Cats – Part 1

How prehistoric big cats influenced human evolution.

Our family decided to get a couple of cats recently, so I read a few books on the species. I had a cat named Oreo growing up and enjoyed her company, but until recently I never realized the full and fascinating historical context of cats’ existence in our lives today.

Abigail Tucker, in her book The Lion in the Living Room: How Cats Tamed Us and Took Over the World, begins by describing how we humans evolved in large part as a result of our early ancestor’s interactions with the now-extinct big cats, mainly the saber-tooth tiger:

Humanity’s early ancestors came of age in Africa during the “heyday of cats,” according to anthropologist Robert Sussman, whose book, Man the Hunted, details our history as a prey animal. In regions where we “overlapped” with cats, he tells me, “they took advantage of us completely”— dragging us into caves, devouring us in trees, caching our eviscerated corpses in their lairs. Indeed, we might not know nearly so much about human evolution if not for big cat kills. The world’s oldest fully preserved skull representing the Homo genus, known as Skull Number 5, was recovered from caves in Dmanisi, Georgia, which likely served as a sort of picnicking ground for extinct giant cheetahs. In caves in South Africa, paleontologists endlessly puzzled over piles of hominid and other primate bones, trying to figure out the source of the carnage. Had our forefathers massacred each other? Then somebody noticed that the holes in some skulls lined up perfectly with leopard fangs. The contemporary landscape also gives clues about the toll that cats likely took on us. Sussman and his colleague, Donna Hart, surveyed modern primate predation data and found that the cat family is still responsible for more than a third of all primate kills. (Dogs and hyenas account for just 7 percent.) … Antipredation strategies persist in a host of modern human behaviors, from our tendency to go into labor in the deepest part of night (many of our predators would have hunted at dawn and dusk) to, perhaps, our appreciation of eighteenth- century landscape paintings, whose sweeping vistas give the pleasing sense that we would have seen danger coming before it ever got close … Predation pressure likely also helped shape our body size and posture (tall, upright bodies allowed us to scan more distant horizons), our preference for community and social life (a glorified form of safety in numbers), and our sophisticated forms of communication.

Tucker describes how our interaction with the big cats led to our taste for meat, and to our big brains:

But the cats’ most significant contribution to our species’ evolution may not have passed from predator to prey, but rather from predator to scavenger. That gift was our own first fateful taste of meat. According to Briana Pobiner, an expert in human carnivory at the National Museum of Natural History, it’s possible that our unarmed, meat- mad predecessors simply chased some of our first prey animals to death, or threw rocks to kill them. But Pobiner— who works in her office beneath the photographed gaze of two very large lionesses— believes that it’s more likely that we were shameless thieves and scavengers, or “kleptoparasites.” Our ungracious “hosts” would have been the big cats who felled gazelles and other grazing animals, ate their fill, and then wandered away to come back later. That’s when our pesky ancestors sneaked in to snatch what they could … [T]he saber-tooths would likely have generated the best leftovers, as the anthropologist Curtis Marean has pointed out, because their big teeth were good for killing but not necessarily for chewing, leaving plenty on the bone. Some scientists have even proposed that saber- tooth table scraps were so bountiful and essential to the diet of early humans that we followed the cats out of Africa and into Europe, in the first great migration of our species … Once our ancestors tasted meat, rich in nutrients and amino acids, they wanted more. Some paleoanthropologists have argued that meat- eating ultimately made us human. It was certainly a crucial step. “Meat-eating was so important that we got better and better at making stone tools,” Pobiner explains. “It was a feedback loop. Being able to get more meat requires good perception of your environment, communication, advance planning. We would not have gone on the same evolutionary trajectory if it had not been for meat- eating.” Indeed, meat-eating may have literally expanded our minds, according to the “expensive tissue hypothesis” (which concerns brain development …) Because vegetarian primates must process large quantities of tough plant matter, they have monstrous, energy- sucking intestines. (This is why otherwise-skinny monkeys look like they have beer bellies.) But an animal with steady access to easy-to-digest meat may have the evolutionary leeway to shrink its guts and spend that digestive energy on something niftier: an enormous brain. This crown jewel of Homo sapiens is extraordinarily costly, taking up 2 percent of our body weight but 20 percent of our caloric intake. It may be that we can afford it because of meat-eating … The biggest jump in our ancestors’ brain size happened about 800,000 years ago— not long after we mastered fire, which we used to cook our meat, preserving it longer and making it more portable. A few hundred thousand years later, we figured out how to bring down big game on our own. Fast-forward several hundred more millennia and the Homo sapiens twig of the family tree finally sprouted, about 200,000 years ago.

