Endosymbiosis – The Appearance of the Eukaryotes
Endosymbiotic Theory Introduction
In 1967 she proposed a contentious new hypothesis whichbecame her most important scientific contribution as the endosymbiotic theoryof the origin of mitochondria as separate organisms that long ago entered a symbioticrelationship with eukaryotic cells through endosymbiosis.
"She is best known for her theory of symbiogenesis, which challenges a centraltenet of neodarwinism.
Endosymbiosis: Lynn Margulis - Understanding Evolution
All evolutionary theories must offer an explanation in mechanistic terms of how it should or could have happened in order to be tested. The difficult thing with the endosymbiotic theory is that it proposes no real mechanism and most textbooks show the simplistic picture of a cell that swallows another cell that becomes a mitochondrion. Unfortunately, it is not so simple as that. There is a difference between the process of endosymbiosis and its incorporation in the germline, necessitating genetic changes. What were those changes? What was the host? Was it a fusion, was it engulfment, how did the mitochondrion get its second membrane, how did two genomes in one cell integrate and coordinate? The theory is also strongly teleological, illustrated by the widely used term ‘enslavement’. But how do you enslave another cell, how do you replace its proteins and genes without affecting existing functions? The existence of obligate bacterial endosymbionts in some present eukaryotes is often presented as a substitute for a mechanism, but they remain bacteria and give not rise to new organelles. So, before we can speak of the endosymbiotic as a testable scientific theory, we need a mechanistic scenario which is lacking at the moment.