Playfulness And Individuality In Mice
The desire to play with others (or with objects) is an aspect of animal behavior that has fascinated researchers for quite some time. Many people seem to intuitively understand the concept of “play.” But like other aspects of animal behavior or cognition — such as “intelligence” or “self-awareness” — humans have struggled with how to define play in animals. Generally speaking, it’s been described as an action that “does not contribute to immediate survival needs, is intrinsically rewarding, spontaneous, voluntary and purposeless, it occurs repeatedly, but not stereotypically, and it is only performed when the animal is in a relaxed state.”
In animal welfare science, play behavior is generally believed to indicate a positive state of welfare because it’s something that happens when the animal is otherwise relaxed and not in a state of stress. The opposite is also true and a lack of play can indicate negative animal welfare. However, scientists are realizing that animals may also show different levels of playfulness related to their individual personalities in addition to their welfare circumstances. Just like some humans are more playful than others, some animals appear to have more playful personalities.
This study of mice in a laboratory set out to test the hypothesis that “the individual level of juvenile playfulness is related to the behaviour shown in later life.” Using strictly controlled housing, groupings, and a set of behavior tests, the researchers observed 30 female mice as juveniles, adolescents, and adults, measuring “playfulness” levels at each stage. They found evidence for “the existence of interindividual differences in mouse playfulness that are associated with behavioural differences in later life.” The results provide further evidence that mice, and presumably other animals, exhibit individual and differentiated personalities.
While these results may be of interest to animal advocates, some will understandably question the methods used to obtain them. If mice show individual levels of playfulness, they likely also experience individual levels of anxiety and trauma. It’s a reasonable question whether or not animal research can ever provide adequate “welfare” to sentient animals who express such individuality.