The antiquarian notion that life can be organised as a ladder, with humans at the top. This concept is implicit in phrases like 'highly evolved' and in statements like 'some people say trees are living beings too". Talking of trees, that is the image currently accepted for life organisation. A leaf is a species, with the branches stretching back in time to join at the last common ancestor. This has the philosophical advantage that all speces are equal in that they have all undergone an similar amount of time and therefore change.

Personally, I consider some species to be more 'highly evolved' because they are more complex. Although Archaea have been around for much longer than we have (their branch is connected to the trunk much lower down), they are less complex. They are single celled and not sentient - but can survive in boiling or freezing temperatures, and are much better 'evolved' for their particular environments. We can modify our environments (and even ourselves) so we essentially are meta-evolved (evolved to evolve ourselves!). However, this does not bring me back to the ladder of life veiwpoint - it is a kind of species imperialism.

Reference:Taxonomy Mnemonic