I remember the first time I took the New York City subway. The station was vibrant with a mix of passengers waiting for their train and a few subway rodents scurrying away with discarded food. Does living in an urban environment make such animals better at solving challenging tasks to find food? Researchers Lara Vrbanec, Vanja Matijević and Anja Guenther from the Max Planck Institute for Evolutionary Biology, Germany, studied the problem-solving abilities of three subspecies of house mice that have lived in human-altered environments for different evolutionary periods.
The house mouse, Mus musculus, has been living with humans for around 13,000 years. During this time, it has evolved into three subspecies: M. m. domesticus (western house mouse) appeared 11,000–13,000 years ago, M. m. musculus evolved 8000 years ago, and then M. m. castaneus turned up approximately 3000 years ago. Although we know the ecological impacts of humans on house mice, our influence on the intelligence of mice was unknown. Animals that can adapt their behaviour to novel circumstances are likely to be more successful in changing environments. So, the scientists wondered whether the mice subspecies that have lived in close proximity with humans the longest are better at solving problems, and can invent novel behaviours or reuse pre-existing ones, than the newer arrivals.
To test their idea, the researchers tested laboratory-based colonies of all three subspecies, which had lived in captivity for several generations after sharing their homes with humans for thousands of years. The researchers set the mice seven tests where they had to access a mealworm reward in different contexts by performing specific manoeuvres, such as pushing, pulling or digging. The scientists found that the captive western house mice were most likely to solve the food extraction tasks, followed by M. m. musculus and M. m. castaneus. As there were no recent differences in the animals’ lifestyles, their different aptitudes could only be accounted for by the amount of time they had spent sharing their homes with humans in the past. The better problem-solving ability of western house mice is probably a result of sharing their living space with humans for the longest time.
However, the team needed convincing that the impressive abilities of the western house mouse are due to their proximity to people and not to some other factor, such as their general inquisitiveness. To test whether any other aspects of their lives drove the animals’ increased intelligence, the researchers connected a cage containing unfamiliar objects to the cages of individual mice and measured how long it took each one to enter the unfamiliar environment. They thought that if the subspecies differed in their motivation to enter the unknown environment, their curiosity could be a possible explanation for why the mice vary in their problem-solving abilities. But they found that the three subspecies did not differ in their inquisitiveness or motivation to explore novel objects, confirming that the western house mouse is better at solving challenging tasks likely owing to its longer cohabitation with humans.
Whether you are a New Yorker or a mouse that evolved in an urban or human habitat, problem-solving is key for survival. The human environment may act as a filter in which individuals with certain behaviour types are more likely to thrive. So, the subspecies of mice that has co-existed longest with humans have adapted well to their new, man-made environment through better problem-solving abilities than subspecies that have lived in our shadow for shorter times. So be warned, it may not be long before some mice learn how to extract cheese successfully from your mousetrap without getting squished.
