It’s been confirmed. All extant life fits in a hiearchy pointing to a common ancestor.
All that exists fits in a hierarchy pointing to one Creator, who brings and brought it into being one step at a time.
There need not have been a common living ancestor. There was likely a time here when there were only unicellular creatures. They may have started with one type of creature, but most likely, many. Each would result in a different lineage, some to plants, some to molluscs and such, others to bugs, and yet others to animals. It may be among a variety of possibilities, but not necessarily, that there existed one life-form that is the common ancestor to all life.
Since all physical beings have been formed from the earth, we might say that it is the common ancestor of all nature. Some would see it is the sun. At some point however, neither the earth nor the sun existed. If we go back to the beginning, we are likely to conclude that in the beginning there was light, from which all else came into being one step at a time. While space remains filled with light travelling in every direction, there was a time when it was all just light, as an amorphous plasma, before the creation of photons. I would consider that light to be a common ancestor of all creation. I would further understand it as the material aspect of the is-ness that is at the foundation of everything brought into being as other, by the Source of all this wonder, now and always.
Let’s step back and consider that accompanying the growing anatomical complexity that occured in time, is an experiential dimension involving at least perception. The simplest would be found in the tactile encounters of unicellular creatures within their environment as they react to what sustains them and what poses a danger. At the other end of the spectrum we have this monitor and these words. Some believe these differences appeared in an instant, but most think that it took a very long time to create. Some postulate that random mutations resulted serendipitously in all this diversity that we see today; most don’t.
This universe is made up of different stuff with specific attributes that did not exist in the beginning. These attributes can be known through our capacity to relate to different forms of being. We exist as they exist, each with our particular given nature. Ours is a human nature, as atoms have an atomic nature. They do what they do and we do what we do, both as one whole being, made up of constitutent parts which have temporarily surrendered their individual being to become part of an encompassing unity. Again, the foundation of all forms of being is light itself. And, light is the material aspect of what is itself, love. In other words, all creation exists within the universe of God’s infinite compassion. Each individual component of the entire cosmos emerges from the eternal Fount of limitless creativity and goodness. There is one common Divine ancestor - one Father, one Son, who became one of us that we might become one with Him, and one Spirit uniting us within ourselves, with one another and with Him - God.
