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A Unit Sequence Which Works
In High School Biology

by Larry Flammer

Introducing Students to the Nature of Science and Evolution

The Nature of Science. Open the school year in Biology with an intensive (two-three week) unit on the nature of science: what it IS, what it is NOT, and the LIMITS of science. This will help to dispel some of the myths students commonly have about science, and effectively lay the groundwork for the entire course. In fact, it would be very useful to administer pre-tests on the nature of science (and even evolution) in the first few days, to determine what pre-conceptions your students have about these topics, before you begin those topics. You can then introduce Biology as a science in this context.

Unit on Classification (survey of life, taxonomy terms & concepts; problems of classification (misfits). I usually open this unit with an introduction to the microscope, the classical tool of biology, with some exercises in its safe and most effective use, then move quickly into this microcosm of life: using it to look at micro-organisms: live bacteria and protists. This "survey" of the protists paves the way into my informal overview of the diversity of life, and the formalities of taxonomy. (This is a good place to introduce the nested hierarchy of biological classification, and how this is NON-arbitrary, in contrast to the usual classroom exercises categorizing different kinds of furniture, vehicles, hardware, etc., which vary with the criteria used. See the Classification lesson to effectively teach this concept.) Nevertheless, there are still a number of classification "misfits", organisms which just don't fit neatly into established major groups, but possess features of two or more groups. Examples are Euglena (plant-animal), platypus (reptile-mammal), coelacanth (fish-tetrapod), and Archeopteryx (dinosaur-bird). At this time, I simply leave this phase as an enigma..."why does this problem exist?"... to be addressed later when the concept of evolution is introduced, in part as a way of explaining these "misfits". This unit also establishes the use of comparative anatomy as one of the criteria for defining categories, and, by extension, degrees of relationship. All of this can lead quite naturally into looking at fossil bones, especially fossil human bones.

Suggested Sequence for Using Human Biology to
Introduce the Topic of Evolution

 For formatted handouts, see the end of this page for PDF files to download and copy.

Day 1: Intro to "Bones Study":
  - Have students, in small groups, study and answer questions about any bones you can get, human and/or other animal bones, just to get them used to handling and thinking about skeletons, bones, and what bones can tell us. See the sample worksheet: "Comparative Anatomy of Vertebrate Bones", fifth sheet in the "Skull Summary" packet.

Day 2: Briefly discuss the "Bones" lab and questions; Introduce "Skull Comparisons":

 - Hand out the "Skull Comparisons" data forms (from the "Skull Comparisons" packet). Using that form, and a few of the skulls to be used, go over the features, showing them on the skulls, and commenting on them; show what and how to measure. It is helpful to use an overhead of the form to work through. See (and show?) the SAMPLE of a partially completed form in the packet to get an idea of how it should look. An overhead of skull anatomy, in different views, might be useful here, too.

- For Homework: study skull diagrams and descriptions (and color them?). 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 $12.80 plus tax and shipping from Barnes & Noble or Amazon.com on the web. See modified versions of two pages from this book (pages 99 and 100) in PDF format at bottom of this unit guide.

- Lab prep for next day's lab: (assuming 32 students, 4/team, 8 teams, one tray per team) in each tray, have: skull on soft foam pad or carpet square, calipers, 30 cm ruler, 2 sheets of cardboard (about 8x10 , to measure distance between two parallel planes), an identification letter (A-D) for the set, which matches the letter-skull matches on the overhead list of species, or the partially completed form.

Day 3: Students do Skull Comparisons with skulls A-D (chimp, gorilla, modern human, Cro-Magnon)
..............For a somewhat less structured alternative to this, see Nickels' "Hominid Cranial Comparison" version.

- Have students work in groups of 3-5, spending about 10 minutes to collect and record data for their skull, then, on teacher signal, students move tray w/ materials to next team, so the 4 skulls are rotated through 4 teams (2 of each skull works best; if you only have one of each, then use skulls E-H (Australopithecus africanus, A. boisei, Homo erectus, and Neandertal) this same day for the other four teams.

- HW: If time, hand out "Chronology" assignment, and show how to start it for HW

Day 4: Do Skull Comparisons with skulls E-H (or with the set of 4 skulls not studied the previous day)

- This usually goes faster, so you should be able to begin pooling the class data before the end of the period. Do this by entering data on an overhead version of the Skull Comparisons grid, getting numbers, etc. from students call them out from their sheets, just to get approximate consensus, and so that all students see that they have collected similar data, and fill in data which might have been missed.

- HW: finish "Chronology" assignment

Day 5: Complete "Skull Comparisons: Summary" sheet, and begin the "Skull Analysis" sheet.

- Collect the "Chronology" assignment (to check, and return next day).

- If necessary, quickly finish pooling class data. The "Summary" is best done with teams giving input to you as you enter summary data on overhead copy of the form. Use remaining time to point out some of the "Interesting Extensions" material (below). If time, students can begin the homework.

- Homework: students can count "A's" and "H's", record the totals at the bottom, and write a brief "Conclusion Statement".

