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Microbial Evolution

June 24, 2010

Exactly 150 years ago Charles Darwin published the first edition of the fundamental book that has become synonymous with the concept of evolution ever since – ‘On the origin of species by means of natural selection: Or, The preservation of favored races in the struggle for life’. Unknowingly, he challenged prevailing public opinion, angered the clergymen, by claiming that life evolves from pre-existing forms of life and that organisms were not put into place by God. I say unknowingly because even after sitting on conclusive evidence in favor of evolution for almost 20 years, Darwin presents his defense rather meekly in the first edition, almost to suggest that it could be one of the many possibilities for variation within species and resemblance between species. Darwin used incomplete fossil records and his records from the voyage on H.M.S Beagle to Central America, especially the Galapagos, to build his theory. As his earliest critics pointed out ‘Darwin never demonstrated how evolution occurs nor did he show proof of evolution in action’.  His theory was turned down as ‘mere speculation’ and a ‘mere hypothesis’.  In the following extract, he admits and explains the inability to demonstrate evolution..

That natural selection will always act with extreme slowness, I fully admit. Its action depends on there being places in the polity of nature, which can be better occupied by some of the inhabitants of the country undergoing modification of some kind. The existence of such places will often depend on physical changes, which are generally very slow, and on the immigration of better adapted forms having been checked. But the action of natural selection will probably still oftener depend on some of the inhabitants being slowly modified; the mutual relations of many other inhabitants thus being disturbed’

Around 300 years ago another fundamental discovery had already been made. Anton van Leeuwenhoek had discovered what we now call bacteria in a human mouth sample under a microscope. Thus, Bacteria were discovered and studied for almost two centuries before evolution, as a theory for the origin of life, was propounded. Ironical as it may seem, these infinitesimal organisms would have landed a final power-packed blow on Creationism had Darwin peered under a microscope.

Neither Darwin nor his successors,for almost a century, did. Bacteria and evolution were studied by two cliques of biologists that never interacted, it seems. Evolutionary theory developed with more fossils records, Mendelian genetics, statistical and mathematical theory but never in tune with microbiology.

Bacteria have a short lifespan. Some divide once every half an hour. Every time a bacterium divides it replicates its hereditary material (DNA) and a copy is thus retained in the two daughter cells produced. Every time a bacteria replicates its DNA there is a slight chance that the machinery does not work perfectly, quite like a quirky printer that sometimes prints out indecipherable symbols. The modified DNA is then passed on to the daughter cells. If the modification is bad, like terrible misprints on a sheet which make us crumble up a page and toss it in the trash, such that it affects the vital functions the cell dies. Rarely, however, the modifications make the daughter cells ‘fitter’ than the parent in the context of the environment  they are floating around in. These daughter cells, Version 1.1, soon take over the population and Version 1.0 just dies out. This too is a form of evolution where natural selection acts upon variation (the parent and daughter cells) leading to the survival of the fittest.

Studying evolution of microbes enables us to watch this enthralling phenomenon, live in action, and this is exactly what I do.  We can take advantage of the fact that these bacteria can be preserved at any point in time (by taking a small sample and freezing it at -80˚C) to leave behind a perfect fossil record that can be dug out, that thousands of generations can evolve in the duration of a PhD thesis, that  evolutionary changes, sometimes rather startling, can be documented in real time. As my former microbiology professor often said ‘Our job is to play God in the microscopic world.’

2 Comments leave one →
  1. Mahesh Nayak permalink
    June 24, 2010 7:19 pm

    WoW!! 🙂

  2. June 28, 2010 10:37 pm

    Well articulated. Cheers.

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