I have previously jokingly called the “Earth biography” a rite of passage for science writers; many authors try their hand at it at some point. Fortunately, the Earth is big and time is deep, so there are numerous ways to tell this story. Here, it is palaeontologist Elsa Panciroli’s turn. Next to many unusual examples by which to tell the story of life’s evolution, her writing stands out for correcting common misconceptions and for its inspired language.

The Earth – A Biography of Life: The Story of Life on Our Planet through 47 Incredible Organisms, written by Elsa Panciroli, published by Greenfinch in April 2022 (hardback, 256 pages)

Panciroli has rounded up the most iconic and important organisms into 47 vignettes. The selection of organisms includes some of the usual suspects; after all, no self-respecting earth biography could do without trilobites, ammonites, or Archaeopteryx. More interesting are the lesser-known representatives of some of life’s major evolutionary transitions. So, as an example of the first animals with a notochord (the precursor of the backbone), she discusses Myllokunmingia found in China rather than the usual example of Pikaia. And as an example of the water-to-land transition of vertebrates, she includes Acanthostega rather than Tiktaalik. When discussing marine reptiles, you learn of Utatsusaurus and the fact (why did I not know this?!) that the evolution of marine reptiles saw terrestrial animals do a U-turn and return to the sea, much like whales would later do.

Panciroli does her best to balance the coverage and there is a nice spread of vertebrates, invertebrates, plants, and (slightly underrepresented) fungi. That last one comes in the form of Prototaxites, a giant fungus that was initially mistaken for a tree because of its concentric growth rings. What I appreciated is that Panciroli includes groups that are not necessarily always considered eye-catching, but that are keystone species in ecosystems (e.g. earthworms, beetles, bees, grasses, or kelp) or are incredibly important to geologists and palaeontologists as index fossils (e.g. trilobites, ammonites, and microfossils such as conodonts, graptolites, and foraminifera). Index fossils are named thus because they are abundant and diverse enough, and show sufficiently rapid species turnover, that you can use them to define different time periods and determine the relative age of rock layers. Or, as Panciroli puts it nicely: “Most of the rock layers of the Cambrian are marked by changes in trilobites, like a fossil clock ticking through deep time” (p. 42).

“Everyone can name clear examples of living and non-living things. However, as so often in biology, there is no sharp demarcation between the two.”

Beyond interesting facts and unusual animals, what ties it all together and elevates this book is the writing, both on account of the excellent explanations and the beautiful phrasing. I keep returning to good explanations in my reviews as I think this is incredibly important, especially where evolution is concerned. Panciroli again: “[evolution] is a seemingly simple concept […] but encompasses such intricate complexity that it is easily misunderstood and mischaracterized” (p. 12), and this is before we get to the deliberate distortion by some groups. Thus she sets you straight on commonly-heard phrases such as living fossils: “thanks to the process of natural selection, no animal remains static, even if superficially their outer appearance changes very little” (p. 70), or missing links: “an outdated term based on the idea of evolution as a straight line. The reality is much messier, with branches shooting in all directions and often ending in extinction” (pp. 162 & 164). Or, particularly common, goal-directed explanations: “Despite the misconception that legs evolved ‘to allow’ animals to walk, this phraseology approaches the process of evolution back-to-front” (p. 88). This was an important theme in Neil Shubin’s book Some Assembly Required: major evolutionary transitions often come about as a result of reusing, repurposing or rejiggling already existing structures and processes. And I could not help but smile at her description of ecosystems, which “can be understood through the flow of energy and materials, which cycle in a pass-the-parcel game through ecosystems via photosynthesis, predation, decomposition and nutrient recycling” (p. 13).

Her effective explanations are, as in her last book, complemented in places by some particularly inspired writing that describes the K–Pg extinction as “the most famous punctuation mark in our planet’s evolutionary story” (p. 167) and supercontinent formation as “a geological rugby scrum” (p. 109). She injects a degree of poetry that makes you see extinct organisms in a new light. Foraminifera have “survived multiple mass extinctions, and now whisper stories of climate change and environments through deep time” (p. 198), while “In the Jurassic[,] beetles suddenly infest the pages of deep time, munching their way across the landscape and leaving behind a glittering confetti of wing casings” (p. 158). And her description of Archaeopteryx made me want to cheer on this audacious little critter: “At the end of the Jurassic, there lived an animal that was part reptile, part bird, and 100 per cent astonishing […] They are sometimes preserved with a halo of feathers, like snow angels in the rock” (p. 162).

“Everyone can name clear examples of living and non-living things. However, as so often in biology, there is no sharp demarcation between the two.”

Panciroli previously impressed me with her debut Beasts Before Us which covered the evolution of early mammals. The current book is, in some ways, a more challenging one to write; it could have ended up as a random collection of interesting factoids and eclectic tidbits. However, she ties the book together by punctuating the short vignettes with introductions to the different geological periods that stress the connections and interactions between evolution, geography, and geology. There are numerous examples of plate tectonics shaping the whole world: the breakup of Pangaea reproductively isolating animals and plants, contributing to increased speciation; the break-up of Europe and North America causing extensive volcanism that led to the Palaeocene–Eocene Thermal Maximum; and subsequent cooling thanks to mountain-building episodes such as the Himalayan orogeny leading to increased silicate weathering that drew down atmospheric carbon dioxide, the Antarctic Circumpolar Current putting Antarctica in the deep freezer, and the Isthmus of Panama interfering with global ocean circulation by preventing warmer Pacific water from entering the Atlantic.

The book is complemented by a nice selection of period and modern illustrations from various picture libraries, as well as drawings by Grace Varnham, all of which have been rendered in the same two-tone pink-green style for a unified look. If The Earth – A Biography of Life is Panciroli’s trial by fire, then she has passed the test as far as I am concerned. The combination of interesting popular science facts, inspired writing, and a mission to correct common misconceptions make this book easy to recommend, and would make for a great gift.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

The Earth – A Biography of Life

Other recommended books mentioned in this review:

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Our planet has been many different worlds over its 4.5-billion-year history. Imagining what they were like is hard—with our limited lifespan, deep time eludes us by its very nature. Otherlands, the debut of Scottish palaeontologist Thomas Halliday, presents you with a series of past worlds. Though this is a non-fiction book thoroughly grounded in fact, it is the quality of the narrative that stands out. Beyond imaginative metaphors to describe extinct lifeforms, some of his reflections on deep time, taxonomy, and evolution are simply spine-tingling.

Otherlands: A World in the Making, written by Thomas Halliday, published in Europe by Allen Lane in February 2022 (hardback, 385 pages)

The 16 chapters in Otherlands, each accompanied by a gorgeous illustration from Beth Zaiken, step back in time by millions or even tens of millions of years to visit a place on Earth and describe its ecosystems and organisms. Halliday includes well-known sites such as end-Cretaceous Hell Creek (66 million years (Ma) ago) and the Carboniferous world of Mazon Creek (309 Ma ago) or Lagerstätten (sites of exceptional fossil preservation) such as the Cambrian Chengjiang biota in China (520 Ma ago) and the Australian Ediacara Hills during the Ediacaran (550 Ma ago). Far more interesting are the little-known eras and places such as the Italian promontory of Gargano during the Miocene Messinian Salinity Crisis (5.3 Ma ago), the sweltering warmth of Seymour Island in Antarctica during the Palaeocene–Eocene Thermal Maximum (41 Ma ago), or the underwater life around the Silurian Yaman-Kasy vent in Russia (435 Ma ago).

