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
is 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, eventually 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 on Earth,
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
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 encapsulate and
protect their inside from the different composition of the
external world. These bilipid
membrane vesicles are reminiscent of simple cells, but
are not 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. 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 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 our cells was created in the big
bang itself. And many of the random events that generate novel
mutations that evolution exploits are due to UV radiation from
the sun, or cosmic rays from distant galaxies, or neutrinos,
some of which are from the big bang itself! Thus, every one of
the dozen or so layers of emergent behavior still participates
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.
Last revised 3/30/2015