Christian de Duve proposed that peroxisomes (which contain enzymes for oxidative reactions) may also have originated as endosymbionts; however, because of their single layer membranes, lack of DNA, and the recent observation that peroxisomes can be formed from the endoplasmic reticulum, it is now generally accepted that they arose endogenously.
Lynn Margulis proposed in 1967 that along with mitochondria and plastids, the eukaryotic flagella was also the result of symbiosis (see the section entitled 'Origin of eukaryotes'). However, this fell largely out of favor when flagella were found not to possess DNA, and subsequently that spirochetes are rather dissimilar to eukaryotic flagella.
See also: Evolutionary Ecology: Overview; Fitness.
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