the LEFT 2 PREMOLARS and 3 MOLARS together by measuring from the back of the last molar to the front of the first premolar to determine the length of the chewing surface of the "cheek teeth". [mm]. (NOTE: Measure the right side if the left side is missing any of these 5 teeth.)