Tiny droplets may have initiated life on Earth

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?

Temporary cooperation

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.

Volvox as seen above is a polyphyletic genus of chlorophyte greenalgae. It forms simple spherical colonies of up to 50,000 cells. Within the spheres the offspring of the colonies are also present. Source: Wikimedia Commons/Frank Fox - www.mikro-foto.de - CC-BY-SA

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.

For further information please contact:

András Szilágyi
ELTE Department of Plant Systematics, Ecology and Theoretical Biology
email: and [dot] szilagyi [at] gmail [dot] com
phone: +36 1 381 2187