Primitive is a descriptive term often used in the field of evolution to describe particular species or traits that are characteristic of an older evolutionary scale of development relative to more recent developments. For example, prokaryotes such as bacteria are often described as primitive because they are older in the evolutionary time scale, and are less complex than later organisms such as eukaryotes.
This term has fallen out of favor with some evolutionary biologists, since it implies that the evolutionary scale is a "ladder" in which each new addition is superior than organisms in the lower rungs. The argument against this limited interpretation is that far more recent or complex organisms are not always superior to older, simpler organisms. For example, archaea, forms of prokaryotic organisms, are able to survive efficiently in a much broader range of extreme environments than can "advanced" humans. It is for this reason that many biologists prefer the dichotomy of simple vs. complex, where the evolutionary complexity of organismal functions determines the relationship between "sets," rather than "levels," of the evolutionary process.
In modern biology, phylogeny, the study of evolutionary relationships, takes the form of extending branches. Instead of having the evolutionary system as a division between higher (superior) and lower (inferior) organisms, each branch extends outwards to represent temporal and developmental distance. The preferred term for cladists is basal; its antonym is derived.
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