Evolution

​As with Mendel in the Genetics unit, I position Darwin historically.  I describe his family's economic situation in contrast to Mendel's.  Again, I point out the Nature of Science in terms of collecting evidence through observations to form well substantiated hypotheses.

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I discuss Darwin's specific observations and point out that Darwin brought together diverse fields of biology, geology, and economics with his theory.  He was influenced by other's work such as geological understandings about the age of earth and economic knowledge about populations and resources

​Then I bring up the specific evidence that supports the theory of evolution: fossils, comparative anatomy and homologous structures, comparative embryology, and comparative biochemistry.

I mention the previously disproved evolutionary theories of Use and Disuse, as well as Inheritance of Acquired Characteristics.  I also describe Darwin's voyage and sometimes show excerpts of Darwin's Darkest Hour  to give students a "flavor of the time".  A worksheet that goes with relevant aspects of this video is available here.

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​Specific elements of Darwin's Theory of Natural Selection are outlined for students:  overpopulation, competition, the environment being the agent of natural selection and organisms competition for survival.  Only the fittest survive.  Those that do survive, pass their traits onto their offspring through reproduction.  I also define speciation for students at this time.

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I explain that Darwin did not have Mendel's knowledge of genetics.  Today we know that the survivors of competition pass on their genes to their offspring.  ​I reiterate:  Evidence of evolution can be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development (embryology).  ​Genes carry the information that determines traits.  ​

Next we discuss Modern Evolutionary Theory.  Today we know that variation occurs due to sexual reproduction and mutations, that the environment is the agent of selection, and that organisms are uniquely adapted for the great varieties of environments in which they live. Students then complete the Natural Selection Lab which offers several examples, notably, the peppered moth

I next review the terms: Gene Pool, Relative Frequency, and Variations.  I use an example of an imaginary population of mice. Students color in 50 mice cartoons and we use the above terms to talk about our imaginary mice population.  Then I use a population of lizard cut-outs to talk about allele frequencies.  The frequency of the sickle cell allele among humans with African ancestry is another useful example, as is the competition between Neanderthals and Homo sapiens.  You can find those examples in the presentation file below.  I relate our discussions of allele frequencies to fitness for varying environments.  ​

​I then move on to genetic drift, genetic equilibrium, and the Hardy-Weinberg Principle.  I explain to students that, in small populations, genetic drift can occur by chance.  In large populations, genetic equilibrium (Hardy-Weinberg Principle) may be reached if certain conditions are met (random mating, no immigration or emigration, no mutations, and no natural selection).  ​

​As an example, I use a large, diverse population of beetles with different designs on their carapaces.  In my example I explain what would happen if small subgroups of that population were separated by a natural event, such as a hurricane.  This offers an illustration of the founder effect.  I model this using colored paper clips.

​Next, I illustrate how the environment/natural selection can affect the distribution of phenotypes with the bell curve:  Directional Selection, Stabilizing Selection, and Disruptive Selection.  Students complete the Patterns of Natural Selection Lab.

I talk about how geographic isolation can lead to reproductive isolation.​  I remind students that reproductive isolation can lead to speciation and we discuss the definition of a species...as we did previously in the genetics unit.  I cover the length of a time it takes for evolution to occur, touching on gradualism and punctuated equilibrium.  Students complete Patterns of Evolution.  I also mention adaptive value:  if an adaptation is beneficial for an organism it will be passed onto future generations.  I use examples of the Manchester Moths and  Galapagos Tortoises

Evolution in bacteria as a good example of how evolution can occur quickly.  Bacterial evolution has led to antibiotic resistance of some bacterial strains.  I talk about inappropriately using antibiotics to treat viral infections and antibiotic use in agriculture and how this likely created an environment where only more resistant bacteria could survive.  Students complete a Bacterial Evolution Lab.

Students complete the NY State Lab:  Beaks of Finches.  They simulate competition between varying bird beak structures. I often follow that up with a lab that deals with creating a phylogenetic tree for an imaginary species of  "inquats".  ​

I discuss early life on earth and the fossil record.  We review that geologic time is broken into eras and periods noted for their different life forms.  Many students have learned this in previous science classes.  I give an overview of the human fossil record.  I summarize a number of hypotheses about how life may have started on earth.  Earth's Early History is an activity where students use the text to learn more about early earth.  

If there is time, I may add the following topics:  microfossil evidence, body plans/homeobox genes,  radioactive decay, Analyzing Amino Acid Sequences. ​

Darwin's Darkest Hour eludes to illness among his children.  Several of Darwin's children had been sick/died early in life.  The Darwin family tree shows that Darwin and his wife were first cousins and students now understand that this can result in undesirable, recessive traits being inherited....which may have been the reason for his children's health issues.

The Presentation and Student Notes files are available here. ​