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:

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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...
  6. 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.
  7. 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].
  8. 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.]
  9. 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.
  10. 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.
  11. 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.
  12. 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