Restless Creatures E-Book

Matt Wilkinson

• Herausgeber: Icon Books
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 612

Veröffentlichungsjahr: 2016

Beschreibung

A billion-year history of movement, from bacteria to Olympic athletes. 'Packed with revelations, scholarly but clear, Restless Creatures carries you from the kinetics of the amoeba to that of the blue whale, from the swim-cycle of spermatozoa, to why skipping works best on the moon. A pop-science treat.' Gavin Francis, author of Adventures in Human Being Despite the overwhelming diversity of life on earth, one theme has dominated its evolution: the apparently simple act of moving from one place to another. Restless Creatures is the first book for a general audience telling the incredible story of locomotion in human and animal evolution. Evolutionary biologist Matt Wilkinson traces this 4-billion-year history, showing why our ancestors became two-legged, how movement explains why we have opposable thumbs and a backbone, how fish fins became limbs, how even trees are locomotion-obsessed, and how movement has shaped our minds as well as our bodies. He explains why there are no flying monkeys or biological wheels, how dinosaurs took to the air, how Mexican waves were the making of the animal kingdom, and why moving can make us feel good. Restless Creatures opens up an astonishing new perspective – that little in evolution makes sense unless in the light of movement.  

Leseprobe

Praise for Restless Creatures

‘It would be hard to find a more companionable guide to the marvels of locomotory evolution than Matt Wilkinson. In Restless Creatures, the zoologist and writer rehearses twice-told tales of animals becoming bilateral, exiting the sea for the land and evolving flight, but makes them fresh. These are wonderfully adept and informed explanations of locomotory modes – whether in birds, gliding snakes, eels, sharks or a host of fossil vertebrates – and there is not a single vignette that I failed to learn something from.’

Kevin Padian, Nature

‘Packed with revelations, scholarly but clear, Restless Creatures carries you from the kinetics of the amoeba to that of the blue whale, from the swim-cycle of spermatozoa, to why skipping works best on the moon. A pop-science treat.’

Gavin Francis, author of Adventures in Human Being

‘[I]ntriguing … With the help of his locomotory worldview, Mr Wilkinson goes on to provide [an] … enlightening perspective on such major evolutionary developments as the transition from wriggling spineless marine organisms to the first vertebrates, the movement of fish out of the water and onto dry land, and the evolution of flight.’

Richard Conniff, Wall Street Journal

‘[An] ingenious but not-dumbed-down history of life’s 4-billion-year progress in getting from one place to another … [Readers] will come away with a deep understanding of an essential basis of life.’

Kirkus Reviews

‘This marvellous book looks at life from an angle that is novel, revealing, and has been fundamental in evolution: how organisms move. If you want to know how sponges sneeze, why all large aquatic predators have similar shapes, and how physics affects the lives of the smallest of organisms, turning water into glue, this is the book for you. Highly recommended!’

Matthew Cobb, author of Life’s Greatest Secret

‘Restless Creatures proves that the 60s song was right, everybody is doing the locomotion. In his original and insightful book, Matt Wilkinson explains how, from whirling bacteria to wayfaring humans, the three-billion-year journey of life has depended on the invention of many ways of moving.’

Sean B. Carroll, author of Brave Genius and The Serengeti Rules

‘Like the restless creatures it describes, and their tracks through evolutionary time, this book wanders; and it wanders wonderfully. Its author, Matt Wilkinson, takes us on a circular trip, starting and ending with our own species. Wilkinson’s conclusion is that our other special feature – the evolution of consciousness – is linked to our wanderlust. This is a bold hypothesis, and it might just be right.’

Wallace Arthur, author of Evolving Animals

RESTLESS CREATURES

Matt Wilkinson

RESTLESS CREATURES

The Story of Life in Ten Movements

Published in the UK in 2016

by Icon Books Ltd, Omnibus Business Centre,

39–41 North Road, London N7 9DP

email: [email protected]

www.iconbooks.com

First published in the USA in 2016 by Basic Books, a member of the Perseus Books Group

Sold in the UK, Europe and Asia

by Faber & Faber Ltd, Bloomsbury House,

74–77 Great Russell Street,

London WC1B 3DA or their agents

Distributed in the UK, Europe and Asia

by Grantham Book Services,

Trent Road, Grantham NG31 7XQ

Distributed in Australia and New Zealand by Allen & Unwin Pty Ltd,

PO Box 8500, 83 Alexander Street,

Crows Nest, NSW 2065

Distributed in South Africa

by Jonathan Ball, Office B4, The District,

41 Sir Lowry Road, Woodstock 7925

Distributed in India by Penguin Books India, 7th Floor, Infinity Tower – C, DLF Cyber City, Gurgaon 122002, Haryana

ISBN: 978-178578-045-5

Text copyright © 2016 Matthew Wilkinson

The author has asserted his moral rights.

