When your cat sees a stranger, does he come and snuggle close or hiss and run away?

Whether a feline friend is a lap cat or a claws-out kitty is largely affected by their socialization as young kittens. But at least part of cats' friendliness may be in their genes. And the widespread practice of spaying or neutering cats before they are adopted may be inadvertently selecting for aloof cats, by ensuring the friendliest animals don't reproduce, one researcher says.

"The very cats that are the friendliest and the ones that don't do much hunting are the very ones we are told we should be neutering," said John Bradshaw, an anthrozoologist at the University of Bristol in England, and the author of "Cat Sense: How the New Feline Science Can Make You a Better Friend to Your Pet" (Basic Books, 2013). [6 Secrets to Unlock Your Cat's Personality]

But not everyone is convinced.

Domestic and feral cats are genetically indistinguishable, so spay/neuter programs are unlikely to nudge the gene pool one way or the other, said Carlos Driscoll, a University of Oxford biologist who is studying the genome of the wildcat from which the domestic cat emerged at the National Institutes of Health in Bethesda, Md.

Subtle differences

Domestic cats arose from a subspecies of cat called Felis silvestris lybica between 10,000 and 20,000 years ago in the Near East or North Africa. But the genetic differences between this wildcat ancestor and its tamer offshoot are very subtle: Wild cats and domestic cats look alike and are able to mate with one another, Driscoll said.

Just 10 to 20 gene changes may be responsible for domestication in the tame cats, though scientists don't know which ones.

Because so few genes are associated with domestication, spay and neuter policies that ensure the friendliest cats don't reproduce could be "pushing domestication backward" to a noticeable degree in the next 50 to 100 years, Bradshaw told LiveScience.

Selecting for less-friendly cats?

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To support that notion, Bradshaw conducted a simple test of cat personality in Southampton, England: He had strangers enter the houses of kittens in the area, try to pick up and stroke the cats, and then watched the kitties purr or hide.

In an area where spaying and neutering rates were highest — more than 98 percent —kitties tended to be a bit more skittish around strangers, possibly because they have to "import" their fluffy friends since their own pals aren't able to reproduce. Less-affluent areas had bolder, friendlier cats. [Images: See How Cats See the World]

"What we suggest is people [in affluent areas] are getting kittens in from the countryside from feral cats that are a little bit wilder," or from a few feral females and just a few tomcats that are "living in the shadows," Bradshaw said.

Therefore, intensive spay and neuter programs may be artificially selecting for the less-tame cats, he said.

"Neutering is — in terms of biology, in terms of population dynamics — a mortality factor," Bradshaw said. "If you neuter, you've removed its genes from the pools, so when you look at the next population, you have to rule it out."

The study has a few caveats: It hasn't been published in a peer-reviewed journal, and the team only looked at about 70 cats in all.

Other solutions

And even if the findings are borne out, Bradshaw isn't suggesting a return to the old days, when cats mated freely and the unwanted kittens were tossed in a sack and drowned.

Cats kill billions of animals a year, so cities rightly want to keep feral-cat colonies in check. But if that's cities' aim, Bradshaw said, they should find the ultimate source of the problem: food.

"Are there people feeding them, are they stealing the food, is it bad hygiene in restaurants?" Bradshaw said.

Reduce the available food, and the feral-cat population will naturally decrease, he said.

Identifying the genes involved in cat personality could also help, by allowing breeders, for the first time, to select for traits such as friendliness and gentleness, rather than just looks, he said.

Skeptics remain

Driscoll doesn't think spay and neuter programs will make cats any less friendly. For one, no studies have ever shown any genetic differences between house kitties and feral cats — which are, after all, just domestic cats that fend for themselves and haven't been socialized to live with humans.

Moreover, simply too many cats with too much freedom are on the prowl for spay and neuter programs to change the entire gene pool.

"The population of domestic cats has been stable for a very long time," Driscoll said. "There's a lot of genetic inertia there. You can go out and spay and neuter all the damn cats you want, and the next year, they're all going to be back."

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