I think this is interesting and, I suppose, one could choose to see it as profound: life is divided into eukaryotes (which have a cell nucleus) and prokaryotes (which don’t; these are bacteria and archaea). In eukaryotic cells, such as those in the human body, there is a cell nucleus with DNA, and also lots of different organelles. One of these is the mitochondrion, the cellular power plant, of which there may be one or many in any given cell. Prokaryotic cells have none of these things: no organelles (or at least few and simple ones), no nucleus. The interesting thing is that mitochondria (and also chloroplasts, the organelles responsible for photosynthesis) have their own DNA, and reproduce a little like bacteria. (Mitochondrial DNA is inherited only from the mother; hence Mitochondrial Eve.) This DNA looks suspiciously like the DNA of a certain kind of bacteria.
This suggests what is called the endosymbiotic theory: that around 1.5-2 billion years ago — when eukaryotic cells started showing up — one cell survived endocytosis (getting “eaten” by another cell) and, somehow, gave the host cell a leg up in the evolutionary race. This symbiotic relationship continued, and developed into the eukaryotic cells we see today, with mitochondria, chloroplasts, etc. In other words, one prokaryotic cell ate another, but instead of annihilation, the eaten cell continued life inside the host, leading to the survival of both the host and the parasite; today, the “parasite” is such an integral part of eukaryotic cells that if you take it out, you destroy the cell. All multicellular life (just about, anyway) consists of eukaryotic cells. Without this symbiosis, there would be no humans, no animals, no birds nor fish nor plants.
Tell that to the next person who calls evolution a heartless eat or be eaten world.
