Blocks and Screws

Authors: Original Lesson - Tim Patterson ENSI, www.indiana.edu/~ensiweb

Craig Nelson – Contrivances: Orchids and the Panda's Thumb

Extensive Modification By - Eddie Bonnell

Date to be taught: 22 & 23 Oct 04

Grade level: 10^th or 11^th

Location:

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).

5. Readings on Contrivances (orchids and panda).

6. Handouts: Primate Pelvis, Primate larynx .

7. Notecards.

8. 2 Dice.

Objectives:

Students will be able to –

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.

Engage:

Teacher does: 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 they are a collection of ancient races of hominids living on another planet. Tell the students that one peculiarity of each of their particular races is that each race is characterized by having an object for a hand. The object could be a pencil, shoe, whatever. The students are then told that they must select their object, and that no two students are to select the same object. 3. After all students have selected their objects tell the students to pretend that the objects they have for the “hands” are particularly suited to the peeling of a particular type of fruit that only their species eats (species are distinguished by the differences in their hands). 4. Now distribute a small block of hardwood and a screw to each student. Tell students that their job is to get the screw (or nail) as far into the block as they can, using their selected object. 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. 5. 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). 6. Inform students to imagine that it is beneficial to an individual on this planet because of certain insects on the ground, to be able to put screws into blocks of wood because it allows that individual to hang their fruit off the ground, and thus prevent it from getting dirty and rotten. 7. Select the student who got the screw in the farthest with their hand and bring him/her up to the front of the class. Ask students that assuming all types of hands peel their fruit equally well, what sort of advantage do they think this student has? What are the effects of this advantage? 8. Now ask the students if the hand that this individual selected is best suited for its new task of screwing screws into wood. Since it is not, how is it that this individual is still successful? In other words, how is this individual still successful despite a hand which is quite awkward at what it does? 9. Now tell the students to imagine that the teacher has recently evolved as a new species, but this time with a special screwdriver hand which is excellent at putting screws into wood, but poor at peeling the fruit in the first place. Ask the students who they think will survive better and why.

Student does: Students will choose an object to act as their “hand”, and then attempt to use that object in screwing screws into blocks of wood. Students will participate in class discussion on how imperfections arise in nature.

Key Questions: What was the original use of the object you used to put the screw into the block of wood? Is it best suited for this new function? Why not? How then is it able to persist? Give an example using your object of how this process might look. What if someone evolved a screwdriver hand, and though it was excellent at the task of screwing screws into wood, it was not very good at peeling fruit? Do you think this would be selected by evolution over the individual with the less suited hand?

Answers: 1. Answers vary. No, my object is not best suited for the new activity of screwing screws into blocks of wood. It is not best suited for this new activity because my hand originally evolved for another purpose, and by utilizing it in this new way, I can maximize the fitness this hand gives me. Evolution allows for imperfections because it is a process of random change acting under set guidelines. Imperfections will continue to exist in a species until randomness leads to an adaptation that is more effective at the job. 2. Pretend you had a nickel for a hand, and just like everyone else in your pack, you used that nickel to peel your food. The nickel hand has evolved to be energetically efficient in that task. Now suppose that you come along one day, one of the people in your tribe has an alteration in their genes, making them more likely to not only use their nickel-coin hand for peeling fruit, but also for getting screws into blocks of wood to hang the food. This keeps the food from rotting, and now he has a slight advantage over the other males in his pack. He produces more offspring because he is not spending so much time sick from rotted fruit that was not stored properly. His offspring then might inherit his gene which encourages screwing screws in blocks of wood. And so on. 3. This would depend on which adaptation resulted in a higher level of fitness for the individual carrying that adaptation. If the screw hand, despite its inability to peel fruit efficiently, lead to carriers of that adaptation surviving better than those with only nickel hands, then it is likely that the screw driver hand would proliferate in the species. However, if the nickel hand, though lacking in efficiency at putting screws into wood, was very effective at peeling fruit and other activities, thus resulting in a higher total fitness advantage to the other screw hand, then it would be selected by evolution.

Evaluation: Check for student participation. Ensure each student contributes to the class discussion on the fitness advantage of different types of hands, by posing different scenarios to test their understanding. An example would be to ask the fitness advantage of a hand that peeled fruit effectively compared to a hand that obtained fruit at a quicker pace. Or, a hand that peeled just one type of fruit versus a hand that peeled another, novel type of fruit heretofore unavailable to animals of that species.

