[Last Update: December 3rd, 2018]
☣ Our Family Tree ☣
Copyright © 2000 C.E. by Dustin Jon Scott
|Image by brian0918 ™ - Own work, Public Domain, Link|
All life on Earth is related. When we look at the 3-dimensional cross-section of life on Earth we are capable of seeing at any given moment, organisms appear quite individuated, however in 4 dimensions we represent a literal Tree of Life, a great family tree upon which every living thing is but a tip upon a twig upon a branch leading ultimately to a root sometime prior to 4 billion years ago. If one could condense life on Earth along the t axis, such that an individual person were but a blurry line leading back to his mother, and she to her mother, ad genetum, one would see this tree as a literal reality. The Tree of Life in biology textbooks is therefore more than just an abstraction; it is by the inherent brevity of our sensory experiences that we are capable of seeing a mere 3-dimensional cross-section of this 4-dimensional Tree of Life that we perceive individual organisms as separate from one another.
The highest-level division of life on Earth was once the kingdom.
The most fundamental distinction among cellular organisms on this planet is that between the Archaea (including we Eukaryotes) and the Bacteria (including the mitochondria inside our Archaea-descended, Eukaryotic cells). We Eukaryotes are a sort of cellular "hodge-podge" of the two prokaryotic domains, although the coding DNA in the nucleus of the Eukaryotic cell is clearly inherited (mostly, and with modification) from the Archaea.
This was a modification of the Woesean tripartite Tree of Life which re-asserted the importance of endosymbiotic theory as the explanation for eukaryogenesis.
While the prokaryote-eukaryote dichotomy is still very useful for morphological/anatomical discussions, it has become considered a sign of grave ignorance to mistake this for a legitimate genetic delineation (much like the even more antequated vertebrate-invertebrate dichotomy used for animals). Though we now know that we Eucarya nest cladistically somewhat deeply within the Archaea, a type of prokaryote (much like we now know that vertebrates nest cladistically within the chordata, a type of invertebrate)...