The Eye: A Natural History by Simon Ings

Bloomsbury

£17.99

TO READ THIS BOOK HAS an odd and unsettling side effect. This is not through any fault of Simon Ings, who is a fine science writer, his prose precise and clear, his research meticulous and comprehensive. Nor is there any problem with the subject matter – the eye is a truly fascinating organ, its complex development, myriad forms and idiosyncratic workings across the animal kingdom making for a truly absorbing read.

Furthermore, Ings argues convincingly that the eye has had a profound effect on our language, perception, philosophy and even consciousness. No, the strange side-effect is brought about because – after reading 300 pages on how the eye works, its little quirks and foibles, its often counter-intuitive processes and processing – you become almost compulsively aware of what your own eyes are doing all the time, which is a bit off-putting.

Try reading this sentence without your eyes jolting from position to position across the page. You can’t, can you? That’s because every third of a second your eye “saccades”, or snaps from location to location, a restless activity brought about by the need to detect motion.

“The eye exists to detect movement,” Ings writes. “Any image, perfectly stabilised on the retina, vanishes. Our eyes cannot see stationary objects, and must tremble constantly to bring them into view.”

This extensive natural history of the eye is full of such delightful and disturbing little revelations. As we read on with our own trembling eyes, Ings expertly guides us through the basics of how eyes work, then into how and why eyes evolved in the first place. Starting with the chemistry of vision, roughly the first half of the book deals with this topic, mainly with the intricacies of Darwin’s theory of evolution and its repercussions for the development of the eye.

Darwin made a big deal of the eye. He realised that it seemed an impossibly specialised device, an organ “of extreme perfection and complication”, that very perfection bringing into doubt his theory of chance mutations and survival of the most advantageous adaptations. Rather than shy away from it, Darwin’s tactic in On the Origin of Species was to tackle the eye problem head-on, demonstrating how it could have evolved naturally over millennia – the implication being that if the eye could be formed through evolution, then anything could.

The evolution of different kinds of eyes for different purposes in wildly varying environments is dealt with expansively and entertainingly; did you know that if human beings had compound eyes, like flies, the organs would have to be a metre in diameter to achieve the same resolution? There is even a cartoon by the German scientist Kuno Kirschfeld of what such a grotesque hybrid might look like. Not pretty.

But while all that evolution stuff is interesting, it is the latter half of this book that grabs the attention. Starting with Chapter 5: Seeing and Thinking, Ings explores in detail the theories of vision and how vision relates to thought processes, memory, language and so on. Having used a lot of chemistry and evolution in the earlier chapters, he is now dealing with a subject where physics, psychology and even philosophy intertwine, and it is certainly thought-provok-ing stuff.

In one sense, the eye can be considered as a remote outpost of the brain, so interlinked are the two organs. How the brain interprets the information sent to it from the eye is still a matter of much debate within the scientific community. Ings does a decent job of taking us through the incredibly complex functions of the eye, explaining that much more “preprocessing” of visual information occurs within it before that information is passed to the brain than was once thought.

And then we get to colour. “Whenever I mention that I’m writing a book about eyesight,” Ings writes, “I am invariably treated to the same story. How one day, as a child, it dawned on the person I am speaking to that their experience of colour might be entirely their own. Who is to say that my experience of green is the same as yours?”

This is, to say the least, a can of worms. How many colours are there in a rainbow? Depends who you ask. The Burinmo hunter-gatherer people of Papua New Guinea have only five colour words, and make no distinction between blue and green. Homer referred to a rainbow as consisting of three colours. In Ancient Greece, honey, sap and blood were all described as “chronos”, a yellowy green, apparently.

How we describe colour is a rather mind-boggling subject, but that’s nothing compared with “the next great unsolved problem of vision: attention”. Vision scientists don’t know how we focus our attention; in fact, they don’t even know how to ask the right questions about the subject. Ings, perhaps wisely, sidesteps this issue for the most part, preferring instead to highlight the nature of the problem with a nice account of the work of the pointillist painter Georges Seurat.

From there we are treated to a discussion of colour blindness, a trawl through recent scientific developments in the field of artificially creating eyes and a sense of vision, and even some speculation on where the eye could evolve from here. Ings deals with these, as he does all parts of this thoroughly engaging book, with refreshing clarity, enthusiasm and vigour. It’s a real eye-opener, if you’ll pardon the pun.

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Extract

The story of the eye is filled with material wonders: mirror eyes, fibre-optic eyes, and eyes crammed full of exquisite lenses; shells that see and spiders that steer by the Sun; eyes less than one tenth of a millimetre across, and eyes one third of a metre across. Birds can focus on two things at once. Tube worms see with their feeding tentacles, chitons with eyes scattered like pimples over their shells.

The fish Bathylychnops exilis has four eyes: one set to look up, and one set to look down; but at what? Nobody knows. The surface-feeding fish Anableps anableps can see clearly both in and out of the water. Mantis shrimps use polarised light to swap messages that no other animal can see. Even a kilometre below the sea’s surface there is, incredibly, still plenty of material my story could have drawn on, if only there were room. Bioluminescent photophores tattoo the sides of lanternfish, fang-toothed fish dangle lures baited with light-making bacteria, and one deep-water fish, Aristostomias, communicates with others by generating pulses of red light – a colour no other neighbouring species can see.

The story of the eye is epic: this book is but the shortest précis of its wonders.

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