Explore:

Teacher does: 1. Point out that these are examples of “contrivances” or “imperfections”, objects used, or modified, to do something clearly very different from what they were normally used for, and are typically not highly efficient. There are many examples of natural contrivances and other “imperfections” in living organisms, even humans. 2. Set up 4 columns on the chalkboard or overhead projector, headed as follows (you may want to omit the parenthetic description 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) 3. 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. 4. 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". 5. 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. 6. 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: · Adaptations: (perfect for the job) Bird's wing is also an example. · Preadaptation: A character that was adaptive under a prior set of conditions and later provides the initial stage for evolution of a new adaptation under a different set of conditions. Examples: bird's flight feathers (from feathery scales on certain dinosaurs, where they served the function of insulation); the vertebrate eye (from a series of light-sensitive organs); barnacle "glue" (from their glue to attach eggs). · Contrivances: (modified for new use) A structure modified and used for a function which is different from the original (or previous) function for that structure in an ancestor. An example would be the radial sesamoid bone in a panda's wrist which is elongated and functions as a novel "thumb" for holding bamboo stems. · Vestigials: (reduced size, unused). An anatomical structure found in all or most normal individuals of an extant species; typically very small in size, and with apparently little or no important function now. Such parts typically would be found in ancestors of this species, but as larger and clearly functional structures. An example would be the ear-wagging muscles in humans. Our wisdom teeth also are an example. · Atavisms: (rarely appears) A vestigial structure found in only a small fraction of the normal members of an extant species (e.g. the rudimentary thigh bone found in about 5% of individual whales, or the extra toes which sometimes appear in horses, enlarged growths from the "splints" of the vestigial toes normally found). The tail on newborn humans is an example. · Imperfection: A "contrivance" which still retains some of the features of its ancestral source structure, to a greater or lesser degree; clearly not fully or perfectly "adapted" to its new function, but serving adequately. Again, the panda's "thumb" is an example here, as are the many contrivances found in orchid flowers. This term could also be applied to vestigial or atavistic structures.

Student does: Students listen to teacher, contributing to the class discussion, asking questions, making suggestions. Students contribute to the class brainstorming of potential adaptation, imperfections, vestigial organs, contrivances, etc.

Key Questions: We said that a bird's wing was an adaptation, whereas something like the pandas thumb was considered an imperfection. Is the bird wing really an optimal design? Why or why not? There are certain beetles called bombardier beetles that exist, which when attacked will release a toxic liquid solution, several hundred degrees in temperature, in the form of a searing jet spewing out of their abdomen. (The mechanism of their spray works thus: Secretory cells produce hydroquinones and hydrogen peroxide (and perhaps other chemicals, depending on the species), which collect in a reservoir. The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. This chamber is lined with cells that secrete catalases and peroxidases. When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones. These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it. Under pressure of the released gasses, the valve is forced closed, and the chemicals are expelled explosively through openings at the tip of the abdomen. [Aneshansley & Eisner, 1969; Aneshansley et al, 1983; Eisner et al, 1989]) What does this say for the possibilities regarding evolutionary adaptations? Can any evolutionary adaptation really be called “best-fit”? Giraffes live in an environment that is extremely flat. Popular opinion assumes that their long necks evolved for advantage of reaching higher leaves in trees. Are there any other explanations that you can think of for the original function of such a long neck? Does this make the Giraffe neck a contrivance or an adaptation?

Answers: In a sense, no adaptation can really be considered optimal design. The only optimal design of a feature is one that allows for an individual to be immortal and to produce infinite offspring. However, this does not mean that certain characteristics, adaptations, are not extremely well suited to their functions. In this sense then, no, the bird's wing is not exactly an optimal design. It is extremely effective in a relative way, at its function however. This again is evidence for the potential diversity which evolution can result in. If one species can evolve wings for flight, potentially, given the right environmental circumstances, another could evolve a jet-pack organ for flight. The possibilities are endless within the wide open physical laws of the universe. Potentially, Giraffes may have evolved their long necks in order to detect approaching predators from a long distance, giving the Giraffe ample time to escape. As to the distinction of whether or not the neck of a Giraffe is an adaptation or a contrivance is relatively unimportant, as all adaptations were at one time or another, contrivances. That is to say all adaptations are modifications on a previously existing structure or structures.

