In January of 2020, at SICB’s annual conference, Darrin Hulsey and Gareth Fraser (@garethjfraser) organized a symposia:
“Teeth have long been a subject of integrative inquiry, but the breadth of studies on teeth is increasing at an exceptional rate. Our understanding of the genomic basis of tooth differentiation is rapidly increasing as non-traditional vertebrate model systems become tractable to genetic dissection…“
In light of her interest in this subject as well, we asked Professor Tanya Smith if she’d talk with us about her book The Tales Teeth Tell.
Here’s what she had to say about her work and its importance followed by our book chat.
The Tales Teeth Tell was inspired, in part, by an undergraduate course I taught for several years at Harvard University on teeth and human evolutionary biology. My aim in the book was to engage and excite people who may not have a background in this subject – nor a love of teeth – but who are curious about human development, evolution, and ancient behavior.
Given how politicized science can be, and how insular academic writing often is, I believe that it’s part of my professional responsibility to explain why science is interesting and important.Tanya Smith
Many of us have to work to be accessible writers in order to help readers understand how we evaluate information and draw logical conclusions. This helps people think critically, which is of particular relevance now as we see how misinformation can corrode social trust in science.
For example, my partner is a nutritionist, and dietary recommendations seem to constantly shift – giving me ample opportunities to playfully critique “food science.” But this changing landscape is often due to advances in our understanding of human biology, more rigorous study designs, and new analytical tools. If we can bring a spirit of transparency to the scientific process, and possibly even cast researchers as “advanced students” rather than “static experts,” things might be safer in the world.
Unfortunately, I don’t perceive institutional incentives for American academics to engage in extensive science communication, particularly for women in the middle of their careers who work in competitive fields. There is a lot of pressure on early career academics to publish in big name “high-impact” journals, build large lab groups, and bring in large research grants.
In Australian universities, we are encouraged to contribute to public discourse and media outlets like The Conversation, which publishes a daily digest of short public interest articles written by academics. I’ve contributed three pieces that have been read over 33,000 times; thus the reach is much greater than through traditional publishing mechanisms or even in a classroom.
What in particular led you to anthropology and biology? Was there a defining moment that lead you in this direction?
I was initially lit up by an introductory biological anthropology course I took during my first semester at SUNY Geneseo. The field encompasses so many of my personal interests in natural history, skeletal biology, and human uniqueness. While majoring in biology, I took every biological anthropology course offered and participated in two field seasons in the Great Divide Basin of Wyoming — where we recovered Eocene mammalian fossils, including tiny primate teeth.
During my senior year at Geneseo I began to read about how scholars were using biological rhythms in teeth to explore ancient human development, and using electron microscopy, I started my own search for these lines in the fossil teeth we found in Wyoming. I write more about a transformative “Ah-Ha moment” in The Tales Teeth Tell that eventually led me to experimentally document the timing of growth lines during my PhD research at Stony Brook University.
Photo by Jeffrey Camden
You state that teeth are examples of how as omnivores we’ve hedged our bets evolutionarily. In your opinion, with the plant based diet aficionados growing in numbers, do you feel our teeth and their history thereof, provide evidence we were meant to be vegetarians?
We are primates, a broad radiation of mammals found throughout much of the world, and primates eat many things—including plants, insects, mammals, and even other primates occasionally. Our closest living relatives, the great apes, are mostly vegetarian, but it’s clear that ancient hominins were scavengers, and ultimately, hunters.
Some anthropologists suggest that consuming highly dense protein sources, such as meat or seafood, has been integral in our brain evolution. We first find evidence for stone tool use associated with butchery ~3 millions of years ago, which became commonplace about the time our teeth started to reduce in size ~2 million years ago.
In The Tales Teeth Tell I refer to the “oral Swiss army knife” in our mouths, reflecting omnivorous hominin diets as well as our deeper history as primates. We have broad front teeth that allow for incision, as exemplified by those of frugivorous primates, and thick-enameled teeth that are good for breaking up hard objects rather like specialized seed-eaters. Our back teeth — premolars and molars — are moderately crested, but not as extremely crested as primates that only shear leaves or crunch insects.
