|FROM ||Ruben Safir
|SUBJECT ||Subject: [Hangout-NYLXS] cladistic allgoeirthms
Cladistics looks for the relationships between taxa in terms of an
evolutionary cost. By minimizing this cost, it is expected to find an
evolutionary scenario that closely matches the hierarchical
diversification process through transmission with modification. In
other words, inheritance of innovations from common ancestors is the
simplest way to explain diversity.
To understand why this can only be achieved by using character (or
parameter) matrix instead of distances that measures global
similarities, consider the case of a journey between two cities.
Looking at a map, you can easily measure the distance between the two
cities with a rule. This might be ok if you fly, but this is not very
useful if you travel by car because then you have to take into account
the landscape and the existing roads among other things.
First you have to look at a precise roadmap, and compute for each road
and considering all possible bifurcations, the true number of kilometers
you will have to travel. Note that there is no trick to avoid looking at
all possible paths. Then you can decide to choose the shortest way
according to the parsimony criterion.
But cost might not be measured by kilometers only. You may consider the
time it takes. Highways are certainly faster, but you should consider
the probability of traffic jams or that of slow trucks or animals on
smaller roads. It is common wisdom that the quickest ways are not
necessarily the shortest or the most direct ones.
You can also think about money with the fuel you will burn. Depending on
your car, depending on the slopes for the different roads, the cost can
be quite different in every case.
Lastly, you can consider the pleasure or the comfort of the journey.
This is certainly less quantitative and objective, but still important.
We have here a typical multivariate problem, and defining an
evolutionary cost is not always straightforward. As the above should
illustrate, character-based methods like cladistics explore an unknown
landscape with a metrics which is defined by the choice of the
multivariate cost. Indeed, for living organisms or for galaxies, there
is no roadmap…
So many immigrant groups have swept through our town
that Brooklyn, like Atlantis, reaches mythological
proportions in the mind of the world - RI Safir 1998
DRM is THEFT - We are the STAKEHOLDERS - RI Safir 2002
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