Ohio's 10th Grade Evolution Lesson Plan
The committee designing this lesson plan took these five "critiques of evolution" directly from the book Icons of Evolution by Jonathan Wells. These five "aspects" are an eclectic mix of topics, which are either blatantly misrepresented or only tangential to true tests of the theory of evolution by natural selection. Below we outline these five "aspects" as given in the lesson plan (outlined in blue), and then present the correct interpretation of these "aspects" in the "Response" section that should be understood by students dealing with this lesson plan.
Aspect 1: Homology
Citations in the General Tips Section may provide a starting point for student research. It is suggested that students employ additional resources in their research.
Brief Supporting Sample Answer:
Different animals have very similar anatomical and genetic structures. This suggests that these animals share a common ancestor from which they inherited the genes to build these anatomical structures. Evolutionary biologists call similarities that are due to common ancestry “homologies.” For example, the genes that produce hemoglobin molecules (an oxygen carrying protein) in chimps and humans are at least 98% identical in sequence. As another example, bats, humans, horses, porpoises and moles all share a forelimb that has the same pattern of bone structure and organization. The hemoglobin molecule and the “pentadactyl limb” provide evidence for common ancestors. Also, the genetic code is universal, suggesting that a common ancestor is the source.
Brief Challenging Sample Answer:
Some scientists think similarities in anatomical and genetic structure reflect similar functional needs in different animals, not common ancestry. The nucleotide sequence of hemoglobin DNA is very similar between chimps and humans, but this may be because they provide the same function for both animals. Also, if similar anatomical structures really are the result of a shared evolutionary ancestry, then similar anatomical structures should be produced by related genes and patterns of embryological development. However, sometimes, similar anatomical structures in different animals are built from different genes and by different pathways of embryological development. Scientists can use these different anatomical structures and genes to build versions of Darwin family trees that will not match each other. This shows that diverse forms of life may have different ancestry.
Response:
Homology as a term has many definitions and can mean different things to investigators in a number of different fields of biology. As a result, data used to exemplify homologies need to be assessed in the framework of a consistent understanding of the term. This is important to keep in mind when reading about critiques of evolution as noted above.
As defined above, homologies are “similarities due to common ancestry.” This is a reasonable, general definition but it does not require that all similarities found among organisms are due to common descent. In fact, it can be that similarities in anatomical and genetic structures may reflect similar functional needs in different animals rather than common ancestry, as is suggested above. Therefore, declaration of homology requires something more than simply an observation of similarity. A better way of putting it is that homologies are similarities observed in the biological world that are BEST explained as being due to common descent. Because the definition requires the similarity to be due to common ancestry, any case of proposed homology must be tested to see if the weight of evidence supports a character as being the result of common ancestry. Such tests are available by comparing physical features (e.g., shapes of appendages, bone number and shape, etc.) and genetic code similarities among the array of plants or animals one is interested in, and using "phylogenetic inference" to infer relationships among these species.
For example, the now extinct Tasmanian wolf (sometimes called the “Tasmanian tiger”) in Australia has many anatomical similarities to placental wolves of the new and old world. Are these similarities due to common ancestry (homology) or to convergent evolution (physical similarities reflecting similar functional needs in organisms that are not closely related)? In the case of the Tasmanian wolf, investigation of genetic structure and anatomy suggest that some of the gross (more obvious) features that result in these wolves looking like new world wolves are the result of adaptations to similar habitats (i.e., convergent evolution). Why do scientists infer that these features not homologous? Because the vast majority of features of these wolves are, in fact, not at all similar to those of placental wolves, which suggests that the two organisms do not have a recent common ancestor. Thus the few features that do look similar (e.g., general body size and shape) are not homologous but are rather adaptations to a similar lifestyle (carnivores of other mammals).
One issue that is not at all clear from the above "challenging" answer is that much of how scientists assess homology is via genetic similarities/differences in parts of the DNA that are "non-coding" (i.e., they are parts of the DNA that are not used for any function). Much of any plant's or animal's DNA is non-coding (for example an "intron" that is embedded within an otherwise useful bit of DNA, called an "exon"). Scientists preferentially use these non-coding regions to test for common ancestry rather than the coding regions (the coding regions can be selected strongly, and this kind of selection can lead to over-estimates of the time since the species have had a common ancestor). Thus, although one can make a claim that coding portions of the DNA may be similar due to similar functions (as suggested in the "challenging" section above), non-coding regions should have no such constraint. Because this alternative explanation for similar DNA sequences does not apply to the comparisons that scientists actually use to assess ancestry of plants and animals, the fact that non-coding regions do show similar patterns of relatedness that were previously assumed by biologists (who had made such inferences on the basis of morphological and anotomical similarities only) strongly supports the theory of evolution by natural selection.
