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BLOCKS AND SCREWS
(or "Screwy Contrivances")

 

Tim Patterson
ENSI 93

EVOLUTION

Adaptations, Imperfections, and Contrivances

 

SYNOPSIS

Each student is given a block of wood and a screw (or nail), and is asked to put the screw (or nail) into the block, without any tool (like a screwdriver or hammer). Their efforts, with varying success, leads to a discussion of "contrivances", using various items and strategies as make-do ("contrived") tools for which they were not intended, and an exploration of many examples of contrivances (exaptations) or "adaptive compromises" and other "imperfections" in the living world, especially in humans. This situation is better explained by evolution rather than the result of "intelligent design".

PRINCIPAL
CONCEPT

Adaptation is a natural process in which structures and behaviors are derived and modified from previously existing structures and behaviors, but put to a different use.

ASSOCIATED
CONCEPTS

1. Many features of modern organisms reflect the structure of their ancestors in ways which vary from highly adaptive through moderately adaptive to non adaptive.

2. The existence of natural, biological contrivances (exaptations) and "imperfections" are more easily explained as a result of evolution over time, contingent on circumstances, rather than being the product of "intelligent design" in a single creation event.

ASSESSABLE
OBJECTIVES

(students will...)

1. list 5 examples of imperfect contrivances, 2 of them in humans.

2. given a list of imperfections in living things, recognize which category of imperfection each one is (contrivance, vestigial, or atavism).

3. recognize that the many contrivances and other imperfections found in living things are best explained by the process of evolution.

 

MATERIALS

1. Class sets of wooden blocks, cut from scrap wood (one per person). Many will be re-usable from period to period and even year to year, but plan on a fresh set for every class. Size is not critical, but 1x2x2 would be minimal, and 2x4x4 would be close to maximum. Hardwood would be preferable to soft wood.

2. Enough screws (wood or sheet metal) so that every student has one each period. Most will be re-usable each period, but have some extras. Screws should be about one inch long. Phillips head screws would make an interesting variation....a greater challenge.

3. Nails (as an option or alternative), about 1 1/2 to 2 inches long could also be used, although they are somewhat easier to use, and encourage hammering on surfaces which could be destructive.

4. List of "Some Adaptations & Imperfections" (overhead table and teacher detail/key sheet).

 TIME

The lesson can be very short (15-20 minutes), or could be extended longer to take an entire period (45-55 min.), especially if you hand out the followup reading assignment, which could be started after discussion of the experience.

STUDENT
HANDOUTS

none

TEACHING STRATEGY
& PREP.

This is an interesting experience that could be used in a variety of contexts. It is most appropriately associated with your unit on evolution, but it could be used in conjunction with any look at adaptive features (in plants or animals), possibly in your classification unit, in your introduction to evolution, or after you have studied natural selection.

 

PROCEDURE

TEACHER:
1. Distribute wood blocks and screws (and/or nails), one of each per person. (Having them pre-sorted into group trays would be more efficient).

2. Tell students that their job is to get the screw (or nail) as far into the block as they can, using any object or device (other than a real tool) that they can. CAUTION students against doing anything which might cause damage or injury to anyone or anything. DO NOT offer any suggestions as to how they might get the screw (or nail) into the block of wood.

STUDENTS:
3. Students will begin to find ways to accomplish the task, such as using fingernails, or coins, or some other object to twist in the screw, to simply hammering it in with heel of shoe or something else, or by banging it on the table or floor (if you see this, be sure they are not damaging the surfaces).

TEACHER:
4. After about 5 minutes of this, stop them (at whatever point they are in accomplishing the task). Ask some questions, such as "How many got the screw all the way in?", "How did you do it?" (ask this several times, to get several different strategies and several different kinds of items they used to help).

5. After several items have been named, ask if that was the originally intended use for those objects (no), and ask if they worked as well as a screwdriver would have worked (no). (If someone happens to have and uses a screwdriver, e.g. on a key chain, remark about how well prepared that person is, but otherwise ignore that tool for now). You could now ask (punningly) "What's the POINT of all this?" After the groaning stops, continue with the next step.

6. Point out that these are examples of "contrivances", objects used, or modified, to do something clearly very different from what they were normally used for, and typically not highly efficient. There are many examples of natural contrivances and other "imperfections" in living organisms, even humans. The process by which such "contrivances" come about is called "Exaptation" or "Pre-adaptation."

7. Set up 4 columns on the chalkboard or overhead projector, headed as follows (you may want to omit the underlined name for each column for now, and add it later, after some examples for each are listed):

 Adaptations
(perfect for the job)

 Contrivances
(modified for new use)

  Vestigials
(reduced size, unused)

  Atavisms
(rarely appears)

8. Point out that, in living organisms, an "adaptation" can often be traced to a structure which served a different function in earlier species (and may still serve that function in other living species), so in a sense, an adaptation can be traced to a contrivance of an earlier time. We can tell that they were contrived from something else from studies of their embryos, the fossil record, and their comparative anatomy with similar organisms. A good example is the wing of a bird, or the wing of a bat.

More obvious contrivances are often less efficient, even awkward, typically still resemble their original structure, and are not "perfectly" adapted to their new job; they are adaptive compromises. Some are obviously re-tooled versions of other structures. Many clearly show their contrived nature; they are really poor (and hardly ideal) design solutions. They seem to challenge the popular notion that all living things are the product of intelligent design. We call these "contrivances", or sometimes "imperfections" since they clearly are imperfect. a good example would be the radial sesamoid wrist bone of a panda being used as a sixth digit "thumb".

