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'''Speciation''' is the process by which new species arise. Speciation occurs when gene-flow stops between two sub-populations due to geographic or behavioral isolation. During such isolation the gene pool of each sub-population reacts differently to the processes of [[natural selection]] and [[genetic drift]] and and such evolve divergently. If this evolutionary divergence becomes great enough that crosses between individuals from different sub-populations can no longer produce viable offspring each sub-population is considered to be a new species and speciation is said to have occurred.

'''Speciation''' is the process by which new species arise. Speciation occurs when gene-flow stops between two sub-populations due to geographic or behavioral isolation. During such isolation the gene pool of each sub-population reacts differently to the processes of [[natural selection]] and [[genetic drift]] and such evolve divergently. If this evolutionary divergence becomes great enough that crosses between individuals from different sub-populations can no longer produce viable offspring each sub-population is considered to be a new species and speciation is said to have occurred.

==Species==

==Species==

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"a group of [[organism]]s, with similar morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring, and are reproductively isolated from other species." - Jones M. & Gregory J., Biology 2, 2001, Cambridge University Press, ISBN 0-521-79714-4<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref>

"a group of [[organism]]s, with similar morphological, physiological, biochemical and behavioral features, which can interbreed to produce fertile offspring, and are reproductively isolated from other species." - Jones M. & Gregory J., Biology 2, 2001, Cambridge University Press, ISBN 0-521-79714-4<ref>Biology 2, Jones M. & Gregory J., 2001, Cambridge University Press, ISBN 0-521-79714-4</ref>

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===Sympatric speciation===

===Sympatric speciation===

In '''sympatric speciation''' reproductive isolation is achieved by newly diverging species without any geographic barriers to gene flow. Sympatric speciation is certainly the most controversial of the proposed methods with most biologists thinking it plays a minor role and many even questioning if it occurs at all. In recent years examples have of sympatric speciation occruring by host shifting by insects and differnces in flowering time in palms have been presented as strong evidence that multiple species of cichlid fish may have arisen without geographical barriers to gene flow in crater lakes.  

In '''sympatric speciation''' reproductive isolation is achieved by newly diverging species without any geographic barriers to gene flow. Sympatric speciation is certainly the most controversial of the proposed methods with most biologists thinking it plays a minor role and many even questioning if it occurs at all. In recent years examples have of sympatric speciation occruring by host shifting by insects and differences in flowering time in palms have been presented as strong evidence that multiple species of cichlid fish may have arisen without geographical barriers to gene flow in crater lakes.  

The commonest method of sympatric speciation is probably '''[[polyploidy]]'''.  Polyploids contain more than two complete sets of chromosomes in each cell.  This can occur if there is an error in [[meiosis]] (production of gametes) so that a gamete ends up with two copies of each set of chromosomes instead of one copy.  Two of these gametes may fuse to produce an organism that has four sets of each chromosome in their cells, called a '''tetraploid''' organism.

The commonest method of sympatric speciation is probably '''[[polyploidy]]'''.  Polyploids contain more than two complete sets of chromosomes in each cell.  This can occur if there is an error in [[meiosis]] (production of gametes) so that a gamete ends up with two copies of each set of chromosomes instead of one copy.  Two of these gametes may fuse to produce an organism that has four sets of each chromosome in their cells, called a '''tetraploid''' organism.