Speciation

A group of organisms that share similar characteristics and can reproduce with each other to produce offspring is called Species .

• During evolution when a new species is formed, we call it Speciation .
• Once a new species is formed, the organisms can only reproduce with others in the same species.
• They cannot biologically reproduce with organisms in older species.

Consider the following;

• Here if you notice, a beetle of one population entered another population and reproduced with the organism of that population. 
• So there was a movement of genes from one population to another.
• This is called Gene Flow .
• This was possible because the populations are only partly separated, not completely.

But if,

• Here, the river has separated the populations even further.
• Since the individuals of different populations cannot mate easily, gene flow between them will decrease.

Now consider a third situation:

• Here, during reproduction or due to genetic drift , a new variety was introduced into the populations.
• The eagles replacing crows altered the natural selection of beetles in one population.
• Thus genetic drift and natural selection together resulted in 2 populations of beetles that are different from each other and are unable to reproduce even if they met.
• This is the very essence of Speciation .

Other possible ways speciation can take place in:

• DNA changes resulting in changes in the number of chromosomes , so germ cells cannot fuse.
• New genetic variation resulting in mating of green females only with green males not red males. This further results in an increase in the population of green beetles.