Which Species Is Felis Catus?

Opinion 3010, issued by the International Commission on Zoological Nomenclature in 2003, was intended to resolve a debate that had lasted over two hundred years. Whether domestic cats should be called Felis catus or Felis silvestris catus had never reached consensus in taxonomic circles. The Commission's final ruling was to retain both names, letting researchers choose for themselves. This decision left neither side particularly happy.

Don Wilson, a researcher in the mammalogy department at the Smithsonian National Museum of Natural History and compiler of Mammal Species of the World, one of the most widely cited mammalian nomenclatures globally, listed domestic cats as a subspecies under the wildcat Felis silvestris in the third edition published in 2005. His reasoning was straightforward: domestic cats can interbreed with European wildcats, African wildcats, and Asian wildcats, with offspring possessing complete fertility. According to the standard definition of the biological species concept, the absence of reproductive isolation means they shouldn't be considered separate species.

In a 2005 interview with Scientific American, Wilson said that taxonomic naming should reflect evolutionary relationships, not how humans use the animal. Domestic cats are descendants of wildcats, so in the classification system they should be placed under wildcats.

But Wilson later acknowledged that this treatment created other problems. The wildcat species itself is complex, divided into several subspecies: European, North African, West Asian, South African, Central Asian. Just how to delineate the subspecies is itself a matter of disagreement. Adding domestic cats into the mix makes the species boundaries even harder to define.

A genetic study published in Science in 2007 by Carlos Driscoll of Oxford University provided new data for this debate. His team collected DNA samples from 979 cats worldwide, including wildcats and domestic cats, and through mitochondrial DNA analysis traced maternal origins. The conclusion was that all domestic cats' ancestors point to the Near Eastern wildcat Felis silvestris lybica. This subspecies is distributed in what is now southeastern Turkey, Syria, Israel, and coincides with the regions where humans first began cultivating grain.

The name Driscoll used for domestic cats in his paper was Felis silvestris lybica, treating them as a subspecies. Wilson believed this supported his position: domestic cats diverged from wildcat populations too recently, with genetic differences too small to justify separate species status.

Stephen Jackson, a biologist at the Australian National University, had a different view. Jackson participated in formulating Australia's feral cat control policies, and his concern wasn't how to describe evolutionary relationships, but how taxonomic names are used in practical management. Australia began implementing a nationwide feral cat culling program in 2015, and the species names written in legal texts directly affect enforcement operations. If domestic cats and wildcats share the same species name, ground-level enforcement personnel face difficulties in determining a cat's legal status.

Jackson discussed this issue in a 2018 article in Australian Mammalogy. He pointed out that the International Commission on Zoological Nomenclature has an old rule giving the scientific names of domesticated animals lower priority than those of their wild ancestors. This rule was written into regulations in the 1920s, when DNA sequencing technology didn't yet exist and genetic data couldn't be incorporated into consideration. He argued that the rule itself needs revision and that a framework from a hundred years ago can't be rigidly applied to today's research findings.

In actual practice, academic journals take a relatively loose attitude toward this debate. Major publications like the Journal of Mammalogy and Journal of Zoology don't mandate which name authors must use. PubMed database search results show that among cat-related papers published between 2010 and 2020, approximately 65% used Felis catus, approximately 30% used Felis silvestris catus, and the remainder used other formulations or mentioned both.

Wilson wasn't surprised by these numbers. The name from Linnaeus 1758 has been used for over two hundred years, and citation habits in academic circles can't be changed by a single ruling. Inconsistent names in cross-referencing can cause retrieval omissions, so many authors write both to be safe.

Driscoll's research also raised another issue. His data showed that the degree of genetic divergence between domestic cats and their wild ancestors is far less than between dogs and wolves. Dog domestication was accompanied by substantial changes in behavioral and physiological traits: reduced aggression, increased sensitivity to human gaze, and obvious cranial morphology changes. Almost no similar domestication signature can be seen in domestic cats.

Wes Warren of Washington University led a deep sequencing of the domestic cat genome in 2014, with coverage exceeding 60x, much finer than the initial 2007 version. They compared domestic cat and wildcat genomes looking for traces left by domestication selection, finding some signals related to fat metabolism, possibly connected to long-term consumption of human food scraps. There were also changes in several gene loci related to fear responses and reward learning. But Warren stated clearly in the paper that the overall signal is very weak, and domestic cats' degree of domestication is far lower than other domestic animals.

This creates a somewhat odd situation. From an evolutionary relationship perspective, domestic cats and wildcats are indeed very close, close enough that treating them as subspecies makes complete sense. But from an actual life history perspective, domestic cats and wildcats' ecological niches have completely separated, one dependent on human settlements, the other avoiding human settlements. Whether this differentiation should be reflected in scientific names receives different answers from different scholars.

The Nomenclature Commission has not issued new opinions on the domestic cat scientific name issue since 2003. When current Commission President Thomas Pape replied to an inquiry from the Journal of Zoology editorial board in 2021, he said the Commission's responsibility is to adjudicate the application of nomenclatural rules, not to judge which species concept is right or wrong. How to delineate species boundaries is an academic question, and the academic community has different views internally, which the Commission does not intend to intervene in.

Pape said if researchers formally propose to abolish one of the names, the Commission would process it according to procedure. But so far no one has. The two names continue to coexist, authors continue to choose for themselves, and the debate remains unresolved.