No part of this book may be reproduced in any form, or by any means, without prior permission in writing from the publisher.

Typeset in Adobe Caslon Pro by Marie Doherty Designed by Jack Lenzo

Printed and bound in the UK by Clays Ltd, St Ives plc

For Dad

Contents

Introduction

1Just Put One Foot in Front of the Other

2Two Legs Good

3Leaps of Faith

4Go-Faster Stripe

5The Improbable Invasion

6A Winning Formula

7Brain and Brawn

8Give It a Rest

9Exodus

10Locomotive Souls

Acknowledgements

List of Illustrations

Bibliography

Index

Introduction

Then God said, ‘Let us make man in our image, after our likeness …’ So God created man in his own image.

—Genesis 1:26–27 (RSV)

That’s as much as the Bible has to say about the origin of man and why we are as we are: if we take the above verses literally, God just felt like making a species that looked like him. As explanations go, it’s pretty thin – one wonders, for instance, why God happened to be humanoid in the first place. Not that the rest of the living world fares much better. The only vague allusion in the first pages of Genesis to a possible link between an organism’s form and its way of life is the description of birds as winged. Such reticence is hardly surprising, given that curiosity is denounced as the mother of all sins a couple of chapters later. Righteousness apparently requires that we take everything for granted. Fortunately, we ended up ignoring this prescription: the first rule of a post-Darwinian, evolutionary worldview is that when it comes to life, we should take absolutely nothing for granted. Living things are as they are largely as a result of the process of adaptation: the gradual accumulation of favourable mutations over countless generations by the action of natural selection.

Now, some would have it that natural selection is therefore the one and only answer to any question about life. But while this claim is sort of true, at least as far as the adaptive features of organisms are concerned, pointing at a single element in a causal chain hardly amounts to an intellectually satisfying explanation. However, we’d be forgiven for thinking that this is about as far as we can go. It’s all very well accepting the authority of natural selection as the agent of adaptive change, but the genetic mutations that create the variation upon which natural selection acts occur by chance. Furthermore, the eventual fate of a mutation hinges on the particulars of the environment in which a population happens to find itself. Are we really any the wiser? Is evolutionary history just one damned thing after another – a long sequence of specifics and contingencies? Have we succeeded only in replacing God with Fortune?

Some would argue that this is indeed the case. Ernest Rutherford – widely regarded as the father of nuclear physics – once said that ‘physics is the only science; all else is stamp collecting.’ And while he would never have sanctioned such scornful language, evolutionary biologist Stephen Jay Gould was really on the same page when he declared that any rerun of the tape of evolution would produce a living world utterly alien to the one we know. In saying this, Gould was tacitly agreeing that, on the grand scale, evolution is an incomprehensible, unruly beast – opaque to the order-seeking searchlight of science. In this book I offer a wholly different view, for I believe that, contrary to first impressions, there is a way of making deeper sense of ourselves and other living things. Life, you see, despite its overwhelming diversity, has a single overriding theme – one that has dominated evolutionary possibility from the very outset. That theme is locomotion – the apparently simple act of moving from one place to another.

It was pterodactyls that showed me the light. These were the animals that attracted my attention when I first became a research zoologist. My choice of subject was partly driven by the usual childhood dreams of dragons and lost worlds not quite snuffed out by a scientific education (thankfully), but it was also a pragmatic one. Flight is not something to be tackled lightly – after all, we humans cracked it only one hundred years ago – so I reasoned that natural selection must have had a particularly tunnel-visioned concern when it came to the pterodactyls. The unforgiving physical demands of flight would surely have dominated their form and behaviour completely, as is the case today for bats, birds, and, indeed, man-made aircraft. Such stringent limitations on evolutionary possibility are an absolute godsend for a palaeontologist. If I bore these constraints in mind, I thought, then even with limited help from the fossils, and obviously no chance to observe the animals’ behaviour directly, I could still go a long way towards reanimating the objects of my affection.

