A Mini-Lesson

NUTS & BOLTS
CLASSIFICATION,
ARBITRARY, OR NOT?
How Classification Reflects Evolution
An Introductory Lesson

Based on a Presentation by
Martin Nickels, PhD
ENSI Co-Director
Prof. Anthropology, Illinois State Univ.
at the NABT Convention in Montreal, 2001

Adapted for ENSIweb by
Larry Flammer

EVOLUTION

 SYNOPSIS

 CONCEPTS

MATERIALS

Link to PDF access page for all Overhead Transparencies

 STUDENT HANDOUTS

TEACHING STRATEGY
& PREPARATION

The following will provide useful background, and is adapted from the Session Abstract by Martin Nickels, with his permission:

As Darwin noted in 1859, taxonomic classification in biology differs fundamentally from the classification of other objects. The difference is that organisms naturally cluster into discrete, non-arbitrary, hierarchically-nested groupings only because of their mutually-shared evolutionary ancestry. This nonarbitrary grouping of organisms is evident from-and only from- congruence across different sets of biological data. We will provide and demonstrate a teaching unit that illustrates this congruence using molecular and morphological data sets from humans, apes and other primates. An all too common-but erroneous-approach in teaching biological classification is teaching that the classification of human artifacts (hardware, furniture, etc.) accurately mirrors biological classification. Another flawed approach entails using drawings or pictures of organisms (or even imaginary organisms) without providing information about their characters that makes clear to students the basis on which the organisms naturally cluster. Both approaches make it seem that all classifications humans devise are just a matter of choosing arbitrarily which of several superficial features one can use in constructing the classification. Such an approach clearly results in the conclusion that any coherent classification of a group is as meaningful and valid as any other classification because there is no non-arbitrary, intrinsically superior scheme.

It is proposed, therefore, that teachers seriously reconsider how they introduce and teach classification. Rather than having their students classify some non-biological materials (e.g. furniture, vehicles, hardware, etc.), spend some time comparing the patterns of similarities actually found in some major group of organisms, looking at their morphology, cytology, and molecular aspects, finding that their degrees of similarities generally conform to the same pattern, suggesting fundamental biological relationships between the members of the group. For pedagogical reasons, and the fact that excellent data sets are readily available, it is suggested that primates be the group of choice, comparing humans, apes, monkeys, and prosimians.

Excellent lessons are available which will facilitate this exploration, and they are on the ENSI web site. A recent addition "Molecular Sequences & Primate Evolution" compares the amino acid sequences of beta hemoglobin in a cross section of primates. In the "Hominoid Cranial Comparison" lesson, resin replicas of the skulls of hominins (formerly "hominids") and apes are carefully compared, revealing a pattern of gradual mosaic change through time. And with the "Comparison of Hominoid Chromosomes", the chromosome banding patterns from apes and humans are critically compared, suggesting degrees of relationship very similar to the patterns found independently in the other two lessons. See links below to access those lessons.

IF you insist on using the classification of non-biological items to introduce the general concept of classification, BE SURE to give your students some experience with the content of these lessons, and, most importantly, help them to discover how such classification DIFFERS from biological classification (into NON-arbitrary hierarchically-nested groups). If they don't see the difference, be sure to lead them to that realization with some hints and coaching.

PROCEDURE

  (loosely adapted from the NABT session):
1. Ask students, working in teams of 3-5, to classify furniture (group different knds of furniture into categories).

2. As teams are arriving at their particular versions, hand out an overhead acetate and pen to each team (or to a few selected teams, based on different formats and early completions noticed during a walk-about). Ask those teams to put their arrangement (groupings) on the acetate. An alternative could be to do this on large sheets of blank newsprint or butcher paper, for subsequent display around the room.

3. When all or most teams are essentially finished, call in the acetates, and display each one in turn to the class, asking the team spokesperson to explain the team rationale for their classification.

4. Point out the different versions, based on different criteria, resulting in certain furniture pieces being placed into different groups.

5. On the overhead, show the only illustration Darwin used (in chapter IV) in his best known publication, The Origin of Species: a generalized branching tree showing descent with modification over several generations, and with most branches going extinct sooner or later. In particular, point out:
a. how only a few early branchings are "successful", leading to species living today which appear in clusters, each cluster tied together by divergence from a recent common ancestor (branching point) in one of those few early branches.
b. Also point out how this pattern prevents sharing of many features which branched off earlier, unless they arise again, independently (a very unlikely, thought possible, event).

