EVOLUTION: MAINSTREAM IDEAS

UPDATING MAINSTREAM IDEAS

About a half-century ago I was confused by the distinction between Darwinism and Neo-Darwinism.  The "Neo" prefix had been added to designate the discoveries of Darwin enhanced by understanding of hereditary or genetic principles clarifying the principles of natural selection.  Such proliferation of terms helps the specialists introducing them but brings confusion to the generalists.

Discovery of details of pogonophoran biology provides near certainty that the abandoned annelid theory of chordate ancestry was actually correct when modified as done in numerous posts on this evolutioninsights blog.  The separation of the chordate line from protostomes via the polychaete - pogonophora - hemichordate - chephalochordaate sequence has sufficient evidence to justify abandoning the old idea that the deuterostome departure from protostomes was near the flatworm level.

Updating the annelid theory

First, the original abandonment of the annelid theory on embryological grounds was dismissed by the drastic differences between protostome and deuterostome development.  This blog (June 24, 2013 etc.) is the only source showing a plausible reason for the change via the pogonophorans.

Second, the current popular distortion of animal phyla relationships is based on faulty research described in this site's blog of May 31, 2013.  The post on Evolution: Molecular Clocks on November 25, 2014 contains numerous citations to research showing the great variations possible in studies based on molecular clocks.

Third, the input from ecological and structural studies shows the simplicity of inversion of systems to deuterostome chordates from protostome annelids via tube-dwelling polychaetes noted in Evolution of systems inversion posted June 28, 2013.  Several other June 2013 posts should also be viewed.

Fourth, the post on EVOLUTION AND THE OLDEST ANIMAL, June 13, 2014, should be a great help understanding the unique evolutionary position of the pogonophorans and their position as a very important connecting link between the two major lines of higher animals.

Updating the Tree of Life

The June 30 2013 and subsequent posts to August 3, 2013 have information about the linking of mainstream invertebrate groups as well as arthropods and mollusks.  There are many important subgroups of sponges, cnidarians, and flatworms in the mainstream.  Interesting sideshoots include ctenophores, rotifers, nematodes.  The protonemerteans are a hypothetical descendent of flatworms preceding the polychaete annelids; they represent the most uncertain guess for continuity in the protozoan to people ancestral tree.  Arthropods and mollusks probably have separate origins from polychaete annelids.

Branches from uncertain places in the tree of life include lophophrates such as bryozoans and brachiopods, and echinoderms; they may be near the pogonophorans in origin.  Chaetognathan origins are uncertain, as are the origins of a number of unsegmented worms.


Joseph Engemann, Emeritus Professor of Biology, Western Michigan University, Kalamazoo, Michigan       October 20, 2017