Answer:
Natural selection: the first cause here that prompts this is variation. Organisms who are more fit survive reproduce and pass down genes to
their offsprings while those who were unable to replicate dies off in cases like this.
In the other hand, natural selection plays a role in interaction of simple compounds that formed the molecules that generated living organisms: At this stage of evolution, early earth environment was extremely harsh, and at such, elements of harshness which may include lightning and meteors hitting the earth actually resulted in the compounds that generate living organisms.
The general outline of how genes are transcribed and translated is now well understood, and a great deal of the detailed structural biology of the molecular processes
is already known, examination of the details in a variety of organisms, however,has shown certain constraints and variations on the basic theme that are evidence
of the evolutionary plasticity of this most basic of cellular processes. An instance could come up as it is seen that the genetic code is not universal, but differs between mitochondrial and nuclear
DNA and from one mitochondrial genome to another. The difference between nuclear and mitochondrial codes might be expected from the origin of mitochondria from invasion by a symbiont, but even if that symbiont differed in its nuclear code from the current nuclear code the current diversity of mitochondria must be the result of subsequent evolution of the mitochondrial codon set. It is not clear how this ancient set of events can be subject to further analysis.
