6 Macroevolution

6 Macroevolution - Speciation Reading: Freeman, Chapters...

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Unformatted text preview: Speciation Reading: Freeman, Chapters 25-26 Many of the figures, and most of my examples, are from Douglas Futumas Evolutionary Biology, an excellent reference if you want to know more about speciation Species Concepts Biological Species are groups of actually or potentially interbreeding individuals that can mate and produce fertile offspring-idea was promoted by Ernst Mayr, an evolutionist who worked on birds. In practice, this applies to most species, but in many cases, it is simply impossible to test whether two species have the potential to interbreed. Phylogenetic A species is a lineage, separate from other such lineages, perpetuated ancestor to descendant, over time. Morphological Morphological criteria are used to define species. Clearly, each school of thought has its strengths and its drawbacks. The biological species concept is great conceptually, but virtually impossible to put into process in most situations. Fossil species, species which do not reproduce in the lab or zoo (the vast majority), and asexual species are sticky issues. The morphological species concept is what most taxonomists actually use in practice, because it is expedient, but it has many disadvantages. It is subjective. Cryptic species, which look identical to humans but are in fact reproductively isolated, are problematic. The phylogenetic species concept is becoming increasingly used-it is most useful when the scientist has a very clear idea what type of lineages they are looking at. Speciation The theory of evolution must explain the origin of new organisms. From the beginning, the origin of species has been a focal point of evolutionary theory. Ironically, Darwin was wrong about the origin of species. He assumed that, given enough time, natural selection would inevitably produce them. This is not actually the case. It takes reproductive isolation. Macroevolution is the origin of new taxonomic groups. Speciation is the origin of new species. With extinction, it is one of two keystone processes of macroevolution. Cladogenesis Cladogenesis, the origin of lineages, is the budding of a new species from a parent species that continues to exist. Cladogenesis promotes biological diversity by increasing the number of species. Although it culminates over thousands or millions of years, cladogenesis is a real event. New species originate by cladogeneis, which is ultimately responsible for the origin of every major group of animals. Why Do We Have Separate Species At All? Sympatric species live in the same place. Without some mechanism preventing allele and gene exchange among sympatric species, distinct species would be impossible, we would probably see a continuum from one form of life to another....
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6 Macroevolution - Speciation Reading: Freeman, Chapters...

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