Researchers at the University of Tokyo have created an RNA molecule that can not just replicate, but “evolve” into a diverse range of more complex molecules. This find could plug a major gap in the puzzle of how life on Earth began.
Exactly how life arose from non-living matter is one of the most profound mysteries of science. It’s long been hypothesized that RNA acted as a kind of precursor to DNA – if these simple molecules existed in the “primordial soup” of early Earth, they could have begun self-replicating and diversified into a range of forms. As the molecules became more complex, they could eventually have given rise to cells with DNA molecules, birthing all forms of life we see today.
As neat as this explanation would be, it remained unknown whether or not RNA molecules could actually undergo this kind of evolution. So for the new study, the Tokyo researchers conducted a long-term RNA replication experiment.
The team incubated RNA replicase molecules in droplets of water encased in oil, at 37 °C (98.6 °F) for five hours at a time. Then nutrients were added, diluting the solution to one-fifth of the original concentration, and the mix was stirred before being left to incubate for another five hours. This process was repeated over 240 cycles, for a total of 1,200 hours of experiment time.
And sure enough, the RNA molecules mutated and diversified over time. The single starting “species” eventually branched into five different lineages, which would fluctuate in population before stabilizing. A network of interactions arose between the different lineages – most intriguingly, cooperation that helped them all replicate more efficiently.
“Honestly, we initially doubted that such diverse RNAs could evolve and coexist,” said Ryo Mizuuchi, corresponding author of the study. “In evolutionary biology, the ‘competitive exclusion principle’ states that more than one species cannot coexist if they are competing for the same resources. This means that the molecules must establish a way to use different resources one after another for sustained diversification. They are just molecules, so we wondered if it were possible for nonliving chemical species to spontaneously develop such innovation.”
While the experiment shows that it’s at least possible that RNA could undergo evolution and lead to complex life, that doesn’t necessarily confirm that this is how it occurred in the real world. The team plans to conduct further experiments to uncover in more detail how RNA could have paved the way towards living systems.
The research was published in the journal Nature Communications.
Source: University of Tokyo
