Sunday, November 29, 2009

Coping with Phylogenetic Systematics.

     I would estimate that I have read no more than 700 books in total since I learned how to read at age 5. While some have been more difficult than others, one of them has been the most difficult of all. The title is Phylogenetic Systematics, written by Willi Hennig in German. It was first printed in English in 1966.

      I have not yet finished reading this book. I gave it a try back in the summer of 2008 and got half way through. The problem was that every few minutes I'd have to look up some word I had never seen before and quickly internalize it, because it kept reappearing in the text. The unfamiliar words piled up and I found myself thinking about words and not ideas.
     The reading is much easier on my second attempt, as I have had time to contemplate many of the ideas in this book as well as ingest the various abstruse words. One such word is chorology, which comes from the Greek word khoros, which means "place". Chorology is thus the study of the spacial distribution of organisms. The distribution can be euryoekous or stenoekous. Again, we have to go back to the Greek to get a handle on these. Eury means "wide" and  steno means "narrow" and I have found evidence indicating that "oekous" can be equivalent to oikos, which means "house of". Therefore, an organism that is euryoekous is tolerant of a wide range of habitats, while an organism that is stenoekous tolerates very few. The problem with the words in this book is that I often cannot find them in my physical dictionary (American Heritage), published in 1992. It's not that the words are new, rather, they are obscure in the most extreme sense. Not even a google search offers any help with some of them. I have found a book, though, titled Animal Behavior Desk Reference which has many of them defined. I would love to buy the book, but it costs $175 at
     While reading this book it is important to keep in mind the differences between three types of genetic relationships. Those are:

1. Ontogenetic relationships, which are those between semaphoronts.
2. Tokogenetic relationships, which are those between individuals.
3. Phylogenetic relationships, which are those between species.

     Don't know what a semaphoront is? Not sure about tokogenetic? Those are the types of early problems I faced while trying to read this book. All of 3 of those relationships together are called hologenetics and the author expressed that the book could be called Hologenetic Systematics. The Greek root holo, which means "entire" was used. It is also common to see this referred to as "Cladistics".
     This book is filled with fascinating definitions. Here's one of them:

     SPECIES: "the study of the evolutionary process in which groups of forms that have hitherto interbred, or at least were capable of interbreeding, become divided into two or more separate groups that for physical reasons cannot interbreed"

     It is also referred to as species cleavage, which you can see here graphically. It is an important concept, something quite obvious that had never occurred to me before.

No comments:

Post a Comment