Or maybe lalafells are the original race, and everyone else is just the results of their magical experiments. It explains why their architecture is so huge: they were expecting to become giants!
But in seriousness, yes, all of the 'races' are part of the same species. It makes perfect sense to me, as they all are basically humans. Additionally, Titan calls the player character and his allies "Sons of Man" (or maybe he was talking about how the "sons of man" were hurting the kobolds. I forgot). Considering the one saying it is an ancient monster as ancient as the world, it's a sure bet that they all share the same ancestor.
But in seriousness, yes, all of the 'races' are part of the same species. It makes perfect sense to me, as they all are basically humans. Additionally, Titan calls the player character and his allies "Sons of Man" (or maybe he was talking about how the "sons of man" were hurting the kobolds. I forgot). Considering the one saying it is an ancient monster as ancient as the world, it's a sure bet that they all share the same ancestor.