...But Egypt’s rigid style wasn’t good enough for the Greeks; their culture still demanded realistic statues, so they did something that no artists had done before: they used their eyes.

They studied every detail of the human body. Bit by bit they strived to understand exactly how to reproduce it in their art. Ears started to look like ears, real torsos began to appear, each artist building on the progress of others. And this explosive period within just a few generations produced what no civilization on earth had ever produced before.

This is Kritian boy, and he’s a milestone in the history of art. He’s carved from marble, and yet his skin appears to be taut over muscles, his thighs look like they’re bearing weight, his back undulates over his spine, which curves down perfectly in a relaxed stance.

Greek artists had created precisely what their society had urged them to: a truly realistic human body. And yet, this is the final clue in our story, not because it’s realistic, but because of the effect this realism had on the Greeks.

This exquisite statue gives us an absolutely historic moment. For the very first time man creates an image of himself that’s fully nude and truly life-like. So for the Greeks this was like the pinnacle of artistic achievement. They’d reached their goal: art as the perfect imitation of life. Now they could carry on producing gorgeous statues like this forever. But that’s just it, they didn’t.

Within a generation the Greeks stopped making realistic statues like this. But why? Why, when their culture had made them strive for reality, did they almost immediately abandon it?

The answer reveals something fundamental about us as human beings. When it comes to images of the body, we’re driven not just by culture but also by something we thought existed only in the earliest humans: it’s that primeval instinct to exaggerate, as observed by Professor Rama Chandran in the Venus of Willendorf. The instinct, he argues, is hardwired into the brains of all humans, even if in some cultures it was suppressed.

The principle of exaggeration must be something that is hardwired in the neuronal machinery of the visual pathways in the brains of every human being. And when you speak of universals, you have to realize that what’s universal is the propensity to do this, but this can be overridden by culture. The problem with the Kritian Boy is it was too realistic, and that makes him boring. If art’s about realism, why do you need art? You can just go down looking at things. They quickly realised that this is boring, but they had to do interesting things with the image, distort them in specific ways, not randomly distorted but lawfully distorted in order to exaggerate the brain's aesthetic response to that body.

So the Greeks dissatisfaction with reality was perfectly natural. They couldn’t know it but they were pre-programmed to want more. Like the nomads thousands of years before them, they were hankering after something more human than human.

Merely exaggerating muscles wasn’t enough, they had to discover their equivalent of the red-striped stick. And in about 450 BC, a sculptor and mathematician called Polyclitus made the breakthrough that would help them achieve just that. Polyclitus wanted to find a way of showing the physical potential of an athlete. He wanted a body that was both relaxed and yet appeared ready to move.

He created a series of theoretical rods passing through key points of the body. He also divided the body down the centre and across the middle. With these four quarters marked out, he began to move his figure in specific ways. He bent one knee and moved the same foot to ensure that it bore little or none of the body’s weight. He bent one arm and left the other relaxed. He rotated the body so that hips and head faced one way and the chest the other.

Now the body was divided into clear quarters: top and bottom mirrored each other; one side in motion, the other at rest. The angles of the body, which were once horizontal, now opposed and also complemented each other. So Polyclitus captured an athlete poised for action.

But for other artists it was also the key to understanding how they could at last represent physical perfection. Everything had been leading to this, the moment when ancient Greece created something more human than human.

They are known as the Riace bronzes. They are what Stephano Mariottini found on the seabed. Now displayed in Reggio, on the southernmost tip of Italy, they’re relatively unknown to the world at large. Polyclitus did indeed want to divide the sections of the body clearly, but here it’s been taken to extremes. The division between top and bottom has been exaggerated by a crest of muscle across the waist that’s more defined than it ever could be on a real human.

The legs have been made artificially long to match perfectly the length of the upper body. To stress the symmetry and separation of the two sides there’s an implausibly deep groove running up the centre of the chest. And while the chest muscles are totally relaxed, the muscles on the back are tense and impossibly well defined. The central channel of the spine is deeper than you’d ever see on a real human. And to improve the line of their back, these men have no coccyx bone at the base of their spine. These are unrealistic bodies. Reality’s been exaggerated, and that’s why they’re so overwhelming.

The instinct to do this had been alive on the brains of early humans, but now been revived. The first civilization capable of realism had used exaggeration to go further. And it’s that instinct which still dominates our world today.