The bubble theory

The Bubble Theory is a hypothesis postulating the simultaneous origin of both cellular and viral strategies of life from early replicators enclosed within liposomes, proposed by Radoslaw Piast. As lipid-enclosed replicators were not cells but a cooperating group of "genes," the term "bubble" was chosen to describe this state and differentiate this stage of the origin of life from liposomes (not containing replicators) and cells (fully fledged living organisms). This led to naming the hypothesis "the Bubble Theory." Piasts bubbles are the intermediate state between RNA world and first cells. They can be described as evolvable conglomerates of individual replicons on their way to become individual cells through cooperation and competition minimization.
According to the proposal, a population of replicators evolved the ability to navigate a bubble, which protected them from external conditions due to environmental pressure. This scenario could have occurred in the tributary of an ancient river that had one of its sources in a Darwinian warm little pond-like subterranean lake. This lake harbored early RNA-based life forms capable of self-replication and peptide production. As the lake produced all necessary substrates for replication, including liposome-producing amphiphiles like lipids, some of these nutrients, along with replicators, could have been packed into liposomes and washed away. The dilution of building blocks necessitated that the liposome-enclosed replicons cooperate to "hunt" other liposomes or bubbles for their nutritious content and remain within the supply zone. Eventually, two possible strategies were developed: a virus-like strategy based on the ability to transmit replicon information to nutrient-rich bubbles, and a cell-like strategy involving the maintenance of the lipid envelope and gaining nutrients via merger with other bubbles.
Stages
The Bubble Theory involves 3 stages crucial for the evolution of cells and viruses:
# The Source - Subterranean lake with properties of Darwinian warm little pond. This body of water was a birthplace of the first living entities - RNA-based replicators able to produce peptides. The source was constantly producing nutrients supporting replication of replicons and lipid-like amphiphiles able to form liposomes.
# Dilution point - Organic matter running from the source was forming a stream. This stream was merging with other rivers in the tributary, resulting in a continuous dilution of nutrients. At this point, only within liposomes' nutrients were not diluted and were able to support the replication. Replicators enclosed within liposomes must have started to cooperate with each other to gain the ability to navigate the whole structure. To distinguish it from liposomes and cells, replicon inhabited vesicles are called bubbles. For survivor purposes, bubbles had to merge with nutrient-rich liposomes from the source. Development of two strategies could be helpful in such an environment: a virus-like strategy based on the ability to transmit replicon information to nutrient-rich liposomes, and a cell-like strategy involving the maintenance of the lipid envelope and gaining nutrients via merger with other liposomes. Helpful in these processes was production of transmembrane peptides/proteins which could work as piluses, fimbria and fusion proteins.
# Solitude point - Far from the source, nutrient-rich liposomes were too rare to support bubbles. At this point replicators had to develop a system increasing their chances for finding new hosts, becoming parasites or had to start maintaining their lipid vessel becoming fully fledged cells.<ref name=":0" />

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