Where do humanity’s evolutionary roots lie? The answer has long been “in Africa”, but this idea is being challenged from various sides. I previously reviewed Begun’s The Real Planet of the Apes as a warming-up exercise before delving into this book. My conclusion was that its discussion of archaic ape evolution, although proposing that species moved back and forth between Africa and Eurasia, ultimately did not really challenge the Out of Africa hypothesis. Not so Ancient Bones. German palaeontologist Madeleine Böhme, With the help of two co-authors, journalists Rüdiger Braun and Florian Breier, firmly challenges the established narrative in an intriguing book that is as outspoken as it is readable.
Ancient Bones: Unearthing the Astonishing New Story of How We Became Human, written by Madelaine Böhme, Rüdiger Braun, and Florian Breier, published by Greystone Books in September 2020 (hardback, 376 pages)
Ancient Bones was originally published in German in November 2019 as Wie wir Menschen wurden. Less than a year later the good folk at Greystone Books have already published the English translation. The challenge to the Out of Africa narrative is twofold here: criticism by palaeoanthropologists and Böhme’s own discoveries. The latter are the novel part of this book and are told with much verve. Two fossils, in particular, take centre-stage.
First, there is the rediscovery of a tooth and a jawbone christened Graecopithecus freybergi. Originally found in 1944 near Athens, together with other animal fossils, they went missing for decades before Böhme tracks them down, in true Raiders-of-the-Lost-Ark–style, in the catacombs of the Nuremberg congress hall, a location infamous for the Nazi party rallies during World War II. With today’s technology, old fossils hold new value. Careful study of the jawbone with computed tomography scanning showed that the teeth resembled early hominins* more than other great ape fossils. Novel magnetostratigraphic analysis of crystals in sediment trapped inside the animal bones from the same dig allowed the whole lot to be dated to about 7.2 million years ago (mya).
“These two important fossils, Graecopithecus and Danuvius, were present in Europe at a time where conventional wisdom has it that Africa was the epicentre of hominin evolution.”
The second discovery is made by Böhme and collaborators in a southern German clay pit. In a nail-biting race against time—the pit is commercially operated year-round to turn the clay into bricks—they manage to recover much fossil material during three field seasons. This includes a partial skeleton of a new primate species named Danuvius guggenmosi dated to about 11.6 mya. Based on several physical characteristics, Böhme and colleagues argue it, too, resembles early hominins more than known great ape fossils.
So, Graecopithecus and Danuvius, two important fossils, are one part of her argument that there were early hominins in Europe at a period where conventional wisdom has it that Africa was the epicentre of hominin evolution. The second challenge to the Out of Africa hypothesis comes from other palaeoanthropologists. For example, there is criticism of the earliest claimed African hominin, Sahelantropus tchadensis**, with some researchers arguing it is a great ape instead. Then there are several fossils from Asia (the Chinese Homo wushanensis, the Philippine H. luzonensis, and the Indonesian H. floresiensis), plus tools that overlap with the African timeline up to 2.6 mya, contradicting the Out of Africa hypothesis (specifically, the Out of Africa I variant).
“As with deserts, savannah ecosystems were in constant flux and integrated across Africa and Eurasia, a region dubbed Savannahstan by some. Perhaps that was the cradle of humanity.”
This criticism is embedded in plenty of background information that benefits tremendously from excellent infographics by freelance illustrator Nadine Gibler. Some topics covered are the history palaeoanthropological discoveries that, thanks in particular to the Leakey dynasty, shifted in focus from Europe and Asia to Africa from 1924 onwards. There is a recap of the history of archaic ape evolution that Begun told in The Real Planet of the Apes. And there is an overview of the anatomical characters that set apart apes and hominins.
Particularly relevant is the palaeoclimatological and biogeographical story. On the one hand, shrinking and growing deserts throughout northern Africa, the Mediterranean, and Asia provided a barrier to migration. On the other hand, the little known Messinian Salinity Crisis*** saw the Mediterranean Sea dry up about 5.6 mya, allowing migration of fauna between Africa and Eurasia, including a lot of animals we now think of as “typically” African. “Why should early hominins be an exception?” asks Böhme on page 194. As with deserts, savannah ecosystems were in constant flux and integrated across Africa and Eurasia, a region dubbed Savannahstan by some. Perhaps that was the cradle of humanity.
