Speciation- the evolution of new species We now know that evolution is simply the accumulation of genetic changes in a population which are a result of random mutations and natural selection. However, this process by itself is not able to bring about the evolution of a new species! What is a species? We can usually tell one species from another by how they look. For example in the picture on the left we have different species of hominoids which mark different stages in the evolution leading to modern man (Homo Sapien Sapien). The thing that makes these individuals different species is not their different appearances but their incapability to reproduce with one another. A species is defined as a population of similar organisms which are able to interbreed to make viable, fertile offspring. Some species such as the horse and donkey are closely related. They can interbreed to make viable offspring but the offspring (mules) are all sterile and can’t reproduce their own young. Speciation Speciation is defined as the evolutionary process, mainly as a result of natural selection, which results in the formation of a new species. This process requires mutations and natural selection but it also requires one more key ingredient, reproductive isolation. This is almost always provided by geographical isolation. There are two reasons this is so important. First, isolation reduces the size of the population, so that single adaptive mutations can have a larger effect on the gene pool of a population. Second, it stops the mixing of genes between populations which will undermine the genetic differences which are accumulating as a result of mutations and natural selection. A perfect example of the process of speciation can be found in the Galapagos island finches. View Power point lesson 4 www.mrlongmanscience.weebly.com Speciation has also been demonstrated in the laboratory on drosophila or fruit fly. These experiments, which were done in the 1980’s, put it beyond doubt that the origin of species is indeed through the process of natural selection of adaptive mutations in reproductive isolation. Interestingly, in these experiments it was found that after a relatively short period of time. The two populations of fruit fly chose not mate with each other even though they could produce viable offspring. Therefore, reproductive isolation was achieved before they were genetically distinct species. In conclusion the 3 requirements for speciation are 1. Reproductive isolation 2. Mutations 3. Natural selection.