Theories of independent origins

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The first group of theories proposes an independent origin and argues that the differences between the three domains of organisms are so profound that they can only be explained by an independent origin. However, we have seen that many of these differences suffer from many exceptions. In particular, the difference in lipid composition between the membranes of the three groups, which is a strong argument for this theory, is no longer tenable. Indeed, in Planctomycetales (eubacteria), the synthesis genes of ether-linked lipids typical of archaebacteria and sterols typical of eukaryotes are present, and were probably acquired by horizontal transfer. This therefore shows that a replacement of genes during evolution can explain the particular compositions of the membranes specific to each group. Moreover, this theory does not really explain how the attributes of the eukaryotic cell appeared!

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