system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why is the Federation so Human-centric?

At that time of the Federation's creation the founding species all seem to have fairly distinctive ship designs, and most of the species are more advanced than humans in multiple areas.  Yet if we look at essentially any TNG era vessel, it's pretty obvious that the designs draw more inspiration from NX-01 than from any of the non-human vessels.

Additionally, humans seem to dominate Starfleet.  NCC-1701D does seem to have a pretty good mix of alien species, but I'd still estimate that over 80+% of the crew is human.  I know there are some Vulcan crewed ships, as well as Vulcan captains and admirals, but where are all the other races in the upper command structure of the Federation?
gpt
Starfleet was an Earth organization before the Federation was founded. Humans were the key to uniting the other founding races of the Federation. Andorians, Tellarites and Vulcans all had a strong dislike of each other, for example. 

Because Humans were the uniting force, it makes sense that the Federation would be founded on Earth (neutral ground) and that Starfleet (a neutral organization) would evolve to include members from all Federation worlds, rather than say, the Vulcans or Andorians becoming the primary space fleet of the Federation.

I would imagine that Federation member worlds still maintain their own fleets of ships. Your average Andorian could choose to join the Imperial Guard, or decide to join Starfleet. Humans, on the other hand, would have to join Starfleet if they wanted to do anything more glamorous than work on a merchant ship, which accounts for their higher numbers on Starfleet ships.