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Dinosaurimony (Re: Definitions...)
A brief diversion (I hope this doesn't spawn a month-long discussion...)
Parsimony. I have always liked the explanation of the principle of
parsimony as: "The simplest explanantion which accounts for the most data
with the least number of unsubstantiated hypotheses and unsupportable
assumptions is the most likely to be correct." I don't know where I got
that, or how different it has become in the hundred-plus times I have
written or spoken it, but I love it.
Mickey Rowe directed us all to the definition of parsimony at Dinosauria.com
We all went and read. And we saw that it was good. Except for one sentence:
> It should be noted that there is no law that states that natural
systems >must behave simply, or parsimoniously.
This is a criticism which is often leveled at the use of parsimony
for the formulation of phylogenetic hypotheses (i.e. in cladistics).
However, no one I know of suggests that evolution occurs parsimoniously.
Indeed, no one has to my knowledge yet defined what "parsimonious evolution"
Here's my view on the question (incorporating the thoughts of other
individuals as well as my own). The use of parsimony in cladistics does not
invoke a particular characteristic of the process of evolution (or of
natural processes in general), it merely assumes that logical evaluation of
evidence can lead you to the true answer. It is presumed that, given all of
the evidence ("all" in a metaphysical, omniscient sense), there is only one
way to account for all the data, and that is by the correct answer. This is
probably tautological, since the historical processes of the generation of
the phylogeny itself are is included within "all" the evidence. Even
excluding this, the concept that, in the presence of all the evidence, the
parsimonious explanation is not the correct one is tantamount to saying
logic doesn't work, that some things cannot be arrived at by deductive
reasoning. If this is true, we might as well just give up now, because
science is bogus.
In the absence of some evidence, it is believed that the most
parsimonious explanation for the evidence we do have is the best model for
the phylogeny (note: not THE right answer, just the best guess). Why? The
answer is logic. Why would you prefer a more complicated explanation?
Let's say you do prefer a more "complicated" explanation. Why?
Because you feel there is some evidence that your explanation is better.
But, if you have *evidence*, it should be incorporated into the analysis
now, shouldn't it? You are, in effect, not rejecting the application of
parsimony, you are simply saying that you have a more parsimonious
hypothesis. You are saying that the old explanation doesn't *account* for
your data, and therefore does not account for *all* the data available, and
is therefore not as parsimonious as yours.
Parsimony seems (at least to me) to be little more than an extension
of the logical thought processes we use to seek understanding of the natural
world. It is a method of reasoning, not a model of evolution or of any other
natural process. Think about it: Do you think it is more logical that flight
evolved independantly in _Archaeopteryx_ and _Passer_? If crocs and birds
both have four chambered hearts, isn't it logical _Tyrannosaurus_ did to? If
you think the arctometatarsus evolved several times in theropod evolution,
don't you amass a suite of characters which you use to link taxa with
arctometatarsi to seperate plesiomorphically-footed taxa? You are applying
parsimony when you answer these questions, and many more questions in science.
Now back to dinosaurs, already in progress.
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"...To fight legends." - Kosh Naranek