“It is not that the fossils found in Africa are not important, but […] the focus on any one particular continent is too narrow […]”
This material is divided over seventeen reasonably-sized, readable chapters in four parts. Depending on how widely you have read on human evolution, the final two parts of the book will already be familiar to you and feel like filler or will be a tasty sampler of other topics. Böhme changes gear here, introducing two questions. One, what made us human? She briefly discusses the hand, above-mentioned Asian Homo fossils and our wanderlust, long-distance running, Wrangham’s thesis that fire and cooking allowed our brains to grow larger, and the physical and genetic evidence for language (this section is a far cry from Rudolf Botha’s critical evaluation in Neanderthal Language). Two, why are we the last ape standing? Rather than Paul Martin’s Pleistocene overkill hypothesis, she favours the (to me novel) idea that that at least Neanderthals and Denisovans simply merged with us. Ancient DNA has revealed we all carry some of their DNA in us, but we do not all have the same pieces. Puzzle it all together, and an estimated 30% of the Neanderthal genome and up to 90% of the Denisovan genome is retained in the current human population.
Ancient Bones is not afraid to go against the grain and be provocative. Though it will no doubt ruffle feathers, my impression is that Böhme draws on a growing body of convincing evidence and arguments to make her case. It is not that the fossils found in Africa are not important, but Böhme’s conclusion on page 271 that the focus on any one particular continent is too narrow is hard to disagree with in light of everything she presents here. What is undeniable is that her decision to involve three others in the writing process makes this a top-notch example of an engaging book accessible to a broad audience.
*Hominins are a taxonomical grouping encompassing humans, chimpanzees, and bonobos, plus their extinct ancestors.
**There is a remarkable personal attack here on Sahelanthropus‘s discoverer who has withheld a thighbone from scrutiny by the wider scientific community for close to two decades pending his own investigations. It could answer whether Sahelanthropus was bipedal or not. When two scientists wanted to present our understanding so far at a meeting their application was rejected. “Could it be that Michel Brunet, one of the icons of French science, Knight of the Légion d’honneur, recipient of the Ordre national du Merité, did not want to be challenged?” (p. 128), is one of the things Böhme asks pointedly. Now, it is not that there are no big egos in science, because there are, but to publicly shame a colleague in a book for a general audience felt, to me, unnecessary. It would have been sufficient to write, as she does here, that his choice is unfortunate and holds back scientific progress.
***The Messinian Salinity Crisis is a fascinating geological event that cries out for a popular treatment. Though some books mention it, as far as I am aware, there has not been a book dedicated to it since 1983, even though our knowledge on it has increased tremendously.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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“How to Walk on Water and Climb up Walls: Animal Movement and the Robots of the Future“, written by David L. Hu, published by Princeton University Press in December 2018 (hardback, 236 pages)
Hu’s entry into this world was water striders and the question of how they move on the water surface. But first, how do they even stand on water? One recurrent theme in a book like this is scaling. The physical rules of the world operate differently at different scales, and, as Hu mentions, small animals are sensitive to forces we would find negligible (see also my review of Scale: The Universal Laws of Life and Death in Organisms, Cities and Companies, and pop-science introductions such as Why Size Matters: From Bacteria to Blue Whales and Nature’s Giants: The Biology and Evolution of the World’s Largest Lifeforms). At their size, water striders benefit from surface tension and the microscopic hairs that cover their legs making it even easier to stand on the water surface. But the question of how they gain the traction to start moving on such a surface was a paradox. Hu describes his observations on live water striders, and his attempts to mimic their movement with a mechanical water strider.
This introduction sets the tone for the book. In eight chapters, Hu looks at different physical principles and modes of locomotion. Using a rather formulaic approach, each chapter discusses two or three case studies. A third-person story introduces the researcher, often catching them in the process of conducting an experiment, outlines the problem or question at hand, gives an overview of what has been done in the past, and explains the latest findings of the protagonist.