Stylistically, Otherlands is a narrative non-fiction book. What that means is that, though everything is grounded in fact, Halliday does not get lost in the details^[1]. Where competing hypotheses exist he picks one and runs with it, rather than detailing the academic debates and different schools of thought. It is a stylistic choice that I can get behind given the quality of the writing that follows.

Because make no mistake, Halliday knows how to craft captivating prose. He won the Hugh Miller Writing Competition in 2018 and the John C. Marsden Medal from the Linnean Society for the best doctoral thesis in biology in 2016. Reading Otherlands, it is easy to see why. I do not know what they feed Scottish palaeontologists, but I was reminded of Elsa Panciroli’s Beasts Before Us. (This might not be a coincidence, she is prominently acknowledged for inspiring him to participate in the above-mentioned competition.) Let me back up my enthusiasm with some quotes that can only touch on a fraction of what is on offer.

“A recurrent theme in this book is that of impermanence: “gatherings of species in time and space may give the illusion of stability, but these communities can only last as long as the conditions that help to create them persist“”

There are the obvious imaginative metaphors to describe animals. The Triassic gliding reptile Sharovipteryx mirabilis (225 Ma ago) is imagined looking rather inelegant once landed “with its membrane retracting and limbs thrown all directions like a collapsing deckchair” (p. 159), while the Ediacaran sedentary animal Dorothy’s Rope (550 Ma ago) resembles upright towers “composed of bulges like knotted rope, as if Gaudi had designed an industrial town” (p. 277). Other descriptions are more poetic. Basilosaurids, the first fully aquatic whale ancestors in the Eocene (41 Ma ago), have yet to evolve the melon organ. They “can listen to the music of the oceans, but they have not yet learned to sing” (p. 86).

Particularly powerful are his reflections on deep time. A recurrent theme in this book is that of impermanence: “gatherings of species in time and space may give the illusion of stability, but these communities can only last as long as the conditions that help to create them persist” (p. 18). Some ecosystems never return. The long-lived Jurassic crinoid colonies (155 Ma ago) that made a home on floating logs blown into the sea during storms disappeared when the evolution of shipworms made “this way of life impossible, something that can and will never be replicated in quite the same way again; wood just doesn’t float for as long as it used to” (p. 151). We now similarly worry about coral bleaching: “continent-scale coral reefs might just end up being one of those ecosystems that never returns, a distinctively Cenozoic phenomenon” (p. xix). And while the world feels old in our day, it is easy to forget the world was already old in the deep past. The mountains of the Triassic (225 Ma ago) “are built from the deep sea“, within which can be seen “the coils and shapes of the long-extinct creatures of the Carboniferous seas, well over 100 million years old even now” (p. 158).

“What made my hair stand on end were Halliday’s reflections on phylogenetics. […] I love how he drowns scientific concepts in poetic language.”

What made my hair stand on end were Halliday’s reflections on phylogenetics, the evolutionary relationships between animals. I love how he drowns scientific concepts in poetic language. Take the Paleocene Baioconodon (66 Ma ago). Beyond one of the earliest placental mammals, we do not really know what it was. “Their anatomy is too non-committal, too similar to and yet too distinct from too many living orders to be placed with confidence. […] They are an unspecialized, Platonic placental, a lump of living clay from which all others are stretched, pinched and pulled into shape” (p. 105). We cannot even describe its young as kits or calves: “it does not yet make sense to talk of cattle or dogs, of monkeys or horses. None of these groups exist yet […] names lose tangibility in the depths of the past, and our language has no description for the young of common ancestors” (p. 104). You start to see why Halliday wrote his way backwards from the present. He makes a similar observation about the Ediacaran biota. Alien to us, “they are aberrant only from a modern perspective” (p. 282). Our confusion is partially because “we are trying to define them the only way we can: on the basis of those few survivors to have found paths to the present“, while the dead-end branches “by the simple fact of having not survived, forfeit a common name” (p. 283).

Similarly spine-tingling are his explanations of evolutionary processes. Species names are artificial designations for a continuous phenomenon. The way palaeontologists deal with this can be compared to rivers. Just as a river can split and its two branches be called by two names from that point in space forward, so can a species that spatially separates be called by two names from that point in time forward. And why did so many higher taxa appear during the Cambrian explosion? One idea is that, once in place, fundamentals cannot be changed easily: “evolution today can only be played within the constraints set by the past“. Another idea is that “there is nothing intrinsically impossible about a new body plan developing today, were it not for the existence of others“. Gould wrote of filling the ecological barrel and Halliday puts it thus: “establishing the basic roles within an ecosystem is like adding large rocks into a barrel […] evolutionary processes […] adding in finer and finer divisions of ecological processes, pebbles and sand falling into the barrel between the gaps left by the larger stones, structures built on other structures” (p. 258). Not only does this ring true, but it is also truly beautiful language.

Otherlands is an exceptional debut that can be savoured like a fine wine. I found myself reciting passages to anyone within earshot. Beyond a fascinating tour of extinct lifeforms, Halliday’s carefully crafted yet poetic descriptions of scientific concepts are a masterclass in spellbinding science communication.

1. ↑ The relevant references are collected paragraph by paragraph in endnotes. One minor annoyance is that Halliday omits the titles of journal articles, which I normally find the most informative bit. No doubt done to save space, I cannot imagine this will bother many people.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Otherlands

Other recommended books mentioned in this review:

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Deep time is, to me, one of the most awe-inspiring concepts to come out of the earth sciences. Getting to grips with the incomprehensibly vast stretches of time over which geological processes play out is not easy. We are, in the words of geologist Marcia Bjornerud, naturally chronophobic. In Notes from Deep Time, author Helen Gordon presents a diverse and fascinating collection of essay-length chapters that give 16 different answers to the question: “What do we talk about when we talk about deep time?” This is one of those books whose title is very appropriate.

Notes from Deep Time: A Journey Through Our Past and Future Worlds, written by Helen Gordon, published by Profile Books in February 2021 (hardback, 322 pages)

For Gordon, a chance encounter with an outdoor information board during a walk on the North Downs near London ignites her interest in deep time. Before long, she is visiting museums and interviewing earth scientists and palaeontologists. Notes from Deep Time is thus very relatable to a general audience who, like Gordon, are not geologists. A few of the 16 chapters in this book have previously been published, but most are new. She has organised them around three topics: geology, extinct life, and the intersection of deep time with human affairs. Having introduced the concept of deep time and how the age of the Earth was slowly uncovered, she delves into palaeoclimatology, stratigraphy, plate tectonics, earthquakes, volcanic eruptions, dinosaurs, the Anthropocene, palaeoart, urban geology, nuclear waste, etc.

