How Probable Was the Development of Eukaryotic Cells

Was it inevitable, this transition from a primitive cell to the awesome complexity of a modern eukaryotic cell? Or was it a fluke? These are difficult questions to answer, not least because the many steps involved in the transition occurred so long ago. One of the first steps must have been loss of the rigid cell wall, even though this would have been fatal to most organisms that attempted it. (Penicillin, for example, works by blocking the formation of bacterial cell walls. Without a rigid wall to protect them, most single-celled organisms are vulnerable to attacks from the environment.) Disposing of the cell wall was ultimately extremely useful, because it enabled phagocytosis to occur. But phagocytosis evolved at a later date and thus could have provided no immediate benefit to the organism that lost the wall. Evolution has no foresight; unless an organism can survive in the here-and-now and pass its genes on to offspring, any potential it may possess will be lost. Somehow, in ways not yet understood, some organism managed to employ new structural proteins — actin and tubulin — and develop a cytoskeleton that helped mitigate the loss of the wall. How likely was this to happen? We simply do not know. The origin of organelles is better understood — it came about by symbiosis as, perhaps, did the cell nucleus — but what about the origin of what may be the most important innovation of all: cooperation between cells?

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