Endosymbiosis

This theory ranks among the most important evolutionary events, as endosymbiosis is a hypothesized process by which prokaryotes (microscopic single-celled organisms) gave rise to the first eukaryotic cells (organisms whose cells have a nucleus enclosed within membranes).  The complex eukaryotic cell ushered in a whole new era for life on Earth, because these cells evolved into multicellular organisms.  Endosymbiotic theory, attempts to explain the origins of eukaryotic cell organelles (tiny cellular structure that perform specific functions within a cell) such as mitochondria in animals and fungi and chloroplasts in plants.  Virtually all the life we see each day, including plants and animals belongs to the Eukaryota domain.  It is thought that eukaryotic cells are actually the descendants of separate prokaryotic cells that joined together in a symbiotic union.

I think that the most significant event in the history of the human race occurred when a free-living bacterium was engulfed by another cell, perhaps as a meal, and it ended up staying as a sort of permanent houseguest.  The host cell profited from the chemical energy the mitochondrion produced, and the mitochondrion benefited from the protected, nutrient-rich environment surrounding it.  If single celled organisms never evolved into multi celled organisms, then humans would not be here and what is more significant than existence.

Written for Fandango’s Provocative Question #44 which asks, “What do you think was (or is) the most significant event in the history of the human race? Please explain.”