I know we need to show and not tell, but is it still okay to sometimes tell instead of having to show it? For example, I wanna let the reader know that humans in my story are actually the same species as another race, but they just evolved under different conditions and that's why they look so different and people think they are two different races when they are in fact both kinda the same species.

This is an important fact I want the reader to find out, but I don't want to give the reader this information as part of a dialog between two characters because this is something that very few people know. Obviously, this information is not something I can just "show" the reader (unless I have the characters find an evolution chart of humans in their world or something), so is it okay if I simply mention it in a paragraph as part of the non-dialog text?