book review: The Vital Question: Energy, Evolution, and the Origins of Complex Life by Nick Lane

Nick Lane has long been one of my favorite science writers, setting aside Varki of course who will always have a special place in my heart.

Nick Lane’s last book “Life Ascending: The Ten Great Inventions of Evolution” discussed the 10 most important inventions of evolution: the origin of life, DNA, photosynthesis, the complex cell, sex, movement, sight, hot blood, consciousness, and death. I read the book 4 times, was enthralled each time, and no doubt will read it again.

An earlier book by Nick Lane, “Oxygen: The Molecule that Made the World” discussed the amazing transformation of our planet by photosynthesis. After reading this book I look at grass with different eyes. And I love to tell the story of oxygen to any soul who will listen.

In his latest book “The Vital Question: Energy, Evolution, and the Origins of Complex Life” Lane has outdone himself.

The book is sweeping in scope, tackles the most cosmic question, as well as some important earthly questions, is beautifully written, and reads like a page turning mystery thriller.

There is so much here, where to begin?

Lane presents the latest science on the origin of life and makes a compelling case that prokaryotic (simple single cell) life is probably common throughout the universe because all that is required is rock, water, CO2 and energy, all of which are found within alkaline hydrothermal vents on geologically active planets, of which there are 40 billion in our galaxy alone, and probably a similar number in each of the other 100 billion galaxies.

Life emerges as a gradual and predictable transition from geochemistry to biochemistry. Life is not some spiritual mystery, but rather a predictable outcome of the fact that the universe abhors an energy gradient, and life is its best mechanism for degrading energy.

This theory elegantly explains why LUCA (the Last Universal Common Ancestor of all life) and all life that followed is chemiosmotic meaning that it powers itself with a strange highly unintuitive mechanism that pumps protons across a membrane.

The human body, for example, pumps a staggering 10 to the 21st power protons per second of life.

If life is nothing but an electron looking for a place to rest, death is nothing but that electron come to rest.

Lane then turns his attention to the origin of complex life: the eukaryotic cell. All of the multicellular life on earth that normally interests us such as plants, animals, fungi, and hot girls or guys, have a common eukaryote ancestor, and it appears this ancestor emerged only once on earth about 2 billion years after the emergence of simple life. Lane considers this the black hole of biology. A vital but rarely acknowledged singularity that requires explanation.

Lane presents a theory to explain the emergence of the eukaryote and shows that unlike simple life which is probable and predictable, complex life is improbable and unpredictable. It depended on a rare endosymbiosis (merging) of prokaryotes (simple cells) somewhat analogous to a freak accident. The resulting LECA (Last Eukaryotic Common Ancestor), having 2 genomes that needed to cooperate and evolve in harmony, was probably fragile, sickly, and vulnerable to extinction which forced it to evolve many unusual characteristics common to complex life such as the nucleus, sex, two sexes, programmed cell death, germline-soma distinction, and trade-offs between fitness and fertility, adaptability and disease, and ageing and death.

As the endosymbiont (cell within the cell) evolved into mitochondria (the energy powerhouses), eukaryotes were able to break through the energy per gene barrier that constrained the morphological complexity of bacteria and archaea for 2 billion years. Suddenly there was enough energy to power the evolution of complex structure, multi-cellular life, nail salons, and the iPhone.

How lucky that our minds, the most improbable biological machines in the universe, are now a conduit for this restless flow of energy, that we can think about why life is the way it is.

This theory will be particularly satisfying to students of human overshoot who understand that abundant non-renewable energy is the main reason for the size and complexity of today’s human civilization.

The universe, life, and complexity are all about energy.

I am a fan and student of Varki’s theory that human success is the result of a rare simultaneous mutation for denial of reality and an extended theory of mind.

Combining Nick Lane’s theory with Ajit Varki’s theory, and an understanding of our place on the overshoot curve, leads one to an amazing and almost mystical conclusion.

Intelligent life with an extended theory of mind is the result of a rare and unpredictable double mutation, layered on the emergence of complex cells, another rare and unpredictable accident. Intelligent life in the universe is therefore rare and will probably exist for only a short time before its intelligence fueled overshoot, and denial thereof, causes it to go extinct.

