Because it hasn’t made sense for quite some time and some are beginning to notice the problem.
The problem that Hejnol sees with the whole system is that the ranks don’t mean anything specific or uniform across all groups of life. Even though species is arguably the most important rank across multiple fields of biology, there are dozens of species concepts in use — and biologists working with different groups of organisms can’t seem to agree on just one. You might think that the other end of the hierarchy would be more settled, but it wasn’t so long ago that domains simply didn’t exist — the three domains we use today (Archaea, Bacteria and Eucarya) were only proposed in 1990. At that time, the top rank was kingdom, and there were five of those; now there are at least six, though some say there should be as many as 32. Similar ambiguities plague all the taxonomic ranks in between — even those often considered to be major, distinct and unambiguous, like phyla.
Perhaps this could all be resolved if the scientific community simply agreed upon a definition for each rank, but there’s no consensus for that.
Christie Wilcox, “What’s in a Name? Taxonomy Problems Vex Biologists” at Quanta
If modern biology began with “On the Origin of Species,” many may be willing to live with chaos to protect the sacred history.
See also: A physicist looks at biology’s problem of “speciation” in humans
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