Evolution: contribution of oxygen (Evolution)

by David Turell , Wednesday, May 19, 2021, 19:05 (1071 days ago) @ David Turell

Role of Great Oxygenation event challenged:

https://www.sciencedaily.com/releases/2021/05/210518205459.htm

"Scientists have long thought that there was a direct connection between the rise in atmospheric oxygen, which started with the Great Oxygenation Event 2.5 billion years ago, and the rise of large, complex multicellular organisms.

"That theory, the "Oxygen Control Hypothesis," suggests that the size of these early multicellular organisms was limited by the depth to which oxygen could diffuse into their bodies. The hypothesis makes a simple prediction that has been highly influential within both evolutionary biology and geosciences: Greater atmospheric oxygen should always increase the size to which multicellular organisms can grow.

"It's a hypothesis that's proven difficult to test in a lab. Yet a team of Georgia Tech researchers found a way --

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"'We show that the effect of oxygen is more complex than previously imagined. The early rise in global oxygen should in fact strongly constrain the evolution of macroscopic multicellularity, rather than selecting for larger and more complex organisms," notes Ratcliff.

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"The results surprised Bozdag. "I was astonished to see that multicellular yeast doubled their size very rapidly when they could not use oxygen, while populations that evolved in the moderately oxygenated environment showed no size increase at all," he says. "This effect is robust -- even over much longer timescales."

Comment: We know tiny organisms can live on almost anything from our extremophile studies, but large size must be oxygen dependent: for organisms without a circulation to deliver oxygen of course it required diffusion. With a circulatory system large size can appear. The progression seems quite logical. Only larger organisms have the required complexity. It seems design is required to develop everything in the most efficient order.