Today is the 59th birthday of Lynn Margulis, an avid promoter of a controversial hypothesis holding that Earth behaves like a living organism. Prior to embracing the Gaia hypothesis, Margulis, a theoretical biologist at the University of Massachusetts, Amherst, formulated a new explanation for how eukaryotes (cells with nuclei) evolved. Her serial endosymbiotic theory proposes that eukaryotes arose, beginning some 2 billion years ago, when various prokaryotes (cells lacking nuclei) formed symbiotic relationships with one another. For instance, mitochondria--organelles in eukaryotic cells that process oxygen--are now widely regarded as remnants of oxygen-using bacteria. Margulis also argues that symbiosis, rather than competition, is the principal driver behind biological change and evolution.
[Source: Emily McMurray, Ed., Notable Twentieth Century Scientists (Gale Research Inc., ITP, 1995)]