The fact that we are alive to witness and understand a very rare peak of intelligent life in the universe is cause for genuine awe.

We should savor it while it lasts.

Here is Nick Lane talking about some of the ideas in his book. I much preferred the book because the subject is too deep to be covered in a 30 minute talk but it’s a taste if you don’t have time for the full meal.

Here is an excerpt from the book’s epilogue.

All life on earth is chemiosmotic, depending on proton gradients across membranes to drive carbon and energy metabolism. We have explored the possible origins and consequences of this peculiar trait. We’ve seen that living requires a continuous driving force, an unceasing chemical reaction that produces reactive intermediates, including molecules like ATP, as by-products. Such molecules drive the energy-demanding reactions that make up cells. This flux of carbon and energy must have been even greater at the origins of life, before the evolution of biological catalysts, which constrained the flow of metabolism within narrow channels. Very few natural environments meet the requirements for life – a continuous, high flux of carbon and usable energy across mineral catalysts, constrained in a naturally microcompartmentalised system, capable of concentrating products and venting waste. While there may be other environments that meet these criteria, alkaline hydrothermal vents most certainly do, and such vents are likely to be common on wet rocky planets across the universe. The shopping list for life in these vents is just rock (olivine), water and CO₂, three of the most ubiquitous substances in the universe. Suitable conditions for the origin of life might be present, right now, on some 40 billion planets in the Milky Way alone.

Alkaline hydrothermal vents come with both a problem and a solution: they are rich in H₂, but this gas does not react readily with CO₂. We have seen that natural proton gradients across thin semiconducting mineral barriers could theoretically drive the formation of organics, and ultimately the emergence of cells, within the pores of the vents. If so, life depended from the very beginning on proton gradients (and iron–sulphur minerals) to break down the kinetic barriers to the reaction of H₂ and CO₂. To grow on natural proton gradients, these early cells required leaky membranes, capable of retaining the molecules needed for life without cutting themselves off from the energising flux of protons. That, in turn, precluded their escape from the vents, except through the strait gates of a strict succession of events (requiring an antiporter), which enabled the coevolution of active ion pumps and modern phospholipid membranes. Only then could cells leave the vents, and colonise the oceans and rocks of the early earth. We saw that this strict succession of events could explain the paradoxical properties of LUCA, the last universal common ancestor of life, as well as the deep divergence of bacteria and archaea. Not least, these strict requirements can explain why all life on earth is chemiosmotic – why this strange trait is as universal as the genetic code itself.

This scenario – an environment that is common in cosmic terms, but with a strict set of constraints governing outcomes – makes it likely that life elsewhere in the universe will also be chemiosmotic, and so will face parallel opportunities and constraints. Chemiosmotic coupling gives life unlimited metabolic versatility, allowing cells to ‘eat’ and ‘breathe’ practically anything. Just as genes can be passed around by lateral gene transfer, because the genetic code is universal, so too the toolkit for metabolic adaptation to very diverse environments can be passed around, as all cells use a common operating system. I would be amazed if we did not find bacteria right across the universe, including our own solar system, all working in much the same way, powered by redox chemistry and proton gradients across membranes. It’s predictable from first principles.

But if that’s true, then complex life elsewhere in the universe will face exactly the same constraints as eukaryotes on earth – aliens should have mitochondria too. We’ve seen that all eukaryotes share a common ancestor which arose just once, through a rare endosymbiosis between prokaryotes. We know of two such endosymbioses between bacteria (Figure 25) – three, if we include Parakaryon myojinensis – so we know that it is possible for bacteria to get inside bacteria without phagocytosis. Presumably there must have been thousands, perhaps millions, of cases over 4 billion years of evolution. It’s a bottleneck, but not a stringent one. In each case, we would expect to see gene loss from the endosymbionts, and a tendency to greater size and genomic complexity in the host cell – exactly what we do see in Parakaryon myojinensis. But we’d also expect intimate conflict between the host and the endosymbiont – this is the second part of the bottleneck, a double whammy that makes the evolution of complex life genuinely difficult. We saw that the first eukaryotes most likely evolved quickly in small populations; the very fact that the common ancestor of eukaryotes shares so many traits, none of which are found in bacteria, implies a small, unstable, sexual population. If Parakaryon myojinensis is recapitulating eukaryotic evolution, as I suspect, its extremely low population density (just one specimen in 15 years of hunting) is predictable. Its most likely fate is extinction. Perhaps it will die because it has not successfully excluded all its ribosomes from its nuclear compartment, or because it has not yet ‘invented’ sex. Or perhaps, chance in a million, it will succeed, and seed a second coming of eukaryotes on earth.

