If we examine the idea of intelligence for its philosophical grammar then it seems that the amoeba is as intelligent as the human.
Just as the human brain is not more intelligent than the human spleen, so the human spleen is not more intelligent than the human cell, and the human cell is not more intelligent than the amoeba. We are led to the odd conclusion that the amoeba is as intelligent as the human. But then each employs a unique set of skills. Each are fully embedded and competent within their particular environment. Environments are filled with unique, species-specific objects.
THERE IS NO PAN-SPECIES SCALE OF INTELLIGENCE.
Intelligence is not manifested by a species. There is no pan-species scale of intelligence because there are no pan-species environmental objects. Intelligence is manifested by individuals within a species as a variable. This is because only within the individuals of a species are there similar environmental objects to be found, and it is this similarity that allows a scalar, comparative, "intelligence", scale to be introduced. The anthropomorphic pleasure of assuming that all animals are quasi-humans living in quasi-human environments within which they can be comparatively assessed for intelligence is a persistent, regrettable, hominid brag.
THERE CAN BE NO ADVANCEMENT OF HUMAN INTELLIGENCE.
An advancement of our species intelligence doesn't describe an advance in intelligence. It describes a new environment populated with new objects, and hence describes a new species. Advancing the intelligence of our species means its annhilation and replacement by something other; and that is a warning to us all.