Aspect 2: Fossil Record
Citations in the General Tips Section may provide a starting point for student research. It is suggested that students employ additional resources in their research.
Brief Supporting Sample Answer:
The fossil record shows an increase in the complexity of living forms from simple one-celled organisms, to the first simple plants and animals, to the diverse and complex organisms that live on Earth today. This pattern suggests that later forms evolved from earlier simple forms over long periods of geological time. Macroevolution is the large-scale evolution occurring over geologic time that results in the formation of new taxonomic groups. The slow transformations are reflected in transitional fossils such as Archaeopteryx (a reptile-like bird) and mammal-like reptiles. These transitional fossils bridge the gap from one species to another species and from one branch on the tree of life to another.
Brief Challenging Sample Answer:
Transitional fossils are rare in the fossil record. A growing number of scientists now question that Archaeopteryx and other transitional fossils really are transitional forms. The fossil record as a whole shows that major evolutionary changes took place suddenly over brief periods of time followed by longer periods of “stasis” during which no significant change in form or transitional organisms appeared (Punctuated Equilibria). The “Cambrian explosion” of animal phyla is the best known, but not the only example, of the sudden appearance of new biological forms in the fossil record.
Response:
To understand the fossil record, one has to understand the geologic record, and more importantly, the stratigraphic record in which fossils are found. Fossils are defined as any remains, including tracks and trails, of a once-living organism. They form when an organism dies and is buried (preferably as rapidly as possible) and becomes preserved in sedimentary rock. Most of the fossil record is made up of invertebrate animals. Trace fossils are also abundant.
The term “transitional forms” is a misnomer often used by those who wish to cast doubt on the completeness of our understanding of evolutionary processes. The process of fossilization is not random, and therefore the fossil record cannot be assumed to be an unbiased snapshot of past processes, as some people assume. Fossil preservation favors the hard skeletal material of an animal, like shells, frustules, tests, bones, and teeth, and thus the fossil record is biased towards animals having one or more of these hard parts. Fossilization is also less likely on land. Vertebrate fossils are rarer than invertebrates because most vertebrates live on land and occur in fewer numbers than invertebrates. This explains why the vertebrate fossil record appears a little more incomplete than the invertebrate fossil record. Thus, because the process of fossilization is non-random, one is more likely to find aquatic animals with prominent hard parts that lived in great abundance in the fossil record. Any “transitional” species that did not fossilize well will, by definition, be likely to be “missing” from the fossil record, which is often seized upon by anti-evolutionists as a “gap” in our understanding of the evolution.
The antiquated concept of ‘missing link’ was coined because the fossil record seems to be “missing” species that would fit well between two related, but morphologically distinct fossil species. Because of the distinctive nature of the fossils showing the supposed gap, skeptics suggest that there needs to be a “link” species that shows an intermediate body form to link the two fossils if evolution proceeds in a gradual way. Often paleontologists do find gradual changes in the fossil record and have to apply geometric and statistical methods, called morphometrics, to quantify the shape changes they find. These numerous findings of gradual changes are universally overlooked by the skeptics seeking to disprove evolution by natural selection in favor of the examples where large changes occur quickly rather than gradually. However, because of the vagaries of the process of fossilization noted above, we will expect such “gaps” to be fairly common. The concept of ‘punctuated equilibria,’ wherein a fossil lineage has long periods of no change in their body’s hard parts followed by relatively rapid changes in those parts, is one of many ways in which macroevolution can occur, and in no way disproves (or even casts doubt on) the process of evolution by natural selection.
While it may be true that complexity has increased through geologic time, there are cases of groups that have not undergone substantial morphological change. We call these “living fossils” and include lingulid brachiopods and horseshoe crabs. While these forms appear to have magically appeared, their ancestry can be determined by looking at fossil forms of organisms existing before them. The fact that these “living fossils” haven’t changed their appearance over long time periods is thought to be because their body shapes have suited them well over the eons, and thus shape change hasn’t been selected. Again, the fact that these creatures have been in morphological “stasis” for millions of years is not a “challenge” to the theory of evolution: evolution does not predict that all species will continually change at the same rates over time. Anyone suggesting this is specifically being misleading.
