Human EDJ study published in PNAS

Ancient human relationships revealed through teeth

October 5, 2020 – Bellingham, WA – Teeth can tell us a lot of things about our ancestors, and now, new work led by the Primate Evolution Lab at Western Washington University has shown that tooth shape can be used in place of DNA to investigate ancient population movement and genetic relationships in the past. The study, led by Dr. Tesla Monson of the Department of Anthropology at Western, compared DNA and tooth shape using micro-CT scanning technology to look underneath the hard enamel surface of teeth from 161 ancient humans living on every continent except Antarctica.

Micro-CT scanning is an advanced technique for looking at different layers of an object without any physical dissection. Using this method, scientists can take images of teeth and use technology to digitally segment each layer of the tissue until the layer they are interested in is visible. Dr. Monson and her colleagues at the University of Zurich used micro-CT scanning to investigate the enamel-dentine junction, an internal layer of teeth. “What’s really exciting about this work,” says Dr. Monson, “is that we have shown that you can use teeth to answer some of the same questions as DNA, which means that you don’t always have to rely on destructive DNA analyses to investigate human relationships in the past.” Many ancient human remains are extremely delicate and rare, and this study paves the way for investigators to avoid applying destructive processes whenever possible.

Teeth are extremely well preserved in the fossil and archaeological records and have a strong genetic signature, making them prime targets for investigating human origins. The enamel-dentine junction (EDJ) is the part of the tooth underneath the enamel surface – it is thus even more well-preserved, because it does not wear away over time through use, even with a very harsh diet. Hominid fossils, for example, often retain EDJ shape even when the enamel has been completely worn away. The goal of this study was to investigate whether EDJ shape reflects genetic relationships between individuals and can therefore be used in place of DNA. This study is the largest investigation of EDJ morphology to date.

Dr. Monson and colleagues compared the shape of the human EDJ with neutral genetic data, parts of the genome that are not under natural selection. “The correlation between neutral DNA and EDJ shape shows that individuals that are more closely related also have more similar tooth shape,” explains Dr. Monson, “so tooth shape can be used to reconstruct genetic relationships in the past. This means we can know more about how closely related fossil individuals were just by looking at their teeth. And we can track peoples’ historical migration around the globe from their tooth shape alone. This is just another example of how much teeth can tell us about human evolution.”

More about the study: The full study was published October 5, 2020 in Proceedings of the National Academy of Sciences and is titled, “Neutral evolution of human enamel-dentine junction morphology.” Contact the author to request a pdf copy of the research article. This study was funded by the Swiss National Science Foundation. For more information, contact



New paper on hominid taxonomy

I am happy to announce that we have a new paper out investigating the validity of species vs. genus taxonomy in the hominid fossil record.

A genotype:phenotype approach to testing taxonomic hypotheses in hominids (Brasil et al. 2020)

We note that genus-level taxonomy is much more informative in the fossil record, particularly when using biologically-meaningful phenotypes. This work uses our previously described dental phenotypes (MMC and PMM; Hlusko et al. 2016) and was led by Dr. Marianne Brasil. This research continues to build on our findings that MMC and PMM are heritable, independent of body size and sex, and have strong phylogenetic signal in mammals (Hlusko et al. 2016, Monson et al. 2019, Zuercher et al. 2020). This is the second application of these dental phenotypes to the hominid fossil record, following previous work from my lab that used machine learning to assess dental evolution in the fossil record (Monson et al. 2018). Research on MMC and PMM is ongoing. But for now, enjoy this paper on the biological philosophy of taxonomy in the fossil record! 

New paper on bat dentition

I am proud to announce our new paper, out now in the Journal of Mammalian Evolution.
This builds from our work in primates (Hlusko et al. 2016) and boreoeutherian mammals (Monson et al. 2019).
This all woman author list was led by PhD student Maddie Zuercher. I trained Maddie to take dental measurements more than 4 years ago, when she was an undergraduate student at UC Berkeley. It’s so rewarding to see a mentoring relationship progress all the way through publication. So proud of her & the other former undergrad coauthors. Just remember undergrads: it’s never to early to get started in research!

New paper on forensic stature estimation

I am excited to share the results of an ongoing international research collaboration with scientists in Spain and Turkey. This work develops new regression equations for estimating stature from the tibia with important implications for forensics. Stay tuned for part 2 of the research, hopefully out sometime this summer! As always, please contact me if you would like a pdf copy of our paper.

Piecewise regression equations for estimating stature: an anthropometric study in Spanish females

New paper out – Craniofacial covariation in cercopithecids

Despite everything that has been going on, I am excited to announce that a paper I started as a graduate student has now been published in The Anatomical Record. “Patterns and magnitudes of craniofacial covariation in extant cercopithecids” looks at cranial variation in African and Asian monkeys with a focus on the orbits and primate vision.

This work was also recently featured in Western Today with a great article written up by one their undergraduate interns. I encourage you to check it out!

Stay healthy out there!

New course offering – Evolution of Cognition

I am excited to be offering a brand-new course for Spring Quarter, entitled ‘Evolution of Cognition.’ There are still spots available, so feel free to sign up. This course also fulfills the Writing Proficiency 3 requirement.

The goal of the course is to discuss the evolution of large brain size in primates and how it interacted with reproductive ecology (e.g., parental care, lactation and resource availability, changes in ovulation/estrus, and mating systems) as well as anatomical changes related to bipedality. Students will be asked to write a grant-proposal style paper on a topic of their choice, related to the class. This is a biology-heavy class focused on the evolution of cognition in our species and other primates (with comments on other animals, e.g., dolphins, canids, elephants), leading to humans today.

Fall quarter is underway!

Fall quarter is officially up and running here at Western! I am teaching ANTH 215 Intro to Biological Anthropology this quarter. This class is designed to introduce students to the biological side of anthropology, including human osteology, primate paleontology, human evolution, and primate behavior, as well as comparative biology, evolutionary theory, and genetics. Additionally, this course addresses modern human biological variation from historical, comparative, evolutionary, biomedical, and cultural perspectives. I have a great group of students in my class, an excellent graduate student instructor running the labs, and I am looking forward to a great quarter!

Another successful ICVM meeting

I just got back from Prague where I attended and presented at ICVM 19. It was an excellent meeting with a lot of really interesting research, and it was great getting to talk science with so many colleagues! While I was there, I presented my ongoing work on human enamel-dentine junction morphology, and I was happy to receive a lot of really useful feedback on the research. I also got spend some time enjoying Prague – it is a beautiful city! Thank you ICVM 19, and I hope to see you in Australia in 2022!

New paper out in Ecology and Evolution

I am happy to report that our new study came out this week in Ecology and Evolution! The paper is open-access and freely available.

This new research investigates the diversity of tooth morphology in mammals, finding that, contrary to previous assumptions, diet does not play a dominant role in the evolution of dental proportions. Instead, the study points to stabilizing selection as a key factor in understanding the diversity of tooth morphology in mammals. The study, a collaboration between scientists in the United States and France, looked at the teeth of more than 1,500 mammals held in museum collections in six countries to investigate the role of ancestry and diet on the evolution of dental proportions. This is the largest investigation of dental proportions to date.

The citation for the article is:

Monson TA, et al. (2019) Evidence of strong stabilizing effects on the evolution of boreoeutherian (Mammalia) dental proportionsEcology and Evolution.