Which of the following is not an attribute of a population?

A population can be defined as a group of organisms of one species occupying a defined geographical area, sharing or competing for similar resources and potentially interbreeding, and usually isolated to some degree from other similar groups. A population has certain attributes that an individual organism does not possess. Following are some important characteristics of a population:

(i) Birth rate (Natality)

(ii) Death rate (Mortality)

(iii) Sex ratio

(iv) Population age