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Unformatted text preview: Chapter 23: Species and their Formation • 23.1 – What are species? o Most species concepts put forward by biologist aren’t mutually exclusive o About 250 years ago, biologist separated species based on appearance o This type of classification regardless of mating behavior or genetics is called the morphological species concept o Coincidentally, the species that were grouped together based on appearance had similar appearances due to having similar alleles o Main drawback is that not all members of a species look alike, and some species look alike but are different o Such a drawback is obvious in the case of cryptic species, which are two species that don’t interbreed but are morphologically indistinguishable o Evolutionary biologists think of species as branches on the tree of life Known as the lineage species concept Each species has a history that starts with a speciation event o Problem with this concept is that certain instances of speciation take thousands of years to occur, making it hard to decide at the moment whether or not it will occur o Most important part of lineage species concept is reproductive isolation, which is a state when two populations cannot exchange gametes anymore o Biological species concept defines a species as a group of actually or potentially interbreeding natural populations which are reproductively isolated from other groups o The different concepts of species are not incompatible, rather, they emphasize different aspects of the species • 23.2 – How do new species arise? o Gene incompatibilities can produce reproductive isolation in two daughter species o In the Dobzhansky-Muller model, when a species undergoes reproductive isolation, two alleles become fixed at different...
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- Summer '05
- 250 years