22.214.171.124 Natural Selection
Describe how evidence led Darwin to develop the theory of natural selection and common descent to explain evolution.
Use scientific evidence, including the fossil record, homologous structures, and genetic and/or biochemical similarities, to show evolutionary relationships among species.
Recognize that artificial selection has led to offspring through successive generations that can be very different in appearance and behavior from their distant ancestors.
Explain why genetic variation within a population is essential for evolution to occur.
Explain how competition for finite resources and the changing environment promotes natural selection on offspring survival, depending on whether the offspring have characteristics that are advantageous or disadvantageous in the new environment.
Explain how genetic variation between two populations of a given species is due, in part, to different selective pressures acting independently on each population and how, over time, these differences can lead to the development of new species.
MN Standard in Lay Terms
The concept of evolution first proposed by Darwin in his book Origin of Species describes change in species over time. This change is attributed to the theory of natural selection. This theory states that over time and under different environmental conditions, different individuals will be more likely to survive the environmental conditions and live long enough to produce offspring and pass on those genes. Over long periods of time and as the environment changes, this leads to many changes within the gene pool of the population so that it becomes substantially genetically different from the original population and this can lead to a new species.
Change over time in the genotype of a species in reaction to environmental changes leads to change in the gene pool of the species. Over long periods of time, the species' genotype (and resulting phenotype) changes so much that the final species is substantially different from the original species.
MN Standard Benchmarks
126.96.36.199.1 Describe how evidence led Darwin to develop the theory of natural selection and common descent to explain evolution.
188.8.131.52.2 Use scientific evidence, including the fossil record, homologous structures, and genetic and/or biochemical similarities, to show evolutionary relationships among species.
184.108.40.206.3 Recognize that artificial selection has led to offspring through successive generations that can be very different in appearance and behavior from their distant ancestors.
220.127.116.11.4 Explain why genetic variation within a population is essential for evolution to occur.
18.104.22.168.5 Explain how competition for finite resources and the changing environment promotes natural selection on offspring survival depending on whether the offspring have characteristics that are advantageous or disadvantageous in the new environment.
22.214.171.124.6 Explain how genetic variation between two populations of a given species is due, in part, to different selective pressures acting independently on each population and how, over time, these differences can lead to the development of new species.
See this page.
Species evolve over time. Evolution is the consequence of the interaction of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutations and recombination of genes, (3)a finite supply of the resources required for life, and (4) the ensuing selection by the environment of these offspring better able to survive and leave offspring (pg 185)
- AAAS Atlas:
See Benchmarks below
Molecular evidence substantiates the anatomical evidence for evolution and provided additional detail about the sequence in which various lines of descent branched off from one another. 5F/2
The basic idea of biological evolution is that the earth's present day species developed from earlier distinctly different species 5F/1
Life on earth is thought to have begun as simple, one celled organisms about 4 billion years ago....Once cells with nuclei developed about a billion years ago, increasingly complex multicellular organisms evolved. 5F/8
Modern ideas about evolution provide a scientific explanation for the history of lif eon earth as depicted n the fossil record and in the similarities evident within the diversity of existing organisms.5F/7
Evolution builds on what already exists, so the more variety there is, the more there can be in the future...........5F/9
Natural selection provides the following mechanism for evolution: Some variation inheritable characteristic with every species; some of these characteristics give individual an advantage over others in surviving and reproduction...... pg 125
Inheritable characteristics can be observed at molecular and whole organism levels in structure, chemistry, or behavior......... pg 125
Natural selection leads to organisms that are well suited for survival in particular environments....... pg 125
Framework for K-12 Science Education
Genetic information, like the fossil record, also provides evidence of evolution. DNA sequences vary among species, but there are many overlaps; in fact, the ongoing branching that produces multiple lines of descent can be inferred by comparing the DNA sequences of different organisms. Such information is also derivable from the similarities and differences in amino acid sequences and from anatomical and embryological evidence. 12LS4.A
Natural selection occurs only if there is both (1) variation in the genetic information between organisms in a population and (2) variation in the expression of that genetic information—that is, trait variation—that leads to differences in performance among individuals. The traits that positively affect survival are more likely to be reproduced and thus are more common in the population. 12LS4.B
Natural selection is the result of four factors: (1) the potential for a species to increase in number, (2) the genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for an environment’s limited supply of the resources that individuals need in order to survive and reproduce, and (4) the ensuing proliferation of those organisms that are better able to survive and reproduce in that environment. Natural selection leads to adaptation—that is, to a population dominated by organisms that are anatomically, behaviorally, and physiologically well suited to survive and reproduce in a specific environment. That is, the differential survival and reproduction of organisms in a population that have an advantageous heritable trait leads to an increase in the proportion of individuals in future generations that have the trait and to a decrease in the proportion of individuals that do not. Adaptation also means that the distribution of traits in a population can change when conditions change.
