Where do numbers come from? Have humans constructed a useful abstraction or do numbers somehow exist as part of the fabric of our universe?
Figure 1. The number sense, more technically known as numerosity, is mapped across the back of the human brain’s top right hemisphere. At top are shown color coded sets from 1 (red; left) to 7 (pink; right). The map shown at bottom right uses the same color coding over the brain area associated with 1 (red) to 7 (pink).
Recent research has shown that non-human animals, infants, and tribal people with no numerical language have an innate ability to distinguish numbers of things or sets. For example, they may distinguish a set of 2 dots from a set of 5. This capability, known as numerosity, appears to be a hard wired sense like touch or vision.
Studies reported in the research article “Topographic Representation of Numerosity in the Human Parietal Cortex” published September 6, 2013 in Science uses brain imaging in human subjects to test if numerosity is mapped across the surface of the human cerebral cortex like the body is for touch and the visual field is for vision.
The research team found a map from small numerosity (set of 1) to larger numerosity (set of about 7) from medial to lateral superior parietal cortex (see Figure 1 above). More cortex was devoted to the smaller sets than the larger sets. This corresponds with the greater accuracy subjects show in perceiving smaller sets.
Remarkably, these data demonstrate that human and non-human brains include structures that respond to the size of different sets of things in the environment. The number sense, the sense of something we may consider abstract in comparison with other brain mapped senses like touch and sight, appears necessary for survival and propagation of humans and at least some non-human animals. Does this call into question what we think of as real as opposed to an abstraction?