Cambrian Explosion: Less oxygen required (Introduction)

by David Turell , Friday, January 19, 2018, 20:12 (2288 days ago) @ David Turell

An opposite point of view from the theory that an increase in oxygen was one of the necessary triggers:

https://cosmosmagazine.com/biology/tumour-behaviour-calls-cambrian-oxygen-link-into-que...

"Previous hypotheses have centred around the idea that an increase in available oxygen may have triggered biological diversification. One 2013 paper published in the Proceedings of the National Academy of Sciences found that high oxygen environments promote greater ecological complexity, and argued on this basis that environmental oxygenation then satisfactorily explains the explosion of life in the Cambrian.

"However, Emma Hammarlund, a geobiologist working at the division for translational cancer research at Sweden’s’ Lund University and guest researcher at the Nordic Centre for Earth Evolution at the University of Southern Denmark, is not convinced by this account. She notes that recent research has questioned the correlation between the Cambrian explosion and increasing atmospheric oxygen.

“'A heated hunt for the geochemical evidence that oxygen increased when animals diversified goes on,” she says, “but, after decades of discussion, it seems worthwhile to consider the development of multicellularity also from other angles.”

"Instead, Hammarlund thinks a biological innovation might be key.

***

"Together they investigated the relationship between oxygen and stem cell biology.

"Stem cells, the pluripotent cells that can become any type of biological tissue, require specific oxygen levels, as do the cancer stem cells responsible for tumour growth. In particular, too much oxygen can wreak havoc with successful stem cell function. Stem cells, and cells that maintain similar properties, such as the tissues responsible for healing, as well as those responsible for tumours, generally require hypoxic, or low oxygen, environments. Certain vertebrate tissues even simulate hypoxia to allow them to work normally.

"The team therefore hypothesises that the evolution of the biological innovation of stem cell properties might well have played a role in the diversification of life in the Cambrian. Such innovation not only could easily have happened in low oxygen environments, but might even have required them.

“'Therefore, we flip the perspective on the oxic setting,” says Sven Påhlman, “While low oxygen is generally unproblematic for animal cells, the oxic settings pose a fundamental challenge for complex multicellularity.

"'Surely, many people would intuitively disagree. But once you flip the perspective on the oxic niche and start to consider it as challenging for stem cell properties and tissue renewal, then puzzling observations from distant fields starts to fit together. And you can't turn back.'”

Comment: Another theory looking for a natural mechanism to create such a huge burst of diverse living forms, with no precursors seen in the evolutionary record of fossils. Perhaps God did it.