Evaluation: Students will make a table in their journals, for each classification of adaptation. The students will then individually brainstorm for ten minutes, two additional examples for each category. After they have done this, they will then make up as many questions as they can about what they have learned today, making sure that they answer each question. The teacher will encourage students to try to make the questions very specific and reasonably difficult.

Explain:

Teacher does: 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. Encourage them to think of as many adaptations as they can. Inform the students that they are now going to be participating in an intense battle of wits called “Name that Adaptation: Evolutionary Dominance in the Classroom”. The groups students are currently in will act as their own distinct species population. At this point, each group should think of their species name and write in on a folded index card for display at their desk. The students will be told that they are competing with other species for the same resources in an environment. Evolutionary Dominance by a species will occur when that species has driven all the other species in the habitat into extinction, as all species in the environment (the classroom) are competing for the same exact resource (AN A!!!!). The rules of the game are, students are to work as the teams with which they are currently affiliated. Each team will begin with a total of five points. They are to suggest (in turn, one group at a time), adaptations for each of the categories on the overhead. Should another group have the same adaptation listed, the points cancel for both teams involved. Another group may challenge a claim, but in so doing must say a specific “challenge phrase” designated by the teacher before hand. Failure to raise a challenge using the challenge phrase will result in the deduction of 1/2 points. Challenge phrases will change throughout the game, according to the teacher's will. They will include: “Sir, I stabeth thee with a sword of conviction rooted in truth.” “Heretofore I have remained acquiescent to the mewlings of ignorance, BUT NO MORE!” “Sir, I'm afraid I am sickened in light of the debaucherous implications with which you affront my refined senses.” “I LIKE BERRIES!” This will work to keep students engaged and the atmosphere light and relaxed. Should one team challenge (using the proper challenge phrase) the claim of another team, the two challenging members of the teams will come to the front of the class for a face off at the face off platform (a cleared table on opposite sides of which they will stand). During a face off, each individual participating in the face off (2 in most circumstances), will have 30 seconds to convince the Lord of the Court (teacher) of their argument. Successful arguments will include logical evolutionary scenarios, and an understanding of the adaptive pressures and responses contained therein. In addition, it must be plausible. After each individual in the face off has presented their case to the honorable judge, he/she will give thumbs up or thumbs down to each member participating in the face off. Thumbs down will result in the loss of a point. Thumbs up will result in the award of a point. Thumb sideways is neutral, no loss no gain. When it is a team's turn to suggest another adaptation, they may take if they choose to, any surplus of points they have (including the initial five they started out with), to attack another group as a simulation of interspecies competition for resources. The teacher should point this out to the students or ask them what they think this activity represents. When attacking another group, two battlers will be forced to come up to the arena (a cleared table) at the front of the room. Then, of the two groups who are not participating in the battle, one will be selected by the teacher to quickly come up with a question (usually one from the questions they made up individually during the evaluation of the previous section) and its answer which will be given to the judge on a sheet of paper for approval. After approving the question, the judge will turn to the attacking group representative and ask them how many points they wish to attack the other group with. After the student tells the teacher, the teacher will then find out how many points the other group wishes to defend with. The teacher will then read off the question chosen by the third-party group. The first of the two (attacker or defender), to hit the table with their palm will have an opportunity to answer. If they answer correctly, they receive an additional point to their cause (attack or defense). If the defense team should win this extra point, it may be used as a one chance counter attack, in which they will have one roll of the dice to attempt to defeat the attacking team. This counter attack opportunity can only be used if the defense team wins the question, and the attacking team fails in their attack (rolling doubles). If an individual is incorrect when answering the question during a battle, they do not lose a point, but the enemy is then able to answer. If neither individual is able to answer correctly, no points will be given. After the question has been asked, and the answers have been attempted, the attacker will be provided two dice. According to the number of attack points he was willing to risk, that is how many rolls he/she is afforded with the two die to receive doubles. However, if the attacker roles double 1's (snake eyes), then it is representative of a disease in their species, automatically awarding the defense team 2 points, and costing the attacking team all of the points they risked and ending the confrontation. If the attacking team rolls doubles of any other number, the defending team has the same number of tries as the amount of points they risked in defense, to roll doubles themselves, effectively “blocking” the attack. If the attack is blocked, neither team is awarded any points and neither team is deducted any points. If the attacker wins the confrontation, his/her team is awarded two points and the losing team is penalized all of the points they risked in defense. Attacks can only be raised when it is a group's turn. Challenges to another groups answer however, can be raised at any time during the battle for Evolutionary supremacy in the classroom. Once a group runs out of points, they become “extinct”, and must join the group that conquered them, simulating the conquering group occupying the newly vacated niche previously occupied by the now extinct team. Thus, it is beneficial for teams to attack and challenge one another. Students should be asked questions throughout the game as to the significance of the game they are playing and what the different aspects of it represent in an evolutionary sense. When a group goes extinct and joins the group that conquered them, thus forming a larger group, that lager group will then have more individuals, and thus a larger collaborative base to raise creative challenges. Eventually, the class should coalesce into two groups, either both large or one extremely large and one small group. At this point it would be good for the teacher to pause the game momentarily and tell the students to look around at their habitat. There are two species occupying it, what do they think the characteristics of these species are in terms of survivability? What are the benefits of a large population? What are the benefits of a small population? Which population, do you think has a higher potentiality for evolution? When the game has finally run to completion and all groups are extinct except for one super-species, hold a brief discussion on the implications of this exercise. Tell students to write down their opinions of what they witnessed in this game, regarding its relevancy to evolution. Encourage them to provide examples for their conclusions.

