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
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 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
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.