After a month of observation, scientists discovered that the algae in the middle continued to remain unicellular. However, they noticed a significant difference when examining algae from thicker rings – they found clumps of larger cells, with some clusters consisting of hundreds of cells. What caught Simpson’s attention the most were mobile clusters of four to 16 cells, arranged in a way that their flagella were all on the outside. These clusters moved by coordinating the movement of their flagella, with the rear ones remaining still while the front ones wriggled.
A comparison of the speed of these clusters to single cells revealed an interesting fact – they all swam at the same speed. This collective effort allowed the algae to maintain their mobility. Simpson mentioned, “I was really pleased. With a rough mathematical framework, I could make some predictions. Observing it empirically confirms the validity of this concept.”
In a fascinating turn of events, when the clusters were removed from high-viscosity gel and placed back in a low viscosity environment, the cells stuck together. This bond lasted for about 100 more generations as observed by the scientists. Simpson noted that the changes undergone to survive high viscosity were challenging to reverse, hinting at a possible evolutionary shift rather than a temporary adaptation.
ILLUSTRATION
Caption: Algal cells in a highly viscous gel began forming clusters, coordinating their flagella to move faster. When returned to normal viscosity, they remained united.
Credit: Andrea Halling
While modern-day algae aren’t early animals, the transformation of a unicellular organism in response to physical pressures into a new way of life that was difficult to revert back from is quite impactful. Simpson believes that exploring how viscosity influences the existence of small organisms could shed light on conditions that led to the proliferation of larger life forms.
A New Perspective
For us, as large beings, the thickness of fluids around us isn’t a concern in our daily lives. Viscosity hardly affects us due to our size. This ease of movement is often taken for granted. Since realizing the significance of movement limitations for microscopic life, Simpson has been deeply engrossed in this concept. Viscosity may have played a crucial role in the early evolution of complex life forms.
Simpson remarked, “[This perspective] enables us to delve into the deep history of this transition and what environmental factors were at play during the evolution of obligately complex multicellular groups, which occurred relatively close together according to our understanding.”
Simpson’s ideas have garnered attention from other researchers. Nick Butterfield from the University of Cambridge, who studies the evolution of early life, acknowledged that Simpson’s perspective on the physical experience of organisms in the ocean during Snowball Earth is innovative. While many theories on the influence of Snowball Earth’s conditions on the evolution of multicellular life focus on oxygen levels, Carl’s idea is considered on the fringes.