Snippet: 9 Minutes (In Three Segments)

Subject: Science/Evolution

Ages: 14+

Length: Snippet: 9 minutes (in three segments). Lesson: Two class periods. Two 45 - 55 minute class periods. Homework: an essay in between the two class periods.

Learner Outcomes/Objectives: 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. Students will also learn about the mechanisms that drive evolution, namely mutations and natural selection, and to relate this to the genetic code and its carrier molecule, the DNA. The fictional elements of this science fiction movie will also allow students to know and discuss the idea that human evolution has come to a halt, held by many researchers and currently under debate.

Rationale: The movie The Time Machine places events 800,000 years in the future and speculates on how the human race might have split into various sub-species, each of which plays different role in the ecosystem they live in. One of the sub-species has developed an advanced ability of mind control through which it uses another one as hunters and the third one as prey on which the other two live on. This scenario assumes and implies various aspects of human evolution.

Description of the snippet: The snippet includes three segments in which scientist and inventor Alexander Hartdegen travels with his Time Machine 800,000 years to the future. During the voyage we see the landscape evolve around him, showing how it changes due to climate changes and erosion. We see Hartdegen trapped in the society he encounters in that time: the woman that has tendered him while recovering from the injuries he got in his previous stop in his time travels belongs to a rather primitive tribe which is attacked by monster-like creatures that come up from underground and hunt them all down. Hartdegen meets a yet different being that tells him how the human species evolved into this three sub-species, one of which controls the minds of the other and uses the third one as food reservoir. Helpful Background: The first of the issues on evolution that will be addressed in this lesson plan is the timescale of evolution. 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. (Homo Neandethalensis (Neanderthal Man) would be a different species, for example). Evolution of other living beings is usually also associated to extremely long timescales, but there are several interesting instances of distinct evolution having been observed in the time lapse of short-term scientific observations. Record holding is the case of the Tropical Blue Moon Butterfly, which has, in just a few years, come up with a mechanism to fight back bacteria which were killing most of its male population (see http://news.bbc.co.uk/2/hi/6896753.stm). There is also talk about a noticeable evolution in the size of adult fish due man-induced “un-natural” selection by fishing. 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 http://www.pnas.org/content/106/suppl.1/9987.full).

Now, how does evolution work? This question brings us to the basics of this matter: there are two important parts in the process by which changes happen in a particular living species by evolution. In order to understand this we need to know that the information about the whole living individual is contained within a molecule called DNA (Desoxiribonucleic Acid) that is present in each single cell of its body. It is as if each cell had a copy of a full “users manual” to build the body, from which it reads only the information relevant to its location and function within the organism. Within the DNA, the information is encoded in units called genes. During the reproduction of the cells, the DNA is copied so as to be again available in each of the new cells, and errors can occur. When a copied gene differs from the original version it is said that a mutation has taken place. If such a mutation happens during the early stage of the development of the organism or in a gamete, it can happen that most or all of its cells carry the altered information. The corresponding feature of the organism will then be correspondingly altered. If this is to the advantage of that particular individual, it may outlive other individuals of its species and thus be more successful in leaving offspring – now with the mutated gene, which in turn will spread fast and produce a new group of organisms that are more apt to survive. 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 in what we call natural selection. An interesting example of this interplay between mutation and natural selection that results in evolution is one of the most recent instance of evolution in humans, namely the inhibition of the switching off in adulthood of the ability to digest milk. Before humans domesticated cattle, the only milk an individual would need to process in his/her whole life would be that provided by the mother in early childhood. But once cattle formed a main source of food for human communities, being able to keep digesting milk as an adult became an advantage that was quickly favored by natural selection once the appropriate mutation took place. This mutation implied that the gene that deactivated the ability to digest milk in adulthood was inhibited. This evolutionary trait is especially interesting because it is a significant example of convergent evolution, that is, the fact that different populations acquire the same new feature through evolution in an independent manner: the ability to digest milk by adults has been found to have appeared at least once in Europe and three times in Africa during the last 6,000 years. More details about this exciting discovery can be found at http://www.nytimes.com/2006/12/10/science/10cnd- evolve.htm. By the time these changes were taking place another recent evolutionary development had happened, between 10,000 and 6,000 years ago. Humans started to have blue eyes. This change has two interesting features worth noting: it is traceable to one single ancestor of all blue-eyed humans and it did not provide an advantage for survival. Natural selection, however was part of the process, because in order to spread, blue eyes had at least not to be disadvantageous. More on the blue eyes mutation at http://www.sciencedaily.com/releases/2008/01/080130170343.htm.

This brings us to the third issue addressed in this lesson plan, one that can be an interesting discussion topic. It has been suggested by some scientists that human evolution has come to a halt. In modern civilized society, individuals that would quickly perish if we were living in the wild competing for food and territory, are taken care of and can grow up and have children. No genes are lost due to natural selection as we fight to cure or counterweight genetically induced diseases or defects. This issue is under debate in the scientific community and many articles and opinions can be found. 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, and not only the fittest, to grow up 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 has already made human life expectancy as long as it could get. It seems that after a century of spectacular increase in lifespan, it cannot be stretched further, as in recent years there has been hardly any improvement. 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. It can easily be seen how monogamy stops this way for the fittest genes to spread fast. Monogamy also lowers the chances for mutations because in monogamous couples the number of children is usually significantly lower (and decreasing) and they are had at the male’s earlier ages, when the cells of their sperm are the result of a smaller number of cell divisions than at older ages. Each cell division is a new chance for a “mistake” (mutation) to happen in the DNA copying process. Some limit the stop in human evolution to the western world – 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 or so many other diseases that prevail due to poverty. 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 we will only be able to evolve insofar as we drive evolution ourselves, through genetic engineering and cloning. Against the stop in human evolution 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. 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: 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).

