This week’s guest is Dr Habiba Chirchir, Assistant Professor of Biology at Marshall University. Habiba is interested in the relationship between skeletal anatomy and behaviour through the study of trabecular and cortical bone. Her work mainly focusses on comparative studies of fossil hominins, modern humans, primates and other mammals, involving data collection in museum laboratories. Prior to her position at Marshall University, Habiba worked at the Smithsonian Institution as a Peter Buck Postdoctoral Fellow, where she continues to be a Research Associate.
What are your research interests and your area of expertise?
My work investigates the relationship between morphology and behaviors such as locomotion and subsistence strategies. I am really interested in how our behaviour, and that of our ancestors and other mammals, influences our skeletal anatomy and the implications of this for our evolution.
To do this, I undertake comparative studies, for example by studying mammals that have similar behaviours to us, such as those that walk and run long distances, or are closely related to us like primates. I do comparative studies to try to understand how bone morphology has changed over time. In particular, I am interested in morphological gracilisation, the ‘lightening’ of the skeleton, and how this is related to processes like domestication and behaviours such as choice of subsistence strategy.
What originally drew you towards biological anthropology and your specific area of research?
I grew up in Kenya and undertook my undergraduate degree at the University of Nairobi in Anthropology. During the course of my studies, I was most interested in biological anthropology, which grew thanks to an internship that I completed at the National Museum of Kenya in the Palaeontology, Archaeology and Osteology departments. Through this internship, I met and worked with graduate students who were interested in bone morphology, and this is how I started to develop my research interests. For my undergraduate thesis, I decided to investigate how bone morphology is influenced by subsistence strategies and after that I applied to graduate school in the US where I moved for my Masters at New York University, where I continued to study bone morphology in relation to different subsistence strategies and food resource acquisition.
For my PhD at George Washington University, I decided to focus on internal morphology, more specifically trabecular bone, as opposed to studying external bone morphology using linear measurements as I had done previously. I started with the question – what differences exist in the trabecular bone of human groups with different subsistence strategies? How do they compare to our fossil ancestors? How do they compare to our closest living relatives? One thing in particular that I noticed from my PhD research was that modern humans are particularly gracile and have low trabecular bone density. As such, my PhD opened up new questions for me, which led me onto my post-doctoral research at the Smithsonian Institution and my research projects to date. So, my research interests are really an accumulation of all these experiences and projects that I have had over the course of my academic journey so far.
How did you find your PhD experience?
Well, a PhD is challenging! But I was in a fantastic department at George Washington University, with wonderful supervisors and colleagues so that certainly helped. I was also very lucky that I had access to lots of resources that allowed me to study what I was interested in. Easy access to the Smithsonian collections was also very useful.
What current projects are you working on?
Overall, I have three main projects that I am currently working on. The first is directly related to human evolution and it is an investigation into the process and quantification of gracilisation over the last 3 million years. Whilst the pandemic has really hindered our work, the idea is that we will be scanning a number of fossils from eastern Africa, which be analysed in comparison with some of the famous European fossils from the late Pleistocene to try and pinpoint exactly when we see this evolutionary shift towards gracile skeletons. My initial conclusion from my PhD was that this change occurred very recently during the last 10,000 years in the Holocene. However, the main problem is that there is a huge gap from around 100,000 to around 2.8 million years ago in the genus Homo where we don’t really know much about what’s going on in terms of gracilisation. We are really interested in finding out whether the ‘lightening’ of the skeleton does actually occur relatively late in human evolution, or whether there was fluctuation in the gracilisation process during this earlier period that we currently don’t know much about. One of the really interesting things we have recently seen from colleagues is that when you look at the Spanish Homo heidelbergensis and Homo antessor fossils at Sima de los Heusos, we do see a fluctuation in gracilisation over time, which is not seen in Neanderthals, as shown through cross-sectional geometry which is one of the ways of quantifying gracilisation. So, much like this work being done in Spain, our project will examine whether trabecular bone in the African and European fossils is consistently high, or whether there is a variation in cross-sectional geometry through time.
