A new model created by Eörs Szathmáry and his colleagues offers a possible explanation for the evolution of life on Earth from simple organic molecules to the predecessors of our cells.
10 February, 2017
Presumably, the immediate predecessors of the first earthly organisms were self-reproducing chemical systems, that is, molecular replicators. Copy speed was of vital importance, as the system which could replicate itself fastest soon gained a quantitative advantage over slower variants. However, when reaching a certain level, this mechanism hinders the complexity growth of living beings. New elements that do not improve the efficiency of replication directly enlarge the defining code of the organism, and thus their presence itself slows down the replication process.
An ancient missing link
Cooperation, which has occurred over the course of evolution on multiple occasions, may open up a new path for complexity growth. Sometimes a group of organisms might create a community, and the selection of the group affects the community in such a way that functions supporting the whole of the community may survive, even though they may not serve the success of individuals forming the community. An example for such a community is the collection of all the cells of a polycellular organism.
A prerequisite for the cooperation of molecular replicators was their separation from their environment, that is, the formation of compartments. The result was probably the emergence of the predecessor of our present day cells, the protocell. If, however, the genetic information required for the operation of compartments was stored by the individual replicators, these, being longer, could be copied more slowly. So the question arises: how could they survive in a contest with faster replicators?
A way out of this seemingly paradoxical situation is outlined by Eörs Szathmáry and his colleagues in their article published in Science. Their chemical and mathematical model experiments proved that the complexity of molecular replicators can grow if the following two conditions are present:
- A natural process repeatedly creates tiny compartments in the medium containing replicators. We are familiar with several such examples: tiny water droplets are produced and joined again, oil droplets are spread and joined again, and other physical processes might produce small, temporary compartments.
- A selectional process affects the compartments.
The researchers proved that when these two conditions are met, some properties might emerge and survive that help the community of temporary compartments. What is more, experiments show that the system of temporary compartments enhances the diversity of replicators, that is, a “genetic bank” aiding the emergence of new functions is created.
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