We explored that dynamic in a previous essay.

Tucker continues:

This ancient stalemate between cats and humans, in which both parties were heavily armed and more or less equally matched in their mutual quest for meat, lasted until about 10,000 years ago, when somewhere in the Middle East, humans got enterprising, or lucky, enough to figure out how to forever satisfy our infinite hunger for flesh: raise and kill our own. The domestication of herd animals and plants, the evolutionary coup known as the Neolithic revolution, allowed hunter- gatherers to settle down in permanent communities, which ultimately led to the birth of culture, and history, and the earth as we know it.

This expansion of human civilization ultimately led to the demise of the big cats. As Tucker explains:

“Cats are very fragile,” the feline geneticist Steve O’Brien tells me. “If they don’t have a lot to eat, they starve, simple as that. It’s not shooting them that’s the problem. It’s planting farms and neighborhoods.” Cats are biologically at odds with the broadest patterns of human civilization. This was true from the first: Egypt, the first great agrarian culture, gradually lost much of its lion population. The Romans— who bagged big cats for processions and Colosseum spectacles— documented regional shortages as early as 325 BC. By the twelfth century lions were gone from Palestine, where they were once common. Before Europeans arrived in India, Mughal emperors fragmented the tiger population by razing forests. And so it went with all kinds of wild cats.

But with the fall of the big cats came the rise of the little cats:

[A] complacent human could see these incredibly numerous little felines— which we most often think of as pets— as living trophies. Just as the Romans flaunted lions in the Colosseum, and medieval kings kept them in royal menageries, perhaps we like to keep our own tiny lions around as evidence of our very recent triumph over our feline archenemies. We like to chuckle at cats’ savagery in miniature, to coo over their teeth and claws— but only now that we’ve won … Maybe a lion purring in our lap or cavorting in our living room evokes our global mastery, our total control of nature. Maybe it’s telling that one of the few places in the world where house cats are not popular pets is India, which is also the rare region where big cats can still do real damage.

Still, as Tucker writes:

But there’s also a strong case that the feline family actually remains unconquered, and that cats are still on top and calling the shots. Yes, man-eating lions have abdicated, but the humble house cat is pressing the same kingly claim in the new millennia … Indeed, for all their strength and prowess, lions didn’t get nearly as far in the world. The house cat has gained ground from the Arctic Circle to the Hawaiian archipelago, taken over Tokyo and New York, and stormed the entire continent of Australia.

As Jonathan Losos writes in his book The Cat’s Meow: How Cats Evolved from the Savana to Your Sofa, cats have conquered the hearts of humans on their own terms, with their DNA remaining pretty much the same since their origins (unlike dogs):

The first cat, Proailurus lemanensis, was about the size of a bobcat. Short legs notwithstanding, it was clearly a cat. This, in fact, has been a hallmark of feline evolution—a cat’s a cat. This may not seem extraordinary, but frequently it’s not the case: for many types of animals, some extinct species were often quite different from their modern relatives. Consider, for example, that the giant ground sloth was nothing like the diminutive tree hangers we know today, lizards that looked like sea dragons grew to fifty feet in length and cruised the world’s seas during the Age of Dinosaurs, and some ancient crocodiles lived on land and had hooves. In contrast, cats seem to have found a winning recipe and have stuck with it … [A]bout twenty million years ago, cat evolution kicked into gear. At that time the feline clan split into two branches. One of these gave rise to the many species of saber-toothed cats, which occurred throughout much of the world. The other branch of the evolutionary tree is referred to as the “conical-toothed” cats. This group, which contains all of today’s feline species, is not well represented in the fossil record … The phylogeny reveals that the common ancestor of all of today’s cat species lived about eleven million years ago. This ancestor then diverged into two lineages, the big cats (Pantherinae), with seven species, and the small cats (Felinae), with all the rest. Domestic cats belong to the Felinae. Their closest relatives, members of a lineage that first appeared about seven million years ago, are species similar in size and habits: the wildcats, sand cat, jungle cat, and black-footed cat … [S]keletal similarities clearly indicated the strongest affinities are between domestic cats and wildcats. Subsequent DNA studies, which I’ve just summarized, then confirmed this conclusion, finding that the closest species to the domestic cat on the evolutionary tree is the wildcat … The scientists found that there are very few genetic differences that consistently distinguished domestic cats from wildcats: only thirteen genes showed evidence of having been changed by natural selection during the domestication process (of course, additional changes subsequently arose in some populations or breeds of cats). By contrast, a similar study comparing dogs and wolves found almost three times as many genes involved in canine domestication … This great genetic similarity between domestic cats and wildcats, paralleling the minimal differences in anatomy and behavior, seals the case that domestic cats evolved from the wildcat.

