“Show me your teeth and I will tell you who you are” Cuvier is reported to have said. That, in short, is the brief of this book. Drawing on a range of disciplines – such as archaeology, palaeoclimatology, materials science, primatology, anthropology and evolutionary biology – this book weaves a compelling narrative of what our teeth, and those of our ancestors, can tell us about our past diets, and how we came to be the species we are today. Why teeth? Because, as Ungar contends, teeth are special.
Peter Ungar is an American paleoanthropologist and evolutionary biologist who has researched teeth and human evolution and written extensively about it (other than 150+ scientific papers, see his books Evolution of the Human Diet: The Known, the Unknown, and the Unknowable, and Teeth: A Very Short Introduction, both with Oxford University Press, and the comprehensive Mammal Teeth: Origin, Evolution, and Diversity with Johns Hopkins University Press). The reason teeth are so interesting is that, due to their high mineral content, they are pretty much ready-made fossils and are the most commonly preserved parts of the digestive system. The narrative of human evolution used to be simple: we left the trees and ventured out in the African savannah and beyond, overcoming new challenges and developing new skills in the process. In Evolution’s Bite, Ungar draws together findings from many different disciplines to show that the story actually is a lot more complex than that.
Ungar starts off explaining how teeth are used to fracture food. So, you can use tooth shape to infer diet. But, as thousands of hours of observations of living primates has shown, what teeth can do and how they are actually used are two different things. Ungar introduces the concept of the “biospheric buffet”: the total of food items that animals can pick and choose from wherever they live. And this buffet is far from constant. Seasonality, competition with the neighbours, longer-term changes in the climate – food choice fluctuates on a monthly, weekly and even daily basis. Chapter 3 gives a crash course on the key players in palaeoanthropology, both the fossils and their discoverers. Over the decades, evidence has been accumulating that environmental change influenced our evolution. This is where Ungar weaves another strand into his story and walks the reader through key palaeoclimatological findings, showing how hominin habitats have flipped back and forth between warm and wet vs. cool and dry, sometimes gradually, sometimes abruptly.
Another telltale sign of what animals actually ate in the past are, what Ungar calls, “foodprints”, the microscopic patterns of wear and tear on teeth revealed via scanning electron microscopy. Since teeth wear down continuously, studying these patterns only tells you about the animal’s diet shortly before it died. This is where isotope analysis comes in (isotopes are the different variants of a chemical element, differing in number of neutrons). Different food sources differ in the ratios of carbon isotopes. These atoms are passed along the food chain and incorporated in the body when building bones and teeth. These add yet more pieces to the puzzle of what our ancestors actually ate.
“Processed food (we’re not talking about what the health-food crowds typically think of when you use these words) […] has had another drawback: softer diets.”
Ungar then continues how palaeoanthropologists have answered the question of how we came to be different from our primate relatives. He dives into the archaeological record to show what we have learned about tool use and traces of our hunting and gathering past, but also looks at anthropological studies on the last few remaining hunter-gatherer tribes such as the Aché people in Paraguay, or the Hadza people of Tanzania. He then briskly walks us through the Neolithic revolution and the shift from humans as roaming hunters and gatherers to sedentary farmers. There’s plenty of archaeological evidence for this transition. But why did it happen? The answer might very well lie in a changing climate.
Ice cores retrieved from the Greenland ice sheet have allowed us to reconstruct a detailed picture of the climate over the last 100 millennia or so (see Alley’s The Two-Mile Time Machine for more on that undertaking). This, too, has left its traces in the fossil record. The discipline of palaeopathology is introduced here: signs in fossils pointing to malnutrition, disease and other conditions. And these seem to have increased as we switched to farming. There was the back-breaking labour involved in farming, but also the switch to fewer, easier-to-grow food items that were less nutritional. Processed food (we’re not talking about what the health-food crowds typically think of when you use these words), that is, the simple acts of milling grain and cooking food, has had another drawback: softer diets. The lack of work-out has resulted in our jaws shrinking with time, bringing with it a host of dental problems (overbites, crowded front teeth, problems with wisdom teeth etc.). Ungar only talks about this shortly here, but wrote an excellent guest contribution on this on the blog of Johns Hopkins University Press back in 2013, around the time of publishing his book Mammal Teeth.
“[T]he Palaeolithic Diet […] like most of these dietary fads, is utter rubbish.”
The book concludes with a short chapter looking at the perennial question of what our natural human diet is, and the popularity of the Palaeolithic Diet. There are many myths about our human ancestors (Marlene Zuk’s book Paleofantasy and Christopher Ryan & Cacilda Jethá’s book Sex at Dawn offer some excellent and much-needed myth-busting) and Ungar makes an excellent point here that this diet, like most of these dietary fads, is utter rubbish. Without even having to resort to nutritional considerations, the question “what is our natural diet?” is a logical non sequitur. This question has no sensible answer because it’s not a sensible question to begin with. As Evolution’s Bite convincingly shows, our diet has been in constant flux throughout our history, both in time and in space. You just cannot point to a particular moment in time and say “here is when we were eating as we were meant to”. It’s the same fallacy that affects a lot of thinking in wildlife conservation: there’s no pristine state of nature to which we can return as our environment has always been in flux (I hope to return to that discussion in an upcoming review of Inheritors of the Earth).
This is not to say that we cannot benefit by looking at the relationship between diet and health through an evolutionary lens. Other than shrinking jaws, highlighted above, Ungar points to the problems caused by table sugar, which only became widely available during the Industrial Revolution. We simply haven’t had enough time yet to evolve a proper response to our increased sugar intake.
With Evolution’s Bite, Ungar gives a sweeping overview of what we currently know about teeth and human evolution. Drawing on findings from many disciplines, he makes a convincing case that a changing climate drove human evolution, largely by influencing the food options available to us on our biospheric buffet. For once, the word “interdisciplinary”, often a buzzword, is entirely appropriate. The earlier chapters sometimes get quite technical when Ungar gets down and dirty with the details, but the book is neatly structured, and by equally focusing on the people behind the findings, he writes a compelling narrative. He also does an excellent job ending each chapter by rounding up the findings before moving on to the next relevant topic. Once the groundwork has been done, and you have been sufficiently briefed on what you need to know, he gathers pace in the last three chapters and brings the book to a convincing and satisfying conclusion. An excellent read!
Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.
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