Lane - The vital question : why is life the way it is?

THE VITAL QUESTION

NICK LANE is a biochemist in the Department of Genetics, Evolution and Environment at University College London and leads the UCL Origins of Life Programme. He was awarded the 2015 Biochemical Society Award for his outstanding contribution to the molecular life sciences. He is the author of Life Ascending: The Ten Great Inventions of Evolution, which won the 2010 Royal Society Prize for Science Books, as well as Power, Sex, Suicide: Mitochondria and the Meaning of Life and Oxygen: The Molecule that Made the World.

THE VITAL QUESTION

WHY IS LIFE THE WAY IT IS?

NICK LANE

First published in Great Britain in 2015 by

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Copyright Nick Lane, 2015

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eISBN 978 1 84765 880 7

For Ana
My inspiration and companion On this magical journey

CONTENTS

INTRODUCTION:
WHY IS LIFE THE WAY IT IS?

T here is a black hole at the heart of biology. Bluntly put, we do not know why life is the way it is. All complex life on earth shares a common ancestor, a cell that arose from simple bacterial progenitors on just one occasion in 4 billion years. Was this a freak accident, or did other experiments in the evolution of complexity fail? We dont know. We do know that this common ancestor was already a very complex cell. It had more or less the same sophistication as one of your cells, and it passed this great complexity on not just to you and me but to all its descendants, from trees to bees. I challenge you to look at one of your own cells down a microscope and distinguish it from the cells of a mushroom. They are practically identical. I dont live much like a mushroom, so why are my cells so similar? Its not just that they look alike. All complex life shares an astonishing catalogue of elaborate traits, from sex to cell suicide to senescence, none of which is seen in a comparable form in bacteria. There is no agreement about why so many unique traits accumulated in that single ancestor, or why none of them shows any sign of evolving independently in bacteria. Why, if all of these traits arose by natural selection, in which each step offers some small advantage, did equivalent traits not arise on other occasions in various bacterial groups?

These questions highlight the peculiar evolutionary trajectory of life on earth. Life arose around half a billion years after the earths formation, perhaps 4 billion years ago, but then got stuck at the bacterial level of complexity for more than 2 billion years, half the age of our planet. Indeed, bacteria have remained simple in their morphology (but not their biochemistry) throughout 4 billion years. In stark contrast, all morphologically complex organisms all plants, animals, fungi, seaweeds and single-celled protists such as amoeba descend from that singular ancestor about 1.52 billion years ago. This ancestor was recognisably a modern cell, with an exquisite internal structure and unprecedented molecular dynamism, all driven by sophisticated nanomachines encoded by thousands of new genes that are largely unknown in bacteria. There are no surviving evolutionary intermediates, no missing links to give any indication of how or why these complex traits arose, just an unexplained void between the morphological simplicity of bacteria and the awesome complexity of everything else. An evolutionary black hole.

We spend billions of dollars a year on biomedical research, teasing out the answers to unimaginably complex questions about why we get ill. We know in enormous detail how genes and proteins relate to each other, how regulatory networks feed back into each other. We build elaborate mathematical models and design computer simulations to play out our projections. Yet we dont know how the parts evolved! How can we hope to understand disease if we have no idea why cells work the way they do? We cant understand society if we know nothing of its history; nor can we understand the workings of the cell if we dont know how it evolved. This isnt just a matter of practical importance. These are human questions about why we are here. What laws gave rise to the universe, the stars, the sun, the earth, and life itself? Will the same laws beget life elsewhere in the universe? Would alien life be anything like us? Such metaphysical questions lie at the heart of what makes us human. Some 350 years after the discovery of cells, we still dont know why life on earth is the way it is.

You might not have noticed that we dont know. Its not your fault. Text books and journals are full of information, but often fail to address these childlike questions. The internet swamps us with all manner of indiscriminate facts, mixed with varying proportions of nonsense. But its not merely a case of information overload. Few biologists are more than dimly aware of the black hole at the heart of their subject. Most work on other questions. The great majority study large organisms, particular groups of plants or animals. Relatively few work on microbes, and even fewer on the early evolution of cells. Theres also a concern about creationists and intelligent design to admit we dont know all the answers risks opening the door to naysayers, who deny that we have any meaningful knowledge of evolution. Of course we do. We know an awful lot. Hypotheses on the origins of life and the early evolution of cells must explain an encyclopedia of facts, conform to a straitjacket of knowledge, as well as predict unexpected relationships that can be tested empirically. We understand a great deal about natural selection and some of the more random processes that sculpt genomes. All these facts are consistent with the evolution of cells. But this same straitjacket of facts is precisely what raises the problem. We dont know why life took the peculiar course that it did.

Scientists are curious people, and if this problem were as stark as Im suggesting, it would be well known. The fact is its far from obvious. The various competing answers are esoteric, and all but obscure the question. Then theres the problem that clues come from many disparate disciplines, from biochemistry, geology, phylogenetics, ecology, chemistry and cosmology. Few can claim real expertise in all those fields. And now we are in the midst of a genomic revolution. We have thousands of complete genome sequences, codes that stretch over millions or billions of digits, all too often containing conflicting signals from the deep past. Interpreting these data demands rigorous logical, computational and statistical know-how; any biological understanding is a bonus. And so the clouds have been swirling around with arguments. Each time a gap opens up, it reveals an increasingly surreal landscape. The old comforts have been evaporating. Were now faced with a stark new picture, and its both real and troubling. And from a researchers standpoint, hoping to find some significant new problem to solve, its flat out thrilling! The biggest questions in biology are yet to be solved. This book is my own attempt to make a start.