Question

What would happen if another species were to discover the fire?

Answer 1

Answer:

Then the other species would have used fire for their purpose and they would have ruled on us by the use of fire.

Answer 2

Explanation:

There are very few other species that could do much with fire even if they understood it. You really need hands to manipulate fire. One could conceive of, say, tigers figuring out that antelope are tastier if you leave them in the brush fire for a bit. But they can't do much with it beyond that.

The only species likely to figure out fire are the ones who have hands, i.e. the primates. They already did discover fire once. After a few hundred thousand years or so, it made them us.