Secret Worlds: The extraordinary senses of animals PDF
Preview Secret Worlds: The extraordinary senses of animals
SECRET WORLDS 1 Great Clarendon Street, Oxford, OX2 6DP, United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University’s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries © Martin Stevens 2021 The moral rights of the author have been asserted First Edition published in 2021 Impression: 1 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, without the prior permission in writing of Oxford University Press, or as expressly permitted by law, by licence or under terms agreed with the appropriate reprographics rights organization. Enquiries concerning reproduction outside the scope of the above should be sent to the Rights Department, Oxford University Press, at the address above You must not circulate this work in any other form and you must impose this same condition on any acquirer Published in the United States of America by Oxford University Press 198 Madison Avenue, New York, NY 10016, United States of America British Library Cataloguing in Publication Data Data available Library of Congress Control Number: 2021934078 ISBN 978–0–19–881367–5 Printed and bound by CPI Group (UK) Ltd, Croydon, CR0 4YY Links to third party websites are provided by Oxford in good faith and for information only. Oxford disclaims any responsibility for the materials contained in any third party website referenced in this work. For Lenny, Sam, and Audrey PREFACE The philosopher Thomas Nagel once posed the question ‘What is it like to be a bat?’ in a thought experiment about percep- tion and consciousness. In doing so, he was really asking ques- tions about what consciousness means, but we might equally pose the same question to think about what the sensory world of a bat is like and how that governs its life. It is easy to fall into the trap of assuming that other animals perceive the world in the same way that we do, but the reality could hardly be more differ- ent, or exciting. What we perceive are but snapshots of the phys- ical world, measured and interpreted by our senses and our brain. The product of our evolutionary past, our senses only allow us to perceive those aspects of the world for which we have the necessary apparatus, used to gather the information we needed to survive. Far from being uniform across species, how an animal perceives the world is heavily dependent on its sensory systems and brain. In the case of bats, many species have a highly sophisticated ability to use echolocation to navigate and hunt for prey. This is centred on ultrasonic frequencies that operate well above our hearing range. Our ears are simply not tuned to detect these frequencies. Each animal’s perception of the world is therefore a product of its sensory systems, and the information detected can differ greatly from other species. It’s worth pausing for a moment to consider how crucial our senses are to everything we do. Vision, smell, taste, hearing, and touch all provide us with an essential ability to respond to threats, communicate with one another, perform numerous daily tasks, avoid obstacles, and interact appropriately with the viii · PREFACE world around us. To people who have lost just one of their main senses, such as vision, many tasks the rest of us take for granted can be challenging. So, imagine what life would be like if we lost our vision, our hearing, our smell and taste, our touch, and so on. Our senses provide a critical gateway to the outside world, allowing us to interact with it. The same is true for all animals— their sensory systems are what enables them to forage, avoid predators, attract mates, navigate, and much more. Without them, individuals would be completely helpless. Human senses do a reasonable job of allowing us to gather information from the world and behave accordingly. But throughout this book we will encounter many animals with senses that, in comparison to ours, seem extremely refined. By contrast, we are more of a jack of many trades, with a range of good but not spectacular senses. I say ‘many’ rather than ‘all’ trades because we lack entirely some sensory systems that other animals possess. Ultimately, the sensory systems of other animals are tuned to widely different stimuli. For example, many animals, from spiders to birds, can detect and respond to ultraviolet light, to which we are blind. Others, including numerous insects, rodents, and bats, can hear high- frequency ultrasonic sounds well beyond our own hearing range. And this is just the tip of the iceberg. Consider the magnetic sense of birds, turtles, and other animals, or the electric sense of many fish and some mammals. Such great differences in sensory ability reflect adaptations to different habitats and lifestyles. And, when sensory systems adapt to different parts of an environment and affect behaviours such as mate choice, they can even drive the formation of new species. This book is about the remarkable sensory worlds that ani- mals experience, often so different from our own. It will explore how different animal senses work; what they are used for; how PREFACE · ix they evolved and were shaped by the ecology of a species, the environment where it lives, and the tasks it must complete during its life. Throughout, we will also see how scientists investigate the ways that animals use their senses, given that we can’t experi- ence their sensory worlds at first hand. What I hope to show is how such work reveals the remarkable diversity of animal life, and how the study of sensory systems has shed light on some of the most important aspects of behaviour and evolution. Work on animal senses covers vast ground and goes back a very long way. Some of the earliest evolutionary biologists, not least Charles Darwin and Alfred Russel Wallace in the mid- to- late 1800s, and many philosophers well before them, investi- gated how the senses function and posed questions about how they differ among species. Much has been learned over decades of research, but there are many outstanding questions too—such as how the magnetic sense actually works at all. It was a challenge from the outset to decide how to frame this book and what to cover. From the start, I decided simply not to cover everything— there is far too much. Instead, for each of the main chapters, I consider one sense in turn, focusing primarily on three animals or animal groups. Of these, I have picked examples of species that we understand quite well, or which are particularly remark- able in how their senses operate or in their level of specializa- tion, although I touch on other examples too for wider context. Together, these three animals per chapter tell the story of how different senses work, and also illustrate broader issues regard- ing the role of animal senses in the ecology and evolution of all species. I have been a little loose with the three-a nimal rule when needed—sometimes one very specific species forms an adequate example, when it has been the focus of a concerted research agenda. This is the case for the star- nosed mole and its sense of touch in Chapter 6. On other occasions, much of what we know
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