Comparing humans and dogs: how two species in close communities relate

Trabecular bone in domestic dogs and wolves: Implications for understanding human self-domestication

by: Habiba Chirchir

Summarized by Maraley Santos. Maraley is an undergrad geology major at the University of South Florida. After graduating high school at the turn of the century, Maraley did what any student with an aptitude in science does when listening to others’ advice. She went to business school! After discovering a dislike of markets and business she put her college career on pause and reassessed life. Understanding her distaste of business but a love for data and science she decided to go back to school and major in her passion, earth science. Maraley believes it is never too late to learn, and this is the mantra she repeats to herself during all those restless nights of studying. She is supported by her wonderful partner in life Jeremy, their awesome daughter Leia, and her loyal pup Charlie. In her free time, she is an aquarist, hiker, rock collector, bassist, and is learning to build things that will work.

What data were usedSamples of the adult femoral head, highest point of the thigh bone, and distal bones, the ankles, of Canis lupus (gray wolf) and the largest Canis familiaris (domestic dog) breeds were acquired from the American Museum of Natural History (AMNH) in New York City, the Field Museum of Natural History (FMNH) in Chicago, and the National Museum of Natural History (NMNH) Smithsonian Institute in Washington D.C.. The 3D image results obtained from CT scans of these samples were analyzed and the qualitative results were summarized using numerous statistical methods. 

Methods: The robustness of bone, or trabecular bone fraction (TBF), was examined in this study to test the difference, if any, between grey wolves and their relatives, the domestic dog. The femora of both species were scanned using an X-ray CT at two separate facilities at the University of Texas (UT) and the University of Chicago (UC) while the distal tibiae (lower leg bone) were scanned using another type of CT scanner. The researchers hypothesized that domestic dogs have a more gracile, or delicate, bone structure their grey wolf relatives and they  scans hypothesized that the scans would show this. 

Results: TBF analyzation in the proximal (top part) femora and the distal tibiae of the domestic dog (C. familiaris)and the wolf  (C. lupus) revealed that the average TBF of these bones in wolves is greater than in domesticated dogs. Statistical analysis showed minimal error and boxplots helped visually assess the significant differences between the robustness of the bones in wolves and dogs, with wolves showing significantly thicker bones. Wilcoxon rank-sum tests (which essentially show if two populations show differences between them or not) showed the proximal femora (figure 1) and the distal tibia (figure 2) of the wolves showed greater TBF than of those in domesticated dogs. 

Figure 1 – proximal femora trabecular bone fraction

Why is this important? The analysis done in this study was used to test the hypothesis that domestic dogs have lower TBF (a more gracile or delicate bone structure) than their wolf ancestors due to self-domestication. In other studies, we see this pattern of gracility in human bodies when comparing it to our ancestors- our bones have also seen a trend of lower TBF through time. The ability of a dog to self-domesticate was due to their propensity of pro-sociality, or friendliness, with humans. This pro-sociality was reciprocated by humans, and the close relationship we see today between these two species is evident. As two species that domesticated alongside each other and live in close communities, we can study the effects of domestication in both species and make comparisons that can help us understand that process in humans. Unlike dogs, humans do not have such close living ancestors, so using relevant examples can help build that understanding.

Figure 2 – distal tibia trabecular bone fraction

The big picture: This study adds to the literature understanding self-domestication, a process that is not only behavioral, but also biological. Research has shown that self-domestication among most species lends to smaller body sizes, decrease in skeletal robusticity and possibly a decrease in bone density. Another hypothesis that is being studied is the effect domestication has on sedentism, the reduction of the need for a species to move long distances for survival (hunting for food and water resources), staying in one place. Studying domestication and understanding humans as being domesticated animals will help identify the long-term effects of sedentary lifestyle on our bodies, diseases that may arise of a lifestyle that isn’t compatible to our biology, and help expose the effects of extreme selection pressures among our best friend, the dog.

Citation: Chirchir, H. (2021). Trabecular bone in domestic dogs and wolves: Implications for understanding human self‐domestication. The Anatomical Record304(1), 31-41.