The Cambrian Explosion is often cited as an example of a ‘sudden appearance’ of biological forms. However, the fossil record extends back billions of years before the Cambrian to the Proterozoic, where we have records of eukaryotic bacteria. Even 93 million years before the Cambrian is a fauna known as the Ediacarian fauna. Many of the major phyla can be recognized in the Ediacarian, but as soft bodied organisms. The only ‘explosion’ that can be seen in the Cambrian is the development of hard parts for these previously soft-bodied organisms. Because these skeletal elements get preserved more readily, they record their existence more easily. Therefore, the supposed “Cambrian explosion” (which some have used to indicate that species do not evolve via small accumulated changes over long time periods) is likely an artifact of the way animals are fossilized (i.e., hard parts are more easily preserved than soft parts) rather being a sign that numerous groups underwent a period of intense speciation.
Another commonly used example of a “challenge” to evolution by natural selection is the supposed “transitional” species that links dinosaurs to birds: Archaeopteryx. Archaeopteryx is not the ancestor to modern birds. At best, it is a side branch to the rest of the lineage. At one time, when we had very few bird fossils (birds typically do not preserve well in the fossil record because they do not live in water), paleontologists thought that it might be. However, the last 10-15 years of fossil discoveries of ancient birds, mostly in China, has brought a new and clearer way of understanding bird evolution. It is not a ladder-like pattern, but a bush-like pattern, with many branches. What we do know is that birds are ancestrally related to dinosaurs, and many paleontologists argue that birds are part of the dinosaur evolutionary tree that remains with us to this day.
Thus, although the fossil record is incomplete and biased towards some types of animals over others, it is our only tangible, demonstrable way to see the patterns of changes in species over long periods of time, which we term “macroevolution.” Even though our views of the types of species that existed on our planet thousands to hundreds of millions of years ago is incomplete (and likely will always remain incomplete due to the vagaries of fossilization), we can make sense of the patterns that we do see in the fossil record using the theory of evolution by natural selection. No alternative theory has been produced that comes anywhere close to being able to explain the fossil record as well as the process of evolution, and thus scientists naturally have supported evolution because it does the best job of explaining what we observe in these rock strata.
Aspect 3: Antibiotic Resistance
Citations in the General Tips Section may provide a starting point for student research. It is suggested that students employ additional resources in their research.
Brief Supporting Sample Answer:
The number of strains of antibiotic resistant bacteria, such as of Staphylococcus aureus, have significantly increased in number over time. Antibiotics used by patients to eliminate disease-causing bacterial organisms have facilitated this change. When some bacteria acquire a mutation that allows them to survive in the presence of antibiotics, they begin to survive in greater numbers than those that do not have this mutation-induced resistance. This shows how environmental changes and natural selection can produce significant changes in populations and species over time.
Brief Challenging Sample Answer:
The increase in the number of antibiotic resistant bacterial strains demonstrates the power of natural selection to produce small but limited changes in populations and species. It does not demonstrate the ability of natural selection to produce new forms of life. Although new strains of Staphylococcus aureus have evolved, the speciation of bacteria (prokaryotes) has not been observed, and neither has the evolution of bacteria into more complex eukaryotes. Thus, the phenomenon of antibiotic resistance demonstrates microevolution.
Response:
The development of antibiotic resistance in bacterial species is one of many examples of the process of evolution by natural selection we have seen in our limited collective life spans. Other examples include the evolution of resistance to insecticides by many insect species, the evolution of resistance to various drug therapies by malaria, and the evolution of resistance to the virus Myxoma by rabbits in Australia. All of these evolutionary changes in these various species have been well documented and are excellent examples of the processes originally predicted by Charles Darwin.
The "challenging answer" given in this lesson plan is one of the worst of the entire set of "challenging" statements. It either underscores the extreme lack of understanding of the processes of evolution by natural selection by the designers of this lesson plan, or is a deliberate attempt to mislead the students. In either case, it most certainly should never have been included in the "model curricula" for 10th grade students in Ohio!
