The first close look at the genetic code of a domestic cat suggests that food rewards from people brought man and feline together, based on genome variations associated with memory and reward behaviors.

The study also identified how cats evolved to lead solitary, meat-eating lives, and finds that, perhaps unsurprisingly, cats arent quite as domesticated as dogs.

The domestic cat genome shows a relatively small number of changed genetic regions compared to domesticated dogs, said Wesley Warren of the Genome Institute at Washington University School of Medicine in Saint Louis, who led the study. Cats are clearly still very independent in their behaviors, and, importantly, still interbreed with wild populations.

Americans alone own 96 million cats, according to the Humane Society. The findings, published yesterday in the Proceedings of the National Academy of Sciences, may help researchers better understand and treat cat diseases, including illnesses shared with humans, such as kidney calcification.

Cat domestication began about 9,000 years ago, an estimate based on the remains of a cat laid carefully next to those of a human at an ancient Cyprus burial site, though most of the 30 to 40 cat breeds today originated just 150 years ago, previous research has found.

To examine what happened during that domestication process, Warren and colleagues sequenced the genome of a female Abyssinian cat named Cinnamon and compared her DNA to genomes from six other domestic cat breeds, two wild cat species, and to the genome of a tiger, dog, cow, and human.

Many of the genes identified as changed in domestic cats have been linked to reward responses, memory and fear conditioning, studies in mice have shown. The genome changes suggest cats became tame as they became less fearful of humans and more responsive to being rewarded with food.

The feline genetic code also offered insight into how cats evolved away from other mammals.

Compared to omnivorous humans and herbivorous cows, carnivorous cats appear to have more quickly evolved genes that bestow an enhanced ability to digest heavy fats found in meat. A study in polar bears published earlier this year found the same genetic adaptation in the DNA of the meat-loving Arctic bear.

In addition, by comparing cat and dog genomes, the researchers found a unique evolutionary trade-off between the two groups: While dogs evolved an unsurpassed sense of smell, cats traded in those smell receptor genes for genes that enhanced their ability to sense pheromones, odorless substances that enable animals of the same species to communicate, such as to find a mate.

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If Your Cat Doesnt Like You Much, Blame Its Genome