Humans all belong to a Single Species, localized on a single small-ish planet... Yet we are incredibly diverse in both Culture and Individual Appearance/Adaptation to our environment. This also seems to be true in relation to a lot of other species on Earth, even without breaking things down into Subspecies or whatever else. This is probably because the Climate and the distribution of land and water vary drastically from area to area, creating different biomes with life that has adapted in different ways in each.
However, in a lot of Sci-Fi, aliens we meet show relatively little divergence from Others of their Species, either culturally or physically? While this can probably be explained by the limitations of whatever narrative medium/framing device you're looking at, or might have some in-universe explanation (there IS a difference but humans find it hard to tell because we aren't familiar with their biology, or a specific COUNTRY on their planet might have sent this bunch, etc.), that did get me thinking... We obviously know very little about what life is like elsewhere in the universe, but based on what we do know, is there any evidence that Earth's extreme diversity might be somehow Anomalous? Or would every planet capable of producing what we might call "People" need to be equally complex in order for them to develop, and as a result would they be just as Diverse as we are? Is there any real evidence that points one way or the other?
I personally tend to feel like it must be the latter, but I'm not really an expert on much of anything, so I thought it would be a good idea to see if anyone else had read any "official"/scholarly material posing or exploring the question, or even had any thoughts of their own with evidence to show where they're coming from? I'm writing a thing with multiple alien species reaching out to each other, and I feel like this line of thought/study could give me some insight into how to handle each population's own Internal Reactions to this. :)