Dyrenes evolusjon [Animal evolution]:
en innføring i systematisk zoologi
og dyrenes stamtre
by Hanno Sandvik, published by Tapir Academic Press (Trondheim, 2001).
ISBN: 82-519-1676-3. 216 pages. Price: NOK 305,.
[an introduction to systematic zoology
and metazoan phylogeny]
[> 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,
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
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.
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
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])
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
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
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.
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.
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.
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.