Another class of imperfections (and therefore poor design) makes its appearance in the form of structures with no clear function, often reduced in size from their counterparts in other (or earlier) species. The origins of these, too, can be traced through their comparative embryological and evolutionary development. If these reduced features commonly appear in all or most individuals, we call them "vestigial" structures (example: our "wisdom" teeth). If they appear only rarely, they are called "atavisms" (example: tail on newborn human). If you like, you could add the term "imperfections" to encompass the last 3 categories.

9. Ask students to suggest examples for each category. They can start with items used for getting the screws into the blocks. Then try to think of examples in living things. If students have trouble here, suggest the following examples:

 

IMPERFECTIONS 

   Adaptations
(perfect for the job)

bird's wing

  Contrivances
(modified for new use)

wrist bone as a "thumb" in pandas

 Vestigials
(reduced size, unused)

our "wisdom" teeth

 Atavisms
(rarely appears)

tail on newborn human

At this point, you could have students form groups of 2-4, in which they can brainstorm, discuss and list as many examples as they can for each column. Remind them to consider features of plants, too.

STUDENTS:
10. Work together in small groups, listing as many examples as they can in each column. Do this for about 10 minutes.

TEACHER & STUDENTS:
11. Call for examples (by column), one from each team in turn. Add these to the lists, as appropriate. Students may challenge items (wrong column, or totally inappropriate), but they must give reason for the challenge. Rotate through all teams several times, until they run out of examples, or class time is about to run out.

TEACHER:
12. Display the list of "Some Adaptations & Imperfections" provided in this lesson (use overhead or pre-printed on large sheets of paper). Reveal (uncover) one example at a time. This should help supplement the student contributions. Be sure to point out examples already submitted by your class. For each item, as it's revealed, ask the class to assign it to one of the 4 categories, and so check it.

13. In conclusion, point out that we find all degrees of imperfection, from incomplete features appearing sporadically (atavisms), to some features causing real survival difficulties or being reduced to non-functional status (vestigials), to some features being clearly but incompletely contrived from other structures (contrivances). This suggests a long time element in the formation of these structures. We would not expect such imperfections in a process of instant "special creation". Time and imperfections are exactly what we would expect in the gradual process of evolution. Therefore, the existence of imperfections in living things provides very compelling evidence of evolution.

ASSESSMENT
&
EVALUATION

Prepare a list of "imperfections" and some adaptations, and ask students to assign each one to one of the 4 categories presented in this lesson.

Prepare a test which addresses the assessable objectives.

Observe degree of participation in the group work.

 

EXTENSIONS
& VARIATIONS

1. In order to involve your students more deeply in this concept, hand out the material on "Contrivances: Orchids and the Panda's Thumb". Assign this as a take-home reading assignment which can be started in class.

2. A very useful extension of this lesson is to challenge your students to look for examples of contrivances and imperfections in the organisms they see or read about. This is an especially novel and challenging assignment for a class (or individual) visit to a zoo, aquarium, tidepool, or natural history museum. This could become an interesting extra credit project for any interested student. You might want to have them clearly indicate (or categorize) which features represent contrivances, which are vestigial structures, and which are atavisms.

3. Go to the outline by Dr. Nickels on Human Evolution, find section #5 on Adaptive Compromises or "Imperfections", and get the graphics showing PELVIC STRUCTURE and LOWERED LARYNX. These would be great for showing on your overhead when you talk about human "imperfections".


OPTIONAL:
3. If you are comfortable with addressing the religious concept of "intelligent design" increasingly heard as the "only reasonable explanation" for the high level of complexity and supposed perfection in the living world, the attached narrative may help. Be sure to use it with discretion and respect for the deeply held religious beliefs of your students.

 

REFERENCES

Shubin, Neil. 2008. Your Inner Fish - A Journey into the 3.5 billion year History of the Human Body. Pantheon Books, NY. Click here for Review.

Held, Lewis I. Jr. 2009. Quirks of Human Anatomy - An Evo-Devo Look at the Human Body. Cambridge University Press. Click here for Review.

Olshansky, S. Jay, Bruce A. Carnes, and Robert N. Butler. "If Humans Were Built to Last". Scientific American. March 2001, pages 50-53.

Jacob, François. "Evolution and Tinkering". Science. 10 June 1977. 196 (4293), pages 1161-1166.

Bardell, David. "Biological Misfits as Evidence of Evolution". The American Biology Teacher. September, 1997. 59 (7), pages 392-394.

Colby, Chris, and Loren Petrich, et al. "Evidence for Jury-Rigged Design in Nature". TalkOrigins Archive: http://www.talkorigins.org/faqs/jury-rigged.html

Darwin, Charles. 1859. The Origin of Species. In the last third of Chapter VI, Darwin discusses the existence of imperfect contrivances in a couple of places.

Gould, Stephen Jay. "The Panda's Thumb" from his book, The Panda's Thumb: More Reflections in Natural History. 1980. W.W. Norton & Company.

---- "Hen's Teeth and Horse's Toes" from his book, Hen's Teeth and Horse's Toes. 1983. W.W. Norton & Company.

---- "Helpful Monsters" from his book, Hen's Teeth and Horse's Toes. 1983. W.W. Norton & Company.

 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: Tim Patterson, 7/93

2. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 10/99

3. Edited / Revised for website by L. Flammer 1/31/99

4. Further and Revised by L. Flammer 10/99

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