Friday, December 12, 2014



The preceding post of December 8, 2014 gives a condensed version of the evolutionary line listing 25 groups going backward from humans to an early animal group, the amoeboflagellates.  The list ignores the many other lines of evolution leading to other existing groups of animals such as echinoderms, mollusks, arthropods, and classes of annelids other than the polychaetes.  The polychaetes also are the earliest common ancestor of those groups as well as of all vertebrate groups.

The time scale of our ancestral tree follows the 25 groups of the first listing, but in reverse order with some additional steps beginning with the creation of elements and three other pre-biotic events not well covered in earlier posts.  The elements were formed in a second or later generation of stars preceding our sun.  They provided the material that eventually produced the more complex molecules from which living systems evolved on earth.

Those complex molecules formed from various processes as the earth cooled and the oceans formed.  Carbon dioxide, ammonia, water, methane, and various minerals were the materials acted upon by heat, radiation, and lightening to produce amino acids and other compounds.  Chance interactions of those compounds were probably enhanced by concentration in tidal pools.  There the mixing by waves may have utilized not only products produced by adhesion to various rocks, but compounds imported by water currents from remote locations.  One of those locations could well be the thermal vent areas proposed by Corliss as a place were life originated.  But similar processes could have been enhanced at inter-tidal locations as lava flows entered the sea or at other volcanic locations.

Following the four pre-biotic steps are five steps leading to the choanoflagellates, the ancestral group from which all animals arose.  Plants presumably are derived from earlier flagellated ancestors.  The remaining steps as well as the preceding steps are only cameos along a continuum of populations of organisms usually much like their closest ancestors and descendants.

Ten steps from sponges to the first chordates took about a billion years to occur.  The preceding evolution of living organisms took almost twice as long.  From the earliest, almost worm-like, chordates to us took a little over a half-billion year.  About eighty percent of that time was taken to produce the first primates.  It is likely our ancestral line never included a monkey that could hang from its tail as some South American monkeys can.

I mentioned the later because a monkey, if it could philosophize, might pity us for having lost our tail.  Likewise, the course of evolution includes many steps that might be considered regressive, but ones enabling later advances.  One of the most prominent, but least known, of such type event is the reduction of systems suffered during the evolution of polychaete ancestors to our pogonophoran ancestors.

Joseph Engemann     December 12, 2014

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