6. On the overhead, show the array of the order Carnivora. Draw a box surrounding the genus Canis and the three species below it (jackal, wolf, and coyote). Do likewise for each of the other four genera, then around the two families and their contained genera and species, and finally around the entire order. Point out how species today naturaly cluster into hierarchically nested groups, based on their shared traits. These are non-arbitrary groups, since they sort consistently the same way, even though based on different cirteria.

7. Draw converging lines down from each species in a genus, to a common branching point (common ancestor), then likewise from each adjacent common ancestor to an earlier common ancestor, etc. (see completed Carnivora diagram).

8. On the overhead, show a series of phylogenetic trees of a particular group of organisms, but based on different criteria, and note how similar each one is to the other. Good examples to use would be primate trees; several can be found in Evolution by M. Strickberger, 1996, and Science and Earth History by A. Strahler, 1987. Another tree is based on comparisons of chromosome banding patterns, from The Cambridge Encyclopedia of Human Evolution, 1992, ed. by S. Jones et al. Adaptations of some of those diagrams are available here (see Materials). In addition, students can build a tree using the morphological features found in selected primates and presented here in the matrix: "Distribution of Primate Skull and Dental Attributes". Such a tree is also included.

9. These Multiple Independent Lines of Evidence (MILEs) constitute a congruence of data sets, in which the pattern of one can be used to predict the pattern of another. This doesn't happen with non-biological groups, e.g. furniture, vehicles, hardware, etc. One might see a continuity of the development of various forms of technology and art, but that is only history, and historical development lacks intrinsic biological relationships, so it doesn't necessarily retain any "ancestral traits", which are natural and mandatory in biological systems. BE SURE YOUR STUDENTS CLEARLY UNDERSTAND THESE POINTS, and the distinctions between biological and non-biological classifications, and why these distinctions exist. Students should be reminded that biological classification is naturally non-arbitrary, while classifications of any non-biological collections are clearly arbitrary.

10. In conclusion, you can point out that the result of biological classification itself, as a consistent nested hierarchy, can be considered as another MILE in the support of evolution.

11. In order for students to fully appreciate these things, they should experience a few of the lessons on this site which produce these kinds of data sets. These can be done in sequence, one after the other, or they can be done at different times in their appropriate context, in which case the students should be reminded then of this introduction to biological classification, and how and why it is different from non-biological classification. The suggested lessons are:
a. the Hominoid Crainial Comparison (the "Skulls Lab")
b. the Comparison of Hominoid Chromosomes (or a useful alternative, Chromosome Clues, in WGBH/PBS Evolution Teacher's Guide, page 24).
c. the Molecular Sequences & Primate Evolution

1. There is a somewhat simplified, self-contained one-page activity which nicely illustrates both the nested hierarchy and the evolutionary basis for that hierarchy in primate classification. See the Primate Classification Lesson (with its worksheet and key). This has worked quite well by showing a boxes-within-boxes visual to illustrate the nested hierarchy of biological taxonomy. It also provides a convenient reference sheet for students throughout the course for checking primate groups.

2. The UCMP (University of California Museum of Paleontology) has an excellent presentation of cladistics, phylogenies, and modern systematics (what, why, when, and how). Take a look at it: (<http://www.ucmp.berkeley.edu/exhibit/phylogeny.html>).

3. See the excellent online tutorial by the UCMP: "What did T. rex taste like?" It makes an excellent introduction to classification, phylogenetic trees, and cladistics. This could be given as a homework assignment (online).

4. For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our review of an article in the American Biology Teacher.

See The American Biology Teacher (Vol. 67 #5, p.283-289, May 2005) entitled Beware of Nuts and Bolts: Putting Evolution into the Teaching of Biological Classification, by ENSI Co-Directors Martin Nickels and Craig E. Nelson.

For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our review of an article in the American Biology Teacher.

Darwin, Charles. 1859. The Origin of Species
Jones, S., et al, ed. 1992. The Cambridge Encyclopedia of Human Evolution. Cambridge University Press.
Strahler, A. 1987. Science and Earth History . Prometheus Books.
Strickberger, M. 1996. Evolution. Jones & Bartlett Publishers.
WGBH/PBS Evolution. 2001. Evolution Teacher's Guide

 ATTRIBUTIONS

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: Martin Nickels 11/8/2001 Presentation at NABT convention in Montreal.

2. Edited / Revised for website by L. Flammer 12/2001