I’m happy to report that my faith was justified. With aerodynamics as my guide, even the most basic data became a rich source of information. Although my later work involved virtual reconstructions and wind tunnel tests, the first thing I did was take my chosen species – a magnificent beast called Anhanguera – and estimate its weight and wing area from its fossil remains. Anhanguera’s wings were enormous – spanning nearly 5 metres, with a 1.2-square-metre shadow – but the creature was also surprisingly light, weighing in at a mere 10 kilograms, give or take. Now, simple physical considerations dictate that weight must be balanced by the force of lift in steady flight, and aerodynamic theory tells us that the amount of lift depends on wing area and airspeed, to a first approximation. With its big wings and lightweight build, Anhanguera could generate enough lift to stay airborne at a remarkably low cruising speed. Which was just as well: those enormous wings weren’t suitable for the vigorous flapping that would be required to make up for a substantial airspeed shortfall.

That was just the beginning. The trouble Anhanguera had with flapping meant that it needed gravity’s help to get up to speed, along with rising warm air currents – thermals – to maintain altitude. It must therefore have roosted on cliffs near tropical seas, whose waters are balmy enough to sustain the thermal fields. In this regard, Anhanguera was a lot like today’s frigate birds, but the resemblance may have gone further than simple habitat choice. Frigate birds are notorious for their aerial piracy – they plunder fish from other birds on the wing. What many people don’t realize is that this objectionable behaviour is born of the birds’ locomotory ‘design’. Because they need the assistance of gravity to take off, frigate birds cannot risk alighting on the water to feed. Attacking other birds in mid-air is a perfectly reasonable response to this difficulty. Who knows – maybe Anhanguera and its kin were the analogous scourge of the Cretaceous skies.

All that information came from just two numbers: weight and wing area. With a little physical know-how I was able to take some petrified bones and return a fully functional animal, placed more or less securely in the ecology of its time. This experience was to be my epiphany – I would never look at the world in the same way again, for once accustomed to a locomotory point of view I realized that flight is not unique in its power to shape adaptation. On the contrary – I began to see the guiding hand of locomotion everywhere I looked. Thanks to Anhanguera I had stumbled upon life’s big secret, hiding in plain sight. Locomotion is perceptually immediate – one doesn’t need a telescope or microscope to discern it; neither does one have to wait generations to see it in action. It’s happening all the time, all around us. My way was clear: I resolved to lay bare the restless heart of the living world. This book is the culmination of my quest.

There are, I think, two reasons for the pervasive influence of locomotion on the design of living things. First, getting from place to place effectively and efficiently is often one of the most important determinants of how many healthy offspring a creature begets, which as far as natural selection is concerned is ultimately the only thing that matters. Survival and reproduction both require that organisms seek out fuel and raw materials for the purposes of growth, repair, and baby-making, while ideally avoiding competitors or any hungry creature that might make a meal out of them. Sexual reproduction often requires that organisms approach each other, and whether sexual or asexual, one’s offspring must eventually fly the nest, so to speak, if they’re not to become entrenched rivals of their parents or each other. All of which means that locomotion tends to enjoy a high priority in the eyes of natural selection.

The second reason that locomotion leaves such obvious marks on living things is of a more physical nature. It doesn’t matter whether we’re considering a corkscrewing bacterium, a climbing ape, a sprinting cheetah, a spinning sycamore fruit, a soaring albatross, a burrowing worm, a swimming swordfish, or a strolling human: everyone without exception must defer to the same underlying physical reality. Organisms are physical objects, after all, and when moving around, they must obey Newton’s laws of motion, along with a few other rules and regulations concerning levers, the behaviour of fluids, and such like. Given the high selective premium placed on efficient and effective movement, these rules typically impose tight constraints on the shape and behaviour of locomotory creatures.

At this point, you might be tempted to employ your own locomotory abilities (metaphorically at least) to run away as fast as possible, but you’ll miss out if you do. The laws of which I speak are really not that scary, and the great importance of locomotion to an organism’s fitness means that the form and behaviour of living things are often attuned to the same physical principles. If there were any doubt as to the truth of this statement, you have only to consider the innumerable cases of convergent evolution that pepper the history of life. Whales and dolphins have been shaped so thoroughly by the demands of efficient underwater locomotion that for a long time they were regarded as fish. The three groups of flying vertebrates – bats, birds, and pterodactyls – have been brought to strikingly similar anatomical destinations by the unbending physical needs of flight. The diversity all rests on one beautifully simple foundation.

