Keshav Bhatia, Academic Content Writer at Edumarz

Speciation is the process by which new species are formed from the previous ones.

We say that a population has split into two species when it cannot reproduce among each other, even if it does, it is not able to produce viable offspring, the offspring produced are sterile.
This is also known as reproductive isolation.

Let us take the beetle example again, and assume that the beetles will continue growing in a big geographical area with abundant foliage, in these huge beetle populations there will be sub populations of such beetles.
Most reproduction would be within these sub-populations.
Sometimes, an adventurous beetle will go to another sub-population, or maybe a beetle would get carried by a predator and accidentally thrown into a different sub-population.
These beetles will reproduce with the sub-population.

Gene Flow would occur between these partly separated populations this way as the reproduction would result in migrant beetle’s genes spreading and entering these populations.
After all, Gene flow is the migration of genetic material from one population to another.

Let us Imagine that two sub-populations of beetles get almost completely separated by a huge river, and that sub-climates of these regions get slowly different from each other, and predators like crows are eliminated by some natural factor like apex predators or disease in the site of one population.

The green beetle variation will not be selected at the site where the crows have been eliminated(because there will be no evolutionary advantage and red beetles will still make the majority), but it will be selected at the site where the crows are in huge numbers and regularly eat the red beetles.

Over time and over generations, genetic drift will accumulate different changes in these sub populations, and together with natural selection these two populations will start becoming more and more different than each other over generations, until they become so different from each other that if they were to meet, they cannot reproduce with each other and give birth to viable progeny(Reproductive Isolation).

There are other ways through which Speciation can occur like:
1. If there is a severe mutation, that even the number of chromosomes changes, the germ cells of male and female beetles will be unable to fuse with each other.
2. Or such variation occurs that the green female beetles decide not to mate with the red beetles, but mate only with the green males, this will manifest into a strong natural selection for greenness.
Even if a red male beetle shows interest, the green female beetle will not reproduce with it.

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