The theory of evolution begins its story with the first replicators. These are simple life forms; strands of genetic material, that can replicate its DNA or RNA and make new copies. The theory assumes these first replicators mutated, got more complex, and evolved to the present. If this was true these simple replicators define our the common ancestry.
The problem with this theory is connected to another branch of science called Abiogenesis. Abiogenesis deals with the earliest events, hundred of millions of years before the replicators, where simple molecules like water, ammonia, methane, etc., reacted and gradually increase complexity, until the first replicators finally appear.
Where evolution goes wrong is it assumes, that Abiogenesis ends when evolution begins, as though these preliminary chemical processes and mechanism of change, which perfected over hundreds of millions of years, suddenly not longer apply. A more reasonable approach is to assume that the underlying biogenetic push, that led to the first replicators, remained in affect, and still operated along side the changes in the replicators. It even participated in these changes.
The Abiogenesis aspect is connected to chemical evolution and mechanisms at the nanoscale; micro scale. While Darwinian Evolution is more about the changes at the macro scale; life forms.The common ancestors are really the small molecules and some unique laws of science associated with life processes.
For example, when proteins are manufactured by cells they fold into exact shapes based on their amino acid composition. This folding is controlled by the water. Water is the majority component of life and seeks to lower its free energy and surface tension. It does this by folding the protein into a minimal energy shape. This action still occurs. It also occurred even before the first replicators. It is one of many continuing processes that gives the 3-D character of life in the macro world. Water is the common ancestor of all life on earth, with water able to replicate the collective shapes of protein to give form to life; life forms.
The DNA is like the hard drive which has all the data. Water is like the processor. If you installed a different processor; different solvent, and used a DNA hard drive, nothing will work and the shapes of things will be different.