system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Single Species Crews?

The crew of DS9 once engaged in a "baseball" game with the crew of another Starfleet ship. The opposing crew was entirely Vulcan, or maybe it was just the senior staff. 

Regardless, how would a Captain be allowed to do this? I can understand a Captain being given some leeway in selecting his crew, especially senior staff, but isn't that discriminatory? It seems very much against the spirit of equality that much of the Federation stands for. Aside from that, it seems a  terribly inefficient and illogical way to deploy resources. Even if Vulcans are "superior" to other races, wouldn't it be better to spread them around the fleet?
gpt
While humans and vulcans are capable of surviving in the same environment, their optimal temperatures are uncomfortable for each other.  Vulcans like things a fair bit hotter than humans do.  Because of that,  ships tend to be primarily one species, with maybe a few officers here and there that wanted a particular assignment enough to deal with being too hot / too cold.  **Entirely** single race ships are rare, but ships that are around 90% a certain species are the norm, not out of some manner of racism, but just basic comfort.