Our Cats, Ourselves


DAVIS, Calif. — IT’S commonplace to call our cats “pets.” But anyone sharing a cat’s household can tell you that, much as we might like to choose when they eat in the morning, or when they come inside for the night, cats are only partly domesticated.

The likely ancestors of the domestic dog date from more than 30,000 years ago. But domestic cats’ forebears join us in the skeletal record only about 9,500 years ago. This difference fits our intuition about their comparative degrees of domestication: Dogs want to be “man’s best friend”; cats, not so much.

Fossils are handy snapshots of the past, but a genomic sequence is a time machine, enabling scientists to run evolutionary history backward. The initial sequence of the domestic cat was completed in 2007, but a recent study to which I contributed compared the genomes of the domestic cat and the wildcat (Felis silvestris) and sheds new light on the last 10,000 years of feline adaptations.

Domestic cats are not just wildcats that tolerate humans in exchange for regular meals. They have smaller skulls in relation to their bodies compared with wildcats, and are known to congregate in colonies. But in comparison with dogs, cats have a narrower range of variation in size and form.

Wesley C. Warren, an author of the study, notes that domestic cats have excellent hunting skills, like their wild ancestors. This, too, supports the notion that cats are only semi-domesticated.

Comparing the genomes of the wildcat and the domestic cat added much to what we had known. Michael J. Montague, the lead author, told me he’d anticipated that the two genomes would be very similar, but our study found a specific set of differences in genes involved in neuron development. This brain adaptation may explain why domestic cats are docile.

Scientists have long observed that domesticated species exhibit a suite of strikingly similar traits, from floppy ears to smaller brains, than those of their wild ancestors. Domestication may select for a few similar traits encoded by genetic changes (like smaller brains), but these may produce what we assume are secondary effects (like floppy ears).

Once they were living among us, cats didn’t need to think so much to stay alive; nor did they need such large jaws after we started feeding them our processed scraps. Hence smaller skulls. The same dynamic holds for dogs: Wolves beat dogs in general intelligence tests.

By examining patterns in our animals’ genomes, we’ve confirmed that the same sets of genes seem to be targeted again and again in evolution. As far back as Charles Darwin, domestic animals in particular have yielded insights about evolution because we know what sorts of selection pressures they were subject to. After all, it was us they were primarily adapting to.

Which brings us to the genome of one critical tame animal: ourselves, humans. The Nobel Prize-winning zoologist Konrad Z. Lorenz once suggested that humans were subject to the same dynamics of domestication. Our brain and body sizes peaked during the end of the last ice age, and declined with the spread of agriculture.

Instead of poring over the meager fossil record, we can survey patterns of variation across tens of thousands of living individuals. Genomics now provides evidence that humans have been subject to a great deal of natural selection over the past 10,000 years. A beautiful example is the ancestors of Tibetans’ absorption of small portions of the genome of ancient human relatives adapted for living at high altitude.

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Deb 26 November 2014
“Dogs want to be “man’s best friend”; cats, not so much.”First, I’ve grown up with dogs & cats, and have dearly loved both. Cats love you…
APS 26 November 2014
Yep, coevolution
brave 26 November 2014
interesting you mention jaws.last week there was an article about birds being able to count. Right after I finished it, I thought «does the…
Our cultural flexibility and creativity since the end of the ice age have not freed humans from evolutionary forces, but have opened up novel and startling paths. Thinking of domestication as an evolutionary process that occurs through “artificial” selection creates a false dichotomy of nurture and nature that plays into a conceit of human exceptionalism. In fact, the idea that we are apart from nature, that it is ours to tame and exploit, is an outmoded approach.

A more useful interpretation is that over the past 10,000 years, humans fashioned their own ecosystem. We were part of a natural process that altered the landscape. In that light, we can think of the domestic cat as an ecological response to the emergence of parasites (rodents attracted by early Neolithic granaries). The same forces that reshaped the genomes of our domesticates also reshaped ours.

No longer roving in small bands subsisting on game and unprocessed plants, we settled down in villages, harvesting the same crops year after year. For millenniums, peasants fed on what we might today term porridge, of various types. Our teeth became smaller — indeed, both dogs and humans show evidence of adaptation to starchy diets.

Just as the fur of our mammalian domesticates, freed from the constraint of needing to fade into the landscape, became a riot of diverse colors, human pigmentation started to change and many populations became light-skinned. With a cheek-by-jowl existence, humans and their animals began sharing diseases, remolding the immunity of whole populations, but leaving those who did not experience this co-evolution untouched and vulnerable. Possibly, some pathogens incubated in cats, like Toxoplasma gondii, may even alter human behavior.

Many of us conceive of our relationship to our pets as analogous to that between a parent and child. But the natural history tells a more pragmatic tale. Cats emerged in the context of profound ecological changes to the post-ice-age landscape wrought by humans.

We were the authors of those changes, but in the process of telling that story, we became protagonists within it. One of the essential steps in knowing ourselves, and seeing where we are going, is to look around and take note of how we’ve reshaped those nearest to us, and they us.

Source: Nytimes.com