Thursday, October 25, 2012

Another phylogenetic network outside science

I have noted before that evolutionary networks are used in both biology and the social sciences, and that you will also occasionally find them elsewhere, as a means of displaying historical relationships among objects or concepts (see this blog post: Phylogenetic networks outside science). However, the uses outside science are not always successful, as shown in this previous blog post (Direction is important when showing history). Here I discuss another example of a phylogeny of ideas rather than objects that has potential problems.

This is labelled as a Computer Languages Timeline but, just like the previous example of a GNU/Linux Distribution Timeline that I discussed, it is actually drawn as a set of linearized genealogies. These are evolutionary networks rather than trees because there is horizontal transfer (ideas added) and recombination (ideas replaced) among the languages.

Click to see the original image.

The basic problem with this example is that it is not time-consistent. That is, the connections between languages begin at one time and end at another time. This does not happen with the GNU/Linux example. Many of the connections seem to have arbitrary begin/end times, which is not only unnecessary but also confusing.

There is, however, a good reason for some of the connections not being time-consistent. This occurs when a previous version of one computer language is used as the source of ideas for a later language, so that the information does indeed travel through time, in the manner that I have already discussed for phylogenies of ideas rather than objects (see this blog post: Time inconsistency in evolutionary networks). Examples in the Computer Languages phylogeny include the use of Fortran I (1956) as the basis for IAL (1958), and the use Fortran II (1957) as the basis for Basic (1964).

It is important to distinguish these two types of time inconsistency. There is a  logical basis for the transfer of ideas through time, in which case the reticulation connections should be drawn to reflect the time inconsistency; but there is no logical basis for the other time inconsistencies, and their use should be avoided in the diagrams.

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