The septum pellucidum (Latin for "translucent wall") is a thin, triangular, vertical double membrane separating the anterior horns of the left and right lateral ventricles of the brain.
allopatric speciation: occurs when a population becomes isolated by a geographic barrier, becomes a new species as it accumulates changes by natural selection or genetic drift. Also known as <em>geographic speciation.</em>
sympatric speciation: a new species that may arise as mating and gene flow are reduced between populations that share the same area. In other words, a group of people from the same ancestral population that may evolve differently until they no longer interbreed and develop into a entirely different species.
polypoid speciation: mostly commonly occurs in plants, where an accident in cell division results in extra set of chromosomes. This has been a major source of speciation in the angiosperms. Polypoidity increases biodiversity and a it is a source of new genetic material for evolution.
Both allopatric speciation and sympatric speciation depends on the establishment of reproductive barriers, which prevents gene flow between a new species and its parent species. Reproductive barriers may arise due to geographical, behavorial, psychological or genetic differences which may prevent species to breed successfully with related species.
Adaptive radiation: occurs when a species gives rise to many new species after colonizing a region with diverse habitats. It is a rapid increase in a number of species from a single common ancestor.
