Speaker: Shawn Hurst
Since the discovery of the fossil Taung child a century ago, human brain evolution has been a contentious subject. Recently however much progress has been made, with an increased understanding of how changes in developmental timing have led from an ancestral chimpanzee-like brain to our modern human one. In this talk I will discuss the history of the field and what these recent findings suggest about what it means to be human.
Shawn Hurst is an Assistant Professor at the University of Indianapolis and an expert on the evolution and development of the brain and its behavior in humans and apes. His work has been published in journals such as the Proceedings of the National Academy of Science and the Journal of Human Evolution, and he has been interviewed by Science, Science News, New Scientist, and Forbes.com.
Sponsored by John Langdon
Program: The Evolutionary Development of the Human Brain
Speaker: Shawn Hurst, PhD, Assistant Professor, Biology, University of Indianapolis
Introduction By: John Langdon
Attendance: NESC: 123; Zoom:22
Guests: Astrid Bricker, Cece Coglianese, D. Loughery, Ann Manders, William McGarvey, Stephen R, Mike Sale, Aurora Vana, Jocelyn Vierra, and others
Scribe: Judy Weitzman
Editor: Carl Warner
Talk’s Zoom recording found at: https://www.scientechclubvideos.org/zoom/10192026.mp4
About the Speaker:
Dr. Shawn Hurst is a homegrown Indiana scholar who earned his bachelor's degree from Ball State University before completing his master’s and doctorate at Indiana University. He has been directly involved in some of the world's most significant hominin fossil discoveries in South Africa, establishing himself as a global expert in primate behavior, human evolution, and the evolutionary development of the human brain. Currently, Dr. Hurst leverages his extensive field expertise at the University of Indianapolis, where he teaches anatomy, human physiology, and evolutionary biology.
Presentation Summary:
In his presentation at the Scientech Club, Dr. Shawn Hurst provided a comprehensive look into human brain evolution by comparing the structural anatomy of human and chimpanzee brains. Rather than focusing on simple differences in size, his research utilizes non-invasive MRI imaging and the study of fossil brain endocasts to track how specific region-by-region transformations allowed the human brain to develop its capacity for higher cognition and language.
To understand these evolutionary changes, Dr. Hurst began by establishing a fundamental baseline of brain anatomy. The brain’s architecture is split into grey matter—the thin outer cerebral cortex sheet composed of neuron cell bodies that act as computational nodes—and white matter, which consists of the myelin-insulated axons that serve as communication cables between those nodes.
As the brain grows, it forms a complex landscape of folds called gyri and deep creases known as sulci. Dr. Hurst noted that tracking these creases is essential for understanding evolution, but researchers must distinguish between primary, secondary, and tertiary sulci.
Primary sulci are deep, appear earliest during gestational development, and are under tight genetic control, making them reliable indicators of evolutionary ancestry. In contrast, secondary and tertiary sulci develop later, are much shallower, and are highly variable between individuals—much like unique fingerprints—meaning they are less reliable for tracking species-wide evolution.
The core of Dr. Hurst's thesis centers on a process called opercularization, where rapid growth causes one region of the brain to fold over and bury adjacent structures. By mapping primary sulci, evolutionary data shows that humans completely lost the occipital operculum and the lunate sulcus, which are prominent visual processing structures in non-human primates. In their place, humans gained unique frontal and orbital opercula. This elongation and folding of the frontal lobes effectively remodeled the brain, creating an expanded prefrontal cortex that houses the advanced cognitive networks unique to humans.
Crucially, Dr. Hurst emphasized that this structural shift is not merely a byproduct of an increase in overall brain volume. While the human brain is globally three times larger than a chimpanzee's, the true driver of modern human morphology is the dramatic expansion of the cortical sheet surface area relative to total volume. This phenomenon is vividly demonstrated during human gestation. In the first two trimesters, a human fetus possesses a primitive prefrontal morphology that closely mirrors that of a chimpanzee. However, during the third trimester, a burst of rapid cortical sheet growth outpaces overall volume expansion, forcing the cortex to fold into the complex, highly gyrated human brain structure. Ultimately, while a newborn human infant has a brain volume roughly equivalent to an adult chimpanzee, it enters the world with a highly derived, modern brain morphology and a cortical sheet that will grow to be four times larger than its primate counterpart.
Our speaker Shawn Hurst (R) and colleague John Langdon (L)
