Contributed by Marielle Grenade-Willis
Everyone remembers singing “The ants go marching one by one/Hurrah, hurrah…” on bus rides home after school or to pass the time on a long road trip during childhood. Numerosity, or “the ability to discriminate arrays of objects on the basis of the quantity of items presented”, is an innate, evolutionary ability that has served humans and nonhuman animals alike for thousands of years. Interestingly, the physiological mechanisms that support this survival capability are different for humans versus other animals but may originate from the same source.
“Brains (both human and nonhuman) have evolved to deal with numerosity, with different regions supporting different mechanisms of numerical representation. These phylogenetically widespread capacities seem perfectly suited to support survival. Any creature that can tell the difference between a tree with 10 pieces of fruit from another with only six pieces, or between two predators and three on the horizon, has a better chance of surviving and reproducing. At the same time, telling the difference between 24 and 28 pieces of fruit (or nine predators versus 10) does not offer much advantage.” – Dr. Michael J. Beran
According to neuroscience researcher Joonkoo Park, humans and many other species possess a basic numerical ability that is rooted in the subcortex, “an evolutionarily older brain structure” which connects the mid brain via the brainstem to the spinal cord in humans. Although this ability is thought to be mostly controlled by the parietal cortex in the primate brain, which is responsible for integration of sensory information, selective attention, and spatial awareness, other animals possess different, evolved neural systems for counting.
Studies have shown crows to possess individual “number neurons” in their end brain which correspond to certain numerical values. Robins are able to differentiate the largest quantity of mealworms when compared with smaller amounts. Free-ranging dogs are able to assess the group size of opponent packs. And insects like bees and ants are able to measure distance. In “Counting Insects“, Skorupski et al. have outlined different kinds of numerosity (counting, estimation, and subitizing) and why most species can only count up to about four items:
“Counting, in the strictest sense of the word, requires a symbolic number system (numerals), developed in some human cultures . In animals, counting-like abilities are said to exist where a response to the number of stimuli in a set can be abstracted to qualitatively different sets of stimuli [29,30]. Subitizing is the ability to perceive the number of items in a small set, which is accurate up to about four items (and in humans is accomplished ‘at a glance’). Estimation is the ability to judge approximately the numerosity of larger sets without counting.”
Nonhuman animals’ counting capabilities allow them to navigate, protect themselves, forage, and find mates etc. Honoring this capability in whatever form it takes physiologically means honoring a myriad of other capabilities that support animal thriving.