I remember reading somewhere that the Cyrodiils interbred with the Ayleids to create what we know as Imperials, is this true? I've always seen Nords as the "men" race of Elder Scrolls and I've never been sure about where Imperials come into it, they're evidently not the same as Nords, but I don't know if that's a result of interbreeding with other races or just through evolution.

Cyrodiils = Imperials = the native people of cyrodiil. If they interbred with ayleid they would be half elf and they are not. They are just regular humans with no interbreeding with other races

There isn't any evidence of true(macro) evolution on Nirn,But it's most likely that the tribes of Tamriel interbred with the Atmorans or Nedes than Ayleids as the Ayleids were elves..
Nords at the present are essentially Atmorans+Nedes.
Reguards-Yokudans
Breton- Nede+Ayleid or some other Mer over a long duration of time.

They're not really native to Cyrodiil, and I kinda meant more along the lines of 1/10 elven heritage, Bretons are half elves, but if a few Imperials were born as a result of interbreeding but then went on to have children with other Imperials that weren't, the elven heritage would slowly deteriorate, and modern day Imperials would still have slight elven blood, and that's what I'm asking, is this the case?

Didn't see your post when I posted that last one nish24may

Don't believe the "From Atmora" hypothesis. It is Nordic Propaganda. There were Men in Tamriel long before then.

It'd be much easier to answer your question if you could present the source.

I really can't remember the source, might have been one of the TES wikis, that's the only place I get the lore from, definitely wasn't an in-game book.