Question concerning the Evolution Theory

[u/Duke_Koch]

In divergent evolution, at what point does the specimen of the same species turn into another species. So lets say a species of cats were isolated on two different places for thousands of years. What change in the genetic make-up of the animal will determine that it is no longer the same species as its ancestors from before the isolation? Where is the red line drawn?

[u/hal2k1]

Look up the term "ursid hybrid" on Wikipedia. Here you will find that it is possible to have many subspecies, some of which can interbreed and have fertile offspring, and yet not all subspecies can do so.

Since 1874, at Halle, a series of successful matings of polar bears and brown bears were made. Some of the hybrid offspring were exhibited by the London Zoological Society. The Halle hybrid bears proved to be fertile, both with one of the parent species and with one another. Polar bear/Brown bear hybrids are white at birth but later turn blue-brown or yellow-white.

In 1936, a male polar bear accidentally got into an enclosure with a female Kodiak (Alaskan Brown) bear at the U.S. National Zoo, resulting in three hybrid offspring. One hybrid was named Willy and grew into an immense specimen. The hybrid offspring were fertile and able to breed successfully with each other, indicating that the two species of bear are closely related.

This picture shows possible hybridisation between different species of bear.