Question

Question: The subject of modern human variation was framed in lecture as being the result of what three major selective pressures. List these and provide examples that illustrate how these pressures have changed the human gene pool over time.

please answer in 100 word or more

Answer 1

Selective pressures contribute to evolutionary change through natural selection. The three major selection pressures are:-

Stabilizing selection- When selection pressure select against two extremes of a trait, it is known as stabilizing selection. The intermediate form of a trait is selected. One of the examples is birth weight of human babies. If the weight is too low, the baby will be very weak and have health issues and if the weight is too high, it experiences difficulty in passing through birth canal. Hence average birth weight is the only sxenario and is favored.

Directional selection:- This causes a population to evolve towards one end of a trait spectrum. If it is applied to population over time, the traits that are selected for will permanently increase, while trait selected against will be lost. An example is of the fossil records that show the size of black bears decreased during interglacial period of ice age and later increased during glacial period due to directional selection.

Disruptive selection- It favors both extreme traits in a population. It is seen more often in high density population and give rise to two distinct populations. One of the famous examples is finch population observed by Darwin in Galapagos. They exhibited disruptive variation in beak size. This leads to speciation.