Changes in the physical environment, whether naturally occurring or human induced, have thus contributed to the expansion of some species, the emergence of new distinct species as populations diverge under different conditions, and the decline—and sometimes the extinction—of some species. Species become extinct because they can no longer survive and reproduce in their altered environment. If members cannot adjust to change that is too fast or too drastic, the opportunity for the species’ evolution is lost. 12LS4.C
Common Core Standards
Math standards can be easily incorporated into this topic.
Minnesota Math 126.96.36.199 Make reasonable estimates and judgments about the accuracy of values resulting from calculations involving measurements.
Minnesota Math 188.8.131.52. Design simple experiments and explain the impact of sampling methods, bias and the phrasing of questions asked during data collection.
This standard can be addressed with all data collection methods Statistical analysis and Graphing can be done -
Common Core Language Arts: Students can write a laboratory report in the proper form and using their knowledge of technical writing skills. Common core standards addressed:
RST.9-10.1. Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.
RST.9-10.2. Determine the central ideas or conclusions of a text; trace the text's explanation or depiction of a complex process, phenomenon, or concept; provide an accurate summary of the text.
RST.9-10.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
Language - Social Studies
RSL - History Social Studies -
(6) Compare the point of view of two or more authors for how they treat the same or similar topics. including which details they include and emphasize in their respective accounts.
"Darwin and other authors of the time such as Lamarck can be analyzed as to their perspectives and interpretations."
Unfortunately, people have many misconceptions about evolution. Some are simple misunderstandings; ideas that develop in the course of learning about evolution, possibly from school experiences and/or from the media. Other misconceptions may stem from purposeful attempts to interfere with the understanding of evolution.
Students have been asked to wash their hands with antibacterial soap for several months now. There are organisms in the classroom which are handled frequently so students are requested to wash with a soap that contains "triclosan". Students read the label on the back. As it turns out the antibacterial soap kills 99.9 percent of bacteria. That starts the class thinking. Who then, is left? Who are the point one percent of bacteria that are not killed by the triclosan in the soap and how many bacteria is that? As students discuss the possibilities they come to the conclusion that the one percent left are those that are not easily killed or that have some natural resistance to the antibacterial soap products. However, now they no longer have competition and the population is no longer held in check by this competition. Have we actually changed the system by selecting for an "antibacterial soap" resistant bacteria?
Students select antibacterial products (soap, disinfectents, contact lens solutions, etc) to see which is the most effective at stopping bacterial growth. (NSE stadard 184.108.40.206)
Now students ask: How does this apply to a hospital setting? Are the bacteria more resistant in a hospital setting. This time they go to the literature to find their information. The discussion continues. Why do bacteria evolve so much more quickly than other organisms? Does this make them more adaptable? The discussion continues . . . . . and may include other settings where people interact.
Suggested Labs and Activities
220.127.116.11.1 Galapagos Experience
The animals of the Galapagos islands were instrumental in helping Darwin compose his theory of evolution. In the middle of the ocean, on islands created by volcanos, the animals were so isolated that they evolved into species seen no where else in the world. There were blue footed boobies, penguins, Galapagos Tortoises, Sea Iguanas, Land Iguanas and others. Students choose and research one of the animals. Students learn about the Galapagos in a variety of ways including documentary (reference) and literature in a "web quest". They then pursue the following: When Darwin saw it, what was his first response? Where do you think the animals ultimately originated from and how did it get to this remote island. What were the challenges that it faced, what were the selective pressures? How are they now different from the original populations? In other words, what did Darwin observe and how did he come up with his theory after those observations.
18.104.22.168.2 Cladogram Construction
Knowledge of cladograms and constructing cladograms from either known species evolutionary relationships or fictional ones (eg. dragons) can demonstrate evolutionary connections between organisms. With a little art added to the project it can also be a great deal of fun and appeal especially to kinesthetic and artistic learners
22.214.171.124.2. Barbellus Fossils shows how fossils are evidence of evolution. Using fictional fossils, students analyze the anatomical differences of the fossils found in different layers of rocks. They put together an evolutionary tree to
Other evidence of evolution: Comparing DNA, homologous structures, embryological pictures.
126.96.36.199.3 Dog Breeding
Students choose their favorite dog breed and then research a pedigree to see how dogs were chosen for that breed. What is the breed standard and what type of dogs are chosen as champions and breeders. Trace a pedigree back as far as possible and propose the artificial selection that selected for those traits. Would these traits be selected for or against if this were natural selection? Extension, students can interview owners of this breed and look for commonalities in behavior, physical attributes and disease susceptibility.
