This article looks at the fossil record and provides four specific examples of evolutionary changes that have been directly observed. Vertebrate legs evolved lobe-finned fish; there are homologies between legs and their fins. The evolution of birds can be seen by looking at bone similarities between birds and dinosaurs. Slight changes to the reptilian-mammal skulls shows a strong evolutionary relationship. Evidence in the whale skeleton suggests that whales evolved from land-dwelling creatures (their closest relative is the hippo). This article is excellent for providing specific evidence which shows direct links, and can help students understand how the fossil record is an essential tool to discover how different organisms are related. Students will read this article and provide specific examples from the text which supports this theory.
When humans cause species to go extinct, the effects ripple throughout the surrounding ecosystem
Alex Szabo's insight:
An article that describes how human populations are encroaching on environmental habitats, which results in a fragmentation of the forest and extinctions. It gives the specific example of the toucan; their numbers are so low, the fruit they typically feed on has evolved so that other birds can now spread its seed. It gives specific reasons how humans are negatively affecting their environment, and shows why conservation is so important, because an ecosystem is a complex relationship. This article is short, and uses simple english; it is a great tool for students to pull out evidence and cite how humans are affecting the natural world.
California salamanders are a case of evolution in action. Video from PBS.
Alex Szabo's insight:
This shows a specific case of differences among salamanders in California. This is a famous evolutionary example of "speciation in action;" as the salamanders moved through the peninsula, they display incremental changes as a result of different selection pressures. Even though species who live in neighboring areas can mate, enough changes have built up so that salamanders who live on the extreme ends. Also see "The Salamander's Tale" in The Ancestor's Tale , page 289.
*this video can be used as a supplement to the Dawkins text, which explains the same theory but in a different way. Multiple mediums is important to help all students understand a concept.
Richard Dawkins traces our evolutionary history; we travel backwards through time, and meet up with our ancestors, who join along for the journey to the beginning. Each ancestor who meets with us tells a story that helps explain evolutionary concepts in a fun and interesting way. An evolutionary "Canterbury Tales," it helps the reader understand how species form, compete, and diverge over time, and even tackles the origin of life and the formation of the first cell, the "orignal replicator." Sections of note: The Beaver's Tale (on extended phenotype, p. 186), The Marsupial Mole's Tale (on convergent evolution, p. 227), The Peacock's Tale (on sexual selection, p. 263), The Salamander's Tale (on Speciation, p. 299).
Potential Difficulties: Advanced Vocabulary and reading level, requires certain background understandings of evolution which may not be realized
Dawkins, R. (2004). The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution. Houghton Miffin, Boston
The Hardy-Weinberg Equilibrium Model can help students understand the benefits of variation in a population, and how the flow of genes will affect populations. It takes certain assumptions - it is extremely theortetical - but it is based on simple math, and leads students to realize that evolution, in its most general sense, is based on gene pool frequencies. This article combines math and science, and guides the reader with easy to follow text. The article also links essential vocabulary terms to their definitions, to assist in comprehension. Possible problems could arise if students feel threated or have a hard time understanding the math; however, the assumptions and the implications of this equation can be useful for all students to make basic conclusions about gene flow.
This video explains the four basic forces that drive evolution. It uses diagrams that are the same as the berkley.edu evolution website (Evolution 101 - Mechanisms) and should be viewed as a supplement, after students investigate the website. It provides specific examples that exemplify each concept. The content is a bit more advanced, and can be used for students who are conducting additional inquiries.
A great introductory resource that explains the basis of evolution and natural selection; pictures and diagrams make these topics easy to understand. Students can navigate using tabs on the left, and explore the four main mechanisms that drive evolution:
1) Mutation - random changes lead to new benefical traits
2) Gene Flow (Migration) - movement of organisms can affect gene ratios in a populatio, and provides variation
3) Genetic Drift - changes in the gene ratios due to random events
4) Natural Selection - organisms with certain traits will be more successful in a particular environment; organisms who live longer tend to leave more offspring, and their beneficial trait will increase in the population over time
*this text is easy to understand, and pictures help illuminate topics in a very simple language. A great resource for ELL students or those who read at a low level
Richard Dawkins revolutionized the idea of a gene when, in 1979, he proposed organisms are nothing more than "survival machines" whose purpose is to pass on our genes to the next generation. It is a gene-centric view, contrary to the conventional organism/group view; a gene is "selfish" with respect to the fact that it will maximize its odds for survival. Interestingly, even though it appears he claims "selfishness" is an evolutionary advantage, it is the opposite; this concept helps explain altruism and other cooperative aspects of the animal kingdom. Chapters of note are 2 - 4, where he lays out the main ideas for his theory; further chapters expound on the theory, and use this idea to explain interactions between organisms.
Potential Difficulties: advanced vocabulary and reading level, students may confuse an organism being selfish, versus a gene being selfish
Dawkins, R. (2006). The Selfish Gene: 30th Anniversary Edition. Oxford University Press, USA.
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