Saturday, 15 November 2014

On The Myth That You Can't See Evolution Happening


 
A strange assertion from evolution-deniers is that the theory of evolution is questionable because "It has never been seen to be occurring". It's a strange assertion because it isn't in the least bit true. Imagine teaching a child to tell the time by showing him how long a second is, how seconds convert to minutes, how minutes convert to hours, how hours convert to days, how days convert to weeks, and so on.  As long as he had enough multiplication data he wouldn’t be unapprised of what a year is like, nor a decade, nor a century, nor millennia.

Evolution is a bit like that - once we have the data that explains how it works, we don't need to live for thousands of years to see evolution happening in individual species. Evolution in the simplest observation would be changes in allele frequencies in a population over time. An allele is one of two or more alternative forms of a gene that may occur on a chromosome, affecting the expression of a particular trait. If we are looking for the simplest evidence that evolution occurs, then our observing bacteria is enough to piece together parts of a jigsaw - it gives us evidence of changes in the genes and gene frequencies in populations.  Bacteria are an effective model because they have both huge populations and incredibly fast life cycles, and as such one can observe quite easily the changes in the frequency of any one allele in a set of genes.

Imagine a huge colony of bacteria with a compound in the substrate; those that can tolerate the compound probably will survive and those that cannot probably will die.  The ones that survive will do so because of a natural variation within the population, and this allele will yield dominance in the colony due to the negative selection against other alleles on that loci.  That is evolution at work - the demonstrable observation of a colony of bacteria and change in the allele frequencies of a specific gene coding for a product through changing generations. This manifests itself with clear observations of mutation and natural selection, from which we can see evolution at work in organisms.

Here's a good real life example. In Japan we have something called "the nylon bug" which arose from a strain of bacterium. These bacteria have evolved a completely new gene for the digestion of nylon. This gene, called nylonase, allows these bacteria to live where there is otherwise no food. This capacity occurred due to a single-step mutation that survived because it improved the fitness of the bacteria possessing the mutation. The acquisition of that function trait was so successful that it has given rise to an entire species of bacteria.  

Evolution is full of examples of similar kinds of mutation and natural selection that have played out in populations. There are types of radiotrophic fungi that have evolved to withstand the highly radioactive interior of the Chernobyl reactor. We have a similar example in the UK, where there are piles of ore outside old lead mines. Lead is toxic to snails, but within the last one hundred years or so, local snails have evolved a mechanism to live in lead-rich areas by incorporating the lead into their shells. 

From this information alone we can see evolution at work, just as a young boy can see linear time at work by looking at the clock on his mantelpiece. We can piece together an epistemological jigsaw and use componential analysis to work out that evolution is occurring in every living organism and has been for billions of years.

* Photo courtesy of docstoc.com

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