I enjoy maturity and evolution models of all kinds, especially for business. There is a stages of maturity model for information technologies and others such as for sales teams and their customer relationships. What I like about stages of maturity models is they provide confidence that regardless what stage one is at – low or high – there is a next step further up that can be attained in an evolutionary way.
In biology there is an evolution of humans that has in earlier stages Australopithecus, then Homo erectus, then Neanderthals, and our current stage Homo Sapiens. Examples of important changes are brain size, hand grip, and a larynx for speaking.