One enjoyable aspect is that Gordon brings in new perspectives, even for topics I was familiar with. When discussing ice cores, she explains the work of pioneer Willi Dansgaard and his discovery of rapid climatic changes subsequently named Dansgaard–Oeschger events. Initially eyed suspiciously by scientists, the idea was soon enough corroborated by evidence from pollen records and ocean sediments. Her discussion of dinosaurs is equally novel, and appropriately titled “what we talk about when we talk about dinosaurs”. She asks why children are so fascinated by them, how fossil dig sites have changed over time, how the palaeontological community is torn over the trade in fossils, and how the story of their extinction forms “an irresistible backdrop onto which to project our own fears of climate change and contemporary apocalypse” (p. 196), something explored further in Sepkoski’s Catastrophic Thinking. When visiting a dinosaur trackway in Utah, she reminds the reader that it is easy to lose sight of the beasts themselves. “Bombarded with plastic figurines and dinosaur memes, familiarity stops me really seeing a dinosaur. […] Touching the edges of one of the theropod’s lozenge-shaped toes, 150 million years almost dissolve in the hot desert air. There really were dinosaurs here. For a moment that fact becomes amazing once again” (pp. 198–199).

“In 2018, a terrible ruckus broke out when some stratigraphers proposed subdividing our current epoch, the Holocene, into three new ages, the most recent one being called the Meghalayan.”

I furthermore appreciated how Gordon pays attention to the subtleties and technicalities of topics. In two chapters she takes a surprisingly deep yet accessible dive into stratigraphy. In 2018, a terrible ruckus broke out when some stratigraphers proposed subdividing our current epoch, the Holocene, into three new ages, the most recent one being called the Meghalayan. Partially this was because others are still working on the stratigraphical case for the Anthropocene. She listens to the arguments put forth by both proponents and opponents of these concepts. She goes into a similar level of nuanced detail when discussing colour as deduced from exceptionally well-preserved fossils. The focus has so far been on melanosomes and the pigment melanin, but Gordon also interviews Maria McNamara who is looking at carotenoid pigmentation and structural colours. These discoveries allow palaeoartists to make more true-to-life reconstructions. An open-hearted conversation with palaeoartist Robert Nicholls touches on his Psittacosaurus model, the importance of thorough background research, and his frank opinion that most dinosaur art that gets published is “regurgitated nonsense” (p. 214). And while I had read about the plans for long-term underground storage of nuclear waste in Finland in Macfarlane’s Underland, Gordon adds an interesting discussion on the challenges of designing warning signs for distant future generations to stay away from such repositories.

Some chapters touched on, for me, completely novel subjects. There is a chapter on chalk, one of the least appreciated rock types amongst geologists. Here, she accompanies a team making a new map of the chalk formations underlying parts of Britain. She discusses the primitive fossil trees found in Gilboa in the USA, and their unusual mode of growth. Another chapter focuses on the difficulty of predicting earthquakes and volcanic eruptions, and highlights that part of the problem is the loss of hard-won knowledge and experience when scientists retire. And she opened my eyes to the phenomenon of urban geology, the idea that the materials used in buildings, especially older ones, can reveal more about local geology.

“When explaining how the theory of plate tectonics came together [Gordon] cleverly points out that “you can tell the story of plate tectonics in many different ways“, depending on whose contributions you focus on.”

What makes this wide-ranging collection of deep-time musings so captivating is Gordon’s language and sharp observations. She talks to the Geological Society’s librarian who highlights commonalities between poetry and geology: both involve “building worlds in your mind and presenting them to others using descriptive language” (p. 8). When we discuss history, we merrily skip over thousands and millions of years. As Gordon puts it beautifully: “if the human brain naturally compresses the past, then the scientists working with deep time are in the business of decompression” (p. 22). When explaining how the theory of plate tectonics came together, she of course pays homage to Alfred Wegener but cleverly points out that “you can tell the story of plate tectonics in many different ways” (p. 75), depending on whose contributions you focus on. And why, of all the proposed new stratigraphical units, has the Anthropocene taken such hold of the popular imagination? Gordon’s answer is that science has been in the business of knocking humans off their pedestal for several centuries. “Considered one way, then, the Anthropocene concept puts humans back at the centre of the world […] and at some level we can’t help finding that attractive—even if the price for that return is environmental disaster” (p. 244). The only thing I felt was missing from this book were illustrations and photos; many of the places and phenomena described here would have benefited from some.

Notes from Deep Time is a fantastic dive into the deep past of our planet that engages with deep time on many levels. Readers will find at least some, if not many chapters that will thoroughly captivate them and induce that most rare of sensations: “temporal vertigo” (p. 1).

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Notes from Deep Time

Other recommended books mentioned in this review:

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Deep time is one of the most mind-boggling yet underappreciated concepts to come out of the disciplines of evolutionary biology and the earth sciences. As an editor with Nature for over three decades, Henry Gee has had a front-row seat to numerous exciting scientific developments that have enriched our understanding of Earth’s vast 4.6-billion-year history. This high-octane popular science book is his take on the genre of the “earth biography”.

A (Very) Short History of Life On Earth: 4.6 Billion Years in 12 Chapters, written by Henry Gee, published in Europe by Picador in September 2021 (hardback, 336 pages)

I admit that my initial response to this book was one of mild surprise: “wait, another one?” A (Very) Short History of Life On Earth was published in the same month as Riley Black’s Deep Time and only months after geologist Andrew Knoll’s A Brief History of Earth that promises to do the whole exercise in eight chapters. Further back, other notable examples have been Robert Hazen’s The Story of Earth and the now-classic Life: An Unauthorised Biography by Richard Fortey. Writing Earth’s biography almost seems like a rite of passage for science writers.

If you have read any of these books, or are familiar with the major events in life’s evolution, you already know what to expect. Earth’s formation, the start of plate tectonics, the rapid evolution of life, the Great Oxygenation Event, the first bacterial cells, endosymbiosis, multicellular life, the spinal cord, tetrapods making landfall, reptiles, dinosaurs, mammals, monkeys, and mankind—the whole circus comes rolling through town in high tempo.

“Gee focuses on those geologic periods and fauna that normally get little love in popular science books […] he sticks up for the fauna of Triassic that often gets overlooked in favour of the dinosaurs”

And yet, the history of life is so full and rich that every iteration of this story can draw on new details. An important backbone to Gee’s version is plate tectonics and the supercontinent cycle. As he explains, the breakup of Rodinia (Pangaea’s predecessor) was accompanied by so much volcanism and extrusion of fresh rocks that the subsequent erosion drew enough carbon dioxide out of the atmosphere to cause planetary-scale glaciation, the Snowball Earth episodes some time before 650 million years ago. In turn, the formation of Pangaea caused the climate on land to be far hotter, drier, and more seasonal. More recently, the opening of the Drake Passage allowed the Southern Ocean to flow uninterruptedly around Antarctica, shaping Earth’s climate to this day.

