Keshav Bhatia, Academic Content writer at Edumarz

Reproduction has an inbuilt tendency to produce variation whether it be DNA copying errors during cell division or the variation produced in sexual reproduction.

There are different factors that drive evolution, mainly Natural selection and genetic drift.

We are going to study these factors using the following examples:







So, in the first example, a mutation happens in the Beetle population and a beetle turns green instead of red.
This beetle can pass over its jeans to its progeny and this green gene is dominant so all its progeny are green
Predators like crows cannot see the green beetles in the Green Leaves of the bushes and the green Leaves of other plants, and therefore they eat these beetles less than red ones.


This will result in green beetles having a higher survival chance in the wild the progeny of the green beetles will survive more.


 In the second situation we see that a color variation arises during reproduction but this does not have any relation with natural selection as the color is blue and it does not give the beetel any evolutionary advantage like camouflage advantage in the first example.

Predators like crows can see the blue beetles as well as the red beetles.


As the population expands there are less blue beetles than red ones but an elephant comes by and stomps on their small population and kills most of the beetles, by chance the ones left alive are the blue ones.

Now the beetle population reproduces and expands again and blue beetles are the ones that form the population.


What is common in these situations is that a simple mutation or variation that used to form a minority in the population became the common characteristic of the population, that the frequency of an inherited trait changed over generations.


In the second situation there was no real survival advantage but that elephant’s foot had killed off most of the red population by chance.

What this shows is that accidents in very small populations can change the frequency of some genes in a population. This is the concept of genetic drift which provides diversity without adaptation.

In the third hypothetical situation, the plants in the area the beetles are living in get a disease and start producing less foliage which is also poor in nutrition.
This results in the beetles losing weight due to poor diet and it continues for generations of beetles as long as the plant disease lasts.
After the disease is eliminated, the beetles start eating well again and gain their healthy weight back, as there is no genetic change.

Let us see another example of Natural Selection:

Most collections of moths before the industrialization showed white clothes as the majority of the population.
That all changed after the industrial revolution, but why?

Tree trunks used to be covered with almost white colored lichens in the pre industrial age, and white winged moths were not as visible to the predators as the dark winged moths due to the lack of contrast in color of the white moth and the tree trunk, they got eaten less by predators such as birds and thus, they formed the majority of the population.

After industrialization the lichens died off due to all the soot and pollution and the tree trunks got darker in color too, this caused the white moths to be highlighted/be more visible due to their high color contrast with the dark tree trunks, and predators started catching the white moths more and easier than the dark winged moths.

This is how the frequency of genes changed in this moth population.


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