Edit: Given the replies, it appears that I may well be wrong, I remember reading it somewhere but I can't find the source nkw. I'll downvote myself but leave the comment up because it enables others to learn from my mistake

The world needs more people who behave this way when shown they are mistaken. Good on you!

Imma need a citation for that since these species of rhinos are said to have diverged between 3.3 and 4.1 million years ago and the first known dispersals of homo sapiens out of Africa were 129 to 75 thousand years ago. And migrations and intermixing kept happening throughout prehistory and history. Maybe it comes down to how exactly you define "more separate" ?

It's a sensitive topic but white and black people are genetically much more seperated than black and white rhinos which we are happy to describe as separate species.

That is simply not true

85% of human genetic diversity exists within local populations. White and black people are genetically less separated than white and white people or black and black people, depending on the specific people. There is much more genetic diversity within populations than between them. A source

There is essentially no genetic support for the idea of races. They are purely a social construct based on some shallow phenotypical differences, culture, and the prejudices of a given time.

I remember reading it somewhere

Yeah, you probably did, it might be one of the pseudoscience things far-right spread on social media presenting them as facts. Sooner or later, they get relayed by factoid pages that don't know they are far right. One such factoid I've seen around is that red hair (and sometimes also blond hair) were going to become extinct due to race mixing. This is also false, but while a rightwing Facebook page is the first place I saw it, I've seen it repeated by many people with no ties to the right wing, who didn't question it.

Another close example I've seen is the IQ map. It's based on a fraudulous study by Richard Lynn, a segregationist behavolioral scientist. His study was actually published in a reputable journal, but later removed when it was found his numbers were bullshit. He then cofounded his own journal with like-minded people. The thing is, while this map is shared by fascists online, it's rarely contested. I've seen many discussions on Twitter where a racist posted the map, and many leftists were talking about how IQ isn't mostly genetic and that these numbers must be a result of poverty, or some began saying the concept of IQ itself was racist... But no one questioned the numbers, altho they were actually wrong and a quick search coul've shown it.

It is frequent that when in an argument, a statement is presented as a fact and another as a conclusion of that fact, many only try to contradict the conclusion and take the original claim for granted. This tendency is often abused for propaganda purpose.