Theoretical courses

 

Folder Species concepts

What type of species concepts exist? 

To date, more then 20 different species concepts have been proposed. It can be difficult to differentiate between these concepts. However, they key out in three larger groups:

  • concepts that require some sort of overall similarity and/or gaps in character distribution. 
  • concepts committed to understanding evolution. 
  • concepts based on phylogenetics.

Why are there different species concepts?

Species concepts have and continue to be central tenets in biological science. From the earliest days of biological thinking until well after Darwin’s (1859) On the Origin of Species, species concepts were essentially of a typological nature. This was the consequence of the rather general belief that all species were created by God and thus were fixed and immutable. As intraspecific variation remained unrecognized, geographical variants and different morphs within and between populations were considered different species.

But, when the causal theory of evolution gained momentum, it became increasingly clear that the idea of fixed created units had to be abandoned. The recognition that species occur as reproductively isolated units gave rise to the biological species concept (BSC) that embraced the dynamical nature of life and its entities. By the 1940’s it seemed that the debate was at its terminus.

However, the fact that the BSC applied only to biparental sexually reproducing organisms and not to asexual and/or extinct species, together with the desire to apply cladistic techniques at the species level, led to the rapid development of phylogenetic species concepts. With phylogeny as a guide; species concepts have become synonyms of diagnosable clades. The debate has been re-opened.

How to use species concepts wisely?

A silver bullet species concept that attends to the biologist’s perceived needs does not exist. Some species concepts have a large theoretical value (e.g. BSC) but are only narrowly applicable in practice. Others are more practical (e.g. the morphological SC) but fail to explain intra- and interspecific variation.

The viewpoint that species represent branches (terminal ones for extant species) of different evolutionary lineages seems to be accepted, in one or another form, by most contemporary taxonomists. The phylogenetic species concept is therefore increasingly used.

Course

 

Sense and nonsense of species concepts (pdf format PDF, English) 

References

 

 

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