system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragon Ball Z] Although they are aliens, why are saiyans so similar to humans? and furthermore how are humans and saiyans able to procreate together?
gpt
Evolutionary pressures on planet Vegeta caused the Saiyans to evolve into humanoid form. Same reason anything winds up in the shape it is.

As for the interspecies breeding? Blind, pure stupid luck that the biology is similar enough for it to go down. Even more lucky that the half-breeds aren't mutated or sterile.