The Tales Teeth Tell Development, Evolution, Behavior

When I picked up The Tales Teeth Tell, the first thing I thought was: “Another book on fossil teeth?” After reviewing Ungar’s Evolution's Bite in 2017 I was worried this might be more of the same. Was I ever wrong! Professor in human evolutionary biology Tanya M. Smith here shows there is a lot more to say about human teeth and their evolution.

Following its subtitle, the book is divided into three parts of three chapters each. With the same kind of clarity she must be applying to her lectures, Smith gives the reader a thorough introduction to how teeth actually form during embryonic development and continue developing after birth. Interestingly, much like trees, developing teeth lay down “growth rings”, or really growth lines, on a daily basis. As Smith explains, there are other patterns repeating on longer time scales that are still poorly understood.

These growth lines react to environmental stressors, including (!) birth. The study of baby teeth has revealed so-called neonatal lines, indicating the moment a child is born. Although teeth stop growing at some point, this record of growth lines can be used to estimate the age of archaeological remains of children, outperforming other methods. Furthermore, diseases and other stressors affect the deposition of growth lines, some so clearly visible that no microscope is needed. As other authors have pointed out (see e.g. Built on Bones and The Story of the Human Body), the development of agriculture and urban civilization led to new kinds of diseases. The change to softer, more easily digestible food meant less tooth wear. But a bigger and more insidious problem is that our bodies showed an evolutionary response by reducing the growth of our jaws (see also Jaws: The Story of a Hidden Epidemic). This, in turn, has led to new problems in the form of crowding and misalignment of teeth.

Smith’s coverage of evolution is similarly insightful. Starting with the earliest jawless fishes some 500 million years ago, she walks the reader through the evolution of teeth (see also Vertebrate Palaeontology and Your Inner Fish). Did tooth-like structures on armour plating migrate into the mouth over time to form the first teeth, or did external skin teeth and internal oral teeth evolve separately? The jury is still out on this, writes Smith. But once they arrived on the scene, a spectacularly diverse array of dentitions evolved in fish, amphibians, reptiles, and mammals (for more technical coverage, see The The Teeth of Non-Mammalian Vertebrates and Mammal Teeth). And though modern birds are toothless, she describes some of the fascinating experiments that have shown they retain the potential to grow teeth.

Due to their high mineral content, teeth are basically ready-made fossils, and, under the right conditions, can even conserve DNA. I have enthused about ancient DNA before (see my review of Who We Are and How We Got Here), something with which Smith has first-hand experience. That book and others such as Our Human Story reveal how the picture of human evolution has become rather complicated. The study of teeth can obviously add to that story (see also What Teeth Reveal About Human Evolution), though – spoiler alert – they do not necessarily make it any less complex. Take for example the reduction in tooth size during our evolutionary history. Though attractive as possible explanations, the timing of tool use and cooking (see Catching Fire) do not match up with the changes in tooth size detected in the fossil record.

It is only during the third part of her book, where she looks at what teeth reveal about behaviour, that Smith overlaps substantially with some of the topics that Ungar covered. She is similarly critical of the Palaeolithic diet and reviews what dental microwear (microscopic patterns of wear and tear), fossilised dental plaque, and isotope analysis instead reveal about our past diets (see also Evolution’s Bite and Evolution of the Human Diet). And if you are not squeamish, she ends with a fascinating look at the use of teeth as tools (all those things your mum told you never to do!), stone age dentistry, and tooth decoration. That last one was practised in the past, and is still done so by some tribes, and refers to the filing, grinding, and drilling of teeth… while they are still in the mouth.

Smith writes enthusiastically about new technologies such as synchrotron imaging, which uses a type of particle accelerator to non-destructively scan the inside and outside of valuable archaeological samples. More importantly, she also shows them. MIT Press went to town on The Tales Teeth Tell, producing a full-colour book printed on slightly glossy paper. Smith has made good use of this and included many excellent colour photos and illustrations that bring her tales alive.

Although this is pure speculation on my part, it is tempting to think that Smith read Ungar’s book, took careful notes, and made sure to minimise overlap when writing hers (edit: the author has since confirmed this was not the case). Regardless, this book is just as good. (Should you pick one? No, get both!) Even if it gets technical in a few places, Smith’s writing is informative, absorbing, and manages to elegantly cover a wide range of topics.