“Flying snakes are dropped off rickety towers […] Dead fish are shown to be capable of passive swimming”
What follows is a miscellany of some truly remarkable organisms and wacky experiments. Undulatory motion is used by snakes, burrowing worms, but also the sand fish, with high-speed X-ray imagery revealing that this lizard effectively swims through sand (see the image on the right). Flying snakes are dropped off rickety towers to study how they deform their body into an airfoil during their gliding fall. Dead fish are shown to be capable of passive swimming. Insects employ crumple zones in their wings to survive frequent impacts with raindrops and vegetation. And cockroaches can flatten themselves to an extreme degree and still run at full tilt (!), inspiring robots that can continue to function while being compressed. And do not get me started on ant colonies. Do they behave as a fluid or as a solid?
Some projects are so well known that multiple authors will write about them, such as the Kilobot robot swarm described by Lisa Margonelli (see my review of Underbug: An Obsessive Tale of Termites and Technology). Others are very obscure, so I was not terribly surprised to see no mention of John Long’s evolving robots (see Darwin’s Devices: What Evolving Robots Can Teach Us About the History of Life and the Future of Technology). But, given that Hu has worked at MIT, I was surprised to read nothing about the walking robots from well-known engineering schools such as the MIT Biomimetic Robotics Lab, Boston Dynamics, or Caltech. Their designs for mobile all-terrain robots are (literally) advancing by leaps and bounds, and the footage coming out of these labs of walking, running, jumping, backflipping, door-opening robots is as fascinating as it is terrifying. They regularly make the news, prompting both clickbaity headlines playing at people’s fears, but also serious concerns about how the military will be using these (a lot of this research is sponsored by DARPA, the Defense Advanced Research Projects Agency of the US Department of Defense). Instead, Hu features Steve Collins’s passive-dynamic walking robot that only uses gravity as a driving force. And where are the titular wall-climbers in this book? Finally, the book lacks much in the way of a discussion of evolutionary and physical constraints that impose limits on locomotion (see e.g. Evolutionary Biomechanics: Selection, Phylogeny, and Constraint, Feats of Strength: How Evolution Shapes Animal Athletic Abilities, and The Equations of Life: The Hidden Rules Shaping Evolution).
“I was surprised to read nothing about […] engineering schools such as Boston Dynamics […] Their designs for mobile all-terrain robots are (literally) advancing by leaps and bounds […]”
Those omissions notwithstanding, the topics that are featured are given a nice treatment. I was especially impressed with the explanatory diagrams, many of them redrawn for this book, the useful black-and-white stills and photos, and the colour plate section. Finally, an author who actually refers to his plates in the text! Without using any formulas, Hu gives concise explanations of biological and physical principles such as allometry, pendulums, propulsion by crack propagation, or conservation of angular momentum. How to Walk on Water and Climb up Walls is not intended to be a complete overview of the field of biomechanics and biorobotics and Hu does not go into great detail, just enough to cover the basics. Interested readers may want to look up Life’s Devices: The Physical World of Animals and Plants, The Biomechanics of Insect Flight: Form, Function, Evolution, Nature’s Flyers: Birds, Insects, and the Biomechanics of Flight, Collective Animal Behaviour, or the forthcoming The Rules of the Flock: Self-Organization and Swarm Structure in Animal Societies to name but a few. A clever conclusion shows the value of this kind of research, which is often lampooned for being a waste of taxpayer’s money.
Where a competing pop-science title such as Furry Logic: The Physics of Animal Life runs the whole gamut of physics (covering some of Hu’s examples), Hu has carved himself a nice little niche by focusing on the intersection of animal locomotion and robotics. Not intended to be comprehensive, How to Walk on Water and Climb up Walls is an amusing and easy read, and Hu’s choice of fascinating examples is likely to suck readers deeper into the topic of biomechanics.
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
Other recommended books mentioned in this review:
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