Since the wobbly days of babyhood Isaac has developed amazing motor control—he can pick things out of his bath that I can’t even see—but the body that makes it possible remains a mystery to him. It exists, as physical and permanent as anything in his toy box, but he has a hard time making allowances for it. Without an awareness of how big it is, and how heavy, it wreaks destruction as quickly as it puts things together. Like his sister before him, his idea of playing hide-and-seek is to stand in the corner and cover his eyes. ‘Watch that body of yours,’ I want to tell him. ‘There’s more to you than you think.'
Awareness of our own bodies seems a relatively recent evolutionary achievement. At the University of Louisiana–Lafayette, Daniel Povinelli has been investigating how only some species of apes (chimps, orangutans and humans, but not gorillas) can recognise their own appearance in mirrors. He argues that our awareness of ourselves as physical entities stems from our common ancestry in the trees. To plan their passage through the canopy (and, in particular, to avoid being dumped on the ground by less sturdy branches), arboreal species need to be able to factor their own weight into their calculations. Land-lovers like gorillas can get by without any such sophistication. For Povinelli, this is a clue to why only some species of apes show mirror self-recognition. Learning the lesson of yourself, it seems, requires some hard bumps in your evolutionary past.
Mirror self-recognition is usually tested with a simple task. A blob of rouge is applied surreptitiously to the participant’s face, and the observers wait to see whether, when confronted with their own image in a mirror, the chimp, gorilla or human infant will attempt to remove it. Toddlers typically pass the rouge test at around eighteen months. To test whether this translates into a practical awareness of one’s own physicality, Chris Moore and his colleagues at Dalhousie University present toddlers with a supermarket trolley rigged up with a blanket attached to the handle. In order to reach the handle to push the trolley, the toddler has to stand on the blanket. The results can be comical. The little volunteers know how the trolley works—nothing satisfies a toddler so much as pushing a trolley—but it takes time for them to realise that their own bodies are impeding its movement, and devise strategies such as kicking the blanket out of the way.
The jury is still out on whether toddlers fail this task because of a general problem in understanding the physics of weight and obstruction, or because they specifically fail to see their own bodies as the obstacle. Isaac still crawls under tables to retrieve something and then stands up straight and clunks his head on the underside. Perhaps he needs parking sensors, or at least a little more experience of how much of him there is. Getting used to the vehicle he gets around in is, like many things, going to be a matter of time.