For today’s episode of “Really Important Concepts That Don’t Have Names,” I’d like to briefly introduce two words shamelessly stolen from the esoteric biological field of taxonomy.
Carl Linnaeus made his place in history through his system of organizing every material, living or dead, into species, branching from a taxonomic tree initially divided into the three classes of animal, plant, and mineral. Hardly the first to attempt such a thing — Aristotle’s system of classification had been used for about two millennia prior — Linnaean taxonomy would gradually incorporate discoveries from archaeological study of ancient species, study of newly discovered forms of ever smaller life, and eventually the discovery of Darwinian evolution.
As naturalists, now referred to as biologists,1 sought to construct ever more accurate trees of life, a subtle change took hold in methodology. No longer was the scientific establishment satisfied with groupings derived solely from similarity with little regard for evolutionary history. This prior way of thinking, then referred to as phenetics, was gradually replaced by cladistics, the practice of categorizing species by shared ancestry.
But with genetic evidence and improvements in the ability to trace ancestral lineages of modern life, the field discovered a problem: sometimes, two species that appear to be very closely related are actually evolutionarily quite distant, and conversely, two species that appear to be quite different may actually be closely related.
The result is a number of taxonomic reorderings that I’m sure Wikipedia will suffice to describe, and two marvelous terms for a situation frequently encountered but poorly described for lack of terminology:
Polyphyletic, when two or more things may appear to be closely related, but actually come from different branches of the tree of life. Typically used to describe situations where two species appear very similar but are actually not very closely related.3
Paraphyletic, when two or more things may not appear to be closely related, but are actually quite closely related. Often used to describe situations where shared ancestry is responsible for an observed set of similar traits.
For a bonus vocab word, because these terms are primarily applicable to scenarios where groups of things share certain traits, those traits shared can be referred to as homoplasies.
So next time you find yourself in the middle of a discussion demanding more nuanced terms to distinguish between things belonging to classes as a result of shared ancestry versus shared traits, there’s a word for that.
A note for the taxonomists in the house, or those who crave their particular flavor of pedantry: as you might imagine, the degree of ancestral relation is of particular interest to those constructing trees of all life on the planet. Where does one draw the line between the polyphyletic and the paraphyletic? If a group of species includes all descendants of a given ancestor, it’s said to be monophyletic (which also happens to be the only one of these terms whose definition isn’t subject to debate). If it includes some but excludes others, it is said to be paraphyletic with respect to the excluded others. If a group is defined by a set of shared characteristics but those characteristics are not the result of shared ancestry, it is said to be polyphyletic.
Technically, the definition of paraphyletic I provided above also (incorrectly) includes monophyletic groupings, even though logically the two labels should be mutually exclusive. Given that the purpose of the vocab lesson is to introduce a concept that can be used to categorize ideas, and ideas, being not of a finite set, cannot be enumerated, monophylesis is practically a non-issue, and so I excluded the term above for simplicity. Feel free to contact me via my LinkedIn for a duel.
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More accurately, naturalism split into biology and chemistry, the latter of which later split into chemistry and physics, likely with a number of additional fields I’m forgetting. ↩︎
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Putting footnotes on footnotes is a rather underappreciated capacity of modern site rendering engines. I’ve taken the liberty of doing so for a fun if brief tangent on carcinization and horoscopes. You may have noticed the symbol for the horoscope cancer is a crab, and carcinoma is a type of cancer. As it happens, the word for cancer overlaps with the word for crab in a great many languages, with the most common explanations noting the hard surfaces and tight grip of tumors in the eyes of early surgeons, and the crab like appearance of the veins around a cancerous growth. Yet cancer again collides with crabs in the naming of carcinoma, from the Greek karkinos meaning crab or cancer, and -oma, which likely began its life as a suffix in the word carcinoma, but now means tumor or cancer. Two largely unrelated connections between crabs and cancer. Wild. ↩︎
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The classic example of this — the exclusion of which may be the most common reason biology teachers are drawn and quartered in the modern day — is the rather absurd number of entirely unrelated species that look very much like crabs. The trend of evolving to be more like a crab is so common it’s even been given a name: carcinization.2 ↩︎