Symbiogenesis and cell evolution: An anti-darwinian research agenda?

Abstract

In 1905, Constantin S. Mereschkowsky (1855-1921) proposed that the green organelles (chloroplasts) of algae and land plants evolved from ancient, once free-living cyanobacteria. This endosymbiotic hypothesis was based on numerous lines of evidence. In a 1910 paper, Mereschkowsky argued that the time has come to introduce a new theory on the origin of living beings; since Darwin's era, so many new findings have accumulated that now an alternative, anti-selectionist theory of evolution has to be established. Based on the principle of symbiosis (i.e., the union of two different organisms whereby both partners mutually benefit), Mereschkowsky coined the term "symbiogenesis theory," which is based on an analogy between the feeding process of amoebae and cellular events that may have occurred in the ancient oceans. Mereschkowsky's symbiogenesis hypothesis explains the origin of chloroplasts from archaic cyanobacteria, with respect to plant evolution. In 1927, the Russian cytologist Ivan E. Wallin (1883-1969) proposed that the mitochondria of eukaryotic cells are descendants of ancient, once free-living bacteria. Here, I outline the origin and current status of the Mereschkowsky-Wallin concept of symbiogenesis (primary and secondary endosymbiosis) and explain why it is compatible with the Darwin-Wallace principle of natural selection, which is described in detail. Nevertheless, largely due to the work of Lynn Margulis (1938-2011), symbiogenesis is still considered today as an Anti-Darwinian research program. I will summarize evidence indicating that symbiogenesis, natural selection, and the dynamic Earth (plate tectonics) represent key processes that caused major macroevolutionary transitions during the 3500-million-year-long history of life on Earth.