We are unique as a species in our ability to point meaningfully. Chimps may draw saleable pictures and create tools, but they do not point. If I point in the direction a thrown ball has gone for the benefit of my slow-witted border collie, she looks intently at the tip of my finger. Declarative pointing  "there's an eagle!"  is also one of the fundamental triangulations of our social being. I point; I use my arm and forefinger to describe a line in space; I point at something or someone; but, for it to be meaningful, there has to be another person there to observe and comprehend the gesture. Raymond Tallis's fourth chapter is concerned with a major exception: that of people on the autistic spectrum, whose inability to appreciate the subjectivity of others is confirmed by a failure to point.

Tallis began this study in 1972 while (over)working as a junior hospital doctor. He even speculated on a universal language called "Pointish", which might be communicable to the most anthropologically remote tribesman or to the putative Martian just landed. This works to a degree. We all end up pointing to menu items or the next diner's plate in foreign restaurants. And we all know that when a politician jabs his finger at us, a "point" is being made.

But it isn't absolutely and universally comprehensible. There are tribes who require a jutting lower lip to clinch the meaning of pointing and there is always the ambiguity of what you are pointing at: an image, the idea of an image, the colour of the image or the paper it is on. Tallis's argument is tight, densely packed into just 140 pages but estimably readable. He sums it up as "a contribution to the unfinishable project of waking to, and out of, the enabling constraints of everyday meaning, of linking our ordinary moments with their extraordinary origins".

And, we might say, with their future destination, for the pointing hand may not just suggest the moment of Creation, as on Michelangelo's great ceiling, but something else. It's worth remembering that it is The South Bank Show that makes the digits of God and Adam meet and spark. Michelangelo leaves a tiny gap between them. Does he intend this to suggest the moment we came out of God (or out or pre-conscious existence) or does he intend us to focus on the moment of separation itself, when we become free and directed, pointing our own way forward?