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Origin of the phyla and cancer
John M. Saul, Lethaia 2007, Vol. 40, pp. 359–363.
Multicelled animals with specialized cells (metazoans) emerged shortly after rising oxygen levels in the seas permitted formation of collagen-family molecules. Certain unicells then formed 3-D clusters, some with disc- or ball-like shapes that happened to resemble blastulas. These became unstable beyond a certain size due to contrasting metabolic styles among their component cells. For whereas cells near their exteriors could employ oxygen respiration, cells closer to the oxygen-deprived interiors were obliged to rely on anaerobic metabolism (fermentation), a process that produces waste molecules that, if retained within cells, cause disproportionate cell growth. Unstable blastula-like forms would either disintegrate or reorganize along surfaces of relative weakness in a process that may be likened to gastrulation. Initial cell-differentiation depended on the quantity and diversity of retained fermentation products and on the pumping of molecules from cell to cell by the consequent electro-chemical gradients. In subsequent contexts, oxygen deprivation, fermentation, excess cell growth, and disintegration or reorganization of tissues produce cancer.