When a stray cat wandered onto the tracks of a midtown 7 train in New York City last month, the MTA halted the entire subway line until the animal was out of harm's way. At the same time, the U.S. government euthanizes millions of stray cats each year.

They're a disaster for the environment: One conservancy organization has called cats the "ecological axis of evil." American cats kill between 1.4 and 3.7 billion birds each year, and they've been implicated in dozens of mammalian extinctions. (The Australian government has funded research into the most efficient methods of cat control -- yielding products like a poison-laced kangaroo sausage called "Eradicat.")

Nearly half of house cats have physically attacked their owners.

Humans' relationship with cats is rife with paradox. There are an estimated 100 million pet cats in the U.S., and their ranks are only growing. "Cat culture" flourishes online. The cat-less can get their fix at "cat cafés" opening across Asia, Europe, and North America.

In " The Lion in the Living Room : How Cats Tamed Us and Took Over the World," journalist Abigail Tucker traces cats' journey from fearsome Near Eastern predator to global intruder, shedding light on how this baby-sized beast worked its way into so many homes.

Science of Us spoke with Tucker about the disturbing similarities between cats and lions, the reason cats failed to uphold the Rabbit Suppression Act of 1884, and the somewhat baffling question of why people put up with them.

You write that cats are a rather unlikely house pet. Why is that?

Cats are uniquely ill-suited for domestication. When people set out to domesticate the first animals, we targeted animals that were easy to keep in confined spaces, and animals that would eat a variety of things -- think of a pig or a goat, which will eat any old swill left over from your kitchen. Cats eat only fancy food, meat that we could eat ourselves.

We also tended toward animals that had social hierarchies that we could dominate. Dogs and cattle have lead animals, and we can control them by acting the alpha dog or the lead steer. But cats are solitary animals that don't have social hierarchies. They're hard to physically control, and they don't tolerate confinement well.

Usually, you don't have to write a 200-page book to figure out why we domesticated an animal. There's a purpose for the animal, and it's really clear: We want its meat or its milk or its fur or its labor. But what on earth did we want cats around for?

As I talked to scientists, it dawned on me that we weren't necessarily the ones who were driving this relationship. House cats sidled up to our first settlements 10,000 years ago, because of big changes we started making to the environment. All of these animals crept into our settlement and were eating our trash -- animals like badgers and foxes, in addition to small wildcats. They got into this new niche and exploited it.

So how did they trick us into feeding them and taking care of them?

Cats have big round eyes located right in the middle of their faces, because they're ambush predators and need good binocular vision. They have little noses, because they don't hunt by smell. They have round faces because they have short, powerful jaws. This set of features, which is actually just an expression of the way the cat hunts, looks to us like our infants. That gave them a leg up on the competition, and made them an intriguing and charming presence, rather than a straight-up nuisance, like a raccoon.

One justification people give for keeping cats around is that they hunt rodents. I was surprised to learn that cats aren't even that good at killing rats.

Cats are magnificent hunters, and they can hunt anything from butterflies to wallabies. They can kill rats but they have no reason to, in our cities. There's plenty of garbage for everybody. Cats and rats have been photographed sharing piles of trash. Why would these animals fight and risk their lives, when they could just comfortably graze together?

People have tried it before -- letting a feral cat colony go within a certain area, with the goal of keeping rat populations down. While they might kill a few rats, the populations of rats are so big that there's no way the cats can ever repress them.

In colonial Australia, there was this act called the Rabbit Suppression Act of 1884. The Australians released hordes of house cats, because they wanted them to kill off these invasive bunny rabbits, which the British had also released. They even built them little cat houses out in the wilderness, so they would have a place to live. But the cats didn't end up killing off the rabbits.

Cats can kill a gazillion rabbits, and there are still more rabbits -- they breed like rabbits. What the cats ended up doing was killing off other more vulnerable, native animals. Cats don't do their assignments the way that dogs do.

Pet owners like to say that caring for their dog or cat confers various health benefits -- mental as well as physical. But what do we really know about how having a cat affects our health?

There have been all these studies about toxoplasmosis, the cat-borne parasite that can get into human brain tissue. Some scientists think that there's a link between this parasitic disease and mental-health problems, especially schizophrenia.

Even if your cat doesn't give you toxoplasmosis, it may not be wonderful for your mental health. There are a few troubling studies that show that having a cat can decrease your likelihood of surviving a heart attack and increase high blood pressure.

People who have cats are less likely to be outside in the world, walking their cats, meeting other people in cat parks. And cats may not be as good a substitute for human companionship as other kinds of pets. Dogs and their owners have this lovely synergy -- they gaze into each other's eyes , and both of them have this flow of oxytocin going.

That doesn't happen so much with cats. In nature, cats don't live near other cats, and they don't have a good expressive repertoire. One way they communicate is by leaving pheromones and other smells around, which humans are completely oblivious to. We're really not built to communicate with each other.

