The origin of life is every bit as mysterious as the origin of the universe. Before the Industrial Age, both were ascribed to supernatural forces in various mythologies and religions. It wasn't until the 19th century that a scientific proposal for the origins of the universe became widely accepted- The Big Bang Theory. However, a generally recognized theory for the origin of life remains obscure, even in 2015. Some scientists think that strong rain, lightning, and a muddy environment- just as the ground was becoming submerged by the sea- created the ideal conditions for life to evolve. Others think that volcanic vents in the ocean were where it first happened. Either way, it hardly matters where it happened; how it happened is most vital to our understanding. DNA couldn't have just come out of nowhere, nor could the proteins that constructed it (which are conversely created by DNA in protein synthesis). Proteins and DNA depend on each other for survival, so the question becomes: which came first?
A cell can't be a cell without a membrane holding it together. It's generally agreed that the first cell membrane was created by a coacervate- a thin layer of molecular aggregates with hydrophobic properties, similar to a bubble. These enclosed themselves around special molecules called amino acids, which were just drifting about randomly in the water. Amino acids are the building blocks of life. There are 20 of them and there isn't a creature in the world that doesn't use them all. They'd eventually assist in the creation of DNA, a superbly complex molecule that serves as a blueprint, or command center, from which a cell can operate. What I propose is that the first coacervate able to replicate itself had the fortunate circumstance of enclosing all 20 amino acids at once. This happened by pure chance (I'm open to claims of divine intervention, but only in a metaphysical sense). Many other coacervates could have enclosed different combinations of these amino acids, but they couldn't have evolved into cells without the full 20.
Proteins are long chains of amino acids. When amino acids bond to each other they are capable of forming every single protein that makes our bodies operate. In a sense, proteins are like our own bodies; their amino acids are like the organs we use to balance anatomical systems. Once proteins developed, they had to create an information system that would remember their design, because there wasn't any other way for them to keep the chain of life going. In order for the proteins to replicate themselves and survive, they had to encode a blueprint for their formation into a strand with optimal spacing. We call this the DNA molecule. DNA molecules are replicated themselves, by means of something called RNA. RNA is then taken to the ribosome of a cell by carrier proteins, where the translation of their code generates amino acids, which in turn give birth to new proteins. Thus, the cycle suggests that proteins are indeed capable of reproduction- something that the very definition of life needs- but not in the same way that traditional life forms reproduce. Proteins were the first thing on Earth that created something they could use to reproduce themselves- something unheard of in the biological world.
Eventually coacervates got stronger and developed into cells, which evolutionary biologists would call a breakthrough. This was when cells began to form nuclei which held the genetic material they needed to operate. Cells evolved from proteins, but they don't reproduce in the same way. They have their own special way of doing it: by splitting themselves in half through mitosis or meiosis. Every rung on the ladder of life can be described by a leap forward in the means of procreation, from the formation of DNA to the splitting of a cell, and from the pollination of plants to the fornication of animals.
In a sense, proteins were the first life-forms. Since they found a way to self-replicate they deserve to be called such, because reproduction is the most essential quality of life. Protein doesn't quite do all of the defined qualities of life, but you could make an argument that they do most of them. They certainly aren't typical molecules, and neither is DNA for that matter. Eventually there was no further need for them to "evolve", since they'd created a way to sustain themselves inside the environment of a cell. The same thing happened to cells. They stopped evolving once they turned into protozoa. In turn, the same could be said of bacteria- protozoa's lesser evolved cousins- because the same species have survived for eons inside beings larger than they are. It's only outside of the microscopic realm that we begin to see species that aren't sustainable inside a controlling body.
There's already an hypothesis which describes this theory, called the Protein Interaction World. It describes an environment in which amino acids naturally found each other and bonded to create the first proteins, long before the creation of DNA. The proteins then found a way to reproduce themselves by building DNA, so that they wouldn't ever have to be born again by chance. It is a theory that isn't well known, and nowhere in it does it say that proteins were the first life forms. But perhaps in the beginning there were long chains of protein that competed against each other inside the first coacervate. Perhaps they were participating in natural selection before the existence of cells and bacteria. The ones that won the battle got a permanent stake in the chain of life, oblivious to the fact that they'd eventually serve the bodies of larger organisms.
Could the same thing happen to a network of plants and animals? I wouldn't be surprised. It could be that we humans, safe and smug at the top of the food chain, will become part of a network inside the body of a greater being, whose existence we won't have any awareness; maybe we already are.
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