By Olivia Marx

If you have ever lived with a domestic, or house cat, you’re probably aware of some distinctly feline habits, such as sleeping most of the day, chasing bugs and toys around, staring out the window, and meowing in a way that you just can’t ignore. Cats are a delightful addition to any home, but domesticated cats are more than a nice lap warmer. They are a product of thousands of years of co-evolution with humans, giving them a completely unique relationship with us that allows them to remain (more or less) independent while truly accepting humans as part of their families.

Cat evolution with humans

Wildcats are generally solitary, territorial, and carnivorous animals, making them a poor candidate for domestication [1]. Many theories suggest that the beginning of farming caused an increase in rodent pests and wildcats hung around to control the mice and rats [2]. While this was beneficial to humans, other mice-catching animals are more efficient than cats at keeping pests away, limiting the practicality of the human-cat relationship. Scholars speculate that wildcats who were comfortable in a human environment simply began to diverge from their wild counterparts, domesticating themselves without much human intervention [1].

As farming spread across the world, so did domesticated cats. Genetic lineage tracing identified five distinct lineages from wild cats throughout Africa, Europe, and Asia, however, one mitochondrial DNA lineage prevailed in nearly all regions domestic cats were found [1]. Mitochondrial DNA is a useful ancestry marker because it is less complex than the somatic genome and so ancestry groups can be directly maternally traced. Therefore, it is likely that cats evolved from a single domestication event in the Fertile Crescent and then migrated with humans and potentially interbred with wildcats of different regions [1].

Genetic testing for cats

Although genetic testing can tell us a lot about the cats that lived with humans thousands of years ago, what about the cats that live with us now? Most people opt for cat adoption or end up finding their cats in unconventional ways. In fact, only about 3% of cats are purchased from a breeder, and thus, most American cats’ breeds and lineages remain unclear. With the rapid advancement of genetic tracing and gene sequencing technologies, tracing your own furry feline’s lineage is relatively easy. Commercial services, such as BasePaws and WisdomPanel,  help owners find what different breeds are present in their own cats. These services work by taking advantage of single nucleotide polymorphisms (SNPs), genetic markers that get passed through generations and mark similar ancestry, or breed, in cats and humans alike. As more genetic markers are discovered in unique populations, lineages will become increasingly detailed and accurate. Figure 1A shows the genetic lineage results of an especially wonderful boy, pictured in Figure 1B with long black fur, along with two other excellent domestic cats.

Why humans love cats

So far, we have learned that domestic cats are just wildcats that found a niche with humans, just as rats and mice, and cockroaches naturally found their way to us [1]. Despite their lack of practical use for food or protection, this popular pet has stolen the hearts of many people. In fact, there are over 2 million cat videos on YouTube with over 25 billion views. It may not be a coincidence that humans love their furry felines. There are known benefits of petting a cat, including that happy feeling from serotonin release and a decrease in stress. In fact, one study found that the stress hormone cortisol was significantly decreased in university students after just 10 minutes of petting cats and dogs [3]. In addition, cat owners have a significantly reduced risk of heart attack [4]. Cats often purr when injured or afraid at frequencies of 25 and 50 Hz. These low frequencies assist bone growth and healing [5] by promoting osteoblast production, though its utility for humans remains debatable. In addition to loving cats because they are entertaining and happy-making, house cats have adapted to manipulate humans with their meows. Most wildcat species only meow as kittens, and even adult domestic cats rarely meow at each other. Instead, this form of communication is reserved for domestic cat-to-human conversations, and in fact, their meows have evolved to mimic the frequency of a human baby’s cry, lending it a sense of urgency that humans feel the need to respond to.

Additionally, an even more sinister manipulation may be afoot in the case of human obsession with cats. Toxoplasma gondii (T. gondii) is a parasite that is present in around 30% of domestic house cats in the USA. Cats have the unique ability to spread this infection through their feces [6]. T. gondii infections are known as toxoplasmosis, a disease which affects around a third of humans, but is generally thought to remain dormant. Toxoplasmosis is known to alter the behavior of rats to make them attracted to danger and cats, but its effect on humans is less clear. Humans born with congenital toxoplasmosis are known to have cognitive disabilities, and studies have associated toxoplasmosis infection with decreased intelligence [7]. As T. gondii has been shown to make rats love cats, some people speculate that it makes humans love cats too, however, there is no scientific evidence to support this.

There are risks and rewards to adopting a cat, but perhaps the biggest downside is their 10–15-year lifespan never seems long enough.

TL:DR

• Domestic cats evolved alongside human society with little to no utilitarian purpose.
• Genetic lineage tracing suggests that domestic cats evolved from a single society in the fertile crescent.
• Domestic cats can benefit a person’s physical and mental health, but they also manipulate humans with their meow that sounds like a baby’s cry.

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References

1. CA Driscoll, DW Macdonald, SJ O’Brien, From wild animals to domestic pets, an evolutionary view of domestication. Proc Natl Acad Sci USA 106, 9971–9978 (2009).
2. Y Hu, S Hu, W Wang, C Wang, Earliest evidence for commensal processes of cat domestication. PNAS (2013).
3. Pendry, P., & Vandagriff, J. L. (2019). Animal Visitation Program (AVP) Reduces Cortisol Levels of University Students: A Randomized Controlled Trial. AERA Open, 5(2).
4. Qureshi AI, Memon MZ, Vazquez G, Suri MF. Cat ownership and the Risk of Fatal Cardiovascular Diseases. Results from the Second National Health and Nutrition Examination Study Mortality Follow-up Study. J Vasc Interv Neurol. 2009 Jan;2(1):132-5.
5. E Muggenthaler, The felid purr: A healing mechanism? The Journal of the Acoustical Society of America. (2001).         
6. JP Dubey, CK Cequiera-Cezar, FHA Murata, OCH Kwok, YR Yang, C Su, All about tosoplasmisis in cats: the last decade. Veterinary Parasitology (2020).
7. JP Webster. Rats, cats, people and parasites: the impact of latent toxoplasmosis on behavior. Microbes and Infection (2001).