A single living thing that can breed/produce fertile offspring

A species is often defined as a group of organisms that can reproduce naturally with one another and create fertile offspring.

Explanation:

if this helps brainliest ?

mammals

A species is often defined as a group of organisms that can reproduce naturally with one another and create fertile offspring. However, the classification of a species can be difficult—even riddled with controversy.

answer: that would be cheating

explanation:

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.