Assertion (A) : Darwin showed how even a slow growing animal like an elephant could reach enormous numbers.

Reason (R) : When resources in the habitat are unlimited, each species has the ability to realise its innate potential fully.

The correct option is: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).

Let us analyze both statements to understand why they are true and how the reason correctly explains the assertion:

1. Analysis of Assertion (A):
Assertion (A) states: "Darwin showed how even a slow growing animal like an elephant could reach enormous numbers."
This statement is historically and biologically true. Charles Darwin, in his theory of natural selection, illustrated that if any organism reproduces unchecked without any environmental constraints, its population would grow exponentially. Even for elephants—which are among the slowest-reproducing animals (having a long gestation period and producing few offspring in a lifetime)—their population would theoretically reach millions in a few centuries if all offspring survived and reproduced. This demonstration was crucial to showing that every population has the inherent capacity to overproduce.

2. Analysis of Reason (R):
Reason (R) states: "When resources in the habitat are unlimited, each species has the ability to realise its innate potential fully."
This statement is also biologically true. According to population ecology principles, when resource availability (such as food, space, and shelter) in a habitat is infinite or unlimited, there are no environmental constraints or competition to limit survival and reproduction. Under these ideal conditions, birth rates reach their maximum and death rates reach their minimum, allowing each species to realize its maximum innate potential to grow in number, which is described as exponential or geometric growth.

3. Link between Assertion (A) and Reason (R):
The reason directly explains the assertion. Darwin's observation regarding elephants demonstrates the practical consequence of a species realizing its innate potential for growth. An elephant population can only reach such enormous numbers if we assume an ideal scenario where resources are unlimited, allowing every individual to survive and reproduce to its maximum capacity. Therefore, the capacity to realize this innate potential under unlimited resources (Reason) is the underlying biological principle that explains why even a slow-growing animal could theoretically multiply to massive numbers (Assertion).