- INTERESTING EXTENSIONS: Skeletal evidence for age, male/female diff., primate/non-primate, reconstruction. Show pictures or slides wherever possible to illustrate:

Age: (3rd molars erupted? cranial sutures: degree of fusion)

Male/Female diff.: bone thickness (reflects muscle size) , size of teeth, pelvis shape; experts: 80-90% accuracy

Cranial Clues of Bipedalism: shorter canines, jaws and smaller brow ridges (all because hands have taken over the functions of threat display and protection, normally done by teeth and jaws in primates); bipedalism leaves the hands free continuously to hold and throw sticks, stones, etc. The foramen magnum is also found more forward and more directly underneath the skull.

Primate/non-primate: primates have nails, not claws; also have closed eye sockets, facing forward

Apes/monkeys: Monkeys have tails, apes don't (most obvious difference)

New World monkeys vs Old World monkeys: N.W. monkeys have prehensile tails, O.W. don't.

Reconstruction: if possible, show pictures or slides of different reconstructions (artistic renderings) of specific hominins, e.g. Neandertal, A. robustus (A. boisei), Homo erectus; most influential features have least evidence in bone materials (shape of nose, ears, lips, hair distribution)

Teeth: Long canines in primates: used for protection, male competition, not for food.

Day 6: Discussion of the Comparative Anatomy of Hominids:

- Before class, arrange the skulls along your front demo desk in the sequence shown on the "Summary" sheet (left-to-right, as viewed by your class: H-G-F-E-D-C and A/B). Be sure to place the modern human and modern apes (gorilla and chimp) all at the right end of the sequence; I place them on platforms above each other. This is important so that the students don't get the idea that hominins have evolved from modern apes!

- Return corrected "Chronologies". Display an overhead version of the key (without the connecting dotted lines), pointing out the rough sequence of hominins, as well as a fair degree of overlapping of existence.

- Referring to the "Summary" sheet, ask them if they see the pattern (generally increasing "H's" and decreasing "A's", going left to right).

- Point out how the left-to-right sequence (H-C) matches fairly close to the existence of those species through time (their chronology). Also, point out the "spotty" (mosaic) yet gradual nature of the changes reflected in the trends.

- Discuss topics on "Skull Analysis" sheet if not already done. See the KEYS for the "Skull Comparisons Summary" and the "Skull Analysis" sheets in PDF format in the "Skull Summary" packet. can be found below.

- HW: Review all Comparative Anatomy of Hominid Skulls material

Day 7: Give quiz on Comparative Anatomy of Hominid Skulls.
  Begin Comparison of Human & Chimpanzee Chromosomes (reading and check questions).

Day 8: Quiz feedback; Continue the Chromosome Comparison lesson (comparative anatomy of chromosomes).
  - If you haven't studied cells or chromosomes yet, you might have students look at slides (microscope or projection slides) of onion root tip sections and/or Drosophila chromosome squashes. In fact, this might be a logical time to do a brief unit on cell morphology, just to learn the relationships of organism to cell, cell to nucleus, nucleus to chromosome, and chromosome to DNA.

Day 9: Begin Molecular (protein and/or DNA) comparison activity, such as.....

- Molecular Biology & Phylogeny: compares amino acid sequences for cytochrome c in several species, suggesting degrees of relationship

- Molecular Sequences & Primate Evolution: compares amino acid sequences for hemoglobin chains in several primate species (by Craig Nelson & Martin Nickels, co-directors, ENSI).

FINAL WRAPUP: When the above lessons are completed, ask for student impressions as to what general patterns seem to be reflected in all of these lessons together. Be sure that they recognize these experiences as examples of Independent Lines of Evidence (anatomical, chromosomal, and molecular), all pointing to the same pattern of similarities in hominids, suggesting a biological relationship from gradual changes (evolution).



Now that a background of experience and examples has been established, your students can now take a look at this thing called "evolution", what it IS, what it is NOT.

If you have not yet done so, you might want to administer an "Evolution Survey" (pre-test) at this time.

Very early in this general introduction to evolution, it is wise to dispel at least some of the popular myths many people believe about evolution. Plan to take a whole period to go over What Evolution Is NOT, then a brief overview of what it IS. It is bound to raise some questions, so be sure to invite such questions, so they can be openly and readily discussed. You may prefer to have your students hold their questions until after going over the list of 12 things evolution is not.

Click here to access a sample evolution pre-test, a student handout with 3-page overhead to use for your discussion of What Evolution is NOT... (all in PDF format and html format). In addition, there is a nice summary comparison of two possible mechanisms of evolution (Darwin's and Lamarck's), along with a useful activity on this.



 In the boxes below, you can obtain the handout sheets used in the Hominid Skulls Comparison unit as described above. If you can use a laser printer (e.g. at your district office, school, or local library), your results should be of very good quality, although inkjet printouts should be quite usable. A fast internet connection would also facilitate your downloading success.

To retrieve each item, just click on its Title. This will activate Adobe Reader, which will display the image, which you may now print. If you need to get the free Adobe Reader application, see the General Info section on this site.

 Skull Comparison Sheets
(3 pages, incl. key)

 Skull Summary Sheets
(5 pages, incl. keys)

 Color Book: Skulls, Front
(1 sheet)

 Color Book: Skulls, Back
(1 sheet)