One of the fascinating things about cats is their adaptability. Even though they are fundamentally asocial animals, they've figured out how to manipulate their human hosts. Feral cats don't meow much, but in the presence of humans, cats learn how to communicate to get what they want. They purr in a manner that embeds this insistent, annoying, almost infantlike cry inside of a pleasant purr, to condition their owners to get them food.

But is it possible to know if cat owners' mental-health problems are the result of having a cat? Might someone who is already lonely or antisocial be more likely to get a cat?

I think it could be both. Somebody who is socially isolated to begin with, or unable to do the rigorous care that a dog needs, might be more likely to get a cat -- but having a cat can be isolating in and of itself. It's interesting that people persistently describe the internet as a digital cat park, where cat people can finally socialize via their pets.

I have seen a lot of articles lately about the cat-borne parasite toxoplasmosis. [One researcher blames the rise of insanity in the 19th century on the rise of toxoplasmosis-infected house cats. Another study says that people with toxoplasmosis are twice as likely to be in a car crash, and suggests that infected drivers have been distracted and worn out by persistent low-level sickness. Toxoplasmosis-infected prey animals like chimps and rats, which are usually repulsed by the urine of predators like leopards and rats, are attracted to it instead.] A lot of these stories seem a little bit hysterical. Do you think the fear around toxoplasmosis is warranted?

I do think a lot of them are overblown. Scientists agree that the parasite gets into our brain and can be very damaging to human fetuses and people with compromised immune systems, but there isn't a ton of support for the idea that cats are manipulating us via this parasite.

I think that the fact that we have glommed onto this idea, and we write so many stories about it, speaks to the fact that cats do have some kind of mysterious power over humanity. These stories about toxoplasmosis remind me of stories that used to come out six or seven hundred years ago about cats and sorcery -- that cats have dark powers we don't understand, that they're witches in disguise.

On that note, cat culture seems pretty female. Whether it's witches or "cat ladies," cats seem to always be associated with women -- what's that about?

From my experience drifting around the cat world, it does seem to be more of a female-centric passion. The simple, slightly sexist explanation is that cats' infantile-looking features prey particularly on female instincts.

There are some interesting ideas from evolutionary psychologists -- that a woman might use a cat to hone her parenting skills or, before having kids, to demonstrate her fitness as a mate. I think that people of both sexes could be guilty of that. It does seem like it's a good way for guys to meet women, to be a passionate public cat-man.

Why are cats such an ecological disaster? How did they end up in isolated island environments like Australia?

Cats are very good shipboard travelers. They don't need a lot of water; they don't need a lot of vitamin C, so they don't get scurvy. They've been able to endear themselves to sailors for the past 10,000 years and sail across the oceans, which are the major barrier to mammalian dispersal. It's usually hard for mammals to get to places like Australia. They have to ride on rafts or get blown in. A lot of islands don't have any mammals living on them at all, let alone apex predators that are hypercarnivores, like cats.

With just a few tweaks, the house cat is basically the king of beasts. Cat species are very different in terms of size, but the feline blueprint -- their behaviors and the proportions of their bodies -- is really consistent across species. You let it go in any environment and it's going to be able to kill anything that's smaller than it, and even things that are a little bigger. It's like a meat-eating machine.

You tell stories of house cats clawing and scratching their human owners, especially children. Why do cats so often turn on the people who feed them?

Cats and humans haven't lived locked inside the same places, in such numbers, until the last few decades or so. We talked about the implications for our mental health, but this arrangement might not be so great for cats' mental health, either. They can get really stressed out in our houses. A lot of things that we consider normal -- everything from the volume of our voices, to our thermostats, to the way that a child is playing with a toy -- can stress cats out.

There's evidence that to prevent cat-human violence, we need to go to more extreme lengths than I'd ever thought. Experts say that you need to give an entire room of your house for the cat's exclusive use. That you should make sure the cat has multiple litter boxes, one per floor, and extra ones for extra cats. That you should never rearrange your furniture. That you should try not to wear perfume. That houseguests are freaky for your cat.

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You're coming at this subject as a lifelong cat-lover. Did learning all of this -- that cats are bad for your health, bad for the environment -- change your relationship with your cat? Why would you still want to have a cat?

I lost a lot of my sentimental regard for cats -- that "oh, my cute fur-baby" response. But I find that I marvel at them more. I can appreciate the backstory, how this little animal managed to carve out a place for itself in the world, and to become a dreaded invasive species and -- culturally speaking -- one of the most powerful animals on the planet.

To me, it's about the wonder of life, and how this animal has gotten so far in the world without giving us much in return. I think that makes our relationship more pure. Humans are so good at extracting what they want from the environment. With cats, we're not necessarily holding the reins. We don't even know what we want, but we love it.

The interview has been edited and condensed.