Molecular systematics - is it all rubbish?

Christopher L. Schardl clscha00 at ukcc.uky.edu
Wed Jun 14 11:09:26 EST 1995


Agneta Guillemot <Agneta.Guillemot at historia.umu.se> wrote:
>But it is'nt koscher. Why? There is one vital factor that molecularr 
>systematicists never seem to take into account in their work:  
>Different species evolve at different rates at different times. 
>Evolution is'nt just a clockwork that goes on and on. What if,  
>for example, the taxa you want to exclude from a grouping of  
>organisms, that you have just discovered, have evolved much faster 
>at some previous time? It will be different, and you will jump 
>to the wrong conclusions.  
> 
>Let's face it: Evolution in a species slows down and speeds up at 
>different times. Some species are left in the backwater, others 
>evolve fast in new evolutionary niches. There is no way of knowing 
>what happened when. The molecular clock does'nt exist! 
> 

If you are ever moved to get up off your keyboard and visit a library, 
you will see that this issue and others relating to the validity of 
molecular data in inferring past evolutionary history has been addressed 
many many times. It is an area of ongoing research leading to extensive 
refinements of the algorithms and statistical tests.

>There is only one school of systematics whose theorethical basis 
>is untouchable. It is of course cladistics. If you apply cladistic 
>methodology to sequence data you come to the right, unquestionable 
>conclusions. Most molecular systematicists seem to ignore cladistics. 
>I hope this will change. 

The untouchable school? This is true evangelism. Cladistic analysis of 
molecular data is very common, and is generally referred to as 
"parsimony." Interestingly, parsimony (as well as many other molecular 
phylogenetic analysis methods) can be misled by unequal mutation rates. 
This has been well documented, and approaches taken and refined to 
identify and correct for the problem. True, it takes more than plugging 
data into an algorithm and publishing the answer (and so should 
cladistics!), but scientists should train and evolve their thinking for 
proper interpretation of results obtained by any method.
> 
>Thank you for your attention! 
> 
>Ludvig Mortberg
>


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