The main problem here is exactly what has been mentioned before in terms of a "test" of macroevolution. By definition, macroevolution is a process that covers thousands to millions of years, and therefore can never be documented in our lifetimes. To state the obvious, that we can only observe changes on the order of increased resistance to antibiotics in Staphylococcus aureus and not the evolution of bacteria (prokaryotes) into eukaryotes, and then claim that this is evidence "critical" of the process of evolution by natural selection is patently absurd. The evolution of the first eukaryotes from prokaryotes took millions of years, and thus no reasonable scientist would ever expect to document such an amazing change in our collective lifetimes! To lead our students into such an argument is teaching them to be ignorant and simple-minded. We will clearly NEVER be able to document "macroevolution" per se. We will only be able to experimentally document "microevolution" and then make predictions about how such processes have played out over the history of life on earth.
An example of how scientists approach such long term processes may be something like the following. A botanist finds a grove of huge redwood trees. They are clearly quite old, but how old? The botanist finds a set small trees in this grove and follows it over the course of 5 years, measuring changes in height among these smaller (and therefore more easily measured) trees. She calculates the growth of these trees over this time span and then calculates how long it would take to reach the height of the adult trees in the grove. Her estimates suggest that the trees are over 1000 years old, and she publishes her results in a scientific journal. Clearly, she couldn't have planted a tree and see if it grew to the height of the others in 1000 years, but nonetheless she did do a scientific experiment that allowed her to calculate the larger trees' ages without having to physically observe their growth over a millennium! Plus, she has now published a scientific hypothesis that can be further examined, for example by having someone else come out and do a tree-trunk core and counting the annual rings to see if this botanist was correct.
Thus, we CAN understand things that occur over huge time spans by approaching them in the correct way and making scientifically based predictions and test those predictions without having to physically observe each step in the process. This is what we do when we measure things in the here and now (microevolution and young redwood tree growth) and then extrapolate those findings to time spans we cannot hope to experience (macroevolution and the life spans of adult redwood trees). Making statements as in the above "challenging answer" totally misses this point, and was clearly NOT devised by any reasonable scientist!
Aspect 4: Peppered Moths (Biston betularia)
Citations in the General Tips Section may provide a starting point for student research. It is suggested that students employ additional resources in their research.
Brief Supporting Sample Answer:
During the industrial revolution in England, more soot was released into the air. As a result, the tree trunks in the woodlands grew darker in color. This environmental change also produced a change in the population of English peppered moths (scientifically known as Biston betularia). Studies during the 1950s have suggested a reason for this change. It was observed that light-colored moths resting on dark-colored tree trunks were readily eaten by birds. They had become more visible by their predators compared to their dark-colored counterparts. This different exposure to predation explained why the light-colored moths died with greater frequency when pollution darkened the forest. It also explained why light-colored moths later made a “comeback” when air quality improved in England. This whole situation demonstrates how the process of natural selection can change the features of a population over time.
Brief Challenging Sample Answer:
English peppered moths show that environmental changes can produce microevolutionary changes within a population. They do not show that natural selection can produce major new features or forms of life, or a new species for that matter—i.e., macroevolutionary changes. From the beginning of the industrial revolution, English peppered moths came in both light and dark varieties. After the pollution decreased, dark and light varieties still existed. All that changed during this time was the relative proportion of the two traits within the population. No new features and no new species emerged. In addition, recent scientific articles have questioned the factual basis of the study performed during the 1950s. Scientists have learned that peppered moths do not actually rest on tree trunks. This has raised questions about whether color changes in the moth population were actually caused by differences in exposure to predatory birds.
Response:
The “challenging sample answer” provided for the case of peppered moths is a very poor starting point for study about the role of natural selection in wild populations. Two basic ideas are presented as the “challenge.” First, the case of peppered moths does not demonstrate that new ‘features’ or ‘species’ emerged (emergence of new species is usually considered a part of ‘macroevolution’). Second, scientists have ‘learned’ that moths do not rest on tree trunks. The first idea will confuse students about what the study of peppered moths has provided: an example of how natural selection can act on biological variation (differences in color of the moth varieties) to produce changes in the frequencies (their relative abundance) of the varieties over time that is associated with changes in the environment (pollution) and the effectiveness of bird predators. The second idea (moths do not rest on tree trunks) is simply incorrect, reflecting the authors lack of knowledge of (or their desire to misrepresent) the scientific studies published about peppered moths. If the “challenge answer” is meant to act as a starting point for student exploration, then students will begin their study by being confused and misinformed. Although starting students off in this manner may be regarded as a useful pedagogical technique under some circumstances (at the college level and beyond) I assume this is not what reviewers of the lesson plan (nor the board of education) had in mind.
