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How and Where did Life Begin?

 

Kevin Loughran

 

 

 

There is a wide range of opinion and argument as to when life emerged; in what form, and by what process.  There is some evidence, limited conclusions and much speculation.

 

Indeed life on Earth may have originated on another world.  This is the hypothesis of 'panspermia' - that living cells or their pre-cursors might have originated on another world and hitched a ride to Earth on a meteorite.  (For this hypothesis to work, two problems have to be resolved: that any biological materials being carried by the meteorite can survive severe heat and survive exposure to radiation).

 

But if life emerged on Earth and expressed itself through a process of evolution, then how did inorganic materials evolve towards life forms?  James Trefil, Harold J. Marowitz and Eric Smith described this as "the great unknown" - when we perceived a deep gap to exist between inorganic materials and life and believed that nature must have made a big leap to cross that gap.1  They saw the process of evolution from inorganic materials to early life as working through incremental steps - a series of "simple, chemical reactions".

 

Did life emerge in many forms or in one form?  One view is that all of life can be traced back to a single form - the 'last universal common ancestor' or LUCA.  Douglas L. Theobald developed a formal test which, he claimed, provided statistical evidence for the unity of all known life (although this LUCA may not have been the first organism on Earth).2

 

Carl Woese suggested that Darwinian evolution may not have been the original form of evolution.  There may have been an earlier phase of evolution dominated by horizontal gene transfer (see Mark Buchanan's 'Another kind of evolution'.)3    Carl Woese proposed also that the three fundamental forms of life which he identified - Bacteria, Archaea and Eucarya - evolved independently of each other and not in a line from a common ancestor.4   However, Tom A. Williams et al. have argued that 'accumulating evidence' supports only two primary domains of life.5

 

Whatever the elements and the processes in the evolution of life, we may be tempted to assume that life has always evolved towards greater complexity;  but has it?  In 2004 a new virus was discovered - in Bradford! - that was several times larger than any other virus known previously.  It was larger than any bacteria.  It was named as a Mimivirus.6   Gary Hamilton reported that it was as "genetically complicated as some free living organisms" - despite the common view of viruses as "non-living bags of chemicals.7

 

Why did the mimivirus have so many genes (almost half of them unknown previously to science)?.  Jean Michel Claverie speculated that the Mimivirus may have been a descendant of a fully fledged life form that was far more complex - possibly existing before the emergence of cells while "nature was still experimenting with simple designs".8

 

And bigger than the Mimivirus is the Pandoravirus.  Two have been isolated so far: one off the coast of Chile; the other in a freshwater pond near Melbourne in Australia.  They were without "resemblance to any previously identified virus families".9   The largest of the two, the virus isolated in Chile, had over 2,500 genes, twice that of the Mimivirus (most common viruses have few than ten each).

 

Larger again is the Pithovirus, around 30% larger than the Pandoravirus.  It was first identified in the Kolmya region of Siberia as the Northern tundra thawed.  Scientists used amoebas to revive or 'draw out' the virus, which does not harm human or mouse cells (it appears),10

 

Viruses qualify as viruses when: they cannot replicate, they cannot process their own DNA - they have to rely on a host to do that for them; they cannot make their own energy-storing molecules; they cannot make proteins; there is no sign of cell division.11

 

But there may be 'life forms' out there that are stranger yet.  Gary Foster of the University of Bristol, argues that as we "look at the extremes of life, we will find many more of these strange things.12

 

Can viruses be considered as a form of life?  And what is the role of viruses in the evolution of life?  Luis P. Villarreal in 'Are viruses alive?'13, wrote that scientists were "beginning to appreciate viruses as fundamental players in the history of life.  He contended, with others, that the cell nucleus was of viral origins.  However, he acknowledged that viruses existed in a grey area between the living and the non-living: they could not replicate on their own, but only in living cells.

 

What is life?  Daniel E. Koshland observed that a great deal was known about life, but that there was not general agreement about what life is.14   He recalled a scientific conference at which many hours of discussion on the question "What is the definition of life?" could not resolve the question.  It seemed that everyone knew what life was ("I'll know it when I see it") but could not agree on a definition of it.

 

From the above we may conclude that:

 

·            we do not know exactly where life on earth began

·            we cannot agree on how life began

·            we cannot say that life evolved in a straight line towards complexity

·            we cannot agree on a definition of life / on what life is

·            although some say that life as we know it has evolved from a single common ancestor, others have disputed this

 

But we can say that life is real; that it is there.  We can achieve an understanding of how forms of life develop; and we can form ideas about life and test those ideas.

 

 

 

Kevin Loughran

 

2015

 

 

 

1  The origin of life, American Scientist.  Vol. 97, May-June 2009.   p. 206

 

2  A formal text of the theory of universal common ancestry, Nature.  Vol. 465, 13 May 2010.   pp. 219-222

 

3  New Scientist.  23 January 2010.  pp. 34-37

 

4  On the evolution of cells, Proceedings of the National Academy of Science of the United States of Americas.  Vol. 99, No.. 13, June 2002.  pp. 8742-8747

 

5  An archaeal origin of eukaryotes supports only two primary domains of life, Nature.  Vol. 504, 12 Dec. 2013.  pp. 231-235

 

6  'Mimivirus' may refer either the single species, Acanthamoeba polyphaga mimivirus (APMV) or to a group of large phylogenetically related viruses.

 

7  New Scientist.  No. 2544, 25th March 2006.  p. 37

 

8  ibid. p. 39

 

9  Philippe Nadège et al.  Science.  Vol. 341, 19th July 2013.  pp. 281-286

 

10  Andy Coghlan.  New Scientist.  No. 2959, 5th March 2014..  p. 10

 

11  Andy Coghlan.  New Scientist.  No. 2927, 27th July 2013.  p. 14

 

12  ibid.

 

13  Scientific American.  Vol. 291, Issue 6, December 2004.  pp. 96-102

 

14  The seven pillars of life.  Science.  Vol. 295,  no. 5563,  22 March 2002.  pp. 2215-2216

 

 

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