Truthfulness, higher and lower are not well definable - they are simply relativistic and work at any point on the spectrum. For example you could say "relative to humans, bovines are lower organisms," but you could also say "algae are lower organisms relative to mammals such as bovines and humans." You could use "complex and simple" in the same way, but to me there appears to be some kind of teleological argument embedded in them. "Higher and lower" are not too much different from "complex and simple" in that they do not come from any "theory" except to say that when a person looks at a chimp, they realize that the chimp is missing a few things that the human being has. That's just a fact, and remains such regardless of any well-crafted teleological counterarguments. ::::: Perhaps what you are really arguing is that "higher and lower" are somewhat 
qualitative terms, and that science should not make qualitative distinctions, only quantitative ones. This is a valid argument, but only if science POV does not trump NPOV. We are all humans who read this encyclopedia, and humans do sometimes need qualitative distinctions in their language.- ( | t | e)