There are several books and other writings outside the peer-reviewed scientific literature about the peppered moths that can be traced as the sources of the misinformed ideas presented in the ‘challenge answer,’ but for a science lesson, students should be directed to scientific sources of information (the scientific literature). Because the first idea (emergence of new forms – macroevolution) is not relevant to the case of the peppered moths, it should be ignored (see responses to aspect 3 and 5 for comments on macroevolution). In the case of the second idea, ‘moths do not rest on tree trunks,’ studies from the scientific literature show just the opposite (the best estimate is that moths rest on tree trunks about 25% of the time). Furthermore, the effects of pollution do not just darken tree trunks, they also darken other parts of trees on which moths spend the balance of their time (and on which moths would also be subject to predation). Moreover, recent studies of the peppered moths in other parts of its geographic range subject to the darkening effects of pollution have shown similar changes in the frequencies of light and dark morphs over time (a parallel pattern in the United States has been established by researchers publishing in the scientific literature).
The case of the peppered moth provides an excellent subject for student study of natural selection: natural variation in biological characteristics has been associated with a survival advantage (revealed by experiments) and differences in survival can be correlated with changes in the environment (pollution) and changes in the relative frequency of the varieties over time. That such patterns have been documented on a wide geographic scale, and corroborated by experiments that test the hypothesized mechanisms (differential capture of the varieties by predators), gives students an opportunity to examine a rich, complex, and well documented example of natural selection.
Aspect 5: Endosymbiosis (formation of cellular organelles)
Citations in the General Tips Section may provide a starting point for student research. It is suggested that students employ additional resources in their research.
Brief Supporting Sample Answer:
Complex eukaryotic cells contain organelles such as chloroplasts and mitochondria. These organelles have their own DNA. This suggests that bacterial cells may have become established in cells that were ancestral to eukaryotes. These smaller cells existed for a time in a symbiotic relationship within the larger cell. Later, the smaller cell evolved into separate organelles within the eukaryotic ancestors. The separate organelles, chloroplast and mitochondria, within modern eukaryotes stand as evidence of this evolutionary change.
Brief Challenging Sample Answer:
Laboratory tests have not yet demonstrated that small bacteria (prokaryotic cells) can change into separate organelles, such as mitochondria and chloroplasts within larger bacterial cells. When smaller bacterial cells (prokaryotes) are absorbed by larger bacterial cells, they are usually destroyed by digestion. Although some bacterial cells (prokaryotes) can occasionally live in eukaryotes, scientists have not observed these cells changing into organelles such as mitochondria or chloroplasts.
Response:
This example has the same exact problem as "Aspect 3": the time scales envisioned here are on the order of millions of years, and thus are NOT possibly observable in a scientist's lifetime (or in 10,000 scientists lifetimes!). Again the authors of this lesson plan are either totally ignorant of the time spans required for the processes they wish to be documented by scientists, or they are being deliberately misleading to attempt to make their point. Either option is unacceptable. If all science were held to the standards of "I need to physically observe the process in its entirety in a laboratory," then many other areas than merely evolutionary biology would need to be thrown out the window! Forget astronomy. Forget particle physics. Forget molecular genetics and DNA research. All of these have aspects that are NOT observable in a lab! However, all of these disciplines use the same approaches as in evolutionary biology to devise theories, come up with predictions of how a system will respond to a given set of circumstances, either produce those circumstances or observe the system when those circumstances arise, and then measure the response of the system and see if it reacts (or did react) as predicted.
The fossil record is a good way to see how natural systems reacted to physical and biotic changes in the past. Paleontologists can make predictions of what they should see across geologic strata containing fossils from many time periods relative to the biotic and physical processes that went on at those various times. We do NOT need to physically observe every process in our own lifespans to be able to do evolutionary biology, just as we don't have to construct a microscope that can physically observe a uranium atom splitting apart to know that nuclear fission is a real phenomenon. There are many ways to approach natural systems, and thus the above "challenging answer" is once again shown to be patently misleading.