So, we’ve “hedged our bets” evolutionarily as omnivores that ate what we needed to survive in different seasons and disparate environments. Of course, all this changed once humans began to cultivate the land, domesticate animals, and settle down — a good topic for a future blog!
Tell us a bit about this quote: “Teeth illuminate our human history like no other part of our anatomy”
It is amazing to me that several months before we even begin to breathe or chew, cellular blueprints are assembled to construct the hardest substance in the body. Each day of our early lives is then recorded by faithful 24-hour cellular clocks ticking away in utero and immortalizing their rhythmic microscopic secretions of enamel and dentine. Because teeth start mineralizing early, we have a permanent developmental record of when you’re born, a birth certificate in your mouth.
This is an even more precise permanent record than what our bones record since our teeth do not remodel in response to adulthood wear and tear like bone. Many of my colleagues like to compare tiny lines in teeth to the rings in tree trunks, although teeth are even more sensitive and durable.
On an even broader level, teeth hold meaningful clues to nearly everything you can think of: growth rates, age, disease, evolutionary relationships, life history, diet, migration, climate, nursing behaviour, and social status — humans have even used teeth as a form of artistic expression for thousands of years. And they are great sources of ancient proteins and ancient DNA!Tanya Smith
You wrote about how engineers are using studies of limpets(snails) teeth in order to make better artificial materials. Are there other areas(fields) where you feel the study of teeth is contributing to other types of research?
Teeth have helped inform how we understand the evolution of human development. Since tooth crowns are made up of more than 95% mineral when they finish forming, these durable “rocks” are the most common body part to be recovered from ancient mammals. The human fossil record contains numerous teeth from over 30 hominin species extending back 7 million years; allowing access to our ancestors’ early lives in astounding detail. This includes hominins such as the australopithecines that ultimately gave rise to humans over millions of years of evolutionary twists and turns.
The permanent microscopic records of tooth growth that are laid down every day
— allow us to determine the precise age of children in the human fossil record. From this starting point we can probe the developmental mechanics of human evolution such as when did brain development begin to slow down, (https://theconversation.com/baby-steps-this-ancient-skull-is-helping-us-trace-the-path-that-led-to-modern-childhood-130535) or which fossils show the elongated period of childhood that distinguishes us from the great apes. Evolutionary anthropologists have been debating these questions for a century, but this analytical approach has been carefully refined and validated over the past few decades.
It turns out that modern humans are quite unusual: our species downshifted its growth, forming teeth more slowly over a longer childhood than our ancestors and evolutionary cousins, including Neanderthals. This may have given us more time to grow our brains or learn complex behaviors before having our own kids. Teeth can also help us to understand the end of the lifecycle. Some scholars have concluded that “old age” only became common very late in our evolutionary history, as there are more fossil human adults with heavily worn teeth than Neanderthal or australopithecine adults.
Since writing your book, have you happened upon anything you wish you could’ve included ?
Yes – we published a recent study in Science Advances showing how teeth record climate variation that can be read on a weekly scale. (https://theconversation.com/what-teeth-can-tell-about-the-lives-and-environments-of-ancient-humans-and-neanderthals-104923?utm_source=twitter&utm_medium=twitterbutton)
We can now explore which season prehistoric individuals were born in, when illnesses were most common, and even when mothers stopped nursing their children. And all of this can be learned from a single fossilized tooth!
First molar tooth from a 250,000-year-old Neanderthal child. Yellow dotted lines indicate the beginning and end of nursing, a red dotted line corresponds to an illness, and blue dotted lines indicate lead exposures. Tanya Smith and Daniel Green.
Amazingly we also found lead in the teeth of 250,000 year old Neanderthal children. This may have been due to their groups moving into caves with natural lead deposits, drinking contaminated water, or burning combustible materials tainted with lead.
Being able to paint an intimate and detailed portrait of the first few years of a young Neanderthals’ life is an exciting example of the phenomenal secrets one can coax from their precious teeth.
Why We Have So Many Problems with Our Teeth
A few of s3’s ARTICLES FOR ICB
The dental lamina: An essential structure for perpetual tooth regeneration in sharks
Grand Challenges in Comparative Tooth Biology