The Science Behind Our Feline Friends
Domestic cats (Felis catus) and humans have an undeniably unique relationship: they seem to tolerate us (in some cases, maybe even love us), but they are also incredibly independent and have no real reliance on humans because of their exceptional hunting skills. The current science behind this relationship, and behind our feline friends, can bring a new appreciation to the small, goofy, vicious predator that we’ve come to accept as our companion.
Domestication of cats dates back to roughly 9,000-12,000 years ago in the agricultural Natufian settlements of the Fertile Crescent, but their story is a little bit different than that of barn animals and dogs. Cats were not bred necessarily for their utility to humans. Living near these communities was favorable at the time due to the lack of predators and the large rodent population feeding on the grains. A harmonious relationship with the humans allowed cats to preserve their stable food source, thus increasing their chances of reproducing successfully. Natural selection, as opposed to artificial selection, is most likely responsible for the close relationship between humans and cats. This may still be the case as at least 97% of nearly 1 billion domestic cats alive today are either feral or random-bred house cats, so their mates are not chosen by humans. In addition, the majority of feral cats do not rely on humans for food (Driscoll et al. 2009, Bradshaw 2013).
Archaeological evidence suggests that the close companionship between cats and humans that we know today dates back to 4,000-2,000 years ago in Egypt, and it’s possible that many of the same behavioral adaptations that allowed cats to cooperate with one another also facilitated their relationship with humans (Málek 2006, Bradshaw 2016). There is also zooarchaeological evidence of cat fur exploitation in medieval Iberia (Lloveras et al. 2017) and association with human populations in the medieval harbor of Qalhât in the country of present-day Oman (Monchot & Guintard 2017).
Cats are more sensitive to human interaction between the ages of 2 and 6 weeks, and their quality of human experience during this time can affect their relationship with humans as they get older. In addition, permanently separating the kitten from its mother at less than 12 weeks of age can increase probability of aggressive behavior (Ahola et al. 2017). The act of feeding your cat can make your relationship closer, but maintaining that closeness requires more interaction during feeding such as speaking with the cat or stroking the cat (Turner 2017).
To show affection for their humans, many cats will rub or lick them to simulate the rubbing and licking usually exchanged between cat friends. Many cats enjoy being pet on and around the head, since that’s typically where friendly contact occurs between cats. The act of kneading (or “makin’ biscuits”, as I like to say) is usually done by kittens the stimulate milk flow from the mothers (Bradshaw 2016). Cats may also miss their owners while they’re gone. In a study with 14 privately-owned cats, cats who have been separated from their owner for 4 hours purred and stretched their body more upon reunion with their owner than cats separated for 30 minutes (Eriksson et al. 2017).
Many cat owners can attest to some of the undesirable behaviors of cats, including refusal to use the litter box. In addition to the use of urine for marking territory and sometimes conveying frustration, the reason many cats poop or urinate outside their litter box has little to do with who previously used the litter box (if in a multi-cat home) or if it smells bad, but more so the physical/visual obstructions that accompany a used litter box (Ellis et al. 2017). Regularly removing these obstructions would minimize the amount of cat waste that doesn’t make it into the litter box.
Domestic cats are obligate carnivores, so they are adapted to a diet high in protein. In human households, however, their diet may be high in carbohydrates. A study of food selection in cats (Salaun et al. 2016) found that when given the choice between a high-protein/low-carbohydrate and low-protein/high-carbohydrate diet, cats will most often choose one high in protein. When presented with a diet high in carbohydrates, cats may limit their daily food intake. This is done to be able to regulate their protein and carbohydrate intake to maintain high and low levels, respectively (Salaun et al. 2016). When domesticated cats, particularly kittens, in a shared living space feed on something that resembled what they would normally eat in the wild, such as beef rib, they exhibit much more aggressive behavior that they normally wouldn’t show if they were sharing some canned cat food. Multiple factors about the meat they’re consuming, such as texture, smell/taste, and monopolizability, can explain the variation in aggressive behavior when feeding (González et al. 2018).
As more and more cats began wandering into agricultural settlements in search for rodent prey, it became favorable to be less aggressive to other cats in order to preserve access to a predator-free, all-you-can-eat dining experience. This required more sophisticated forms of communication that goes beyond forming a few friendly relationships. These cats needed to be able to assess each others’ intentions and negotiate. One way domestic cats overcome this barrier is by extending their tail straight up in the presence of another cat as a sign of friendliness. If both cats extend their tail, it is okay for them to approach one another. They will then solidify their friendship by briefly rubbing their heads or flanks together then separating, or they might begin grooming and stroking one another-- this has been described as the “glue” of the cooperative relationship between members of the cat colony (Bradshaw 2013, Bradshaw 2016).
Cat colonies are most often formed between related females and their offspring, with adult males either solitary or floating between colonies. This is likely because cooperative hunting was needed to supply enough prey to feed multiple kittens, resulting in coalitions between female cats while male cats remained solitary and did not evolve cooperative behavior. In addition to providing a stable food source, these coalitions offered protection from predators and competing colonies. However, bonds can easily be broken between unrelated cats and cats who have not been together since birth. The lack of submissive behaviors in their repertoire may be to blame for their poor conflict resolution, and it may explain why introducing cats to one another can be a challenge. To maximize success of your feline introductions, they must be done gradually and include the introduction of each cat’s odor in a neutral setting (Bradshaw 2016).
