While writing my EDNA book, I needed to check a couple of things in biology, and I stumbled across a sentence that shocked me. It said that all life on Earth was made of cells, with or without a nucleus. Immediately I wondered why there were no non-cellular life forms, and on checking that, although there is a Domain for them, it had hardly anything in it except for viruses and a few self-reproducing prions and the like. I realised that cells are not needed if confinement could be provided by nature in other ways, and I quickly wrote up my thoughts. The paper is on Amazon at the lowest price they allow $2.99, but actually, for many people, the following paragraphs might well suffice:
The advantages of using cell walls or membranes to encapsulate the fluids, chemicals and organelles of life are very clear, but these are not essential. Just as a virus relies on other organisms for its reproduction, non-cellular life forms could rely on other organisms or certain parts of the physical environment to provide an enclosed and limited fluid in which they could live. In the natural environment, tiny water droplets or small areas of thin films can offer similar volumes to large cells. Inside other organisms, as well as cells themselves, body fluids and internal surface defects also provide many niches with sufficiently sheltered and limited volumes of fluid.
Non-cellular life could have come into existence independently of other life forms, and could even be the ancestor of the first cellular life, with cell walls or membranes only evolving after many years of evolution without them. The first life on Earth might therefore have been non-cellular, perhaps evolving in small droplets in wet areas around hot springs and geysers, volcanic vents or waterfalls.