If you are a cat owner, you’ve probably gazed at Whiskers on the couch and asked, “Why does he sleep so much?” The answer is very simple, says a noted Texas A&M University animal behaviorist: It’s in their DNA.

Bonnie Beaver, a veterinarian at Texas A&M’s College of Veterinary Medicine & Biomedical Sciences and a former president of the American Veterinary Medical Association, says cats are natural sleepers–and they are very good at it.

When it comes to sleep, the news about cats is hardly out of the bag. Many cats sleep 16-20 hours a day, more than any other animal.

“Over the thousands of years that cats have evolved, so have their sleeping habits,” Beaver says in a release. “Early on, they had to hunt for food to stay alive, and that desire for food can require a lot of energy. So sleeping helped cats conserve their energy, and even though the common housecat does not have to hunt for its next meal, a cat is still conditioned for sleep.

“House cats sleep a lot more than feral cats do because they don’t have to spend a lot of time searching for food.”

A lot of that time–maybe as much as 40%–is spent resting and not in deep sleep, Beaver says.

So with all of that sleeping, do cats dream? “We know that dreaming occurs in REM (rapid eye movement) sleep, and cats very much have an REM phase of sleep,” she says.

“They also exhibit movements during REM sleep, so it is possible they can dream. What are they dreaming about? Since we can’t ask them, we really don’t know.” She adds that if a cat’s whiskers or paws twitch during sleep, it’s very possible it is dreaming.

And while dogs are known to snore, cats tend to be quiet sleepers, Beaver says. “Most cats don’t snore because they don’t have a loose, soft palate like many breeds of dogs do,” she says.

There’s also the flip side–if Fluffy appears to sleep very little, it may not be a true cat-astrophe, but it could be a sign that something is wrong. “Each cat is unique, so if it does not seem to sleep much, it may be its normal routine. It is more important to note changes in behavior. If it seems like the cat is not sleeping as much as it used to, it could meaning something is wrong; perhaps it’s suffering from hyperthyroidism. If that is the case, the cat needs to see a veterinarian.”