How is a sex of new born determined in humans ?

Natural selection is preferential survival and differential reproduction of individuals of a population which possess variations that provide better

adaptability to the existing environment. Peppered Moth of England has two forms, light grey and dark grey. Prior to industrial revolution, tree

trunks in the forests around.

Manchester were light greyish green due to presence of lichens. Most of the Peppered Moth found in the area were light coloured with dark spots

which could not be spotted easily by predator birds. During 1845 to 1890, air pollution killed the lichen flora. The deposition of soot changed the

colour of the tree trunks to blackish one. Peppered Moth of the area also exhibited switch over to melanic or blackish form.

It provided better survival value against dark background. The light grey form largely disappeared as it could be easily spotted by predator birds

and devoured.