Multicellular Computing:
Emergence of Multi-Level Biological Systems
More than a dozen intermediate stages of emergence were required to evolve
multicellular life, and they all still play a role in everyday living
systems.
The many successive levels of emergence that led to life on the planet
Earth today cannot be known precisely. The short story, as best my partial
understanding of science can say, begins at the
“big bang” with quarks and gluons and strings (Oh My!). A
brief sketch of the many levels of emergence thereafter are outlined
below:
- A couple of seconds after
the big bang, the quarks, gluons, leptons, etc. condensed into a dense
sea of disassociated particles such as neutrons,
protons,
electrons, positrons, and neutrinos.
- As the universe expanded and cooled over a few hundred thousand years,
many of these particles joined into the stable sets of subatomic
particles we call atoms
– mostly hydrogen atoms with some helium and a tiny admixture of the
next lightest nuclei: deuterium, lithium and beryllium. None
of the other elements vital to life existed then.
- Perhaps 600 million years pass until gravity
interactions generate the third level organization: galaxies and stars.
- Deep inside these first-generation stars, gravitational
pressure creates temperatures that ignite fusion reactions. Light
nuclei fuse together to create the heavier nuclei of elements up
to iron, including the elements vital to life as we know it such as
carbon, oxygen, nitrogen, sodium, potassium, calcium, etc.
- However, some of the heavier elements vital to life, such as zinc and
iodine, are not created in first-generation stars because normal fusion
processes fail for nuclei heavier than iron[1],
The heavier elements are created by neutron capture processes such as
those that take place in the brief, violent death of stars in
supernovas. Supernovas not only create many of the remaining heavy
elements,
e.g., lead, gold, uranium, etc., their violent explosions also spew all
these newly created elements out into interstellar space where...
- Time passes, stellar dust from supernovas
eventually condenses again by gravitational attraction to form second
generation stars and
planetary systems with the full complement of chemical elements needed
for rock, water, air and, ultimately, life.
- Time passes in our little solar
system and the earth cools. All sorts of
autocatalytic chemical reactions in the
earth’s oceans and
atmosphere create the early carbon-based compounds that slowly combine
to create successively larger and more complex organic compounds[2].
- Eventually small
protocells surrounded by fatty acid membranes or bilipid
membrane
vesicles
filled with water and complex sets of organic chemicals arise. They are
reminiscent of simple cells, but aren’t alive, i.e., they cannot gather energy from the outside world nor can
they replicate. [Note: the details of this step are still speculative.
An
alternative "first step toward life" posits agglomeration of organic molecules
on tiny grains of clay rather than inside bilipid vesicles.]
- Perhaps 3.8 billion years ago, unexplained “magic[3]”
creates mechanisms for replication that allows the emergence of simple
single-cell life.
- For a couple of billion years,
single cell organisms evolve dizzying complexity in many steps: absorbing
mitochondria and chloroplasts, creating the nucleus, and so forth.
- About 3.5 billion years ago, cyanobacteria
evolved physically co-located cooperative relationships held together by sticky
secretions from the cells (e.g., gel or slime). These
are possibly the first step
toward multicellular life. They are believed to be responsible for the
conversion of Earth's early
carbon dioxide atmosphere into the oxygen-rich atmosphere of today.
- Finally true multicellular (Metazoan)
organisms form sometime between a billion and 600 million years ago[4].
From the early multicellular organisms to mammals, then
to humans, is yet another series of emergent levels too complex and too
poorly understood to go into here. [That is not to say that we
understand levels 8-12 all that much better.]
All of the levels described above are
evident in every living cell or organism today. The
biochemistry that emerged in the Earth’s oceans clearly operates in
every cell. Virtually all of the energy
used by every living cell comes from that produced by nuclear fusion in
the sun and captured via photosynthesis in plants. All the
hydrogen in cells was created in the big bang itself.
And many of the random events that generate
novel mutations that evolution can exploit are due to UV radiation from
the sun,
cosmic rays from distant galaxies, and neutrinos, some of which are
from the big bang itself! So, every one of the
dozen or so layers of emergent behavior still participate in a great
cosmic dance, one small figure
of which is Earth’s biosphere containing all the various species of
living organisms.
[1]
Including copper, zinc, tin, iodine, silver, gold, lead, and uranium,
many of which are needed for life. Zinc, for
example, is crucial to many DNA binding proteins that control gene
expression. Molybdenum is crucial to bacterial and eucaryotic
oxotransferase enzymes. Cobalt is crucial to some
methyltransferases. Copper is crucial to the function of
cytochrome c oxidase, a central enzyme in the generation of ATP in
mitochondria.
[2]
For example, carbonyl sulfide (COS), a simple volcanic gas, induces the formation of polypeptides from individual amino acids in water solution. Science, vol 306, 8 October, 2004, pp. 283-286.
[3]
We don’t know the steps that led to the evolution of the
fantastic mechanisms of RNA, DNA, protein, etc. that support
replication, hence life. The term “magic” simply reflects
that ignorance. It is not intended to endorse any particular belief system.
[4]
This time estimate is very imprecise because the earliest metazoans were probably
small, soft, creatures like hydra that did not leave fossils.
Contact: sburbeck at mindspring.com
Last revised 8/12/2009