Meowing what is most often thought of as the domestic cat’s primary form of communication, but feral cats are generally silent. Though all cats know how to meow, it’s done primarily to communicate with humans. Domesticated house cats have likely developed their meow and other noises through trial and error, depending on how their humans respond. Because of this, it’s possible a cat and its owner may have their own “language” that only they can understand-- not other cats or humans. When cats purr, it’s thought that they’re seeking physical contact in a variety of contexts. Cats purr not only when they’re content, but also when they’re anxious and even during the moments right before death (Bradshaw 2013, Bradshaw 2014). During weaning, both kittens and their mothers exhibit behavior that minimizes conflict as they go their separate ways: the kitten begins to stop calling for the mother and the mother ceases to come when the kitten calls (Bánszegi et al. 2017).
Cats can recognize each other by the smell of their poop (Miyazaki et al. 2018, Uetake et al. 2018) and can communicate using other olfactory (i.e. smelly chemical) signals through gland secretions, scratching, saliva, and urine. Signals produced by cats in their home range or by their mothers if they’re a kitten can make cats feel more safe in their environment, and signals produced by cats who are friendly to each other may facilitate friendly interaction if the cat is in the presence of an unfamiliar cat/human (Bradshaw 2016, Vitale Shreve & Udell 2016).
Cats’ individuality is one of the most common things reported in the literature on domestic cat behavior (Turner 2017). In a survey of 2,820 domestic house cats in New Zealand and South Australia, five main purr-sonality factors were identified out of 52; these factors represent traits related to neuroticism, openness, agreeableness, impulsiveness, and dominance. Additionally, an analogue of the Facial Action Coding System (FACS) was developed for analyzing cat facial expressions (CatFACS, www.catfacs.com). This system identified facial actions associated with fear (blinking, half blinking, left-gaze bias) and frustration (hissing, raising of upper lip, lowering of lower lip, dropping jaw, licking nose, parting of the lips, vocalization, showing of the tongue, mouth stretching) that can vary with the presence of humans (Bennett et al. 2017).
Mutations in genes that are involved in the production of neural crests (a group of cells that form during development and later give rise to the neurons, glia, bone, cartilage, and connective tissues of the face) may underlie the evolution of docile behavior, or “tameness”, in domestic cats. In mouse models, these genes are associated with behavior and reward (Montague et al. 2014).
There were not as many cat genes that changed during domestication as dog genes. This makes sense because cats were domesticated more recently than dogs, and they underwent minimum artificial selection from humans. Most of the color differentiation in cats occurred during domestication, before the appearance of the < 30-40 genetically distinct cat breeds we know today (Montague et al. 2014).
Cats and Disease
Cats are a definitive host of microscopic parasite Toxoplasma gondii, which means cats are the host in which the parasite reproduces. The parasite is excreted in the feces where it can be picked up by nearby rodents, grazing animals, and humans to reside in the brain and other body tissues. (McAuliffe 2012)
People who are pregnant, when exposed to the parasite, can pass the infection to their offspring, potentially resulting in severe brain damage or death. Healthy children and adults don’t experience anything worse than flu-like symptoms, but T. gondii can be a threat to humans with weakened immunity (McAuliffe 2012).
After humans initially fight off the parasite, there may be latent infection in the brain. This may cause symptoms such as delayed reaction time, and people who are infected are more likely to be in car accidents than non-infected individuals. Infection in humans may also result in heightened anxiety, which can manifest itself differently between men and women. Infected men are more likely to be distrusting, introverted, oblivious to others’ opinions, and disregard rules while the opposite effect is seen in infected women who are more trusting, outgoing, and rule-abiding. T. gondii infection may play a role in human mental health by reducing gray matter in the brain of schizophrenia patients and potentially increasing rates of suicidal behavior (McAuliffe 2012).
In infected rats, infection will lead to altered states of fear, anxiety, and sexual arousal as they relate to cats: it will make rats more attracted to cat urine to ultimately make it easier to be eaten by the cat, allowing the parasite to complete its life cycle and reproduce inside the cat. Infected rats are more active and less weary of open spaces, which makes them easier prey targets (McAuliffe 2012).
Humans can come in contact with the parasite in more ways than just cleaning out the litter box: eating unwashed vegetables and raw/undercooked meat can also increase chances of exposure (McAuliffe 2012). Gardens and farms where cats defecate are “hotspots” for T. gondii if populated by domestic cats (Simon et al. 2017, Bastien et al. 2018).
In Rio de Janeiro State, Brazil, domestic cats also play an integral role in the epidemic of sporotrichosis, a zoonotic (i.e. can be transmitted to humans from other animals) disease caused by Sporothrix schenckii fungi (Macêdo-Sales et al. 2018). Cats can also harbor a number of helminths, or parasitic worms. In a survey of 66 cats and 101 black rats on Christmas Island, 61 cats and 85 rats were found to be infected by at least one helminth, and the number of helminth species found in cats was larger than expected for an island, with many of them involved in diseases affecting humans (Dybing et al. 2018).
Cats and Other Species
The diet of domesticated cats ultimately depends on what’s available and can be fairly flexible, which is one of the reasons they can be a threat to surrounding wildlife. They prey on birds, rodents, and other small mammals as well as invertebrates, reptiles, amphibians, fish, and carcasses of other animals (Carrión & Valle 2018, Széles et al. 2018). Cats can also have an effect on the reproductive cycle of the house mouse (Kvasha et al. 2018). Collectively, domestic cats have contributed to the extinction of at least 63 vertebrates through predation, disease, and fear-related behavior (Loss & Marra 2017).
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