In article <1992Jul28.004905.7322 at bronze.ucs.indiana.edu> jlogsdon at sunflower.bio.indiana.edu (John Logsdon) writes:
>>In a recent paper in _Science_ (v257: 232-235, 10 July 1992), the authors
>claim to have found fossil eukaryotic algae that are ca. 2.1 BY old. This
>is striking to me because this lineage likely represents a fairly derived
>eukaryotic lineage itself. In other words, there are a number of eukaryote
>lineages which branched off before this one did. This makes these other euks
>older than 2.1 BY. In fact, Archaezoa (euks with out mitochondria, ie:
>_Giardia_, that wonderful intestinal parasite) are probably MUCH older than
>the Algae they found (_Grypania_). Given this and that the root of the
>tree of life is EVEN DEEPER [either between eubacteria and
>archaebacteria+eukaryotes, OR between two groups of archaes (see _Science_
>v257: 74-76, 3 July 1992)], this seems to put "life" (ie: the common ancestor
>of all life: the "progenote") fairly ancient, perhaps ca. 3.5 BYA.
>There is only confusion if the current dogma of the serial symbiotic
origin of the eukaryotic is accepted verbatim. SUPPOSE
The earth was covered with prokaryotic organism of many types,
photosynthetic, respiratory, and parasites living off of the carbon and
energy cycles between these two major ecotypes. Many
symbiotic relationships evolved, some becoming increasingly obligate.
Eventually, some of these minimal ecological units consisting of a
photosynthetic prokaryote (prochloroplast), a resripatory prokaryote
(promitochondria) and an organizing parasitic administrator (pronucleus)
became so interdependant that they formed a new organizational level of
organism (urkaryote or proeukaryote).
Thus the early prokaryotic earth was a source of different units for
each of the functions: rd, green, golden, brown for the chloroplasts,
a couple of different types of respiratory units for the eventual
mitochondria, and a few different types of nuclear units. If one
studies the algae, there are many monophyletic groups which could be
assembled from the appropriate selection of one each of each of the
three elemental units.
There could have been direct polyphyletic origins of many protistan by
simultaneous (vs. serial) formation of the initial eukaryote for each
lineage. Mix and match one of each unit to get a eukaryote.