There have been quite some questions about racism and Middle Earth, and whether or not Tolkien or his work were racist. My question abstracts away from the notion of racism, and focuses on race itself.
I am aware that Tolkien's work is a work of fiction, and that we should be careful putting our political concepts and view of the world on literature. What we do know, is that there were indeed different races of Man. Probably the most notable distinction is the one between the people of the West and the Men of the East, at least that is how I saw it after seeing the Lord of the Rings in theaters: Men of the East had a notably different accent, were dressed very differently, and seemed culturally much more distant from other large groups such as the people of Gondor, Rohan, and even the Men of Laketown in The Hobbit. I would assume that Black Numenoreans were physically close to the Gondorians.
This might be a topic of discussion but I would argue that Easterlings (Haradrim as well as the people from the Rhûn and Umbar regions), typically have black hair and brown eyes. They would also have a darker skin. I admit that this may be an unintentional, subconscious idea on my part. However, the LotR Wiki seems to agree.
[The Haradrim] were dark skinned Men and waged war on great Oliphaunts or Mûmakil.
The thing is that they do not cite a source as far as I can tell.
I am curious, because in our world skin colour is a genetic trait that is passed on generation after generation. Only after years and years of evolution did it happen to be the case that there are multiple human races with distinctive skin colours. In Middle-Earth, though, Man is created by Ilúvatar, not born out of evolution. How can we explain differently coloured people from this perspective? Do the books provide any background on different houses of Numenoreans (with different skin colour) travelling to different parts of Middle-Earth?
As a side note: this question came to me after seeing the new trailer for Middle-Earth: Shadow of War which features a black man in Gondorian (?) armour.
After searching I also found that Peter Jackson's view on LotR includes black people in Gondor. From a genealogical, evolutionary perspective, how can skin colour distinction between human races be explained?
Note: I am not a native English speaker, so if I happen to word something the wrong way that is degrading or insulting to any group of people, please let me know and I will correct my mistake.
Update 3rd of December 2017 -- contains spoilers
The black man featured in the trailer for Shadow of War mentioned above is Baranor.
In the game, he reveals to Talion that he was born near Umbar, in Harad, and that his family sent him to a Gondorian family as it would ensure peace between the two factions/families. More information can be found on the ME:SoW Wiki page which mentiones that Being born in Harad before adopted by the wealthy family makes him the only Gondorian with Black racial ethnic features.