The personality of modern semi-domesticated cats also differs little from those of their wildcat ancestors, with the exception of their increased friendliness to humans. As Losos writes:

[S]cientists compared behavioral tendencies, such as aggressiveness and sociability, among five feline species ranging in size from the housecat to the African lion. The paper’s primary conclusion was that personality-wise, there aren’t many differences among cats, regardless of size. Zookeepers have told me the same thing: if you can read the expressions and body posture of your cat, you can understand what a lion or tiger is thinking … [T]he research reveals an important fact: in many ways, a cat’s a cat, whatever its size … In terms of behavior, too, most domestic cats differ little from their ancestors. Sure, they’re friendlier—or at least more tolerant—of humans, and sometimes more sociable to each other, but in other ways—their hunting, grooming, sleeping, and general manner—they behave just like wildcats. Indeed, the ease with which abandoned cats go feral and revert to their ingrained, ancestral ways is evidence of how little the domestic cat has evolved … For this reason, domestic cats are commonly referred to as “barely” or “semi-domesticated.”

As Losos explains, this history of cats stands in sharp contrast to the history of dogs:

In contrast to cats, “fully domesticated” species are substantially different from their wild ancestors. Consider the barnyard pig. Big, portly, pink, curly tail, floppy ears, very little hair. Sus domestica is the quintessential domesticated animal, a species sculpted by humans, greatly modified from the ancestral boar (Sus scrofa) to suit our needs and desires. Or contemplate cows, far removed from their majestic wild cattle ancestors, turned into meat- and milk-producing machines by our selective breeding over the millennia.[*] Similar selection applied to plants has created food crops like corn and wheat that are vastly different from their wild progenitors. Not so for domestic cats. Look underneath the paint job—the variation in hair length, color, and texture—and most domestic cats are nearly indistinguishable from wildcats. The many great differences in anatomy, physiology, and behavior that distinguish most domesticated species from their ancestors don’t exist in cats. Recent genome studies confirm this view. Whereas dogs have diverged from wolves in many genes, domestic cats and wildcats differ in only a handful. Cats truly are scarcely domesticated … [The] behavioral difference between domestic cats and their wild cousins is relatively modest. Consider how greatly transformed dogs are by domestication: wolves, no matter how they’re raised, are nothing like their slavishly obedient, owner-adoring descendants. Compared to the wolf-to-dog transition, the difference between African wildcats and domestics is much less dramatic.

As Tucker writes:

Indeed, dogs are so in tune with humans, and their behavior is such a perfect mirror of our own emotions, that without people in close proximity they are unfinished beings. Dogs are existentially rooted in their dealings with us: they take our cues and meet our gazes and engage in a sort of mutual communion. They come alive through personal interaction and cannot be fully enjoyed from afar. Cats, though, are self-contained. They don’t need people to complete them.

Today’s semi-domesticated cats also retain their keen senses of their ancestor wildcats. As Thomas McNamee writes in his book The Inner Life of Cats: The Science and Secrets of Our Mysterious Feline Companions:

Cats have five times more surface area inside their noses than we do, and three times more receptor nerves per unit of area lining that surface. Of those receptors there are hundreds of types— the possible combinations of scent perceptions, therefore, being nearly infinite … A cat’s hearing is extremely acute— the widest range, in fact, of any mammal except bats. It is equally superior in its directionality: Watch your cat’s ears twitch and swivel, each moving independent of the other, as she tunes in on the precise place from which a sound is coming … With more than twenty muscles controlling them, [cat ears] can swivel an entire half-circle … [Cats] could tune in to the ultrasonic chatter of rodents deep in their tunnels. Cats can hear higher- frequency sounds than any other terrestrial mammal, quite a bit higher even than dogs— up to one hundred thousand hertz (cycles per second). People max out at about forty thousand, if they haven’t been to too many rock concerts or ear-splitting bars … An adult cat’s eyes are as big as a human adult’s, and she can open the pupils three times as wide. A sort of crystalline mirror behind her retina, the tapetum lucidum, amplifies incoming light by as much as 40 percent. That’s what produces the familiar gold-green shine when a cat meets a flashlight beam in the dark. It is that amplification that allows cats to see in almost complete darkness. They do pay a price for that brilliant advantage, however, some of which you can easily see— the narrow slit that her pupils become in bright light, evidence of her intolerance of excessive dazzle— and some of which you may think a disadvantage but doesn’t really matter to the cat, namely, not much in the way of color vision. Another deficit is a meaningful one: Cats really can’t focus very well up close. When you extend your palm with a couple of treats as a reward for good behavior or a trick, you may notice that your cat hesitates a moment, sniffing— finding the treat not with vision but by smell … The cat’s visual cortex records images much as an old-fashioned movie camera does— as a fast-moving series of still pictures (faster than the camera, however)— allowing a precise measurement of speed. Hence your cat’s ability to intersect the flight of a ball— or of a hummingbird— unerringly.

