Question

Differentiate between Directional natural selection and Disruptive natural selection. 

Answer 1

If the selection favours small or large-sized individuals, more individuals of that type will be present in the next generation. With continued selection over generation mean size of the population would have changed it. It is directional selection which brings about evolution in the population. In the natural selection, both small size and long sized individuals, natural selection would be disruptive type. It produces two peaks in the distribution of traits that may lead to the development of two different population.

Answer 2

Aspect	Directional Natural Selection	Disruptive Natural Selection
Definition	Favors one extreme phenotype and shifts the population's trait distribution towards that extreme.	Favors both extreme phenotypes and acts against intermediate phenotypes.
Effect on Population Mean	The mean phenotype shifts towards one extreme.	The population may split into two distinct groups, increasing variation.
Role in Evolution	Causes a consistent directional change in traits, promoting adaptation to changing environments.	It can lead to speciation by dividing a population into separate groups if gene flow is prevented.
Frequency of Occurrence	More common, especially when environment gradually changes.	Less common, but important in creating biodiversity.
Example	Shift in beak size in birds towards larger or smaller sizes based on food availability.	A population with individuals having either very dark or very light coloration, but few intermediates.