In biology, species refers to a group of organisms with common characteristics and the ability to interbreed to produce a fertile offspring. At this point, we would like to stress on the fact that only the group of organisms that have the ability to interbreed and produce fertile young ones can be considered a 'species'. Moving further, animals belonging to two different species usually do not mate, and if at all they do, the resultant offspring is sterile, i.e., incapable of reproducing. An apt example of the same will be the offspring of a horse and donkey―a mule. As the resultant hybrid is almost always sterile, mating between two closely related species is a waste of efforts and thus, best avoided. This is where the concept of reproductive isolation kicks in. It's basically a mechanism that prevents interbreeding in closely related species by employing a set of behavioral and physiological barriers. These barriers are divided into two groups:

• Prezygotic barriers: They prevent the process of mating to prevent the formation of hybrids.
• Postzygotic barriers: They reduce the viability or reproductive capacity of the resultant hybrid.

Prezygotic barriers are further categorized into five types, namely ecological isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation. Of these, the most potent reproductive isolation mechanism is behavioral isolation. It's a well-known fact that geographical isolation eventually leads to speciation by splitting the population into two distinct groups, each following a unique evolutionary path. In the same way, even behavioral isolation leads to speciation. In this case, two populations of a species develop different courtship behavior and continue to diversify, eventually splitting into two different species.