What I particularly enjoyed is that Gee focuses on those geologic periods and fauna that normally get little love in popular science books. There was the invertebrate fauna of the Ediacaran that defies categorization and makes even the weirdos of the Cambrian explosion look normal in comparison. Gee is similarly knowledgeable about the rise of the backbone and introduces you to vetulicolians and yunnanozoans, one of which, Cathaymyrus, “looked like an anchovy fillet […] sans head, sans scales, sans ears, sans nose, sans brain—sans nearly everything” (p. 38). He discusses the fantastic flora of the Carboniferous, and the unique conditions that gave rise to 90% of today’s coal reserves. And he sticks up for the fauna of the Triassic that often gets overlooked in favour of the dinosaurs. In reality, “the dinosaurs were a relatively small sideshow in the Triassic carnival of dicynodonts, rhynchosaurs, rauisuchians, aetosaurs, phytosaurs and giant amphibians” (p. 99).

Indeed, when he gets to the dinosaurs, Gee cleverly refrains from trying to write an overview, as so many excellent books already exist on this topic. Instead, he focuses on several biological aspects that made them so successful: the evolution of bipedalism, the innovations in respiration that allowed them to grow so large, and the transition to powered flight. This is embedded in the history of mammal evolution that simultaneously happened in the background, though I was surprised to find no mention of Panciroli’s Beasts Before Us, which is the current go-to book on this topic.

“Gee repeatedly reminds his readers that evolution is not goal-directed. […] one group of ungulates “with enthusiasm, and, in evolutionary terms, great haste” returned to the water and evolved into whales.”

Some other enjoyable details include an increasingly zoomed-in timeline^[1] at the beginning of some chapters—too few books use good infographics. Gee’s extensive footnotes are frequently as interesting as the main text, provide plenty of further references, and clearly signpost where he ventures into speculation. Some of his writing is particularly memorable. Of the first cells, he writes that: “these foamy lathers of soap-bubble cells stood as tiny clenched fists, defiant against the lifeless world” (p. 7), while the evolution of photosynthesis that harnessed previously damaging UV radiation meant that “harm had become harvest” (p. 8).

Importantly, Gee repeatedly reminds his readers that evolution is not goal-directed. “It wasn’t as if eukaryotes looked at their calendars, and, seeing that it was 825 million years ago, unanimously decided to become multicellular” (p. 217). Furthermore, “the tetrapod commitment to land was, for many millions of years, no more than equivocal” (p. 68). Both early and modern birds have secondarily lost flight on numerous occasions, while one group of ungulates “with enthusiasm, and, in evolutionary terms, great haste” (p. 141) returned to the water and evolved into whales. And the profusion of early hominins should not “give the impression that a series ever more bipedal species replaced one another in some orderly, preordained fashion” (p. 155). There is one place where Gee seemingly throws this caution to the wind: “Dinosaurs had always been built to fly” (p. 105) and “[…] spent millions of years accumulating everything they needed for flight” (p. 113). In hindsight, it seems the writing was on the wall, but I was reminded of Neil Shubin’s insight that: “innovations never come about during the great transitions they are associated with“.

“Gee looks ahead with an unusual mix of optimism and nihilism […] Ours is but a “mayfly existence“. This reminder of our cosmic insignificance is a sobering but fitting conclusion to [his] epic tale.”

The first two-thirds of A (Very) Short History of Life On Earth are, in my view, the strongest. After the end of the Cretaceous, the book takes a rather anthropocentric bend, focusing on primate and hominin evolution only, as if life was on the highway to humankind. What, for example, of the explosive radiation of birds? Gee also stops rather abruptly with our departure from Africa and our interbreeding with Neanderthals and Denisovans. Recent milestones, such as language, animal and plant domestication, and agriculture are skipped over.

Instead, in his last chapter, Gee looks ahead with an unusual mix of optimism and nihilism. In an upbeat manner, he writes that we are already phasing out fossil fuels and can expect our world population to plateau. Part of his optimism might stem from his agreement with e.g. Michael Hannah that technically it is too early to be speaking of the sixth mass extinction. On the other hand, he thinks our extinction is merely a matter of thousands of years. When he reflects on the long-term future of Earth, he asks: “What, then, will be the human legacy? When measured against the span of life on Earth—nothing. The whole of human history, so intense and so brief […] will leave no more than a layer, millimetres thick, in some future sedimentary rock“. Ours is but a “mayfly existence” (pp. 232–233). This reminder of our cosmic insignificance is a sobering but fitting conclusion to Gee’s epic tale.

In 1997, Ted Nield wrote of Fortey’s book that “The tale of life needs constant retelling“. I believe this sentiment still holds, both because our understanding advances and because we need periodic reminders of the importance of deep time. Gee succeeds on both these fronts and dishes out interesting nuggets at a brisk clip, making A (Very) Short History of Life On Earth a high-octane popular science book.

1. ↑ This reminded me of the introduction to the sitcom The Big Bang Theory, and there is more than a passing resemblance between the theme song by Barenaked Ladies and Gee’s energetic take on the subject.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

A (Very) Short History of Life On Earth

Other recommended books mentioned in this review:

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We walk on layered history. The ground beneath our feet is shot through with traces of our past, some in plain sight, many buried and badly eroded. Writer and artist Tom Chivers will concur that nowhere is this more true than in cities. London Clay is the result of a decade of exploration on foot, tracing vanished rivers, lost islands, and geological strata hiding under the concrete bedlam of modern London. The city’s untidy edges, its brownfields and derelict buildings, the very lay of the land—in Chivers’s hands all of these become cracks through which the past oozes back in. An unlikely chimaera of nature writing and urban exploration, this lyrical book offers a fresh way of looking at the built environment.

London Clay: Journeys in the Deep City, written by Tom Chivers, published by Doubleday in September 2021 (hardback, 450 pages)

The genesis of this book is hard to pin down. Born in South London in 1983, Chivers has been fascinated since childhood with exploring the city. Throughout his twenties, he continued to chronicle London through barely-read poems, pamphlets, and books. Just as this creative impulse was petering out, arts charity Cape Farewell approached him to be their first poet-in-residence, in turn leading Chivers to produce a series of audio walking adventures along London’s lost rivers. This, if anything, provided the impetus for the writing of London Clay.

In eight chapters, the reader follows Chivers as he walks the course of now invisible rivers. South of the Thames: the river Effra and one of its arms, the Ambrook, into Dulwich and Sydenham, the Neckinger into Southwark, or the lost island now subsumed in the district of Bermondsey. North of the Thames: the river Walbrook into Broadgate and Shoreditch, the river Fleet all the way into Camden Town and Hampstead, the former delta on which Westminster was built, or the Lower Lea Valley in Stratford and Hackney that hosted the 2012 Summer Olympics.

