The definitions of semaphoronts, species, and supraspecific

Kirk Fitzhugh kfitzhug at
Wed Apr 28 20:47:32 EST 2004

I have fond memories from the first two international polychaete conferences, 
Sydney 1983 and Copenhagen 1986, when there were some vigorous evening 
discussions on the topic of "What is a species?" Many of you have probably 
noticed similar recent discussions on TAXACOM, indicating that while there are 
several "species concepts" from which to choose, there is no consensus among 

As part of my research on the philosophical foundations of phylogenetic 
systematics, I have completed work on a slide show which presents what I think 
to be the most appropriate [sic] definition for the term species. As a result, 
definitions of the terms semaphoront (sensu Hennig 1966) and supraspecific 
taxon are also provided.

My suggestion that these new definitions are the most appropriate comes from 
recognizing that the terms semaphoront, species, and supraspecific taxon must 
accurately represent our hypotheses of the causal events of ontogeny, 
tokogeny, and phylogeny, respectively - these being clearly illustrated by 
Hennig's (1966: 31) figure 6. If we assume that figure 6 accurately represents 
the reality of causal events (which can accommodate asexual and heterogenetic 
organisms as well), then it is the assumption of the reality of our inferred 
causal events which dictates the nature of our definitions of these terms.

Another interesting outcome of this investigation is that by recognizing the 
distinctions between tokogenetic and phylogenetic events, the actual relevant 
place for 'maximum likelihood' methods, i.e., the requirement of considering 
'branch lengths' as part of the inferential process, is at the level of 
tokogeny, not phylogeny. The inferences of tokogenetic and phylogenetic 
hypotheses are quite distinct.

This new slide show, "The Inferential Structure of Semaphoronts, Species and 
Supraspecific Taxa," is at, 
and is one of six shows in this series:

I. The Inferential Basis of Phylogenetic Systematics

II. The Inferential Structure of Semaphoronts, Species and Supraspecific Taxa

III. The Philosophical Basis of Character Coding

IV. The Requirement of Total Evidence

V. Homology vs Homogeny 

VI. Testing Phylogenetic Hypotheses 


J. Kirk Fitzhugh, Ph.D.
Associate Curator of Polychaetes
Invertebrate Zoology Section
Research & Collections Branch
Los Angeles County Museum of Natural History
900 Exposition Blvd
Los Angeles CA 90007

Phone: 213-763-3233
FAX: 213-746-2999
e-mail: kfitzhug at

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