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.
