That heroic labeller of living things, the 18th century Swede Carl Linnaeus, painstakingly grouped into discrete categories everything which grew breathed or moved. His meticulous ranking of “kinds” made the scientific examination of the living world a whole lot easier. His legacy is greatly valued and his system is still universally used today.
However as time has unfurled, a problem arose in the observation that nature does not always agree with the human desire for rigid boundaries -- of what makes a family, genus or species. It has been observed that nature is actually a lot more fluid in its relationships.
In the last quarter of a century there has
been a new direction in taxonomy (posh
word for scientific classification). We have an increasing understanding of the
genomes of living things including the human species (which are multi-celled eukaryotes)
down to single celled bacteria (prokaryote) and by learning the DNA of
everything, we now have a scientific arbitrator to sort out which really
belongs to which taxon (i.e. rank or
species). It is the DNA which determines the degree of connectedness of one
species, genus or family to another. It is the essential nuts and bolts of taxonomy
and the essence of how evolution is described.
Armed with this new genome tool a marvelous discovery has been made at the humble end of the ladder of life. Sometimes the “connectedness” of one branch of life is puzzling because of not having apparent genetic links but if evolution is true then they must exist.
How did the archaic single celled critters evolve into more complex life? Well, over simplified here for the sake of brevity; some of the single celled animals arranged all their DNA into a nucleus and then (trumpet fanfare) clumped together to form multi-celled critters (some jellyfish and corals still use this method of being a composite or colony of different animals). There are also wonderful living demonstrations of other primitive cells which coalesce only when short of nourishment. (e.g. Dictyostelium discoideum- a favourite in micro biological circles!) Are you still with me?
Nature was unwittingly exploring diversity
by mutation and chance encounters due to wind movement and climate change, with
chemicals, rocks, gases and divergent genomes. We have evidence such as the mitochondrial
cells even in us, we have taken on board as it were, alien life and incorporated
it into our hominine genome. Some of you Trekkies will remember the “symbionts”,
yes humans have actual microscopic symbionts functioning in every one of our cells
and so did the early forms of complex life. Symbiotic life, absorbed because it was useful to the host and later adopted as part of the geneome.
This understanding (admittedly my crude description of it) gives a part explanation to the matter of how increasing complexity arose in the earliest, single celled life which was the only game in town for billions of years.
Recently Japanese researchers according to New Scientist, have found something else. Noticing a familiar DNA signature in a marine deposit they were struck by the fact that it came from a prokaryote, the DNA was previously identified only with more complex life. Bingo! As unlikely this chance find is, they seem to have found that rarest avian: a missing link, i.e. the genetic inheritance factor between the prokaryote and the eukaryote. This is DNA from one of the simplest life forms which ultimately connects it to all which followed including mammals and therefore us. It is exactly what evolution theory would predict.