Dyrenes evolusjon [Animal evolution]:

en innføring i systematisk zoologi og dyrenes stamtre
[an introduction to systematic zoology
and metazoan phylogeny]

by Hanno Sandvik, published by Tapir Academic Press (Trondheim, 2001). ISBN: 82-519-1676-3. 216 pages. Price: NOK 305,–.

[> Norsk hjemmeside]

Welcome to the English homepage of this book!
This text book is written in Norwegian and has undergraduate students as its primary target group.

Below you find a survey of the chapters.


[chapter 1, 2, 3, 4, 5, 6, 7, 8, 9]

1. Evolution
This chapter briefly defines important terms and concepts (evolution, microevolution, macroevolution, phylogeny, natural selection, genetic drift, mutation, recombination etc.) and reviews three important evolutionary debates:
Adaptationism – constraints, the unit of the genotype, and the "selection for"/"selection of" distinction are discussed.
Levels of selection – the distinction between interactors and replicators is introduced and other reasons for the confusion about "units of selection" are mentioned. A list of 12 biological levels that can act as interactors, is presented.
Gradualism vs. punctualism – reasons for stasis are discussed, and the concept of punctuated equilibrium, and how it differs from saltationism, is explained.

2. Species
Different nondimensional species concepts and, after a discussion of how species originate (speciation processes), dimensional species concepts are presented. The relative role of scientific disagreements on the one hand, and arbitrary decisions on the other hand, for species debates is emphasised. Phylogenetic species concepts are shown to be a recent example of arbitrarily delineated taxa. The conclusion is defended that disagreement on one "ideal" species concept is unavoidable as long as different users have different expectations of the word "species". However, this should not make us forget that agreement is larger than some debates would make it appear: nobody doubts that populations of potentially interbreeding organisms exist in nature, and few doubt that they do so as what philosophers consider to be ontological individuals. Whether one likes to call them "species" is of semantic interest only, and not as biologically relevant as many believe. Furthermore, factual disagreement will often center on when (rather than whether) a given lineage achieves species status, a question of minor importance when large scales (such as phylogenetic time scales) are concerned.

3. Macroevolution
After defining som essential terms (taxon, monophyletic, paraphyletic), four macroevolutionary questions are discussed:
How do higher taxa, i.e. taxa above the species level, arise? (by branching and extinction processes)
How can one measure phenotypic gaps between taxa? (you can't, at least not as an overall measure)
How do new ground patterns arise? (the ambivalence of "body plan" concept is dicussed, along with the processes leading to new ground patterns, such as Hox mutations)
How do evolutionary trends come about? (by natural selection [at the individual level] or by species sorting [i.e., by extinction-driven and/or speciation-driven natural selection at the species or higher levels])

4. Phylogenetics
Terms such as homology, convergence, homoplasy, apomorphy and plesiomorphy are defined. The method of the cladistic analysis is explained and illustrated with an example. Questions regarding character polarity, conflicting characters, and the debate between pattern cladism and maximum likelihood analysis are discussed.

5. Metazoan phylogeny
Using 20 cladograms, the phylogeny of the Metazoa is outlined. For each group, monophyly is established by mentioning a few – mainly morphological – apomorphies. Cases of disagreement are shown by hollow, broken or dotted lines in the cladograms (for taxa of doubtful monophyly, taxa sedis mutabilis and taxa incertae sedis, respectively), and are discussed in the text. In order to avoid anthropocentricisms,
– efforts were made to present cladograms as balanced as possible,
– Linnean categories were avoided, and
– the position of taxa along the horizontal axis of cladograms was determined by alphabetical order.

6. Comparative biology
While phylogenetics, as an idiographic branch of biology, is concerned with unique events (the evolution of homologies) and considers homoplasy as nuisance, the opposite is true of the nomothetic branches of biology: in comparative biology the main goal is to reveal lawfulness in nature, i.e. one is concerned with homoplasy and uninterested in homology. The chapter shows that phylogenetics and comparative biology are two sides of the same coin: given knowledge of a phylogeny and species phenotypes, it is possible to infer microevolutionary processes; given knowledge of microevolutionary processes and species phenotypes, it is possible to infer phylogeny. The necessity of phylogenetic information for comparative methods is explained (because of the non-independence of species, and in order to sort out homologies and homplasies). Two methods (independent contrasts and concentrated changes) are explained in some more detail. Using examples from a variety of biological disciplines (co-evolution, key innovations, conservation biology, community ecology, anatomy, parasitology), the power of the phylogenetic-comparative method is demonstrated. In the final section, the lawfulness of evolutionary progress and the concept of complexity is questioned, highlighting the pitfalls of anthropocentricism and wishful thinking.

7. Systematics
In an explanation of the concepts and principles of systematization, classification and taxonomy, it is shown that a close correspondence between biological systematics and phylogenetics is not a necessity but rather a historical contingency – if a fortunate and succesful one. The struggle between systematic schools during the 1940-1980s is shortly revised, and it is concluded that the disagreements have largely become obsolete by now because what other biologists ask for today is a phylogeny, rather than a system, of their taxon of interest. The most basic rules of nomenclature, the role of museum collections, and the artificiality and arbitrariness of Linnean categories are explained.

8. Paleontology
Using examples from Amniota and Arthropoda, it is shown how taxon names become equivocal when extinct lineages are considered. It is then shown how this ambiguity can be avoided by specifying whether taxon names are crown-based, node-based or apomorphy-based. Different approaches to classifying fossils, including the plesion concept and Pan-monophyla, are presented. Finally, the significance of fossils to evolutionary biology and phylogenetics is discussed: fossils are not the sine qua non of inferring past relationships; nevertheless, they are important to phylogenetic analyses by providing further datapoints, by assisting in the homologisation of organs, and by revealing character polarity. Furthermore, fossils are necessary for absolute datings of both taxa and events, important for testing hypotheses regarding evolutionary processes, and interesting simply by widening our perspectives on what kinds of body plans are possible.

9. Philosophy
The final chapter shortly touches the philosophy of science, ontology and ethics: What is science; are evolutionary biology and systematics science, and, if so, what kind of science? The difference between nomothetic and idiographic sciences is emphasised, as well as the importance of not mixing their respective methodologies. Evolutionary biology contains both nomothetic and idiographic elements. Phylogenetics is one of its idiographic disciplines, even though some biologists, by pretending otherwise, have greatly confused its methodology. Systematics (less phylogenetics) is not science at all, but convention (which does not necessarily make it less important). The ontological distinction between individuals and classes, already mentioned in the chapter on species, is explained in more depth. Finally, the view that evolutionary ethics cannot be (and, hence, should not attempt to be) a normative ethics is defended.


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Last updated 12 February 2006.