Natural selection

In 1857, Charles Darwin introduced the concept of natural selection. We will try to simplify the process and understand what it means. The technical definition is:

The differential reproductive success of pre-existing classes of genetic variants in the gene pool.

What on earth does it mean? View this animation to understand the concept:

A certain creature C gives birth to young every 5 years. But unfortunately, a mutation causes a recessive allele to become dangerous. The offspring having two of these alleles will naturally get the disease. This disease causes the creature to become very weak and tends to be more susceptible to germs. In the generations to come, the allele will be passed on and many will contract the disease. This allele is detrimental to the animal and causes a higher mortality rate (death rate) in the species. Out of say 20 young ones, maybe 3 might die or later the mortality rate might just increase.

If this continues, this allele may cause the extinction of the species. This is where something known as natural selection intervenes.

The reproductive success means how many of the offspring live to reproduce another generation.

Natural selection tries to increase the reproductive success rate. It tries to remove this gene from the gene pool so that the chances of the offspring living long enough to reproduce increases. So, natural selection will try to remove traits that are harmful to the creature and support traits that are useful in terms of reproductivity.

Natural selection helps an organism to adapt to its changing environment. There is a living example bearing the effect of natural selection - the peppered moth.

The soot dis-charged by great factories killed the lichen that grew on tree trunks, leaving the tree trunks bare and dark. The white peppered type was camouflaged on a lichen-covered trunk, but not on a bare lichen-less trunk. Birds began to eat up the white moths. With lesser parents (white moths), the number of offspring began to decrease. This is clearly a decrease in reproductivity. However the moths used the techniques of camouflage to adapt themselves and the black moth population increased. But the underlying process is this - the increase in black peppered moths ensures a larger number of children. A majority of thse might live to give birth to the next generation. This leads to a higher reproduction success rate.

To be more scientific, a process caused an increase in the frequency of the allele, which is responsible for the black colour in the majority of the offspring and a decrease in the frequency of the allele, whichis responsible for the white colour. This process is called natural selection. The removal of the allele for the white pigment form the gene pool helped to adapt as well as increase the reproductive success rate.

TO SUM UP:

While mutation produces variation, selection determines which variants will increase in the population and which will decrease depending on which variants are passed on more . For example, if a certain allele is harmful to the reproductive capability, natural selection will try to remove the variant from the population. Therefore the main criterion is reproductive success. It will try and continue the life of the species as a whole.