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22 23 sPeCiation dont play with those children, Rose When two or more groups of a species are separated and evolve in different directions so far that they can no longer breed with one another, scientists talk of speciation, the creation of new species. Speciation is often precipitated by the isolation of and subsequent readaptation of a part of the population. In the case of mankind it seems likely that events created a selection pressure. Two short ancestral ape chromosomes fused together into a new chromosome 2 in a single individual and in an isolated group below. Chimpanzees today still have the original 24 chromosomes. Darwin stuggled to explain how new species evolved from a single ancestral species when no physical isolation or barrier was involved allopatric speciation. In fact, differing behavior and inclinations in subpopulations can be all that is required for them to genetically isolate themselves. A useful model is that of cichlid fish. In a population frequenting two favorable habitats separated by a barren area, fish inclined to remain within the favorable habitats stand a better chance of survival. Over time natural selection takes the two populations in different directions until they become subspecies and then entirely separate species, unable to interbreed. Opposite and above Speciation caused by isolation. Opposite The ape ancestor of humans becomes separated by a huge rift. A single mutation in the isolated group fuses two chromosomes together 6 millions years ago resulting in the creation of a new species. Above Chimapanzee ancestors play together across a young Congo river. The Congo widens, separating two groups which evolve into modern toolwielding common chimpanzees and the sexobsessed Bonobo chimpanzees. Above Speciation in a pond. Fish evolve that prefer living under lily leaves. A new area of lilies appears across the pond. The fish show no interest in crossing the barren area between the two areas, so each evolves separately. Above Speciation in a mixed population. A varied species, with large, small, light and dark fish, begin to develop sexual preferences for their own size and colour. Eventually two distinct species evolve.
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