Human history is etched into the DNA of domesticated animals, which is when we bend the evolutionary trajectory of species to serve our own purposes. We primates have domesticated many animals, including (possibly) ourselves, but the domestication of the cat has especially intrigued scholars and feline pet owners alike.
Maybe it's something about the innate mysteriousness and independence of cats, which often behave more like demanding roommates than pets. A popular theory is that cats actually domesticated themselves, possibly more than once — in other words, deliberately plopping down into our lives. If true, that would be a far cry from the laborious domestication process early humans may have undertaken with horses, dogs, cows and sheep.
Now, a new study in the journal Heredity investigated the genetic diversity of modern cat populations across the globe and put a date on when they morphed into the domestic animals we know today. The researchers believe our close relationship with cats came about around the same time humans began tinkering with agriculture, around 10,000 years ago. That's a bit more recent than dogs, which are believed to have been domesticated in Siberia around 23,000 years ago — long before we undertook cultivating plants instead of scavenging for them.
So why would cat domestication correlate with agriculture? As humans unlocked the ability to massively stockpile food, it attracted rodents and pests. Cats were likely magnetized to this abundant, consistent source of food. And we kept our new mouse security teams around. This research suggests it took relatively little time for humans and cats to agree to this relationship once we got the farm going.
It's an interesting theory, but researchers at the University of Missouri can now back up this hypothesis with genetic analysis using nearly 200 different genetic markers. In retracing where the first domesticated cats came from, it also outlines the history of colonialism, or the long, bloody practice of nations controlling and exploiting other countries.
"We can actually refer to cats as semi-domesticated, because if we turned them loose into the wild, they would likely still hunt vermin and be able to survive and mate on their own due to their natural behaviors," Leslie Lyons, a feline geneticist and professor at the University of Missouri's College of Veterinary Medicine, said in a statement. "Unlike dogs and other domesticated animals, we haven't really changed the behaviors of cats that much during the domestication process, so cats once again prove to be a special animal."
Genetic evidence makes it clear that, as humans spread out, the cats followed.
To start, we need to go back to the beginning of the Holocene, an epoch marked by the end of the last major ice age around 12,000 years ago. Holocene comes from the Greek for "entirely new," and it truly was a bold, new era as the glaciers slowly receded and saber-tooth tigers died out.
Around this period is when some of the earliest evidence for human agriculture appears. Humans were primarily hunter-gatherers prior to this development, but learning to farm allowed us to secure regular food sources (barring drought or famine), leading to an explosion in our population and the dawn of civilization.
Somewhere along the ride, a few kitties joined up with the humans. But first, they were wild, most likely descended from Felis lybica, the African wildcat. Feline domestication seems to have sprung up in many different places across the globe, including China and the Indus Valley of Pakistan, but it most likely all began in the Fertile Crescent in the Middle East. Genetic evidence makes it clear that, as humans spread out, the cats followed.
"One of the DNA main markers we studied were microsatellites, which mutate very quickly and give us clues about recent cat populations and breed developments over the past few hundred years," Lyons said. "Another key DNA marker we examined were single nucleotide polymorphisms, which are single-based changes all throughout the genome that give us clues about their ancient history several thousands of years ago. By studying and comparing both markers, we can start to piece together the evolutionary story of cats."
To get the cat DNA, Lyons and her colleagues swabbed the cheeks of cats and analyzed donated blood and gonad samples from neuter clinics, including four African wildcats and 10 hybrids of domestic and European wildcats. Most of these cats were "random-bred," meaning they were semi-domesticated, lying "somewhere between 'habituation' and 'commercial breeds and pets,'" the authors wrote.
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They ended up with more than 2000 samples of cat DNA from around the world, from places like Brazil, China, Italy and South Korea. The samples from Iraq were donated by the Medical Detachment Veterinary Medicine, who were deployed to occupy Iraq from 2007 to 2009. When this genetic data was distributed on a global map, it became clear that the more closely related a sample was, the more likely it originated near the Fertile Crescent, a region home to the some of the world's earliest known settlements and civilizations, including the Babylonians, Sumerians and ancient Egyptians.
"Populations were significantly isolated by distance," the authors wrote. "Among populations, the genetic distance increased as the geographic distance increased."
As humans spread across the Earth, we brought cats to places where they didn't exist before, from the Silk Road to places in India and Sri Lanka and to colonies in the Americas and Australia, which has had huge outcomes for the local ecosystems. Cats are indiscriminate hunters and have been known to effortlessly drive some animals to extinction. This actually makes domesticated cats an invasive species, and their spread encapsulates some of the darker chapters in human history.
"Migration of cats rose with imperialism, exploration and colonization, which increased the number of ships traveling to the Americas," Lyons and her colleagues explained.
But as cats moved around the globe, it created pockets for genetic diversity to spread out, which is a prevailing theory for why there are so many different cat breeds, from Sphynx to Persian and everything in between. These breeds and what regions they exist in can serve as reminders of the past.
"The data suggest cats in distant areas from the Near East, including Australia, the Americas, and colonial regions such as Tunisia and mainland Kenya, are close derivatives of Western European cats, reflecting Western European colonization," Lyons and her colleagues wrote. "The admixed genetics from Western Europe and the Near East cats were subsequently spread to Portuguese colonies in the Americas."
As large shipping vessels started spreading across the world's oceans in the 1500s, cats came with merchants, creating a sort of feedback loop. Cats were so useful on ships, protecting stores from rats and other vermin, they made the process much easier and more profitable.
"Migration of cats rose with imperialism exploration and colonization, which increased the number of ships traveling to the Americas," Lyons and her colleagues explained. Cats are some of our closest companions — we love them and their outsized internet presence for a good reason. But it's clear that in many ways, their history is also our history.
Questions still remain about some of the origins of domesticated cats, with Lyons and her coauthors interested in the genetics of Felis lybica ornata, the Asiatic wildcat, which is native to Iraq, Iran and parts of India.
"Further studies on ancient, regional wildcat populations would further decipher cat origins," the authors conclude. "The patterns of genetic diversity and differentiation observed in worldwide random-bred cats parallel those of other species, especially humans once they became farmers, suggesting human history is written in the DNA of domesticated species."