The theory of common descent states that every organism on the Earth came from a common ancestor in the past. The organisms which are more closely related have a common ancestor in the near past. Through evolution, the ancestors give rise to different species based on their adaptations. However, many genetic similarities can be seen in these organisms which tell that they might have had a common ancestor in the past.
Diversifying or disruptive selection increases genetic variance when natural selection selects for two or more extreme phenotypes that each have specific advantages.
