Snippet Lesson Plan: Evolution
Subject: Science/Biology; Science-fiction;
Ages: 13+ Middle School and High School (Rated PG-13 for intense sequences of action violence)
Length: Snippet: 9 minutes (in three segments); Lesson: Two 45 – 55 minute class periods. Homework: short essay between the two class periods
This film is available from Amazon.com.
Using the Snippet in Class:
Students will learn about the timescale of evolution through the fictional evolution of humankind 800,000 years into the future into different sub-species that live in a complex relationship of predation and reproduction. They will also be introduced to the mechanisms that drive evolution, namely mutations and natural selection, through examples of some dramatic mutations such as the Blue Moon butterfly and relatively recent mutations in the human species such as the ability of adults to digest dairy products and the appearance of blue eyes. Students will discuss the idea that human evolution has come to a halt, held by many researchers and currently under debate. They will also be introduced to the concept of genetic engineering.
The movie “The Time Machine” will add interest and variety to the study of evolution.
In the first of three segments, scientist and inventor Alexander Hartdegen travels with his Time Machine 800,000 years to the future and is injured in the process. During the voyage we see the landscape evolve around him, showing how it is altered due to climate changes and erosion. In the second snippet Hartdegen visits the society of that time and stays with a relatively primitive tribe. He starts to develop a relationship with the woman who tends to his injuries, but she is seized along with several other tribe members by monster-like humans that come up from underground and hunt them down. In the third segment, while trying to rescue his new friend, Hartdegen meets a yet different being that tells him how the human species evolved into three sub-species, one of which controls the minds of the others and uses the primitive subspecies that Hartdegen first met as a herd of cattle to be harvested by the monster-like creatures.
The first of the issues on evolution that will be addressed in this lesson plan is the timescale of species change. Human evolution is commonly understood as beginning 2.5 millions of years ago with the appearance of the Homo Habilis, the first beings considered as belonging to the genus homo, within which we (Homo Sapiens Sapiens) are a subspecies of the species Homo Sapiens. For example, Homo Neandethalensis (Neanderthal Man) is a different species of Homo Sapiens. The distribution of a trait throughout a population of a particular species has usually also required extremely long timescales, but there are several interesting instances of distinct evolution having been observed in the time lapse of short-term scientific observations.
One of the quickest evolutions on record is the case of the Tropical Blue Moon Butterfly. (Click here for a picture to show to the class.) The butterflies carry a parasitic bacteria that was killing most male embryos before they hatched, reducing the male population from 50% to a mere 1% of the total. Due to a mutation, the genetic information of the butterfly started to include a gene that allowed the butterflies to produce an anti-bacterial chemical or somehow keep the bacteria in check. This led to a larger proportion of males carrying this gene and a rapid spread of the gene in successive generations of butterflies. The male population is now back to almost half of all specimens. Butterfly shows evolution at work from the BBC News, July 12, 2007) and But Madame Butterfly, Where are all the Males? by Sourish Basu, Scientific American, July 13, 2007.
There are also observations indicating that there has been a noticeable change in the size of adult fish due to man-induced selection. Regulations limit the size of the fish that may be caught. Smaller fish must be left in the sea or thrown back, which allows smaller adults an opportunity to breed. It is considered a possibility that the catching of the larger fish of highly consumed species is inducing an evolutionary pattern towards a smaller adult size. See Human-induced evolution caused by unnatural selection through harvest of wild animals Fred W. Allendorf and Jeffrey J. Hard, Proceedings of the National Academy of Sciences of the United States). Some call this “unnatural”, human-induced selection. But hasn’t it always been true that a dominant species could affect the environment, and therefore the natural selection, of other species?
Most mutations do not result in changes that are beneficial to the individual and the individual dies before birth, leading to a miscarriage, or if it lives, it will not have offspring and the mutation will die out. However, if the change caused by the mutation is one of the few that gives the individual an advantage in relation to the environment in which it lives, the individual may be more successful in leaving offspring – now with the mutated gene, which in turn produce a new group of organisms that are more apt to survive. If the advantage is great enough, over what is usually a long period of time, most members of the species will come to have that mutation. Strictly speaking it cannot be said that a particular species has “developed” a new feature. Rather, the competition for survival has selected those individuals that are more fit through a process called natural selection.
Since the environment is always changing, what is beneficial is always changing as well. An interesting example of the interplay between environment and natural selection has been the recent acquisition by human beings of the ability of adults to digest milk. In most animals, and in all human beings who lived more than 9,000 years ago, the ability to digest milk was for the young. It switched off in adulthood. In early hunter, gatherer societies, the only milk an individual would need would be the breast milk provided by the mother. But then, about 9,000 years ago people domesticated cattle. Once cattle were domesticated and formed an important source of food, being able to keep digesting milk increased the available food supply for those adults who carried the trait. Those adults obtained an advantage in natural selection.
The evolutionary trait of the ability by an adult to digest milk is especially interesting because it is a significant example of convergent evolution which occurs when different populations independently acquire the same new feature through evolution; over the last 6,000 years, the ability to digest milk by adults has been found to have appeared at least once in Europe and an additional three separate times in Africa.
