Chapter 4 Speciation and Phylogeny

Chapter 4 Speciation and Phylogeny - Chapter 4: Speciation...

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Chapter 4: Speciation and Phylogeny What are species? - Microevolution refers to how populations change under the influence of natural selection and other evolutionary forces - Macroevolution refers to how new species and higher taxa are created - Species can usually be distinguished by their behavior and morphology o Chimpanzees and gorillas are similar in many ways They both are tailless, bear weight on their knuckles when they walk, and defend territories o However, they are also different Chimps are smaller, gorillas have smaller testes, and gorillas have a fin of bone on their skulls while chimps have rounded skulls Chimps use tools, gorillas beat their chests while chimps flail branches, and gorillas live in smaller groups o There are no intermediate species between them o There is little problem identifying a particular specimen from its phenotype But biologists are much less certain about how species should be defined because they don’t agree on why they exist - There is a lot of controversy about the processes that give rise to new species and the processes that maintain established ones The Biological Species Concept - This concept defines a species as a group of interbreeding organisms that are reproductively isolated from other organisms o Reproductive isolation means that members of a given group of organisms do not mate successfully with organisms outside the group - Successful mating leads to gene flow, which tends to maintain similarities among members of the same species o Gene flow tends to make the members of a species evolve as a unit - Reproductive isolation prevents species from genetically blending The Ecological Species Concept - Critics of the biological species concept believe that gene flow is neither necessary nor sufficient in maintaining species boundaries o Instead, they believe that selection plays an important role in preserving the boundaries between species - Medium and large ground finches often interbreed, but they have not yet merged into a single species because these two species represent two of the three optimal beak sizes for ground finches o These are based on the types of the seeds of available; hybrids are selected against because their beak sizes fall in the “valleys” of the selective “peaks” - Also, there are other butterflies with populations that are separate but never interbreed - Another testament to the ecological species concept is the existence of asexual organisms The Origin of Species - Speciation is difficult to study empirically
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o New species evolve too slowly for any single individual to study the entire process, but too rapidly for the process to be recorded in the fossils Allopatric Speciation - If geographic or environmental barriers isolate part of a population, and selection favors different phenotypes in these regions, then a new species may evolve o This is called allopatric speciation - If birds became separated by a large body of water for a long period of time, then they would
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This note was uploaded on 04/21/2009 for the course ANTH 200Lg taught by Professor Yamashita during the Fall '07 term at USC.

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Chapter 4 Speciation and Phylogeny - Chapter 4: Speciation...

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