Tesla Monson’s Research Sheds New Light on the Evolution of Vision in Primates

At Western Washington University’s Primate Evolution Lab, new research led by Assistant Professor of Anthropology Tesla Monson is looking into the relationship of primate cranial shape and eye orbits and how these features evolved and changed the vision of early proto-humans to help them succeed.

Monson, who completed her doctorate in Integrative Biology at the University of California, Berkeley, said the skull contains more than just the brain, it holds almost all of the special senses like vision.

“These important components of primate biology have shaped our evolution,” Monson said. “Through this project, we are able to get one step closer to understanding how primate vision and skull shape evolved, thereby shedding light on many of our own uniquely human attributes.”

Her new research paper, “Patterns and magnitudes of craniofacial covariation in extant cercopithecids,” published online in The Anatomical Record, looks at the variation of cranial shape and eye orbits (also known as eye sockets) in cercopithecids, a family of primates that includes baboons and langurs. By analyzing the integration and modularity of cercopithecid orbits, Monson hopes to understand how different parts of the skull relate to one another. Integration refers to how different skull traits connect with other parts, while modularity refers to an independent group of related traits that are separate from others.

“One of my primary goals for this research when I first started looking at cercopithecid skulls was to try and understand the variation that we see in these monkeys,” Monson said. “Some have really long faces, some have really short faces, and some have really broad faces. I am really interested in the evolution of morphological variation– how did the amazing diversity of shape that we see around us evolve?”

These concepts help to describe how different traits evolved over time. When a certain trait is more independent, it is able to evolve separately from the rest of the skull. If a trait is more integrated with other parts of the skull, all parts have to evolve in tandem, which can restrict their structural evolution.

Those differences led to the variation of cranial shapes seen today.

“I definitely think that it tells us a lot about these groups of monkeys,” Monson said. “We don’t know much about the morphology of the skulls of these monkeys. This research tells a lot about vision and orbits and it suggests there is some constraint there that needs to be investigated.”

Monson said understanding the evolution of eye sockets in baboons and other primates can help us understand the evolution of our own eyes. Humans are primates and have evolved under many of the same ecological pressures as other primates. That means humans share almost all of our genetic and development pathways with primates, especially ones that are closely related to us like baboons.

“Humans are in many ways unique,” Monson said. “But in order to understand how we evolved to be unique, and how we deviate from other primates, we must first understand what normal variation looks like. Only then can we understand how our own evolutionary pathway diverged from other primates in the past.”

I am really interested in the evolution of morphological variation– how did the amazing diversity of shape that we see around us evolve?

Monson began her research while she was a graduate student. Since then, she has analyzed the skulls of 291 primates at the Anthropology Museum in Zurich, Switzerland and the Smithsonian Museum of Natural History in Washington, D.C. She hopes this research might challenge the assumptions being made about variation in primate fossils.

She said the next step in her research is to continue the analyses, but this time using 3D scanning technology.

“3D scanning allows you to capture more of the shape of the orbits than traditional morphometrics like height and width,” Monson said. “Ultimately, it’s a quantitative way of more thoroughly analyzing 3-dimensional anatomical shapes, like the eye orbits.”

Monson is the founder of the Primate Evolution Lab in Western’s Anthropology Department. For more information on her primate evolution research, contact Monson at (360) 790-0006 or monsont2@wwu.edu.