Several readers sent me a link to or news report about a new paper in Proceedings of the National Academy of Sciences by Yaowu Hu and colleagues (reference and link at bottom). The paper reports the discovery of cat remains associated with a 5200-5500-year-old human settlement in east-central China. Since the earliest domesticated cats from China were previously known from only 2000 years ago, this pushes Chinese cats back a considerable distance.
The question is to determine whether these really were semi-domesticated cats, and that’s the main problem of this paper. The evidence is suggestive, but not super-compelling. But first let me tell you what we know about the history of cat domestication. Rather than rewrite the paper’s introduction, I’ll just present it verbatim, as it’s clear enough.
Studies of mitochondrial DNA from modern wildcats and domestic cats demonstrate that ancient populations of Near Eastern wildcats (Felis silvestris lybica) were the maternal ancestors of domestic cats. A wildcat phalanx from the site of Klimonas shows that they were introduced to Cyprus 11000–10500 B.P. (all dates are reported in calibrated years before present), providing the earliest connection between humans and cats. The earliest cat to demonstrate a close association with humans is also from Cyprus, where a young wildcat was interred next to a human at the site of Shillourokambos ca. 9,500 y ago. Isolated cat bones have been found at Near Eastern sites, such as Jericho, but little is known about the crucial period for cat domestication between 9,000 and 4,000 y ago. Healed fractures on the forelimbs of a young swamp cat (Felis chaus) buried in a ca. 5,500-y-old grave at Hierakonpolis in Upper Egypt indicate that wildcats were actively cared for by ancient Egyptians. However, the first evidence for domestic cats is based on Middle Kingdom Egyptian art dated to ca. 4000 B.P. Trade in cats was prohibited in ancient Egypt, but they were nevertheless exported to Greece around 3,000 y ago and from there to Europe. Cats were thought to have first appeared in China around 2,000 y ago. Claims for earlier cats in the region have been made (Table S1), but without precise dates or detailed biometric measurements these have been difficult to evaluate.
The authors hypothesize that some subspecies of Felis silvestris (perhaps native, or perhaps a semi-domesticated immigrant from the Middle East) was becoming more domesticated by associating with the people from this site, who raised and ate grain (the authors found remains of millet and a bit of rice). Because the bowls for storing grain at the site were shaped in a way to discourage rodents, and because the authors also found rodent bones at the site (including the Chinese “zokor”), the idea is that cats domesticated themselves by hanging around the settlement nomming the grain-attracted rodents. Then, the story goes, they became tamer, their flight distance became reduced, and, at least in China, humans began feeding them grain. This is not a new story: it’s the old idea that cats weren’t domesticated by humans, but domesticated themselves.
At any rate, here’s a sketch of one of the anti-rodent pots, taken from the paper’s “supplemental material.” I guess zokors couldn’t climb up the outward-sloping sides:
More evidence for domestication: the authors found 8 cat bones at the site (mandible, humerus, pelvis, tibia, and femur) from at least two individuals (though, curiously, the graph below suggests three). One of the jawbones—”A” in the figure below—showed a “worn fourth premolar and first molar.” The authors imply that aged cats mean semi-domesticated and well-fed cats, though I’m sure some cats in the wild can live long enough to get worn teeth. Carbon-14 dating put the cat bones at about 5300 years old.
The third piece of evidence is based on body size. The cat from the Chinese site (they measured just one set of bones) is larger than modern house cats measured in Czechoslovakia, but smaller than modern European wildcats, although this intermediacy is not uniform. The pelvis of the Chinese cat, for instance, is 79 mm in “GL” (not sure what that means, though perhaps “girth left,” since they measured only the left side), compared to a mean of 44 mm for modern Czech cats and 53 mm for modern European wildcats from the Carpathians. The cat is also a tad smaller in some bone measurements than cats from ancient Egyptian sites.