An important question may by now have occurred to you. If all organisms are contending with the same physical reality with the same underlying rules, why don’t they all look and behave the same? Why is the living world so astonishingly diverse? There are two principal answers to this question, one more intuitive than the other. First, of course, different organisms inhabit different physical environments where (to put it in prosaic terms) the values of certain variables in our equations of motion aren’t the same: they may dig through soil, swim through water, fly through air, or move on an interface between these realms, each technique requiring different anatomical and behavioural traits to pull it off effectively. On similar lines, a creature’s size has an enormous impact on its physical experience. The largest locomotory entity – the blue whale – is one thousand million million million times bigger than the smallest – a Mycoplasma bacterium. The physical changes across so vast a size range have all kinds of locomotory consequences. An elephant can’t bound around, for instance, because its legs would need to be impractically thick to withstand the enormous forces involved. A mouse, on the other hand, rarely does anything but bound. Air, whose physical presence is barely noticeable to us in most situations, is positively treacly to the tiniest flying insects, so they can get away with wings that are just tufts of bristles. Such a design is not recommended for a Boeing 747.

The second, less intuitive answer to the diversity question concerns the impact of the past on a creature’s present. Evolution is usually a gradual process, for there are strict limits to the extent of viable change from one generation to the next. While big changes are possible (witness the occasional two-headed mutants), they tend to cause catastrophic losses of fitness, and so are quickly eliminated from the gene pool. Future evolutionary pathways are therefore heavily constrained by the present state of an evolving population. By extension, one needs to know a creature’s evolutionary past to fully understand why it is as it is now. For no walk of life is this proviso more important than locomotion. Two creatures moving in the same environment may face the same physical challenges, but their adaptive solutions may be wholly different, just because their ancestors came at the problem from different angles. The flying vertebrates again provide a useful illustration. Their wings are superficially similar, but not identical: birds use feathers, bats stretch a skin-like membrane between their elongated fingers, and pterodactyls, despite also carrying membranous wings, supported each with only one finger. These distinct takes on flight in the three groups trace back to differences in their respective ancestors, some subtle, some not so subtle, when they began to test the air.

The history of locomotion may thus be conceived as a 4-billion-year dance between the physical rules of propulsion and the logic of natural selection, with each step dependent on the one that came before. In this book I will retrace this long dance, and in so doing will show how the need to move has shaped the living world. I begin in Chapter 1 with ourselves. Human locomotion is wonderfully amenable to personal exploration and experimentation, making us the ideal platform for learning the ropes of biological propulsion. As a species, we’re also surprisingly capable movers by the standards of our close ape relatives. This is something we usually take for granted – when asked to say what makes us special, most people talk about our superior mental faculties. Yet I’d guess that a similar majority would grant far higher status to elite athletes than to Nobel Prize winners. The subconscious high regard in which we hold our locomotory skills is also betrayed by the extent to which the terminology of movement pervades the language of achievement: when we do well, we’re ‘going places’, ideas need to ‘get off the ground’, we ‘chase’ goals, ‘get up to speed’ at a new task, make ‘leaps’ of understanding, and ‘jump at the chance’ to try something new. And while we don’t often consciously consider the value we place on locomotion, we certainly miss it if it’s gone – our locomotory freedom is one of our most prized attributes.

In considering human movement we’re going to come face-to-face with our first evolutionary puzzles, the most obvious being our use of two legs rather than the standard mammalian four to get ourselves from place to place. This mystery will serve as a springboard for our journey back through the evolutionary history of locomotion, for it’s only by peeling away the layers of recent adaptations that we can hope to find an answer to this curious anomaly. However, in doing so, we’re going to uncover yet more locomotory puzzles that will inevitably take us back even further, until we eventually reach the very origin of locomotion itself. Given our interest in understanding ourselves, the focus of our backward trek through time is our own ancestral lineage, but that doesn’t mean that the story is ours alone, for the deeper we go, the more widely shared are the ancestors we encounter. That means that the more we learn about our own locomotory past, the more we’ll come to understand the broader canvas of the living world, and the more obvious the universal signature of locomotion will become.