If, like me, you are not a Londoner, you might be unaware that there is quite some interest in its subterranean rivers, the bricked-over tributaries of the Thames. At a young age, Chivers already laid his hands on Nicholas Barton’s 1962 book The Lost Rivers of London, and he later takes Tom Bolton’s 2011 London’s Lost Rivers with him. However, London Clay is not a walking guide: although each chapter is preceded by a map, these outline geological strata and a few modern and historical landmarks only. One might be able to retrace Chivers’s steps, but it would take some puzzling. It is also not a photographic book akin to Paul Talling’s London’s Lost Rivers, instead relying on some atmospheric illustrations by Rohan Daniel Eason. Similarly, Chivers walks largely aboveground, at no point crossing paths with the urban exploration scene that crawls through London’s sewers and tube tunnels. And although he ends up on the intertidal shores of the Thames more than once, mudlarking only features sparsely.

“London Clay is the result of a decade of exploration on foot, tracing vanished rivers, lost islands, and geological strata hiding under the concrete bedlam of modern London”

Instead, these are a poet’s ramblings, tracing “a procession of ghost-lines retreating in time” (p. 67), following the meanders of barely visible channels, “the desire line of water” (p. 69). Chivers calls it an exercise in “deep topography”, linking to what Nick Papadimitriou did for London’s outer limit in his 2012 book Scarp. Or, I might add, what Iain Sinclair did before that with e.g. his 2003 book London Orbital. Effectively, Chivers’s book is part of a fairly young tradition of writings on psychogeography, an arts term for the effect of place on our emotions and behaviours.

Next to this, without wishing to sound snooty, there is also a fair bit of amateur sleuthing in here. Chivers excuses himself for being “neither historian nor geographer, but [writing] with the poet’s compulsion for rumour and conjecture” (p. 6). He delves into books and maps, traces the linguistic origin of place names, and accompanies caretakers, local historians, and archaeologists as he walks the city. Several historical periods feature prominently. One is, logically, the late 19th-century construction of London’s sewer, overseen by engineer Joseph Balzagette. This is when many waterways were incorporated into the sewer system and disappeared from sight. Chivers is furthermore attracted to the sites of former Tudor-era playhouses and theatres, such as The Boar’s Head in Whitechapel, or The Rose in Bankside that is currently sheltered in the basement of an office block. And remains of Roman and later Anglo-Saxon London keep surfacing during construction projects.

“I was foremost reminded of China Miéville’s The City & The City […] It is exactly the way Chivers’s writing seamlessly transitions from now-London to past-London that evokes this, laying bare a city that lies in plain sight but that most of us do not see.”

Further back still, Chivers delves into London’s geology. “Geological time reduces the human story to a footnote in the history of the planet […] This London is rarely seen, but it is always there, pressing its immanence into our world” (p. 5), he writes. It is his channelling of deep time that most brought to mind Robert Macfarlane’s Underland, from which he quotes on several occasions (and of which London Clay‘s cover reminded me). There is even a surprise appearance of a young Patrick Nunn. Chivers describes his 1983 idea of how the Thames, as climate and sea levels changed over thousands of years, “slowly progressed north, like a snake coiling and uncoiling, before reaching the meandering form we know today“. In turn, this “left behind a series of ‘relict channels’ and some of these subsequently flowed as tributary streams—the so-called lost rivers” (p. 274).

It is tempting to draw comparisons to Neil Gaiman’s London as it features in Neverwhere. But I was foremost reminded of China Miéville’s The City & The City. Here, two cities entwine, with citizens overlapping in contact zones. Yet, from birth, they learn to not just ignore but to studiously unsee their counterparts. An Orwellian government organisation strictly monitors for cases of Breach, rounding up anyone who accidentally or purposefully interacts with the other side. It is exactly the way Chivers’s writing seamlessly transitions from now-London to past-London that evokes this, laying bare a city that lies in plain sight but that most of us do not see.

By offering a model for how to look at our everyday environment with a different set of eyes, London Clay might just foster a renewed sense of care and custodianship in city dwellers. Even if it would not achieve this lofty goal, it is an entrancing book that, though steeped in London lore, is fascinating even for those of us not living there.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

London Clay

Other recommended books mentioned in this review:

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History will forever associate Charles Darwin with the theory of evolution, but the idea was in the air. Had not Darwin published his famous book, someone else would have likely snatched the prize. Husband-and-wife duo John and Mary Gribbin here examine the wider milieu in which Darwin operated and the many thinkers who preceded him. Given their previous collaborations, the first two parts of On the Origin of Evolution read like a well-oiled machine, but the book falters when they turn their eyes to the legacy of Darwin’s ideas.

On the Origin of Evolution: Tracing ‘Darwin’s Dangerous Idea’ from Aristotle to DNA, written by John Gribbin and Mary Gribbin, published in Europe by William Collins (a HarperCollins imprint) in November 2020 (hardback, 288 pages)

When you study the history of science, it seems there is just no way around Aristotle. In the context of this book, his legacy is the idea of the great chain of being: the notion that life can be ordered from simple to complex forms, with humans at the top as creation’s crowning glory. It was readily adopted by Christian thinkers and hamstrung evolutionary thinking for millennia.

Still, as the first third of this book shows, some people did ponder both man’s place in nature and the relationships between living beings. Liberally quoting from their writings, the authors introduce you to notable characters and their brilliant early flashes of insight. For example, Thomas Aquinas, writing in the 13th century, allowed for species to develop in their striving for perfection but rejected the idea of new ones arising after God’s act of creation. Fossils were long misunderstood, neither recognized as ancient nor as the remains of extinct creatures. I was therefore particularly fascinated by 17th-century British polymath Robert Hooke who may well have been one of the first to recognize fossils for what they were. His ideas on species formation and extinction seem prescient. In the 1770s, Lord Monboddo already argued that humans descended from apes. And yet, the dots were not connected into a bigger picture. Particular sticking points were extinction and the age of the Earth, a puzzle to which James Hutton and other geologists would later contribute much.

When the book gets to Darwin, the tempo slows right down and the middle third of the book examines Darwin’s life and simultaneous developments around him. The Gribbins sketch how Darwin, ever careful, worked on his ideas for decades, also because he felt that, as a geologist, one could not “examine the question of species who has not minutely described many” (p. 134). Something he subsequently spent years on. The history of how Alfred Russel Wallace later came to similar conclusions and ran them past Darwin in a letter, and how Charles Lyell and Joseph Hooker presented both their work at a meeting of the Linnean Society, is well-known. What the Gribbins here clarify is that, if it seems strange to us now that Wallace’s letter was publicly presented by a third party without his consent, this was the custom of the time. Communications of scientific interest were expected to be made public as quickly as possible. Various quotes from Wallace indeed show nothing but a man who was very chuffed to have his work mentioned alongside Darwin’s.