I think we can reasonably conclude that complex life will be rare in the universe – there is no innate tendency in natural selection to give rise to humans or any other form of complex life. It is far more likely to get stuck at the bacterial level of complexity. I can’t put a statistical probability on that. The existence of Parakaryon myojinensis might be encouraging for some – multiple origins of complexity on earth means that complex life might be more common elsewhere in the universe. Maybe. What I would argue with more certainty is that, for energetic reasons, the evolution of complex life requires an endosymbiosis between two prokaryotes, and that is a rare random event, disturbingly close to a freak accident, made all the more difficult by the ensuing intimate conflict between cells. After that, we are back to standard natural selection. We’ve seen that many properties shared by eukaryotes, from the nucleus to sex, are predictable from first principles. We can go much further. The evolution of two sexes, the germline–soma distinction, programmed cell death, mosaic mitochondria, and the trade-offs between aerobic fitness and fertility, adaptability and disease, ageing and death, all these traits emerge, predictably, from the starting point that is a cell within a cell. Would it all happen over again? I think that much of it would. Incorporating energy into evolution is long overdue, and begins to lay a more predictive basis to natural selection.

Energy is far less forgiving than genes. Look around you. This wonderful world reflects the power of mutations and recombination, genetic change – the basis for natural selection. You share some of your genes with the tree through the window, but you and that tree parted company very early in eukaryotic evolution, 1.5 billion years ago, each following a different course permitted by different genes, the product of mutations, recombination, and natural selection. You run around, and I hope still climb trees occasionally; they bend gently in the breeze and convert the air into more trees, the magic trick to end them all. All of those differences are written in the genes, genes that derive from your common ancestor but have now mostly diverged beyond recognition. All those changes were permitted, selected, in the long course of evolution. Genes are almost infinitely permissive: anything that can happen will happen.

But that tree has mitochondria too, which work in much the same way as its chloroplasts, endlessly transferring electrons down its trillions upon trillions of respiratory chains, pumping protons across membranes as they always did. As you always did. These same shuttling electrons and protons have sustained you from the womb: you pump 10²¹ protons per second, every second, without pause. Your mitochondria were passed on from your mother, in her egg cell, her most precious gift, the gift of living that goes back unbroken, unceasing, generation on generation, to the first stirrings of life in hydrothermal vents, 4 billion years ago. Tamper with this reaction at your peril. Cyanide will stem the flow of electrons and protons, and bring your life to an abrupt end. Ageing will do the same, but slowly, gently. Death is the ceasing of electron and proton flux, the settling of membrane potential, the end of that unbroken flame. If life is nothing but an electron looking for a place to rest, death is nothing but that electron come to rest.

This energy flux is astonishing and unforgiving. Any change over seconds or minutes could bring the whole experiment to an end. Spores can pull it off, descending into metabolic dormancy from which they must feel lucky to emerge. But for the rest of us … we are sustained by the same processes that powered the first living cells. These processes have never changed in a fundamental way; how could they? Life is for the living. Living needs an unceasing flux of energy. It’s hardly surprising that energy flux puts major constraints on the path of evolution, defining what is possible. It’s not surprising that bacteria keep doing what bacteria do, unable to tinker in any serious way with the flame that keeps them growing, dividing, conquering. It’s not surprising that the one accident that did work out, that singular endosymbiosis between prokaryotes, did not tinker with the flame, but ignited it in many copies in each and every eukaryotic cell, finally giving rise to all complex life. It’s not surprising that keeping this flame alive is vital to our physiology and evolution, explaining many quirks of our past and our lives today. How lucky that our minds, the most improbable biological machines in the universe, are now a conduit for this restless flow of energy, that we can think about why life is the way it is. May the proton-motive force be with you!