An international team of researchers had recently carried out one of the largest-ever genomic analyses, which helped them map the evolutionary history of eukaryotic genes in unprecedented detail.
The study, published on August 19 in Nature, builds upon (and lends evidence to) the theory of “punctuated equilibrium” which holds that evolution, even though a slow process for the most part, occasionally proceeds in great leaps over short periods of time. The theory was proposed in 1972 by the famous palaeontologist Stephen Jay Gould and his colleague Niles Eldregdge, who claimed that the degree of gradualism commonly attributed to Charles Darwin is largely non-existent in the fossil record, and that stasis dominates the history of most fossil species.
To find out how these great jumps happen, the research team looked at the evolutionary history of both prokaryotic and eukaryotic organisms. Traditional models had shown that lateral gene transfer (the flow and swapping of genes between two individuals) happened in prokaryotes and thus helped explain the enormous diversity they have compared to eukaryotes.
With this in mind, the researchers asked: could these leaps be explained by the same type of gene transfer in eukaryotes?
“The big surprise of the study was that eukaryotes don’t engage in this kind of continuous gene swapping nearly as much [as prokaryotes] – though when they do, it’s a really, really important event and in early evolution, it corresponded to the origin of organelles. These events were huge evolutionary leaps,” said project leader Professor Bill Martin from the University of Düsseldorf.
Previous research has shown that the organelles of eukaryotic cells emerged in the distant evolutionary past as two cells came together to share genes and form a hybrid organism.
Adding to this picture, the team’s computer model has revealed that after the initial hybrid-forming stage the newly-created organism starts losing its genetic information – a process not unlike a chess match where each cell starts out with a full set of genes lined up at either side of the board, but as the game progresses start losing their pieces one by one. To see how the game went, the researchers have to look at the remaining pieces and trace the moves back in time.
According to the study authors, their findings prove that great evolutionary leaps happen when prokaryotes and eukaryotes mix their genes together in an endosymbiotic event. This lends some fairly robust evidence that the theory proposed by Gould and Eldredge more than 40 years ago is right, and could prove highly useful in explaining the breadth and origins of complex life on Earth.