Evolution Question 6
6. In a species, the weight of newborn ranges from 2 to $5 kg$. $97 %$ of the newborn with an average weight between 3 to $3.3 kg$ survive whereas $99 %$ of the infants born with weights from 2 to $2.5 kg$ or 4.5 to $5 kg$ die. Which type of selection process is taking place?
[2019]
(a) Directional selection
(b) Stabilising selection
(c) Disruptive selection
(d) Cyclical selection
Show Answer
Answer : b
Hints & Solution
(b) Stabilising selection is a type of natural selection in which the population mean stabilises on a particular non-extreme trait value. This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time. The result of stabilising is the over-representation in a specific trait. For example, human birth weight, the number of eggs a bird lays, and the density of cactus spines. The given data shows stabilising selection as most of the newborn having average weight between 3 to $3.3 kg$ survive and babies with less and more weight have low survival rate.
