David Quammen - The Tangled Tree - A Radical New History of Life

William Collins

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This eBook first published in Great Britain by William Collins in 2018

Copyright © David Quammen 2018

Jacket design by Jack Smyth

David Quammen asserts the moral right to be identified as the author of this work.

A catalogue record for this book is available from the British Library.

All rights reserved under International and Pan-American Copyright Conventions. By payment of the required fees, you have been granted the non-exclusive, non-transferable right to access and read the text of this e-book on-screen. No part of this text may be reproduced, transmitted, down-loaded, decompiled, reverse engineered, or stored in or introduced into any information storage and retrieval system, in any form or by any means, whether electronic or mechanical, now known or hereinafter invented, without the express written permission of HarperCollins.

Source ISBN: 9780008310684

eBook Edition © September 2018 ISBN: 9780008310691

Version: 2018-07-31

To Dennis Hutchinson and David Roe, my attorneys of the soul

Contents

Cover

Title Page

Copyright

Dedication

THREE SURPRISES:An Introduction

PART I:Darwin’s Little Sketch

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

Chapter 7

Chapter 8

PART II:A Separate Form of Life

Chapter 9

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Chapter 15

Chapter 16

Chapter 17

Chapter 18

Chapter 19

Chapter 20

Chapter 21

Chapter 22

Chapter 23

Chapter 24

Chapter 25

Chapter 26

Chapter 27

PART III:Mergers and Acquisitions

Chapter 28

Chapter 29

Chapter 30

Chapter 31

Chapter 32

Chapter 33

Chapter 34

Chapter 35

Chapter 36

PART IV:Big Tree

Chapter 37

Chapter 38

Chapter 39

Chapter 40

Chapter 41

Chapter 42

Chapter 43

Chapter 44

Chapter 45

Chapter 46

Chapter 47

Chapter 48

PART V:Infective Heredity

Chapter 49

Chapter 50

Chapter 51

Chapter 52

Chapter 53

Chapter 54

Chapter 55

Chapter 56

Chapter 57

Chapter 58

Chapter 59

PART VI:Topiary

Chapter 60

Chapter 61

Chapter 62

Chapter 63

Chapter 64

Chapter 65

Chapter 66

Chapter 67

Chapter 68

Chapter 69

PART VII:E Pluribus Human

Chapter 70

Chapter 71

Chapter 72

Chapter 73

Chapter 74

Chapter 75

Chapter 76

Chapter 77

Chapter 78

Chapter 79

Chapter 80

Chapter 81

Chapter 82

Chapter 83

Chapter 84

Notes

Bibliography

Illustration Credits

Index

Acknowledgments

About the Book

About the Author

Also by David Quammen

About the Publisher

Life in the universe, as far as we know, and no matter how vividly we may imagine otherwise, is a peculiar phenomenon confined to planet Earth. There’s plenty of speculation and probabilistic noodling, but zero evidence, to the contrary. The mathematical odds and chemical circumstances do seem to suggest that life should exist elsewhere. But the reality of such alternate life, if any, is so far unavailable for inspection. It’s a guess, whereas earthly life is fact. Some astounding discovery of extraterrestrial beings, announced tomorrow, or next year, or long after your time and mine, may disprove this impression of Earth’s uniqueness. For now, though, it’s what we have: life is a story that has unfolded here only, on a relatively small sphere of rock in an inconspicuous corner of one middling galaxy. It’s a story that, to the best of our knowledge, has occurred just once.

The shape of this story, in its broad outlines as well as its finer details, is therefore a matter of some interest.

What happened, over the course of roughly four billion years, to bring life from its primordial origins into the fluorescence of diversity and complexity we see now? How did it happen? By what concatenation of accident and determination did it yield creatures so wondrous as humans—and blue whales, and tyrannosaurs, and giant sequoias? We know there have been crucial transitions in evolutionary history, improbable incidents of convergence, dead ends, mass extinctions, big events, and little ones with big consequences—including some fateful contingencies that have left behind evidence of their occurrence embedded subtly throughout the fossil record and the living world. Alter those few contingencies, as a thought experiment, and everything would be different. We wouldn’t exist. Animals and plants wouldn’t exist. Why did it happen as it did, and not some other way? Religions have their responses to such questions, but for science, the answers must be discovered and then supported with empirical evidence, not received in a holy trance.

This book is about a new method of telling that story, a new method of deducing it, and certain unexpected insights that have flowed from the new method. The method has a name: molecular phylogenetics. Wrinkle your nose at that fancy phrase, if you will, and I’ll wrinkle with you, but, in fact, what it means is fairly simple: reading the deep history of life and the patterns of relatedness from the sequence of constituent units in certain long molecules, as those molecules exist today within living creatures. The molecules mainly in question are DNA, RNA, and a few select proteins. The constituent units are nucleotide bases and amino acids—more definition of those to come. The unexpected insights have fundamentally reshaped what we think we know about life’s history and the functional parts of living beings, including ourselves. In particular, there have come three big surprises about who we are—we multicellular animals, more particularly we humans—and what we are, and how life on our planet has evolved.

One of those three surprises involves an anomalous form of creature, a whole category of life, previously unsuspected and now known as the archaea. (Their name gets uppercased when used as a formal taxonomic category: Archaea.) Another is a mode of hereditary change that was also unsuspected, now called horizontal gene transfer. The third is a revelation, or anyway a strong likelihood, about our own deepest ancestry. We ourselves—we humans—probably come from creatures that, as recently as forty years ago, were unknown to exist.

The discovery and identification of the archaea, which had long been mistaken for subgroups of bacteria, revealed that present-day life at the microbial scale is very different from what science had previously depicted, and that the early history of life was very different too. The recognition of horizontal gene transfer (HGT, in the alphabet soup of the experts) as a widespread phenomenon has overturned the traditional certitude that genes flow only vertically, from parents to offspring, and can’t be traded sideways across species boundaries. The latest news on archaea is that all animals, all plants, all fungi, and all other complex creatures composed of cells bearing DNA within nuclei—that list includes us—have descended from these odd, ancient microbes. Maybe. It’s a little like learning, with a jolt, that your great-great-great-grandfather came not from Lithuania but from Mars.