Hi guys. I was wondering, could you please explain why there are no human equivalents evolved from different ancestors?

For example, humans evolved from the Hominidae speciate, so why aren't there any intelligent beings evolved from the Hylobatidae speciate (for example)?

My science teacher said it's something to do with there being an available niche for the second species to exist in. If we evolved first and filled that niche, then evolution and natural selection would only let the one species continue. But aren't there animals (like lions, tigers and panthers) of different species with similar niches? Or why is there no specie of human intelligence with a different niche (e.g. Mermen - that would be so cool)?

Thanks guys :)

Your science teacher is right, but the scenario as a whole is really complex.

Between a few hundred thousand years ago and a million or two, there were multiple species of hominid, all more or less as intelligent as each other. Neanderthals, for example, were around at the same time as us.  However, it is now believed that the two species interbred and the Neanderthal populations were assimilated into Homo sapiens.

One reason panthers, lions, tigers etc all co-exist is that they exist in different parts of the world, and occupy different niches (panthers in the jungles of south america, tigers in tthe jungle of india/china, and lions the savanah of africa).  So because they occupy different places and environments, they are isolated enough to breed seperately and form slightly different species. It's worth noting that these examples are all from the same genus. When humans spread over the world, they were less isolated that the Panthera examples.