At the time these changes were taking place another recent evolutionary development occurred. Between 10,000 and 6,000 years ago some human beings started to have blue eyes. Before that time everyone had brown colored eyes. This change has two interesting features worth noting: it is traceable to a single ancestor of all blue-eyed humans and scientists cannot figure out how the trait provides an evolutionary advantage to people who have it. There are other hereditary traits for which scientists have not found an evolutionary advantage. These include hair color, baldness, freckles and beauty spots. Even if there was no advantage conferred by these traits, natural selection played a role in their spread through the population because they are not disadvantageous. Professor Eiberg, one of the scientists who discovered that the mutation for blue eyes probably came from a single ancestor said, “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”
It has been suggested by some scientists that human evolution has come to a halt. In modern civilized society many individuals who would have quickly perished if we had been living in the wild survive and have children. No genes are lost or gained due to natural selection as we fight to cure genetically induced diseases or defects. This issue is under debate within the scientific community and many articles and opinions can be found on either side. Some of the major points in this debate are as follows.
The main argument in favor of human evolution having come to a halt is that the pressure by natural selection has all but vanished, allowing anyone, not only the most fit, to survive and have children. No “disadvantageous” genes are lost. More subtly, it is argued that there is no room for further improvements in the human species, after medical and biological research have made it relatively easy to live into the child bearing years.
Also the increased mixing of genes due to the fact that in modern societies people meet and have children with partners from all over the world is said to produce a gene blending that blocks evolutionary changes. It is argued that this blending will end up making all humans of the planet more uniform, beginning with skin color, which is expected to become equally brown for all humans in a few generations.
Monogamy has also been considered an obstacle for evolution. In an animal herd, the fittest male would be father to a significantly large fraction of the offspring of all females. In addition, weaker females will die whereas stronger females will live longer and thus have much more offspring from those fittest males. In cultures that practice monogamy, no matter how genetically superior a male or female might be, the number of children will be limited.
Others see human evolution limited to the mind – perhaps better-prepared humans to live in a profit and technology-driven society are more likely to have children (because of their extra wealth), and the underlying genes – if this is a matter of genes at all – will spread faster. Yet others affirm that the wealthier and the professional class actually have fewer children than families in poverty and that the society will get less intelligent as a result.
A final argument that natural selection is no longer a force in developed societies is the is that it will move into areas of genetic preference. There are sperm banks that describe the donor’s occupation and personality traits. See e.g. International Cryogenics – Donor List. In the future, scientists may be able to manipulate genes so that certain traits are enhanced or suppressed. But if people are selecting for the traits that they feel will benefit their children in society, isn’t this a form of natural selection? After all, haven’t people been choosing mates for similar reasons for thousands of years?
Against the argument that human evolution has stopped it is argued that natural selection has not necessarily stopped for humans: environmental issues like increased UV radiation on the surface of the Earth due to the hole in the ozone layer could still select against those less prepared to endure the resulting altered conditions. Each individual might be looked after, but as a whole, communities with higher death rates due to, for example, melanoma (skin cancer) are less likely to have descendants. In third world areas there is still a high degree of mortality and therefore an evolutionary pressure that favors those more resistant to malnutrition, AIDS, malaria or other diseases that prevail due to poverty or geographic location.
A further argument points towards natural selection acting all the time but mostly going unnoticed because the effects on one individual are tiny. These effects would only become evident over generations. It is estimated that every human carries about two mutations with respect to the parent’s genetic code. Only very few are patently visible as diseases or dramatic changes in appearance: most of them might affect an individual’s capability to reproduce by a small percent. On the long run, however, it is argued, such genes do disappear (if they affect reproduction negatively) of spread (if they are positive for reproduction).
Finally, there is a middle ground position, acknowledging the validity of all the arguments as describing forces which affect natural selection in the modern world. In this view, natural selection continues but is being affected by the vast changes that technology and advanced forms of social organization have made in modern society.
1. Become familiar with the exact location of the snippets and cue the DVD to the first snippet.
1. Ask students what they understand by “evolution.” During the ensuing discussion, it will probably become clear that most students associate evolution with very long timescales. (Make a note – on the board or on a sheet, for later use – of other features related to evolution that come up during the discussion, especially those related to mutations, natural selection, and genes).
2. Introduction to Segment #1: Note for students that the film departs substantially from the book. Provide the following short introduction to the segment.
The story takes place in New York City and starts in the early 1900s just at the time that automobiles are first appearing on the streets. Hartdegen is an inventor and university professor. He proposes to a woman that he loves while they walk during the evening in Central Park. She accepts and Hartdegen puts a pretty engagement ring on her finger. Just then a man steps from the shadows with a gun. He demands their money and then, after Hartdegen gives up his wallet, the thief demands the fiance’s new ring. This is too much for Hartdegen; he struggles with the thief. A shot rings out and the fiance is mortally wounded. The death of his fiance throws Hartdegen into a deep depression. He isolates himself in his laboratory and after years of research produces a machine that will carry him backward and forward in time. His goal is to go back in time and change the events of the fatal walk in the park. Unfortunately, Hartdegen cannot change what occurred in the past and so he goes into the future.
