I spy, I spy with my little eye… humans are visually oriented creatures and eyes are fascinating organs. Michael Land, an emeritus (i.e. retired) professor in neurobiology at the University of Sussex, is a world expert on eyes, having studied vision for over 50 years. Next to hundreds of papers, he co-authored the textbook Animal Eyes, which was published in a second edition in 2012, and the short primer The Eye: A Very Short Introduction. Eyes to See is his opportunity to reflect on a long career and simultaneously showcase the astonishing variety of vision, as the book’s subtitle would have it.
Far from the in-depth overview his textbook offers, this pithy book nevertheless gives a complete introduction to the evolution of eyes and the eight principal types of eyes known in animals. People are often warned that what has been seen cannot be unseen, and so it was with evolution: once vision developed, there was no way back, and a scramble for visual dominance took off (see also In the Blink of an Eye: How Vision Kick-Started the Big Bang of Evolution). Time and again, solutions have evolved for organisms to perceive light and see the world. Darwin was initially concerned that eyes, with all their complex optics, could not have evolved to such a state of perfection through natural selection, going so far as to call this “absurd in the highest degree”. We now know of plenty of organisms displaying the intermediate steps along the way though, so next time a creationist tries to spin up that tired old argument, hand them a copy of OUP’s other great book on eyes, Evolution’s Witness: How Eyes Evolved.
The book then takes a tour of some of the more unusual eyes known. It gives the lowdown on compound eyes, explaining, for example, the striking occurrence of pseudopupils that make it seem as if insects are always looking back at you (they are not, it is a byproduct of how their eyes are constructed). Or the uncanny ability of flying insects to intercept moving targets with great speed and accuracy.
“[…] once vision evolved, there was no way back, and a scramble for visual dominance took off”
It also talks of the many adaptations to seeing (and prevent being seen) in the deep sea. If you have read my review of Deep-Sea Fishes: Biology, Diversity, Ecology and Fisheries, or have browsed more pictorial works such as Creatures of the Deep: In Search of the Sea’s Monsters and the World They Live in or Life in the Dark: Illuminating Biodiversity in the Shadowy Haunts of Planet Earth you will have seen the bizarre adaptations showcased by fish and invertebrates. From bulging barrel-shaped eyes pointing upwards to secondary eyes that are pointing downwards. But it is not just eyes. Fish scales have particular properties that render fish virtually invisible underwater. And bioluminescence is widely used to attract, confuse, or observe (see Bioluminescence: Living Lights, Lights for Living and Luminous Creatures: The History and Science of Light Production in Living Organisms for more on that topic).
But vision requires more than just eyes. Brains to process all this visual information are also required. Where these are lacking in complexity, organisms tend to use simple rules of thumb to make sense of their visual environment, and Land discusses how fiddler crabs tell predator from conspecific (Is it bigger than me? Yes? Then run for the hills), and how males of different species vary the timing and speed with which they wave their ridiculously large ornamental claw to attract females of the right species. Most spiders have no fewer than eight eyes, all adapted for different visual tasks. And the mantis shrimp made headlines for having twelve visual pigments, instead of the three that humans have, though Land is quick to dispel notions of super-vision. Their eyesight is actually quite poor and signals from these pigments are processed completely differently (though, in other respects their eyes are amazingly complex). In many of these examples, the eyes do all the hard work of processing and selecting visual information, rather than relegating this task to the brain.
But in other species, such as humans, brains do do a lot of the visual processing and Land has also worked on such questions as: “where do people look?” Whether that is when reading a book or sheet music, driving a car, making a cup of tea, or batting a ball during a game of cricket. Finally, he touches on the hard problems that have kept philosophers up since time immemorial. Is the red that I see the same red that you see? What is red anyway?
“Appropriately for a book on eyes, this book relies heavily on visual aids.”
Throughout, Land weaves in anecdotes of his own research. From the accidental dismantling of an interference microscope lend to him by his PhD supervisor, the very recognisable low-tech methods employed by field biologists (a cotton reel on a piece of string to entice fiddler crabs), or the first attempts at constructing miniature head-mounted cameras to observe eye movements in human study subjects.
I always make a song and a dance about illustrations and have previously complimented Oxford University Press on really going to town in providing well reproduced, instructive illustrations. Appropriately for a book on eyes, this book relies heavily on visual aids. In a book just under 200 pages long, Land manages to include 92 diagrams and black and white photos, as well as 8 colour plates, heavily plundering his earlier book Animal Eyes. These schematic drawings are of great help in explaining the optical mechanisms discussed in the text.
Eyes to See does not shy away from going into detail where optical principles or anatomical features are concerned. But with helpful illustrations, a glossary, and an understanding that some optical solutions to life’s challenges are really quite complicated and need careful explaining, Land has produced an intriguing and accessibly written little book on vision. If textbooks heavy on the physics of optics sound like hard work, then Eyes to See comes highly recommended as a place to start reading into this topic.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
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