Emma Bingham, QBioS Thesis Defense

Biophysical scaffolding in the evolution of complexity

Friday November 21st, 2025
At 9:00am EST
Krone Engineered Biosystems Building (EBB), CHOA Seminar Room 1005 

https://gatech.zoom.us/j/92410817040?pwd=cs5FG5mN4qidh9COKaka6LpIrBRM8k.1
Meeting ID: 924 1081 7040

Thesis Advisors:
Peter J. Yunker, Ph.D.
School of Physics
Georgia Institute of Technology

William C. Ratcliff, Ph.D.
School of Biological Sciences
Georgia Institute of Technology 

Committee Members:
Saad Bhamla, Ph.D.
School of Chemical and Biomolecular Engineering
Georgia Institute of Technology

Jennifer Curtis, Ph.D.
School of Physics
Georgia Institute of Technology 

Daniel Weissman, Ph.D.
Dept. of Physics
Emory University

ABSTRACT: Pressure to become larger is thought to be a driver of the evolution of multicellular organisms. Large size can help an organism avoid predation, resist stress, use resources more efficiently, and more. However, though size can solve many problems, it also creates new ones, and it is not clear how nascent multicellular organisms overcome these problems, since they are simple clumps of cells that lack the group-level adaptations of established organisms. 

One problem with large size involves nutrient limitation: nutrients usually cannot penetrate more than a few tens of microns at most into a group of cells, meaning that cells on the inside of a large group will be starved, and growth will be limited. However, our model organism for early multicellularity, snowflake yeast, defies these uptake limits. Over 1,000 days of selection for large size, these yeast evolved to grow exponentially to millimeter sizes, far larger than previously-demonstrated uptake limits. Snowflake yeast does not have cilia to move fluid around, nor does it have complex multicellular adaptations like a circulatory system. Instead, the organism's metabolism drives a rapid, long-range buoyant flow that enables nutrient-rich fluid to move throughout the cluster of cells. 

In this thesis, I examine the phenomenon of metabolic flow and the organismal and environmental characteristics that make it possible. I argue that it is not merely unique to snowflake yeast clusters placed in perfectly still media with plentiful nutrients, but is possible across a wider range of environmental and organismal characteristics. I show that metabolically-driven flow remains effective in an environment with substantial external flows, widening the range of possible environments. I also examine the organismal characteristics that make flow possible for snowflake yeast, including permeability, toughness, and nutrient uptake rates. I suggest that emergent phenomena can circumvent the need for nascent multicellular organisms to evolve a morphologically complex body, including features like a circulatory system, in order to solve problems of large size. Instead, large size can evolve first, and the existing form and physics of the group can scaffold the subsequent evolution of development of the body plan.