Student does: Work together in small groups, listing as many examples as they can in each column. Do this for about 10 minutes. Students may then also collaborate to think of more evolutionary/adaptation questions. Students participate in the “Name that Adaptation: Evolutionary Dominance in the Classroom” game. Students answer questions posed by the teacher.

Key Questions: What does this game model? Explain. What are some benefits of a large population? What are some benefits of a small population?

Answers: The game models interspecies competition. Each group represents a different species, with all of the species in the environment of the classroom competing for the same exact resource. When two species in nature compete for the exact same limiting resource, barring exterior influence, one species will dominate while the other evolves to use other resources or go extinct. In this game, the option of extinction is the only one available to a waning species. The adaptive strategies used by all the participating species are directly modeled by the strategies employed by the students in each group. Whether the students of a certain group decide to be full aggressors from very early, whether they decide to remain on the defensive, or keep a low profile and wait until the end, all depends on which adaptive strategy they decide will be most successful. In addition, the fitness of each population is modeled on how well the students in that group know the material. Students who have not paid much attention in class and therefore do not know the material very well, will be less “fit” than those who have paid attention. Their relative fitness disadvantage will affect the performance of their species. When a species challenges another species, this represents direct competition between two species in nature for the limiting resource. In deciding how many points to attack or defend with, each group is modeling the adaptive strategies of their species. The dice are indicative of the relative amount of uncertainty in these sorts of encounters despite the odds being weighed heavily in one direction or another. In nature there is always an element of uncertainty. Disease may spring up at any time (double 1's), thereby limiting the effectiveness of a species at competing. A storm may come along and damage one species that is otherwise more fit than another competing species. When a group goes “extinct”, and joins the species group that defeated them, this represents the victorious group's radiation into the newly available niche occupied by the other group. Once a supply of resources opens up in a highly competitive environment, species will rapidly radiate to occupy those resources. In attack and defense confrontations, the potential for gaining a “counter-attack” point by the defense is meant to give recklessly aggressive species some second thought before blindly rushing into battle unprepared. This forces students to think about the consequences their species might have to face and determine if the risks are worth the gain, very much akin to what happens in nature on a much more unconscious level. The benefits of a large population are one of buoyancy. They are much less likely to be wiped out by a single defeat or a single epidemic. This is directly modeled in the game. In addition, mutations (which are usually deleterious and disadvantageous to an individual's fitness), have less of an effect on the whole population, allowing for stability and gradual evolution. The benefits of a small population are few and far between in a highly competitive environment, barring extenuating circumstances. Though not modeled directly in the game, smaller populations living in rather open and uncompetitive environments have the potential for rapid growth and evolution as a result of the surplus of abundant resources. The environment modeled by the game however is highly competitive, and thus there are no direct benefits as a result of being a small population.

