Multicellular Computing:
Emergence of Multi-Level Biological Systems
More than a dozen intermediate stages of
emergence
in the universe
were required to give rise to
multicellular life, and they all still play important roles in
everyday living
systems.
Many successive levels of emergence led to life on the planet
Earth today. They cannot be known precisely but the story,
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 small stable sets of
neutrons,
protons, and electrons thereby becoming simple atoms
- mostly hydrogen atoms with some helium and a tiny admixture
of the
next lightest nuclei: deuterium, lithium and beryllium. None
of the heavier atomic elements, many of which are vital to
life, existed
in the
universe then, not even carbon, the sixth smallest element.
- Perhaps 600 million years pass and the universe continues
to
cool until gravity exaggerates slight differences in the
density of
matter in vast sub regions of the universe
to create the third level organization: the first galaxies and
stars.
- Deep inside these first-generation stars, gravitational
pressure created the enormous temperatures that ignite fusion
reactions. The lightest
nuclei, hydrogen and deuterium, fuse together to create
successively heavier
nuclei. This process continues, creating the elements up
to iron, including carbon, oxygen and the majority of other
elements vital to life as we know it.
- However, some of the heavier elements also vital to life,
such
as
zinc and
iodine, are not created in first-generation stars because
normal fusion
processes cannot create elements with 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, but also their violent explosions spew
all
these newly created elements out into interstellar space
where...
- Time passes, stellar dust from supernovas, containing all
the elements,
eventually condenses again by gravitational attraction.
Thus second
generation stars with
planetary systems form. They include the full complement
of chemical elements
needed
for rock, water, air and, ultimately, life.
- In our own little solar
system much more, time passes and the earth cools enough for
liquid
water to condense: liquid water without which life as we know
it cannot exist. All sorts of catalytic 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 are thought to have arisen: water and complex
sets of organic chemicals that are surrounded by fatty acid
membranes
that separate their inside from the different composition of
the
external world. These bilipid
membrane
vesicles are
reminiscent of simple cells, but aren’t alive, i.e., they
cannot 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, mechanisms that allowed
protocells to replicate emerged via unexplained “magic[3]”.
Replication marks the emergence of simple
single-cell life.
- For a couple of billion years thereafter,
single cell organisms evolve dizzying complexity in many
steps:
developing motility, absorbing
mitochondria and chloroplasts that had been free-living simple
cells,
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). This is
possibly the first
step
toward multicellular life. These colony bacteria are
believed to be responsible for
the
conversion of Earth's early
carbon dioxide atmosphere into the oxygen-rich atmosphere of
today.
- Between a billion and 600 million years ago[4]
true multicellular (Metazoan)
organisms evolve that develop from a single fertilized
cell and share the same DNA. The precursor cooperative
colonies of single cell organisms such as biofilms still play
important roles in our planet's ecology. However, they
consist of many
single cell species each with its own independent genome
rather than sharing one common genome.
From the early multicellular organisms to mammals, then
to humans, requires yet another series of emergent levels too
complex and too
poorly understood to explore in this brief story. [That is not to
imply
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. For a more extensive
review of the
geophysical, geochemical, and biological processes involved in
this
long process, see the Review paper: Mineral evolution,
Robert M.
Hazen, et al, American Mineralogist,
Vol. 93, pp.
1693-1720, 2008 A
.pdf
can be found here.
[3]
We don’t know the steps that led to the evolution of the
fantastic mechanisms dependent upon RNA, DNA, and
proteins that
support
replication, hence life. The term “magic” simply reflects
that ignorance. It is not intended to endorse any particular
belief
system, either scientific or theological
[4]
This time estimate is very imprecise in part because the
earliest
metazoans were probably
small, soft, creatures that did not leave fossils.
Contact: sburbeck at mindspring.com
Last revised 7/17/2013