For the origin of life there are competing theories that life evolved from replicators, from lipids and from metabolisms among other things. Has anyone investigated if these things evolved independently, then developed a symbiotic relationship forming the first prokaryotes?
Eukaryotes are supposedly just prokaryotes which developed symbiotic relationships with each organelle once being an independent organism, have people investigated if the origins of life had something similar? I assume the answer is yes, if so who?
Lipid spheres, given the right chemical environment, will probably spontaneously form fairly easily and commonly. Replicators of the right sort (for natural selection to get a toehold, you need replicators that can copy themselves with almost, but not quite, perfect reliability) are going to be a lot harder to get and are likely to form abiotically only very rarely. What is more, they are going to be relatively large, complex, and thereby delicate, molecules. It may well be that the first of them to successfully survive long enough to get life going was a molecule that formed within a lipid sphere, or whose properties included the attraction of pre-existing lipids to form a protective coat around it. So it is possible that one of the crucial events was the coming together of lipids, possibly pre-existing lipid spheres, and a replicator molecule.
In most respects, metabolism probably arrived later, thanks to natural selection. Initially the only metabolism going on was probably the replicator molecule forming (sometimes imperfect) copies of itself from the surrounding soup.
Of course, apart from very general constrains that we can derive from the laws of chemistry, none of this can be much more than informed speculation. The actual origin of life on Earth was a unique, flukey event that did not leave direct fossil evidence of itself (or if it did, it is a virtual certainty it has long since been destroyed).
Exactly. Evolution requires reproduction, so by definition, the two of your three categories that aren’t “replicators” didn’t evolve - they were just there.
The lipid spheres/globules may well have been “just there”, but a metabolism can’t be. It has to be a metabolism of something (of some organism) or else it is just some random chemical reactions. Even the simplest replicators, however, will inevitably entail a rudimentary metabolism: the assemblage of copies of themselves out of raw materials in their environment. More complex metabolisms, more worthy of the name, presumably evolved as the replicators evolved, but they are not “just there”, they are made by the replicators.