188.8.131.52.4 Concept of Hardy Weinberg Analysis without statistics.
Fishy Frequencies - Can be done with simple arithmetic using the Hardy Weinberg equation or done as a discussion based on the premises of Hardy Weinberg (example: large population, no migrations, no selection etc).
184.108.40.206.5 Bean Lab
Two environments are created on tables with fabric samples (black forest - black fake fur and red plains - smooth red multicolored fabric). Red, white and black beans (available at the grocery store) are spread out on the fabric samples. The students are given one of three tools - plastic fork, plastic spoon, plastic knife. The students hunt for beans in their environment and then those with the most beans survive while the others die. The ones that die then become the offspring of the survivors (with the same eating tool). At the end of the game one tool reigns triumphant in each environment, one bean survives in each environment but neither are the same. This activity does an excellent job of demonstrating survival of the fittest and natural selection in two different environments.
220.127.116.11.6 Rat Speciation
In a scenario where rats on a shipwreck all end up on different islands. Students are given the descriptions of the different island (i.e. mountainous, tropical, desert, etc). They then draw the rat adaptations to survive in that particular environment. The different kinds of food on each island can also be incorporated.
Evolution is woven throughout the teaching of biology. Evolution can be taught effectively through inclusion of concepts in chemistry, cells and genetics (including DNA), and in the context of the nature of science
Respect for religious viewpoints and assurances that students do not have to choose one viewpoint or the other has met with success in teaching evolution. However students should understnad that any "controversy" surrounding the reality of evolutionary change is a cultural phenomenon, not one that exists within the mainstream science community.
It is important to help students understand the immense amount of time that evolution requires.
Teachers of science need to have confidence in their scientific understanding (not belief) in evolution. These are some ideas to research and have resources that support your understanding:
Science is based on observation, experimentation and the collection and analysis of data. This is "evidence". Religion is based on faith and is not based on scientific evidence. When teaching science it is imperative to teach that science must involve the collection and analysis of data. In religion this is not the case nor should it be. These are two different ways of viewing the world and they do not have to compete.
The lessons and video clips are from a series of DVD's from PBS "Evolution"
Evolution and the Nature of Science website with lots of evolution activities and background information
Book: Teaching About Evolution and the Nature of Science. This has good information for teachers who are concerned about the evolution controversy and asked why they don't teach "other viewpoints". Frequently Asked Questions About Evolution and the Nature of Science. It also has a some good activities. It can be downloaded free.
- Evolution - The process of change over time based on change in the genetic composition of a population.
- Artificial selection - selective breeding of plants and animals to promote the occurrence of desirable traits in offspring
- Competition - When organisms attempt to use the same limited ecological resource in the same place a the same time.
- Selective Pressure - Environmental conditions leading to differential fitness based on the value of a particular trait.
- Charles Darwin - A naturalist who developed the theory of natural selection to explain how biological evolution occurs. His theory explains how modern organisms evolved over long periods of time via descent with modification.
- Adaptation: Heritable characteristics that increases an organism's ability to survive and reproduce in an environment.
- Natural Selection - Process by which organisms that are most suited to their environment survive and reproduce more efficiently and effectively than those not as well suited.
- Environmental changes - Changes in the abiotic and/or biotic factors in which the organism lives. These changes challenge the ability of the organism to survive as they obtain food, maintain homeostasis and the ability to reproduce.
- Genetic Variability - The diversity and proportion of diversity of the different genes in the gene pool which contribute to the varying phenotypes of the population.
Social studies lessons may occasionally focus on evolution. For example: the The State of Tennessee v. Scopes Trial, informally known as the Scopes Monkey Trial-was a landmark American legal case in 1925 in which high school biology teacher, John Scopes, was accused of violating Tennessee's Butler Act which made it unlawful to teach evolution. It might be interesting for students to combine their knowledge of science and social studies and study the historical aspects of the trial.
Assessment of Students
Several cartoon concepts for formative assessments on several evolution concepts.
Summative In the North there are wolves. Some wolves have thick coats and some have thin coats. A series of very bad winters (30 below zero for long periods of time). Which wolves will be left and what would their offspring look like?
Students should answer that only the thick furred wolves will survive and since genetics shows that children inherit their genes from their parents, it is reasonable to assume that they will pass on the thick coat genes and that the population will have evolved to have thicker coats.
Summative. Triclosan is an antibacterial agent in soap that kills 99.9 percent of bacteria. What happens to the other .1 percent of bacteria and who are these bacteria? Could this be an example of evolution? (see 18.104.22.168)
The bacteria that are left are in all likelihood, the ones that are resistant to triclosan. If the others are destroyed, they will have less competition and can reproduce more easily. This would be evolution as antibiotic resistant bacteria are repeatedly selected for.
Summative. Compare and Contrast the processes of artificial selection and natural selection.