Another project I’m working on looks at the effects of domestication on the skeleton. Human self-domestication has been proposed to have been one of the primary drivers of gracilization. Whilst there are many studies that have explored this hypothesis in humans, the strongest evidence of the effects of domestication on morphology comes from carnivores, specifically dogs. There is a famous study of Siberian foxes which demonstrates that when tameness is selected for over aggression, offspring eventually become more gracile in their morphology. Recently, I explored this idea through a post-cranial comparison of dogs and wolves bone morphology, complementing and extending previous studies of crania and external morphologies such as coat colour. I found that dogs have low trabecular bone density when compared to wolves as a consequence of domestication. I also want to extent this to other wild dogs, and I have students helping with data collection and imaging of dingoes, grey hounds, jackals, African hunting dogs and coyotes. So, that is a very exciting project!
The third stream of my research is focussed on the modern human skeleton. This project looks at how different subsistence strategies leads to different bone morphologies in different populations. We have expanded our samples and have a nice collection of images of skeletons from North America, pre-agricultural and agricultural Egypt, Tierra del Fuego as well as individuals from the Upper Palaeolithic. I have an undergraduate student who will be starting to analyse this data in Autumn.
Why is your research important for understanding human evolution?
As humans, we are interested in our past, and so we want to understand what changes took place over time that led to how we look and behave today. However, in a more applied sense, I’m really curious about how the ‘lightening’ of the skeleton in modern humans made people, especially in industrialised countries, more susceptible to bone diseases like osteoporosis. Through my research, we can investigate whether gracilization occurred due to a reduction in physical movement in recent societies, or whether it was a by-product of another deep-rooted evolutionary process. In this way, by exploring what happened in our evolutionary history, we can better understand the problems of the today.
What project or publication or discovery are you most proud of?
All of them are my babies – I can’t pick one! I think they are all interesting in their own ways. My recent paper on dog domestication is really awesome because it is the first study on the gracilisation of the post-cranial skeleton. If I think back a little bit, I wrote a paper on trabecular bone density in the human fossil record that I am proud of. However, I am really pleased about all of my work, and I feel grateful that I was able to do it.
What is your favourite memory from the field?
Sadly, I haven’t been in the field for a long time – I went to the field a few times during my PhD with my supervisor in northern Kenya which I thoroughly enjoyed. However, whilst not linked to my current research interests or projects, one of my favourite memories from the field is actually from a Roman excavation in Oxford. It was my first time abroad and my first archaeological dig on a more recent site. We were excavating a Roman settlement with multiple rooms and walls and we found a pot which we dug inside to find goat or sheep bones! That was my favourite experience, as it was all very new to me, and I enjoyed that it was very clear what we were finding, unlike excavations of much older material. I was part of a big international team which was very exciting as a young person.
If you were not a biological anthropologist, what would you be?
Perhaps a zoologist, as that was my other option as an undergraduate if I did not get onto the anthropology course. If I was not in academia at all, I would probably be a gardener as I love gardening and being in nature.
What features do you most admire in your colleagues?
Hard work, dedication, and curiosity. However, I also admire people that can balance this with having fun. Academia has its ups and downs, and each one of us needs to be able to prioritise what matters most to us. Being able to work hard whilst not overwhelming yourself is very important, such as knowing when to stop and leave work for the next day. I think that I may have found this balance (although I think a lot of my colleagues work harder than me!), and I enjoy seeing my colleagues do the same.
If you had a time machine, how far would you ask to go back, where would you go, and what would you want to see?
Because of my research, I think I would go back to the Plio-Pleistocene and see how Australopiths were behaving. Were they climbing trees or were they walking, or both? The morphological traits of Australopiths are intriguingly ambiguous, so I would really like to know exactly how they moved around. Thinking about it, I would also really like to go back to that Roman settlement we were excavating in Oxford. Our conclusion about the pot was that it represented a ritual offering, but I would love to find out what was really going on there.