Evaluate: Teacher monitors student participation. At the end of the game, students will turn in their sheets containing suggested adaptations, opinions regarding the game and how it represents the evolutionary process and interspecies competition, and questions on evolution/adaptation with the answers included.

Elaborate:

Teacher does: 1. 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.

Student does: 1. Students will follow along in their list of “Some Adaptations & Imperfections” worksheet. 2. Students will provide suggestions and participate in the class brainstorming activity.

Key Questions: What are the adaptive benefits for hollow bones in birds? If many cave dwelling species have sightless eyes, wouldn't it be better if they didn't have any eyes at all? Why do you suppose this is? Why hasn't it happened yet? What is the point of anteaters developing teeth during fetal development if they are just going to loose them before birth?

Answers: Hollow bones in birds provide them with a strong yet light bone structure so they do not have to expend so much energy in flight. Yes, it is likely that it would be better for a cave dwelling species to just forgo eyes altogether. This is because organisms who did not bother making eyes can use the energy they would have used to make eyes, doing something else. Maybe investing the energy in fortifying another structure in their body. Or perhaps the mother of a sightless individual would not have to invest quite so much energy in her young forming eyeless embryo as compared to a mother who has to ingest food to convert it to energy with some of that energy being devoted to eye formation. To ask what the point is of anteaters having teeth and then losing them is a misnomer. There is no point to the entire process, in the sense that the fetal development of anteaters is not a conscious process but rather an automated systemic interaction of hormones and chemicals resulting in the formation of a fetus when certain requirements are met to initiate the process. Anteaters having vestigial teeth is merely a relic of an earlier form of the process. It is a sort of unused scrap of an earlier version of the same process where anteaters' ancestors had teeth.

Evaluation: Students will turn in their worksheet checklist for adaptations and imperfections.

Evaluate:

Teacher does: 1. Give your students the two "Panda" readings (on pandas, and on orchids) to read. After they finish, ask them to answer questions 1 and 2 on the Reading/Discussion Guide. 2. After students have done this, have them break up into small discussion groups to go over their answers and to discuss together questions 3 and 4, for about 15 minutes. 3. As a class, discuss what they came up with in their groups. Lead the discussion into the concepts of atavisms and preadaptations as other examples of imperfections that are explained by evolutionary theory. 4. 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.

Student does: 1. Students read the “Panda” readings, answering questions 1 and 2 in the reading/discussion guide. 2. Students collect into groups and answer the rest of the questions. 3.Students participate in the class discussion on atavisms and preadaptations

Key Questions: 1. We have said that atavisms are enhanced vestigial organs found in a very small percentage of a population. What do you suppose causes these enhanced vestigial structures? 2. What are preadaptations? Give me an example of a preadaptation. 3. What do vestigial organs tell us about whether or not evolution occurs? How?

Answers: 1. The driving force behind all evolution in genetic mutation. Genes are the core, the fundamental essence and information bank for all of life. The contain the instructions for which cells should be a part of which tissues and organs, how the animal should behave and react, etc. In addition, genes in an organism can be turned on and off according to the activities of other genes. Occasionally certain genes are activated by the products of other genes. It could be hypothesized that genes which are normally dormant in an organism could be “turned on” through mutation. Either in another gene which then produces a product to activate this gene, or directly on this gene. Thus, the normally dormant gene which is now activated, activates other genes, eventually resulting in an atavistic structure like a vestigial tail in humans. 2. Preadaptations are: A character that was adaptive under a prior set of conditions and later provides the initial stage for evolution of a new adaptation under a different set of conditions. Examples: bird's flight feathers (from feathery scales on certain dinosaurs, where they served the function of insulation); the vertebrate eye (from a series of light-sensitive organs); barnacle "glue" (from their glue to attach eggs). An example of a preadaptation that we saw today was the hand that each of us used to screw the screw into the block of wood. 3. Vestigial organs are direct evidence that evolution did and still does occur. All organisms are evolving, including humans, and evolution is evidence of this process by showing us direct evidence by way of presenting to us relictual forms of organ systems utilized by our ancestors.

Evaluation:

Students turn in their Panda worksheets from the reading.