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Summary: authors, accordingly (Benda, Meves) they have been regarded as representing a mechanism
of "cytoplasmic heredity" comparable in importance with that represented by the
chromosomes. This view, still very far from substantiation, remains a subject of contro-
versy and must be taken with proper scepticism; but in spite of its doubtful status it should
be kept clearly in view in all cytological discussions of these problems.
Today, there can be little doubt that mitochondria, as they are universally now
known, indeed play a pivotal role in biochemistry, development, cytoplasmic inheri-
tance and evolution (Lane 2005). In particular, the evolutionary origin of mitochondria
from endosymbiotic bacteria is widely accepted (Allen et al. 2007; Gray et al. 1999).
Until the discovery of mitochondrial DNA (mtDNA), however, pioneer scientists in
endosymbiosis were disregarded and their conclusions displaced by other theories. A
predominant theory at the time was that all structural elements of the eukaryotic cell
evolved sequentially, in one lineage. Also, it was generally assumed that mitochondria
are synthesised de novo as differentiated compartments within a wholly autogenous
eukaryotic cell, as reviewed critically by Margulis (1970, 1981). In 1905, a Russian
scientist named Constantin Mereschkowsky published a theory describing our contem-
porary concept of endosymbiosis (Martin and Kowallik 1999; Mereschkowsky
1905). Mereschkowsky made prodigious assumptions for his time, such as that
chloroplasts, which he termed chromatophores (colour bearers), and autotrophy
descend from cyanobacteria (then known as unicellular algae), and that nuclei
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