“[…] the first two parts of On the Origin of Evolution read like a well-oiled machine, [numerous] details left me with the impression that the authors have been meticulous […]”

The Gribbins also pay attention to Erasmus Darwin (Charles’s grandfather) and relevant contemporaries such as Jean-Baptiste de Lamarck and Georges Cuvier. They give Lamarck his due and note the irony of him accepting evolution but denying extinction, and Cuvier denying evolution but accepting extinction. If the two had not ended up bitter enemies they might have put two and two together. Another lesser-known figure who came tantalisingly close, and virtually coined the term natural selection, was arborist Patrick Matthew who buried his thoughts in the appendix to a book on naval timber. Darwin was unaware of his work despite Matthew’s later public charges, the Gribbins write. Other notable details are a public admission to a change of heart over whether a letter from Darwin to Wallace was intended to warn Wallace off. The Gribbins used to think so, but are now persuaded it was not. They also clarify the oft-repeated factoid of On the Origin of Species selling out on the day of publication: “this is only true in the sense that all the copies had been bought up by the bookshops, ready to sell on to their customers” (p. 166). An observation that, working for a bookseller myself, rings true. These and other details left me with the impression that the authors have been meticulous up to this point. (I admit this is a risky thing to say; whole academic careers have been built on studying Wallace and Darwin’s lives, so cue people more knowledgeable than myself pointing out errors next).

On the Origin of Evolution competes for your attention with Rebecca Stott’s 2012 book Darwin’s Ghosts, which similarly traced Darwin’s intellectual forebears. That book ended with the above-mentioned presentation at the Linnean Society, so the Gribbins have the opportunity to set themselves apart with the last third of their book, which examines the development of Darwin’s ideas by later scientists. Although I enjoyed the book up to this point, the last part is where it fell a bit flat for me.

The Gribbins weave their narrative through the work of Gregor Mendel and its triple rediscovery decades later; the discovery of the structure of DNA, honouring the long course described in Unravelling the Double Helix; and the discovery of how DNA codes for amino acids. It touches on horizontal gene transfer, epigenetics, and twin studies and the discovery of polygenic traits. All important topics for sure, but they omit so many others as to make this part of their history rather haphazard.

“[…] the last third of their book, which examines the development of Darwin’s ideas by later scientists. […] omits so many [topics] as to make this part of their history rather haphazard.”

Two oversights stand out. They discuss how extinction ultimately became accepted but leave out the next chapter: the mass-extinction debates, which was a conflict between uniformitarianism and catastrophism. Similarly, they recognize Wallace as the grandfather of biogeography but leave out how the long-resisted idea of plate tectonics explained palaeobiogeographic patterns. Basically, they completely ignore the rise of palaeobiology and its contributions to evolution. Beyond these, they mention horizontal gene transfer, but not Carl Woese and his proposal of a Last Universal Common Ancestor. They feature Thomas Hunt Morgan’s research on Drosophila, but not the emergence of evolutionary developmental biology. They profile Barbara McClintock’s struggle to get her discovery of mobile genetic elements accepted but not Lynn Margulis‘s struggle to get endosymbiosis recognized. And although the Sources and Further Reading section lists other major thinkers, there is no discussion of, say, Ernst Mayr and the problem with species definitions, the work of Stephen Jay Gould, or the debate on levels of selection. Sexual selection and phylogenetics are completely absent.

They cram this last part in a mere 70 pages while repeatedly mentioning not being able to go deeper. I am not sure why. At 253 pages of text, the book is not particularly long. Had they spent another 50 or even 100 pages, I feel they could have done it more justice. I will be the first to concur that writing such an overview is challenging. Part of the problem, I think, is that the authors (John a science journalist with a PhD in astrophysics, Mary a teacher) do not have a thorough background in (molecular) biology and reach into unfamiliar territory, as evidenced by some elementary mistakes. On p. 218 they mention DNA contains three purines and one pyrimidine, and correct themselves two sentences later (there are two of each). They mix up the DNA base pairs on p. 226 (CT and AG pairs) but get it right on p. 227. And on p. 244 they mention the human genome consists of 6 billion base pairs which is double the actual number. Anyone who has had to study Alberts’s brick will have had these facts drummed into them, but their acknowledgements are silent on whether fellow biologists provided feedback on the manuscript. Now, I do not want to blow a few factual errors out of proportion, but together with the brevity of the material included, and the many other topics not covered, this last part left me less than satisfied.

Overall then, this book is an excellent introduction to the history of evolution before and up to Darwin that retains important detail despite being relatively brief. I was less impressed with the coverage on the developments since Darwin, which would benefit from supplementary reading. I hope a future review of The Black Box of Biology will fill in some of the blanks regarding molecular biology.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

On the Origin of Evolution

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After three previous books in this format on fossils, rocks, and dinosaurs, geologist and palaeontologist Donald R. Prothero here tackles the story of evolution in 25 notable discoveries. More so than the previous trio, this book tries to be a servant to two masters, resulting in a mixed bag.

The Story of Evolution in 25 Discoveries: The Evidence and the People Who Found It, written by Donald R. Prothero, published by Columbia University Press in December 2020 (hardback, 360 pages)

Prothero has organised The Story of Evolution in 25 Discoveries in a logical fashion. After convincing the reader that the universe and our planet are, indeed, really old, he considers some of Darwin’s lines of evidence for evolution, followed by several great transitions in evolution as revealed by the fossil record, more recent evidence from genetics and molecular biology, and, of course, evidence for the evolution of humans.

As in his previous books, Prothero manages to dig up some remarkable stories. For example, Darwin initially mistook the finches on the Galápagos for wrens, blackbirds, and other species. Only when he handed them to the famous ornithologist John Gould for a second opinion did it become clear that these were all finch species adapted to local conditions on the different islands. It later fell to others such as Peter and Rosemary Grant to do the long-term studies that elevated them to the icon of evolution they have become. Meanwhile, Othniel Charles Marsh’s monograph on primitive birds that still had teeth was unexpectedly branded a waste of taxpayer’s money when US congress was looking for excuses to cut funding to the US Geological Survey in the 1890s.

In many places, Prothero is careful and balanced in his coverage. He highlights the contribution of the historically overlooked Alfred Russel Wallace who independently hit on the idea of natural selection after Darwin had already been labouring on it for decades. And while Ernst Haeckel was accused of fraud over his famous drawings showing the embryonic development of different vertebrates, Prothero explains how there is a kernel of truth to Haeckel’s claim that ontogeny recapitulates phylogeny, even if “he may have been a bit overzealous in his drawings” (p. 69). On Jean-Baptiste de Lamarck and his ideas, Prothero clarifies how there was much more to him than the caricature of the “guy who got evolution wrong” (p. 198) that he became.

“In many places, Prothero is careful and balanced in his coverage […] he clarifies how there was much more to Jean-Baptiste de Lamarck […] than the caricature of the “guy who got evolution wrong””

There are classic topics such as convergent evolution, the evolution of the eye, and Lynn Margulis and her theory of endosymbiosis. The relatively young branch of evolutionary developmental biology and the discovery of Hox genes showed that, actually, yes, nature does make leaps and does not always result in slow and gradual changes. Throughout, Prothero repeatedly reminds you that the evolutionary relationships between organisms are like a bush, and not a linear progression from primitive to more advanced creatures. He explains that evolution does not always result in perfect adaptations—they only have to be good enough to help in producing the next generation. And he points out that natural selection can only ever work with the material at hand, resulting in many jury-rigged contrivances, including in humans.

