Why should natural selection reinforce reproductive isolation? Can species be formed in ways other than geographic isolation? Evolution and Its Many Forms Today we continue a three-lecture sequence on biological, or organic, evolution. Evolution is a unifying theme of this course, and the concept of evolution is relevant to many of our topics. The word "evolution" does not apply exclusively to biological evolution. The universe and our solar system have developed out of the explosion of matter that began our known universe.
Chemical elements have evolved from simpler matter. Life has evolved from non-life, and complex organisms from simpler forms. Languages, religions, and political systems all evolve. Hence, evolution is an appropriate theme for a course on global change.
The core aspects of evolution are "change" and the role of history, in that past events have an influence over what changes occur subsequently. In biological evolution this might mean that complex organisms arise out of simpler ancestors - though be aware that this is an over-simplification not acceptable to a more advanced discussion of evolution.
A full discussion of evolution requires a detailed explanation of genetics, because science has given us a good understanding of the genetic basis of evolution. It also requires an investigation of the differences that characterize species, genera, indeed the entire tree of life, because these are the phenomena that the theory of evolution seeks to explain. We will begin with observed patterns of similarities and differences among species, because this is what Darwin knew about.
The genetic basis for evolution only began to be integrated into evolutionary theory in the 's and 's. We will add genetics into our understanding of evolution through a discussion activity. Definitions of Biological Evolution We begin with two working definitions of biological evolution, which capture these two facets of genetics and differences among life forms. Then we will ask what is a species, and how does a species arise? Definition 1: Changes in the genetic composition of a population with the passage of each generation Definition 2: The gradual change of living things from one form into another over the course of time, the origin of species and lineages by descent of living forms from ancestral forms, and the generation of diversity Note that the first definition emphasizes genetic change.
It commonly is referred to as microevolution. The second definition emphasizes the appearance of new, physically distinct life forms that can be grouped with similar appearing life forms in a taxonomic hierarchy. This lists the logos of programs or partners of NG Education which have provided or contributed the content on this page. Powered by. Speciation is how a new kind of plant or animal species is created. Speciation occurs when a group within a species separates from other members of its species and develops its own unique characteristics.
The demands of a different environment or the characteristics of the members of the new group will differentiate the new species from their ancestors. The finches are isolated from one another by the ocean. Over millions of years, each species of finch developed a unique beak that is especially adapted to the kinds of food it eats.
Some finches have large, blunt beaks that can crack the hard shells of nuts and seeds. Other finches have long, thin beaks that can probe into cactus flowers without the bird being poked by the cactus spines. Still other finches have medium-size beaks that can catch and grasp insects.
This is called allopatric speciation. There are five types of speciation: allopatric, peripatric, parapatric, and sympatric and artificial. Allopatric speciation 1 occurs when a species separates into two separate groups which are isolated from one another.
A physical barrier, such as a mountain range or a waterway, makes it impossible for them to breed with one another. Each species develops differently based on the demands of their unique habitat or the genetic characteristics of the group that are passed on to offspring. When Arizona's Grand Canyon formed, squirrels and other small mammals that had once been part of a single population could no longer contact and reproduce with each other across this new geographic barrier.
They could no longer interbreed. The squirrel population underwent allopatric speciation. Today, two separate squirrel species inhabit the north and south rims of the canyon. On the other hand, birds and other species that could easily cross this barrier continued to interbreed and were not divided into separate populations.
When small groups of individuals break off from the larger group and form a new species, this is called peripatric speciation 2. As in allopatric speciation, physical barriers make it impossible for members of the groups to interbreed with one another. The main difference between allopatric speciation and peripatric speciation is that in peripatric speciation, one group is much smaller than the other. Unique characteristics of the smaller groups are passed on to future generations of the group, making those traits more common among that group and distinguishing it from the others.
In parapatric speciation 3 , a species is spread out over a large geographic area. Although it is possible for any member of the species to mate with another member, individuals only mate with those in their own geographic region. Darwin, C. London, UK: John Murray, Feder, J. Genetic differentiation between sympatric host races of Rhagoletis pomonella. Nature , 61—64 Funk, D.
Isolating a role for natural selection in speciation: Host adaptation and sexual isolation in Neochlamisus bebbianae leaf beetles. Evolution 52 , — Maan, M. Mechanisms of species divergence through visual adaptation and sexual selection: Perspectives from a cichlid model system. Current Zoology 56 , — Mallet, J. Space, sympatry and speciation. Journal of Evolutionary Biology 22 , — Mani, G.
Mutation order — A major stochastic process in evolution. Mayr, E. Systematics and the Origin of Species. The Evolutionary Synthesis. Niemiller, M. Recent divergence with gene flow in Tennessee cave salamanders Plethodontidae: Gyrinophilus inferred from gene genealogies. Molecular Ecology 17 , — Nosil, P. Host-plant adaptation drives the parallel evolution of reproductive isolation. Nature , — Ecological explanations for incomplete speciation.
Divergent selection and heterogeneous genomic divergence. Molecular Ecology 18 , — Panhuis, T. Sexual selection and speciation. Ramsey, J. Pathways, mechanisms and rates of polyploid formation in flowering plants. Annual Review of Ecology, Evolution, and Systematics 29 , — Ritchie, M.
Annual Review of Ecology, Evolution, and Systematics 38 , 79— Rundle, H. Ecological speciation. Ecology Letters 8 , — Schluter, D.
Ecology and the origin of species. Evidence for ecological speciation and its alternative. Science , — Seehausen, O. Speciation through sensory drive in cichlid fish. Turner, T. Genomic islands of speciation in Anopheles gambiae. PLoS Biology 3 , e On the origin of species by natural and sexual selection. Via, S. Sympatric speciation in animals: The ugly duckling grows up.
The Hardy-Weinberg Principle. Evolution Introduction. Life History Evolution. Mutations Are the Raw Materials of Evolution. Speciation: The Origin of New Species. Avian Egg Coloration and Visual Ecology. The Ecology of Avian Brood Parasitism. The formation of new biological species is called speciation. Speciation is a result of:. The diagram illustrates what could happen to populations of animals, which become geographically isolated.
Once two groups are isolated different mutations occur in each group.
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