From the intermediacy of these measurements between modern house cats and modern wild cats, they conclude that the data “are suggestive of domesticated cats.” But I don’t find this at all convincing. They’re implying that domestication leads to smaller cats, which may be true, but size is also determined by nongenetic factors like health and nutrition. Moreover, if there was an ancient subspecies of Felis silvestris in China that was smaller than the modern European wildcat, these could be pure wildcats that were hanging around the settlement. I find the size measurements unconvincing evidence for domestication.
Finally, the authors give isotope data (carbon and nitrogen) taken from bone collagen collected from specimens at the site. From this they try to infer something about diet. Here are the plots for δ13C (the ratio of C13/C12) and δ15N (the ratio of N15/N14) for each animal measured, including humans. Here are the plots. The cats (why are there three dots instead of two?) show intermediate values for the nitrogen ratio and higher values for the carbon ratio. Sadly, no pure carnivores were measured, as there were none at the site.
From these data the authors conclude—well, nothing that I can sign onto. For example, it’s clear that the cats weren’t eating the same stuff as deer and fish, but since cats are carnivores and neither fish nor deer are, that’s not surprising. But they also say that the high δ13C ratio for humans “suggested that the individual consumed a large amount of C4-based animal protein”. Just a few paragraphs later, though, they say that “the common Chinese zokor [a rodent] had a high δ13C value, indicative of the consumption of millet products”. Well, which is it? The data also suggested to the authors that the cats were eating millet, too. But cats are carnivores, and why weren’t they eating rodents? Will cats eat millet if they can get it, or are fed it by humans? Do the data even suggest that cats were eating millet?
In the end, I can’t make heads or tails of the isotope data (though it may be simply reflect my own ignorance). Nevertheless, interpreting that data seems to involve a lot of speculation. The authors say, for instance:
Together, the spread of millet farming and commensal rodent populations attracted cats and provided incentives for farming communities to support them. The cat population at Quanhucun survived for several hundred years, with one of the individuals that we studied living to a considerable age, suggesting a favorable environment for cat survival. One animal stands out from the others, with a high δ13C value (−12.3‰) and low δ15N value (5.8‰), suggesting that it ate large quantities of agricultural products and did not rely as heavily as expected on rodents or other small animals for food. These data are intriguing, raising the possibility that this cat was unable to hunt and scavenged for discarded human food or that it was looked after and fed by people.
That is a LOT of speculation. Had I been the editor of this paper (it was Dolores Piperno from the Smithsonian), I would have suggested that the authors need to clarify a lot of things, and avoid so much speculation. If I can’t understand the isotope data after two readings, then neither will the average reader.
But the paper is still valuable in other ways. It gives evidence, for instance, that cats were living in at least loose association with humans more than 5,000 years ago in China, just at the time when they were supposed to be getting domesticated in the Middle East. (Mitochondrial DNA tells us that all modern housecats descend from Felis silvestris lybica from the Middle East.) So if these are domesticated cats, and ones not domesticated in situ in China, how did they get from the Middle East to Shaanxi? There are Asian subspecies of F. silvestris, too, and perhaps those were domesticated independently and later acquired their mitochondrial DNA by hybridizing with cats brought from the Middle East. (Mitochondrial DNA introgresses rapidly between subspecies and species, while nuclear DNA can remain distinct.)
What this all tells us, I think, is the unsatisfying but common conclusion that “more work needs to be done.” The problem is that it’s very difficult to look at nuclear DNA from bones, and I’m not sure how much to trust the isotope data. At any rate, we’re not justified in concluding either that cats were originally domesticated in China (which some newspapers have suggested), or that the cats domesticated themselves in China, eating both grain and rodents. That must await further work.
Hili, are you reading this?
Hu, Y., S. Hu, W. Wang, X. Wu, F. B. Marshall, X. Chen, L. Hou, and C. Wang. 2013. Earliest evidence for commensal processes of cat domestication. 10.1073/pnas.1311439110 Proceedings of the National Academy of Sciences, early edition.