Why arent all populations completely devoid of genetic varia

Why aren’t all populations completely devoid of genetic variation, even though they must have a finite number of individuals? (genetic drift)

Solution

Biology follows evolution that is rule of nature and it occurs through natural conditions so populations cannot be sustained without genetic variations. For example populations of colder region needs to adapt according to their respective habitat and this adaptation causes genetic variations or mutations in their paternal genetic material and as this population get shifted to other niche they have to adapt again according to that respective niche. This is also known as genetic drift that with time lapse certain new traits will be adapted and old traits can be omitted through natural selection.