Now, Prothero is also a noted sceptic. A good deal of this book has the secondary aim of showing that creationism is an utterly flawed idea and that the evidence for evolution reveals no traces of intelligent design whatsoever. The thing is, he already did this exercise in Evolution: What the Fossils Say and Why It Matters, so does it need repeating? He spends no fewer than seven chapters here on examples of transitional fossils that provide a detailed picture of fish leaving the water, whales returning to it, birds evolving from dinosaurs, giraffes evolving longer necks and elephants longer trunks, horses losing their toes and snakes their legs, and turtles acquiring shells. You almost get the feeling that he just cannot help himself.

I have few gripes with the topics that Prothero chose to include here, but I felt somewhat disappointed by all the topics he left out as a consequence of this secondary mission. Two notable omissions are the process of domestication, even though Darwin used numerous examples of it in On the Origin of Species and then wrote a separate book about it. The same is true for Darwin’s other big idea: there is no mention of sexual selection, sperm competition, or mate choice.

“[…] this book has the secondary aim of showing that creationism is an utterly flawed idea […] but I felt somewhat disappointed by all the topics he left out as a consequence […]”

Beyond these, there is little on speciation and biodiversity, the formation of higher taxa, or the difficulty with species concepts. Epigenetics is mentioned, but not by name. The textbook example of the peppered moth is included, but there is no further discussion on camouflage, mimicry, or warning signals. Richard Dawkins has to make do with two brief mentions, but there is nothing about the different levels of selection, whether selfish genes or group selection. And I am sure Prothero could have beautifully explained the difference between the modern and extended syntheses.

The focus on convincing the reader of the evidence against design raises the question of who this book is written for. For evolutionary biologists like myself, Prothero is preaching to the choir, while creationists are unlikely to pick this book up. The best this might achieve is to remind biologists of the evidence for evolution if we ever find ourselves debating creationists.

Prothero is a fantastic science communicator, and I really enjoy this format of 25 vignettes by which to examine the many facets of a topic. The material that he did choose to include is written with verve and balance. In my opinion, however, the dual motive underlying The Story of Evolution in 25 Discoveries means that he left out many relevant topics and has written a book of narrower focus than the title might suggest.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

The Story of Evolution in 25 Discoveries

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Life most likely originated in the oceans, and it is to oceans that astronomers are looking to find life elsewhere in the universe. With the publication last year of Kevin Peter Hand’s Alien Oceans, I decided this was the right time to finally review Ocean Worlds, a book that I have been very keen to read ever since buying it some years ago. This, then, is the first of a two-part dive into the story of oceans on Earth and elsewhere.

Ocean Worlds: The Story of Seas on Earth and other Planets, written by Jan Zalasiewicz and Mark Williams, published by Oxford Press in December 2017 (paperback, 302 pages)

Palaeobiologists Jan Zalasiewicz and Mark Williams have previously collaborated on The Goldilocks Planet. Here, they provide a deep history of our oceans. As soon as I tucked in, it became clear that they go deeper than Eelco Rohling did in the previously reviewed The Oceans: A Deep History, a book that focused heavily on palaeoclimatology. Even though most of the action in Ocean Worlds takes place on Earth, and the wider universe is only considered in the opening and closing two chapters, the book is characterised by an almost cosmic perspective on the subject. The writing of Zalasiewicz and Williams is such that I felt as if was surveying major developments in the history of our universe from an elevated, slightly detached, almost omniscient position. The result is thrilling and at times awe-inspiring. What follows are some of the big questions and outrageously fascinating topics they consider.

To have an ocean we first need water. Hydrogen was an immediate byproduct of the Big Bang. Oxygen, however, did not appear until after the universe had gone through its first cycle of stars being born and dying, as its creation required nuclear fusion. Likely, the formation of water had to wait for a few hundred million years, though some have argued it could have started much sooner. As is usual when dealing with processes that took place in such a distant past, opinions are divided and there are several reasonable scenarios.

“the book is characterised by an almost cosmic perspective on the subject […] The result is thrilling and at times awe-inspiring.”

With water present in the universe, how did Earth acquire its oceans? After all, “There is a wild card here, which surely had an impact” (p. 18). We have good evidence that our proto-Earth, called Tellus by some, was hit by a small planetoid, Theia, with the resulting debris forming our current Earth–Moon system. This event would likely have obliterated what early oceans we had, if any. Various authors have proposed that certain meteorites (carbonaceous chondrites) or comets might have subsequently been water’s cosmic delivery vehicle.

However it got here, the first major effect it had was kick-starting plate tectonics. The early Earth was hot, but without the lubrication provided by water, the heat-venting mechanism of plate tectonics was not in place. How did molten rock make its way to the surface? Some scientists argue that it was through simple vertical conduits, so-called heat pipes, which would have made for a radically different surface topography: “the fundamental proportions of land area and ocean area […] would have been utterly different to today’s familiar patterns” (p. 34). Though, again, this idea is contested by others. The puzzle of when plate tectonics started, possibly 3 billion years ago, relies on truly ancient rocks, 3.5 to 3.8 billion years old, of which we have precious few remaining in places such as Australia and Greenland.

Beyond those earliest days, Ocean Worlds has much interesting material about later episodes. Life likely started in the oceans, this much I knew, but these were iron seas. Water without oxygen can hold large amounts of dissolved iron, and early organisms used this in their biochemistry to generate energy. This was the realm of the Archaea: the salt-tolerant, heat-loving, chemoautotrophic microbes for whom oxygen was poison and the Great Oxygenation Event murder. It was also a time when banded iron formations (BIFs) were built up, relevant to us today as they formed the ore deposits providing most of our iron and steel. Though, as clarified here, their formation was anything but straightforward. Other fascinating episodes are the Messinian Salinity Crisis, some 5.6 million years ago, when the Mediterranean repeatedly dried up, leaving behind kilometre-thick salt layers that reduced global ocean salinity.

“However it got here, the first major effect [water] had was kick-starting plate tectonics.”

Of course, a book about oceans has to consider current human impacts. With due diligence, the authors tackle the problems of overfishing, shifting baselines, trawling, litter, ocean warming, oxygen loss, and acidification, and conclude that: “there currently seems not the faintest chance of stopping carbon emissions over many decades, let alone overnight” (p. 191). Does this sound gloomy? I prefer the word “sobering”. Consider, they write, that the “more-than-tripling of human population” (p. 183) was enabled by the invention of the Haber–Bosch process and the plentiful artificial fertiliser it made available. To this, they add geologist Peter Haff’s argument of the technosphere that resonated with me. “The 7 billion humans on Earth today are kept alive only through the continuous action of an enormous, globally interlinked system of transport and communication, metabolized by the use of vast amounts of energy […] Without it, most of us would not be alive—and therefore we are forced to keep it going” (p. 197).