Using the snippet in class

Preparation

1. Be familiar with the location of the segments and cue the DVD to the first segment.

Segment 1: Chapter 12. From 0:33:20 to 0:34:50. Hartdegen has had a narrow escape from the year 2037, where he encountered a world on the verge of being destroyed because the moon is breaking up. He sits unconsciously in the Time Machine, while it travels into the future at full speed and without control. We see the landscape evolving until Hartdegen regains consciousness and stops the machine in the year 802,037.

Segment 2: Chapter 16. From 0:50:03 to 0:54:06 Hartdegen has recovered with the help of Mara, a female inhabitant of this future society that looks surprisingly primitive. He goes to see how the Time Machine survived the last trip, but while he considers travelling back to the past, the tribe of humans he is with suffers an attack by creatures that emerge from the ground and start hunting them all down. The chapter ends in the middle of the fight.

Segment 3: Chapters 21 and part of 22. From 1:08:14 to 1:11:45. Hartdegen has been captured as well and is allowed to visit the being that seems to control the hunting creatures from underground. This being explains the way things work in this future society and how it came about. The segment ends when he tells Hartdegen “Who are you to question…800,000 years of evolution?”

2. Review the links in this Guide, pick those that are appropriate for the class and the lesson, and decide how to present them to the class. Step by Step First Class Period

1. Ask students what they understand by “evolution”. During the ensuing discussion it will probably become clear that most of the students associate evolution with very long timescales. (Make a note – on the board or on a sheet, for later use – of other features related with evolution that come up during the discussion, especially those related to mutations, natural selection and genes).

2. Play the first segment commenting to the students that, as they have said themselves, evolution takes place over very long timescales. The movie “The Time Machine” allows us to imagine jumping 800,000 years into the future, and this segment shows what can happen over such a long period in terms of the geology of the earth (erosion produces canyons and arcs in rock, climate changes occur, with mild periods between glaciations…).

3. Bring up the surprising two examples of rapid evolution mentioned in the section Helpful Background, the Tropical Blue Moon Butterfly and the size of adult fish in commercially interesting species. This two examples can be the starting point to explain the process of evolution and its two driving mechanisms, mutations and natural selection:

a. The Tropical Blue Moon Butterfly: The butterflies carry a parasitic bacteria that was killing most male embryos before they hatched, leaving the male population at a mere 1%. Due to a mutation, the genetic information of the butterfly started to include a “suppressor” gene that is able to 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. Male population is now back to almost half of all specimens. b. Fish and fishing practices: International regulations set a lower limit to the size of fish that can be caught and commercialized. In those species affected by the regulations, adult specimens above this limit are caught while the smaller ones are left back – and have more time to breed. Genes that produce a smaller adult size are therefore favored by the regulations and by intense fishing, which play the role of natural selection (in a rather un-natural fashion). It has been established indeed that the size of adults in commercially interesting species has shrunk, and it is explained in these terms of human-induced evolution. 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”. 4. Ask students to think (and to search in literature and/or internet to find documental support) on how human evolution might develop over the coming 800,000 years. This assignment can be done either individually on in groups. The latter option will make it less time consuming to go over the conclusions reached at the beginning of the second class period.

Second Class Period

5. 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 everyday 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.

6. 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.

7. Comment on the blue eyes mutation in humans, with its two interesting characteristics, its traceability to one single ancestor who first showed this mutation, and the fact that blue eyes did not provide any advantage for surviving. Explain how natural selection still was part of the process (see explanation in the Helpful Background section above and the link therein).

8. Play the second and third segments, in which the future scenario is shown and explained by the character played by Jeremy Irons, representative of the “Über- morlock” species that controls the mind of the others.

9. Point out that the moviemakers incur also in the same error mentioned above, namely ascribing an intention, 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 was destroyed. 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 closest real case to this situation is the gradual and human induced increase in the size of cultivated cereals, as farmers naturally select 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 vegetal and animal life, accelerated and human-induced evolution (see http://www.worldagroforestry.org/projects/allanblackia/domestication.html).

10. 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.

Supplemental Materials and Links

An interesting interactive tool to explore human evolution from the Smithsonian Institute’s National Museum of Natural History: http://humanorigins.si.edu/evidence/human-evolution-timeline-interactive

An interactive timeline of human evolution from New Scientist. http://www.newscientist.com/movie/becoming-human

An interactive timeline with detailed information on each hominid species http://www.archaeologyinfo.com/species.htm

On the debate on human evolution having come to a halt: http://discovermagazine.com/1992/aug/hashumanevolutio95 http://www.guardian.co.uk/science/2002/feb/03/genetics.research http://www.blackchampagne.com/articles/evolution-stopped.shtml http://www.timesonline.co.uk/tol/news/science/article4894696.ece