Interestingly, in contrast to human development, cats who drew near humans gained intestinal length and lost brain size (specifically, they lost the fear-triggering part of their brains). As Losos describes:

[F]eral domestic cats have intestines forty percent longer than European wildcats … In theory, there’s a ready explanation for this finding, one that Darwin himself proposed: “The increased length appears to be due to the domestic cat being less strictly carnivorous in its diet than any wild feline species; for instance, I have seen a French kitten eating vegetables as readily as meat.” Meat is much easier to digest than plants or other types of food. For that reason, species that normally eat nothing but meat, like cats, have short intestines. Species with mixed diets—omnivores—have middling-length guts, and the plumbing of plant eaters is extensive … Feral cats that scrounge a living around human habitations eat whatever they can find, including grains and other plants. It’s easy to envision that in the early days of domestication, natural selection favored individuals with longer intestines to better digest the scraps they were eating, and that this led to the greater intestine length of today’s domestic cats … Contrarily, in the brains department, domestic cats are less well endowed than their wildcat brethren. Two studies remarkably came to exactly the same conclusion that European wildcat brains are twenty-seven percent larger than those of domestic cats. A more recent study has confirmed that African wildcats also have more gray matter than domestic cats, though not quite as much as their European cousins. Reduced brain size is a common phenomenon in domesticated species and has been reported in sheep, pigs, horses, dogs, llamas, mink, and many other species … Fear not, though, this does not mean that Sylvester and Fido (nor Porkie and Bessie) are stupider than their wild cousins. Rather, the reduction in brain size is concentrated in the parts of the brain associated with aggression, fear, and overall reactivity. This, of course, makes sense for domesticated animals living around people. High-strung animals prone to flight and stress wouldn’t survive; natural selection would favor any individual less sensitive to such matters, and thus reduction in parts of the brain underlying these behaviors would be favored … As far as [differences between domestic and wild cat] anatomy goes, that’s it: intestinal length, brain size, and, in African wildcats, rusty-red ears. If you’re in the African bush or a European forest, those are the only traits that you can always rely on to determine which species you’re examining.

As Tucker puts it:

[Semi-domesticated cats] exhibit the single most vital and distinctive sign of the domesticated body type: house cats have shrunken brains, smaller than lybica’s by about a third … [B]rain reduction is a standard feature of domestication in animals ranging from turkeys to llamas. It does not mean the animals are stupid; rather, it allows them to survive in our settlements. Typically, the reduction involves the forebrain, which includes the amygdala and other components of the limbic system, controlling perception and fear. A whittled- down fight- or- flight response means that an animal is better suited to stress— the crux of domestic existence. In large part because of their reduced fear responses, house cats are brazen, and— if exposed to enough human contact early in the first two months of life— can display the docile and even downright friendly behaviors (rubbing ankles, licking faces) that their owners appreciate today. But here again, because human beings weren’t actually steering the process, it took ages for the cat brain to shrink. Analysis of Egyptian cat mummies from just a few thousand years ago shows that those animals still had brains as big as their wild relatives’ … Scientists now suspect that domestication syndrome may be caused by a deficit in embryonic stem cells called neural crest cells, which help determine an animal’s forebrain size. Interestingly, the neural crest cells also influence a remarkable array of factors like skull shape, cartilage formation, and coat colors when they migrate to different parts of the body during fetal development. Favoring tamer animals with smaller forebrains and reduced startle responses in species ranging from cows to carp, humans may have inadvertently selected for these impaired neural crest cells and all their myriad consequences— weird colors and droopy ears and twisted tails included … So after the first intrepid felines breached our communities very, very gradually— much slower than they would have had humans been running the show— the offspring of certain wild cats became ever more frequent and emboldened guests. Over the centuries they shrank their brains so they could stand to live among us and grew their guts so they could help themselves to more of our meaty garbage. Along the way they acquired some pretty white spots … [In contrast to smaller brain size,] house cats have … lengthened their intestines— a hypercarnivore’s concession to the more varied, difficult- to- digest protein sources available in human settlements … Apart from those few stingy changes, however, house cats barely twitched a whisker to accommodate humanity— not then, and certainly not today. Which again begs the question: Why did we let them stay?

The answer to that question will be the subject of the next essay in this series.