Speciation 

BACKGROUND

SPECIATION (the generation of independent lineages)

• Lineages can be considered independent of each other if they do not exchange genetic information.
• Two possible mechanisms for limiting genetic exchange: geographical barriers or biological barriers.
• Geographical barriers are often not permanent, and this is ever more true in the modern world.
• Biological barriers can prevent the coalescence of lineages when geographical barriers are removed.
• Biological barriers can be divided up by considering when they take effect
• Pre-zygotic (pre-mating) barriers prevent the exchange of gametes between individuals.
• Postzygotic barriers result in the death of the embryo or sterility later in its development.
• Pre-zygotic barriers can result from behavioral mechanisms or physiological mechanisms.
• Behavioral mechanisms include things such as courtship displays.
• Physiological mechanisms involve the developmental or biochemical incompatibilities.
• Applied aspects of species definitions 
• Conservation
• Gene exchange between species: escape of transgenes, antibiotic resistance, origin of crop plants, acquisition of disease resistance, etc.
• Origin of new species

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