Hartdegen has a narrow escape in the year 2037, where he encounters a world on the verge of being destroyed because the moon is breaking up. He is knocked unconscious. In this scene, Hartdegen sits helplessly in the time machine, while it travels into the future at full speed and out of control.
3. Play the first segment.
4. Post-segment Discussion: Make sure students understand that Hartdegen is able to stop the machine in the year 802,037, more than 800,000 years from today. Ask students to describe some of the changes that they have observed. These should include erosion, canyons, and arcs in rock, climate changes occur with mild periods between glaciations.
5. Proceed to discuss with students the first two examples of genetic selection discussed in the Helpful Background Section: Blue Moon Butterflies and smaller sized fish. These will serve as examples of the process of evolution and its two driving mechanisms, mutation and natural selection. Finish by recalling that these cases are indeed exceptions, and that evolution does indeed take place over very long timescales, as those considered in “The Time Machine”.
6. Introduction to Segment #2: After Hartdegen’s rough trip to the 800,037 he was injured. A woman of a rather primitive group of humans who now inhabited the area that had been New York City took him in and tended to his wounds. As the scene opens, they are going to check on Hartdegen’s time machine.
7. Play the second snippet.
8. Ask the class to think over the question, “Are the predators human?”
9. For homework, ask students to think about the following question. They can also be asked to search in the printed literature and/or the Internet to find documents supporting their conclusions. The question is: “How might human evolution develop over the coming 800,000 years?” This assignment can be done either individually on in groups. Ask students to write a short, one-page discussion of their conclusions, citing their sources, if any. The paper should conform to the appropriate written composition rubric for the class.
10. Ask students to explain briefly to the class what conclusions they have reached as to how human evolution will develop over the next 800,000 years. Try to detect in their conclusions errors that may stem from an incorrect understanding of the driving mechanisms of evolution, mutations and natural selection. A wrong comprehension of these mechanisms underlies most misunderstandings and non-scientific debates on the issue of evolution. For example, it must be insisted upon the fact that evolution is not a “finalist” process by which a species pointedly tries to solve a problem that menaces its existence – in fact, extinctions occur every day because species are unable to solve fatal disadvantages – , but rather the result of random mutations sometimes being useful for survival. Thus evolutionary changes are not the answer to questions like “why” did this or that species develop one or the other feature, but rather to questions asked in terms of “how” this species ended up having this or that feature.
11. Comment on the example of human evolution of the ability to digest milk as adults described in the Helpful Background section above, introducing the concept of convergent evolution.
12. Describe for the class, the blue eyes mutation in humans, with its two interesting characteristics, that it can be traced to one single ancestor and the fact that blue eyes do not provide any advantage for survival, so far as scientists can discover. Explain how natural selection still was part of the process (see explanation in the Helpful Background section above).
13. Play the third segments, in which the course of evolution of the homo sapiens into three subspecies is explained by the “Über-morlock”, a member of the subspecies that controls the mind of the others.
14. Ask the class whether the movie makers made a mistake in having the Über-morlock ascribe an intention or a goal to the evolutionary process that has led to the depicted scenario. The Über-morlock explains that they “decided” to specialize in mind control “in order” to adjust to the new living conditions on Earth once the Moon had been destroyed. The argument that this is not realistic, is supported by the fact that even if his species decided to “select” for reproduction only those individuals with apparently the largest mental capabilities, so as to favor the corresponding genes, the changes would be barely noticeable within a single generation, leaving nothing to select from and no direction to go for those charged with the task of selecting. In addition, this would bring about severe moral issues within that allegedly intelligent species, regarding the prohibition to reproduce to all but the most mentally fit. The contrary argument is based on the fact that as science progresses scientists may develop the ability to actually manipulate genes to give offspring traits that the parents want. Another example of this are the various sperm banks which offer descriptions of the donors, allowing people to choose traits for their children. See citations in the Helpful Background Section. Another example that is reasonably close is the gradual, human-induced increase in the size of cultivated cereals, as farmers have selected the largest seeds to sow, and generations succeed each other on a yearly basis, allowing for changes to be noticeable within the working life of a single farmer. This is usually referred to as a “natural” way of genetic engineering. It is, in fact, as are most kinds of domestication of plant and animal life, accelerated and human-induced evolution.
15. Propose the issue of human evolution having arrived at a standstill, as suggested by part of the evolutionary scientists, as a topic for debate. Let students know that there is no “correct” answer to this question, as the debate is currently taking place in the scientific community. Use the debate as an occasion to observe the students’ arguments and to insist, if necessary, on a correct understanding of the mechanisms that drive evolution. See Helpful Background Section for a summary of arguments on this topic.
Students can be assigned to watch the film Gattaca, and write a persuasive essay defending or criticizing the solution of the society shown in Gattaca to the question of genetic engineering.
This Snippet Lesson Plan was written by Erik Stengler, Ph.D., and James Frieden. It was published on February 10, 2011.