While often conflated with the Theory of Evolution, the idea that all living organisms surviving to the present day are descended from a single common ancestor is a separate notion (although there is overwhelming evidence for both). Given the common characteristics of all known forms of life, especially the mechanism by which DNA is encoded and translated into proteins, it is very probably that a single instance of abiogenesis is responsible for all life, although we cannot rule out the possibility that other replicators – with a completely different genetic system – that we would still readily classify as “alive” existed at some time but died out. We tend to think that the development of “life” from “nonlife” would be so rare as to happen only once, but it may be that just one of several survived. In any case, the “frozen accident” of the existing DNA code created such a deep “local minimum” in the adaptation landscape that it was not possible for an organism to go back and change it, whether it is the best conceivable system or not.
We can make some interesting suppositions about the lifestyle of the universal common ancestor based on characteristics common to all life. In a certain sense, multicellular organisms expend at lot of effort to RECREATE this environment. Our bodies are almost like reverse scuba suits (as in The Far Side cartoon, in which a fish could walk outside its bowl) providing a salty, aqueous mileu akin to the “warm little pond” that Darwin envisioned as the birthplace of life. The blood and intersititial fluid provide a high sodium, low potassium environment (compared to the interior of cells) that UCA would find comfortable. As discussed in The Spark of Life by Frances Ashcroft, these needs are so engrained in the way our cells function that they require special ion channels to keep the Na+ and K+ ions out and in, respectively, and many neurotoxins exploit this universal need as molecules that block or prop open the channel, with very deleterious effects.
Thinking about all life as related causes some unsettling philosophical conclusions. For example, every act of predation is, in a sense, fratricidal. Perhaps an unconcious unease with thinking about Man and louse as being in any way comparable led to notions like spontaneous generation. The death of which was the slaying of a beautiful theory by an ugly fact according to Thomas Henry Huxley. In any case, by applying moden bioinfomatic methods to patterns in human DNA code allow us to recreate migration patterns, or establish that we are all part Neanderthal. The latter conclusion was apparently confirmed in the most direct way possible when the remains of the child of a such a union were discovered.