Introduction
Cats are one of the smallest domesticated animals. The average domestic cat weighs between 8 to 10 pounds, while wildcats like lions can weigh over 400 pounds on average. Cats’ diminutive sizes compared to their wild cousins raise the question – how did cats evolve to be so small?
Ancient Wildcat Ancestors
Modern domestic cats are descendants of larger, wildcat ancestors that lived in the Fertile Crescent of the Near East over 10,000 years ago. The earliest evidence of cat domestication comes from a 9,500 year old burial site in Cyprus that contained a human buried with a cat (source). Wildcats likely began associating with human settlements in the Fertile Crescent to feed on rodents attracted to stored grains. This mutualistic relationship between cats and humans led to the self-domestication of cats over thousands of years.
The Near Eastern wildcat (Felis silvestris lybica) is the main ancestor of domestic cats. This wildcat inhabited grasslands and deserts and was larger than modern domestic cats. However, over time cats began evolving smaller sizes more suited to living closely with humans.
Self-Domestication
Cats essentially domesticated themselves by living in close proximity to humans. As humans began settling down and farming, storing grain attracted rodents, which in turn attracted wildcats. These wildcats realized there was an abundant food source by living near humans. Additionally, human settlements provided shelter and safety for cats. Over time, the cats became accustomed to human contact. As cats self-selected for tameness, they gradually evolved to become domesticated house cats.
According to this video, cat domestication was driven by natural selection, not artificial selection by humans. Cats with less fear of humans got access to more food and shelter, and therefore passed on their genes. On the other hand, more aggressive cats were not tolerated by humans. This demonstrates how cat domestication arose organically from cats living in proximity to humans, rather than humans intentionally breeding cats to be tame.
Rodent Control
As cats became domesticated, humans quickly realized their usefulness for controlling rodents around settlements. Rodents were a major nuisance and health hazard, consuming and contaminating food supplies. Cats proved to be excellent natural pest control, hunting and killing mice, rats, and other rodents.
According to research, the earliest records of cats being used for rodent control come from ancient Egypt around 1500 BCE. Egyptian artwork depicts cats helping to protect granaries and homes from rodents. This alliance with humans likely reinforced selection for smaller size in cats, as those able to live alongside humans would thrive.
With their keen hunting abilities, agility to chase rodents, and smaller size fitting human homes, cats offered pest control services that larger wildcats could not. This gave cats living near humans an evolutionary edge. As cited in this article, the symbiotic rodent control relationship was a pivotal development in the domestication of cats.
Genetic Changes
Evolutionary pressure selected for smaller size as cats became domesticated and this was caused by a series of genetic changes. According to The genes that turned wildcats into kitty cats, at least 13 genes changed during the domestication process from feral cats into friendly housecats. These genetic mutations affected things like memory, reward seeking, and tameness. Domestication also changed genes related to starch digestion and fat metabolism, allowing cats to thrive on the food humans provided.
Additional research from Genetics of randomly bred cats support the cradle of cat domestication being in the Near East showed that compared to wildcats, domestic cats evolved reduced aggression and fear response, allowing them to Tolerate living with humans. These genetic changes impacted behavior and physiology in ways that facilitated coexistence with humans in more confined spaces.
Less Need to Hunt
When cats were domesticated and living with humans, they had less of a need to hunt for all of their meals, as humans began providing them with food. This consistent access to food from humans allowed domestic cats to hunt less frequently. With hunting being less crucial for their survival, there was less evolutionary pressure for cats to maintain the larger body size required for taking down substantial prey. Being freed from the need to hunt extensively, domestic cats could thrive at a smaller size that required less energy for survival.
Additionally, the provision of food by humans likely selected for cats that were satisfied with readily-available food from humans, as opposed to expending energy by roaming far and wide to hunt prey. Cats that were content staying nearby and eating the food humans provided had an evolutionary advantage. Over time, this would have contributed to the smaller average size of domestic cats compared to ancestral wildcats.
Smaller Prey
As cats became domesticated, they no longer needed to hunt larger prey like rabbits to survive. With humans providing food, cats could focus on hunting smaller rodents near human settlements. According to Kids’ Inquiry of Diverse Species, domestic cats are skilled at hunting rodents and other small prey. The typical diet of an outdoor cat consists primarily of small mammals like mice, voles, and chipmunks as well as small birds.
Cats are well suited for hunting and killing small, fast moving prey with their quick reflexes, flexible bodies, sharp claws, and teeth. As they evolved alongside humans, cats specialized in controlling rodent populations which was beneficial for humans trying to store grain and food. This symbiotic pest control relationship with humans reinforced cats’ hunting instincts and ability to survive on smaller prey.
Smaller Territories
As cats became domesticated and lived around human settlements, they no longer needed to roam vast territories to hunt prey and find mates. Instead, pet cats would stay within the confines of a home or village. This reduced territorial range enabled cats to thrive in more confined living spaces.
Whereas wildcats may patrol home ranges up to 3 square miles, free-roaming domestic cats have territories averaging 0.1 to 0.4 square miles. Owned house cats often restrict their movements even further, especially if provided food and shelter by caring owners.
With smaller territories to protect and reduced competition over resources, cats could afford to shrink in size. Their smaller bodies required less energy and enabled greater maneuverability when navigating their surroundings.
So as cats stopped wandering far and wide to survive, they evolved to become more compact companions perfectly suited for their domestic domains.
Smaller Litters
As wildcats became domesticated, they began giving birth to smaller litters. A key factor affecting nursing behavior in mammals is litter size. Research shows that as litter sizes increased in cats, the amount of time spent nursing decreased [1]. With smaller litters, domestic cats could spend more time nursing each kitten. Smaller litters require less energy expenditure for the mother cat as she does not need to produce as much milk. The decreased energy demands from smaller litters enabled domestic cats to be smaller in size compared to wildcats who had larger litters.
Conclusion
In summary, there are several key factors that led to the evolution of domestic house cats becoming smaller in size compared to their larger wildcat ancestors:
– Self-domestication, as cats began living around human settlements for easy access to rodents
– Reduced need to hunt as humans began providing food, allowing cats to expend less energy
– Hunting smaller prey like mice and rats instead of larger game
– Defending smaller territories focused around human homes rather than large wild areas
– Having smaller litters as food was more abundant and competition reduced
Taken together, these evolutionary pressures resulted in natural selection favoring smaller cat body sizes over generations. This allowed domestic cats to thrive living closely with humans.