To mark the journey down our ancestral lineage I have chosen as way stations a number of key locomotory transitions, each of which forms the central story of a chapter. These shifts in the tempo and meter of the dance of life all granted access to fruitful new ways of moving, and so have special significance in the grand evolutionary narrative of locomotion. In Chapter 2 – the first step on our historical journey – we will explore how our tree-dwelling ancestors became two-legged and eventually left the forests behind. Then, in Chapter 3, we will briefly divert from our ancestral lineage to turn our attention to the skies, and to the various origins of the lucky flying animals that now roam therein. In Chapter 4, we will dive beneath the waves, to examine how natural selection for swimming caused the appearance of the vertebrate backbone, before moving on in Chapter 5 to our closer fishy ancestors, who turned their fins into limbs and crawled onto the land. In Chapter 6, as our journey takes us ever deeper, we will learn how the demands of locomotion shaped the fundamental anatomical blueprint of the animal kingdom, with its clearly defined fore-to-aft axis and left/right symmetry. Chapter 7, on the other hand, will look into how animals ended up controlling the locomotory movements of their finely honed bodies, thanks to the origin of the nervous system. Through these major locomotory transitions we will learn how our ancestral lineage was forged and reforged by the demands of movement, and how biological locomotion works in different environments and on different scales.

Many aspects of the transitions I cover on these first six legs of our evolutionary journey are very obviously related to locomotion – such as the origin of flight, of human two-leggedness, and the transformation of fins to limbs. Other changes have a relationship with movement that might seem a little more surprising. Our much-lauded opposable thumbs, for instance, originally had nothing to do with tool use – the digit’s realignment was a climbing adaptation. The famous Cambrian explosion – the relatively rapid diversification of animal body types that began about 545 million years ago – was kick-started by crawling adaptations, as we’ll see in Chapter 6. Perhaps most striking of all, as discussed in Chapter 7, the brain and sensory organs were originally nothing more than a guidance system – a computer – to coordinate the body’s movements to and fro. The evolution of locomotion is about far more than legs, wings, and fins – indeed, the deeper we dig, the more apparent it will become that few if any aspects of an animal’s being aren’t related in some way to its present or past adaptations for movement.

Chapter 8 takes a different tack, by exploring the various occasions when locomotion was abandoned – or rather, ostensibly abandoned, for we’re going to find that the lifestyles of the static owe much to their history of motion. Indeed, I hope to convince you that, strange as it may seem, locomotion has actually dominated the evolution of plants almost as much as it has that of animals. Although plants themselves usually can’t move around, their seeds and pollen must for the purposes of sexual reproduction and dispersal. These imperatives have impacted not only on the design of the dispersal agents (witness the helicopter-like fruit of sycamore trees) but also on the form of the stationary plant that releases them. Height is an obvious dispersal-assisting quality, and flowers are so good at ensuring pollen gets delivered exactly where it needs to go (via insect couriers) that one could regard them as indirect locomotory organs.

The various narrative twists that we’re going to encounter on our long journey show that a creature’s evolutionary history shouldn’t be regarded as a mere straitjacket. Adaptations can open doors to future possibility as well as close them, and this is never more likely than when those adaptations have a locomotory impact. If a creature acquires a new way of moving, through its travels it may end up exposing itself to a whole new set of selective pressures: pressures that might push its descendants in an entirely unexpected evolutionary direction. After all, an organism must experience a new environment before it can adapt to it. Consider flight again: it’s a fantastically effective way to get around, but only those creatures that move in the complex world of the forest canopy are ever likely to stumble upon the selective pressures that might eventually make it possible. But this power of locomotion to unlock new ways of living doesn’t just apply to the colonization of new environments, as will become very obvious once we embark on the final leg of our journey back in time. In Chapter 9, we’re going to see how the adaptive refinement of locomotion in single-celled creatures laid the groundwork for the great multicellular kingdoms that were to come, before we arrive at last at the most important locomotory transition of all: the beginning of locomotion itself. Judged on its evolutionary consequences, this was undoubtedly the most significant transition in the history of life since its origin. Before locomotory powers evolved, life was little more than unusually complex chemistry. Once organisms started to move around, however, they began to encounter each other, opening the doors to predation, parasitism, sex, and symbiosis. In other words, it was thanks to locomotion that life took on its essential character, and it’s had the leading role in the unfolding drama of evolution ever since.

The book will end where it began – with ourselves, or rather our mind, for it turns out that we have locomotion to thank for more than our body alone. In Chapter 10, we will see that our curiosity, our joy, even consciousness itself all owe their intangible existence to propulsion. This shaping of our mind by the dance of natural selection and locomotion gives added significance to our search for self-understanding. We’ve been gifted with an insatiable desire for movement, but this wish has brought us to dangerous territory in recent years, with our locomotory technologies now threatening the health of both our bodies and our minds. Appreciating how we’ve been built by life’s long locomotory dance is therefore no mere academic concern – it may in the end be our best chance of finding a way to live more healthy, meaningful, and fulfilling lives.

Let the journey begin.