If that was not sobering enough, what really made me feel small was when they pulled back from our timescale and the current “brief ecological wrecking spree” (p. 195), to the long-term future. Our oceans are not forever. As the Sun grows hotter they will evaporate, though the “end of the oceans is not likely to be simple” (p. 207). Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits, and plate tectonics will once again grind to a halt. As this process “is unlikely to simply just stop, smoothly and without fuss” (p. 211), expect some extraordinary landscapes.

“Our oceans are not forever. […] Whether through a moist greenhouse phase where water is gently siphoned off into space by solar winds, or a runaway greenhouse hot enough to melt rock, a dry future awaits.”

Amidst these grand, cosmic scenes, the authors highlight the human stories behind this research. Such as the pioneering contributions to oceanography by the people on board the HMS Challenger expedition, the mapping of the seafloor by Marie Tharp, or the work of Wally Broecker who established a link between ocean currents and rapid climatic changes. And while Svante Arrhenius is better remembered for linking historical changes in carbon dioxide concentrations to past ice ages, both he and Fritz Haber tried to extract gold from sea water. Unsuccessfully, I might add.

In the last two chapters, the authors turn their gaze to the skies once more, discussing past and present oceans inside and outside of our solar system. With the many discovered by the Kepler space telescope, “We are on the verge of not just a new chapter in oceanography—or exo-oceanography, if you like—but of setting up an entirely new library of oceans, for the diversity and complexity of cosmic oceans will be beyond anything that we can dream of” (p. 264).

I explore this topic more in-depth in my review of Alien Oceans. But, as a warming-up exercise and a proper deep history of oceans, Ocean Worlds is a fantastic book that strikes the right balance. Zalasiewicz and Williams present fascinating science with enviable ease, without smoothing over the fact that science is rarely a straightforward affair, proceeding by means of conflicting scenarios and competing hypotheses. The deep-time perspective and big questions asked make this one awe-inspiring book.

Ocean Worlds

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Planet Earth might just as well be called Planet Water. Not only is our planet mostly ocean, life also started out here. Following his 2011 book Convergent Evolution, palaeobiologist George R. McGhee returns to MIT Press and The Vienna Series in Theoretical Biology to expand his examination to oceanic lifeforms, with the tantalising promise of applying the insights gained to astrobiology. I was particularly stoked for this second of a three-part dive into what I consider one of evolutionary biology’s most exciting topics.

Convergent Evolution on Earth: Lessons for the Search for Extraterrestrial Life, written by George R McGhee, Jr., published by MIT Press in November 2019 (hardback, 317 pages)

Just to get you up to speed, convergent evolution refers to the ubiquitous pattern of evolution repeatedly hitting on the same or similar solutions to a problem in different organisms. McGhee’s coverage of this topic in his 2011 book was wide. Next to morphologies and behaviours in terrestrial animals, he examined convergent evolution in ecosystems and molecules such as DNA and protein. He also introduced the abstract concepts of theoretical morphology and the hyperdimensional morphospace where life is probing all possible and allowed options.

Convergent Evolution on Earth can be thought of as an extension of his previous work. There is no repetition of these concepts and the coverage across different levels of organisation is absent. McGhee assumes familiarity with this and readers would do well to read the two books in sequence. If you do, the approach here will feel familiar, as most chapters again revolve around lists with examples. What is new is that McGhee broadens his examination of convergent evolution to behaviours and morphologies in marine organisms.

“[…] the question “who is convergent on who?” is much more relevant [here, as] it is the land plants who convergently evolved similar forms to much older marine animals”

I will come right out and say that I found this book a more challenging read. The terrestrial species examined in his last book will be familiar to most, but this book deals with marine vertebrates and, mostly, invertebrates. There are numerous groups here that even biologists will not necessarily be familiar with, also because many extinct groups are discussed. Thus, the convergent evolution of chemosynthesis found in deepwater species far away from light covers ciliophorans, polychaete and oligochaete worms, and a wide array of living and extinct mollusc groups. The convergent evolution of different morphologies to deal with living on soft and unstable substrates covers sponges, corals, extinct bivalves such as bakeveliids, and all sorts of echinoderms. More familiar groups such as fish and cephalopods feature when discussing adaptations to moving and living in the water column (McGhee’s mention of the repeated re-evolution of the whole spectrum of ammonoid shell forms following mass extinctions made me smile, as it reminded me of Danna Staaf’s discussion of this phenomenon in her excellent Monarchs of the Sea). And the convergent evolution of fundamental organ systems (e.g. nerves, muscles, or immune systems) reaches all the way back in time to some of the earliest invertebrate groups such as ctenophores, cnidarians, and bilaterians.

Of course, our land-dwelling, backboned vantage point makes us biased—for the longest time these invertebrate forms dominated life on Earth, and they are still instrumental to our ecosystems. Even so, most of us will not know what they look like, and this where the lack of images is much more noticeable than in McGhee’s previous book. The recent The Invertebrate Tree of Life is a good reference work to have at hand, not just for the imagery, but also for the taxonomical content. Though it was published just after Convergent Evolution on Earth and McGhee will not have had access to it, the taxonomy he has adopted closely mirrors that of Giribet & Edgecombe, with some exceptions deep in the tree of life that are known areas of contention.

“[…] what of the promised lessons for astrobiology? […] I felt a bit let down by the subtitle—it promised more than the final […] chapter to which this discussion is now limited.”

Next to showing the very deep roots and fundamental nature of convergent evolution, the question “who is convergent on who?” is much more relevant and appropriate this time around. Though we have named many sea creatures after land plants (e.g. sea lilies and moss animals), this book makes clear that, to solve the same fundamental problems, it is the land plants who convergently evolved similar forms to the much older marine animals. A notable advance is the adoption of new, recently proposed terminology, distinguishing between iso-convergence, allo-convergence, and retro-convergence. These terms respectively describe whether convergent traits evolved from the same or different precursor traits, or are a case of re-evolution of ancestral traits.

But what of the promised lessons for astrobiology? There is a look at Mars’s geological history, the possibility of life on water worlds in our Solar System such as the moons Europa, Enceladus, and Titan, and there is the conclusion that biological signatures are likely found on water worlds and technological signatures on water worlds with landmasses (readers interested in this will want to check out the massive Life in the Cosmos). Although what McGhee covers here is interesting, I admit that I felt a bit let down by the subtitle—it promised more than the final, 25-page chapter to which this discussion is now limited. My feeling is that most general readers will be better served by Kershenbaum’s The Zoologist’s Guide to the Galaxy. For those wanting to get to grips with this topic more in-depth, I end this three-part series with my review of Contingency and Convergence which revisits the question of their relative importance and applies this to astrobiology in a thought-provoking manner.

Convergent Evolution on Earth is not for the faint of heart. For evolutionary biologists, this is an interesting add-on to McGhee’s previous book, though requiring a certain level of background knowledge. For many other readers, there is probably less astrobiology in here than they would like.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

Convergent Evolution on Earth

Other recommended books mentioned in this review:

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