Both artificial and natural selection change the hertitable traits of a population or species over time. In both cases, organisms with certain traits are more likely to survive and reproduce than organisms with other traits. In artificial selection a breeder or farmer decides which organisms reproduce . In natural selection, environmental conditions determine with organisms reproduce.
Assessment of Teachers:
1. What is the definition of species? Is this a soft or hard definition and how do you explain that some species can cross breed.
A species has been defined as populations that do not naturally interbreed. The dividers include such things as time, location and behavior but they also can include more permanent dividers such as physical and/or genetic changes that interfere with cross reproduction at either prezygotic or post zygotic stages of reproduction. Some of these separational factors can be over-come while others are more permanent. Biological species (Ernst Mayr) appears to be a continuum of genetic diversity. The further apart on the evolutionary scale that the species are, the more likely that the division between the species is insurmountable. The closer the species on the evolutionary scale, the more likely that they can interbreed. (Example: Species of tortoises on the Galapagos - can interbreed and hopefully the offspring are fertile (see George); Tiger and Lion can interbreed but the offspring are different from either parent; Donkey and Horse - can interbreed but the offspring is sterile)
2. How confident are you in teaching evolution? How can teachers become more comfortable in teaching evolution? Where can you get more resources to support the teaching of evolution?
3. What is the Hardy Weinberg Law and how can it help teach evolution?
Although students do not need to be able to manipulate this equation, teachers should understand it in order to adequately explain the concept of evolution. It is a means of measuring the diversity of the population and should remain constant as long as the following do not happen: selective breading, mutation, migration, etc. The results of the Hardy Weinberg equation explain much of how these factors change the proportion of genes in a population and that evolution is based more on a "reproportion of the alleles already in the population" than on any other factors.
This is a good way for teachers to check their own understanding of evolution
Struggling and At-Risk
A proportion of these students have difficulty with race and religion and may come from families with many of these same issues. It is critical that they are given the opportunity to discuss these issues openly without fear of recrimination so that they can work through them. Two ways to accomplish this is for students to a keep a journal and/or meet in out of class time forums with leaders in the school and the community to discuss their concerns.
These students always want to see relevance. The vingette above gives the opportunity to shows an example of modern day evolution.
The vocabulary in evolution can be especially subtle. The use of word walls can help. Care must be taken that students keep track of the vocabulary and that the "organism" and the "population" focus is very, very clear. Evolution can only be understood by understanding that the population changes and not the individual organism. This distinction can be a problem for English language learners as in language it can be subtle.
Student can become very involved in molecular evolution. This may include a study of the origin of human beings following the mitochondrial DNA of women back in time. The data is available on the internet and appears to link all races back to several women from Africa. Students can access some of these sequences and see if they can trace the evolutionary path back for themselves.
Students can also analyze the sequence of DNA coding for different proteins such as hemoglobin or histone proteins from one organism to the other in order to trace biological species. Today the classification system is changing due to DNA technology. This has been seen recently with a variety of bird species and it has been shown that phylogeneticly they been sorted incorrectly. Example: the vulture is not a raptor but rather fits in with the storks.
Changes in population variation based on Hardy Weinberg principles can include mathematically and or real life scenarios.
There may be some religious objection to the teaching of evolution. This is best handled with patience and a respect for the viewpoint of others. If taught properly with appropriate background knowledge and well grounded examples, the objections can be greatly minimized. Warning: Don't turn this into a confrontation.
A particularly well received concept with multi-cultural students is the Human mitochondrial study which links all races to a common few women in Southern Africa. This work provides compelling evidence that all humans come from a common ancestry and that there is truly no such thing as "race" but rather there are "families" and we are all related. The teaching of this concept has done much to combat many of the racial issues in schools and rather shows how our origins are all the same.
Although abstract, many of these concepts can be easily grasped through the use of "manipulatives". Beans, beads, cards etc, work well to make these concepts tangible and practical for all students but especially for Special Education students who have some difficulty with the process of learning.
Administrators will see a variety of discussion and activity. They may see students standing around a table with a fuzzy black covering and another group around a smooth flowered cover as they are excitedly hunting beans with varying eating utensils. They might be having a spirited discussion involving the merits of various dog breeds. Ultimately, however, they are exploring the concept of variation within a population and the re-assortment of genes as populations adapt to changes in their environment.
When hiring new staff, administrator should inquire as to the teacher's approach to the teaching of evolution. Additionally, science teachers of other science disciplines should be asked how they would respond to students inquiries about evolution.
Parents may occasionally object to the teaching of evolution based on religious principles. This is best handled by respecting their beliefs but telling them that you are teaching their children what the concept is. They need to know about this to be educated and knowledgeable in science. They may then choose whether they wish to believe it or not. It is important to respect the viewpoints of others and not to overly force the issue. On the other hand, if taught in a logical manner, very few objections seem to appear.