Human interrelationship
The traditional way to view how life developed on earth historically has been via something called a Phylogenetic Tree. The tree shows various steps of classification, illustrating how all life once was one thing and charts in steps how then we evolved into other things. At its most basic, this process can be seen below.
But where did this "Root" come from? Was it chicken first or egg first?!? Simple single cell (prokaryotic) life emerges as a gradual and predictable transition from geochemistry to biochemistry, in the presence of rock, water, CO2, and energy, all of which are found within alkaline hydrothermal vents on geologically active planets, of which there are 40 billion in our galaxy alone, and probably a similar number in each of the other 100 billion galaxies.
It is thought that life started from simple inorganic molecules, which interacted to make other molecules which could replicate themselves. After this it was just a matter of millions of years (a blink of an eye in earth's history) before more complicated organic replicants came to being.
Once the earliest life was created it took another 3.5 billion years for it to make us. Whilst the stepped classification is useful as it gives specific delineation for scientific study, in fact the process was much more fluid. Similar to the roots of a tree branching out, although many stems are produced it is still the same macro organism.
