Wilhelm Johannsen, who coined such terms as “gene”, “genotype”, and “phenotype”, noted in 1911 that,
It is a well-established fact that language is not only our servant, when we wish to express – or even to conceal – our thoughts, but that it may also be our master, overpowering us by means of the notions attached to the current words.
Even widely used and (apparently) simple terms can cause substantial confusion when the notions attached to them are unwarranted, a problem that is particularly common in evolutionary biology. Think “theory“, a term that is not only poorly understood to begin with in its scientific context but is actively misrepresented by anti-evolutionists.
The misinterpretation of other terms may cause, or be caused by, particular assumptions about the nature of the evolutionary process. Take the term “primitive” for example. The use of the term can be either deeply misleading or entirely appropriate depending on what one considers to be the opposite of the term. Here are the two most common uses, the first problematic and the second legitimate.
1) Primitive versus advanced.
In this comparison, the term “primitive” has pejorative connotations of inferiority relative to “more evolved” species. Evolution is implied to be a progressive process characterized by improvement rather than simply of change. This is the usage one finds in popular media, for example in the all-too-well-known “evolutionary line-up” showing progressive improvement in anything from primate species to any manner of product being advertised as new and improved. However, biological evolution is not a progressive process, and this use of the term is inappropriate.
2) Primitive versus derived.
In technical parlance, “primitive” can be used to mean that one form of a trait is “more like a common ancestor” relative to another form of the trait (i.e., as synonymous with “ancestral”). It is an expression of the differential quantity of change that has occurred since two or more lineages diverged. The opposite of primitive in this usage is not “advanced” but “derived”. There is no automatic implication that change has been progressive in this sense.
So, one should not draw a comparison between “primitive versus advanced”, but “primitive versus derived” is not problematic. It bears noting, though, that the terms primitive (or ancestral) and derived are actually applicable to particular characters, not to entire organisms. As Crisp and Cook (2005) noted,
Once two lineages have separated, each evolves new characters independently of the other and, with time, each will show a mixture of plesiomorphic [inherited largely unchanged from the ancestor] and apomorphic [newly evolved and thus not possessed by the ancestor] character states. Therefore, extant species in both lineages resemble, to varying degrees, their common ancestor. Consequently, whereas character states can be relatively ancestral (plesiomorphic) or derived (apomorphic), these concepts are nonsensical when applied to whole organisms.
Crisp, M.D. and L.G. Cook. 2005. Do early branching lineages signify ancestral traits? Trends in Ecology and Evolution 20: 122-128.
Johannsen, W. 1911. The genotype conception of heredity. American Naturalist 45: 129-159.