Ring Species Concept

An Evolutionary Idea with no Examples

The Ring Species Concept is defined as a series of connected populations which spread around a geographic barrier where neighboring populations are able to interbreed but the distant populations that meet after the barrier are unable to interbreed. The basic idea was first suggested in the early 1900’s and the concept was formalized in the 1940’s. This idea was to show in a spatial dimension what is typically expected of evolution in a time dimension. Only a few species have been suggested as potential Ring Species, but with further study each has been found to not qualify as true Ring Species. Therefore, the Ring Species concept is an evolutionary idea lacking any proven examples.

History of the Ring Species Concept

In 1905, David Jordan suggested the basic concepts of what would become known as Ring Species. In 1942, Ernst Mayr solidified the concepts and requirements for what he called ‘circular overlaps’. It was not until 1954 that the term ‘ring species’ was brought out by Arthur Cain. Within this topic of study, the term ‘rassenkreis’ may be encountered which is the German equivalent for a ring of populations.

Ring Species Illustration

Source: Todd Elder

Ring Species Characteristics:

  • 1) A species splits into two continuous grades of populations
  • 2) In the shape of a ring (typically surrounding a geographic barrier or unsuitable habitat)
  • 3) Populations acquire new traits as they move away from ancestral home
  • 4) Hybridization and gene flow occur in neighboring populations
  • 5) The two populations where the ends of the ring come together are two distinct, coexisting forms which are unable to interbreed
  • … In other words using the illustration: an original population splits into two lines – Populations 1,2,3,4 and populations a,b,c,d – where each population overlap can hybridize except Populations P4 and Pd.
  • Problems Defining a Species

    There are many difficulties in defining a species and this becomes quite apparent in the concept of Ring Species. If a ring were truly found, the two ends that are unable to interbreed would act like two separate species. Yet, the entire ring, from one end to the other, is able to breed and would therefore be considered one species. Darwin introduced the term ‘incipient species’ to suggest varieties predicted to become separate in the future. This idea is a large ‘what if’ as evidence so far has shown suggested ring species merge, rather than diverge, when they come back together – the opposite of what is needed for evolution to occur.

    Evolutionary Importance of Gene Flow

    Most of the time, speciation is considered to occur because of reproductive isolation. Within Ring Species, the possibility of speciation without such isolation would be a great find toward showing Darwinian style evolution as it would create a situation where a single species could become two species, due to divergent populations, even with some connected genetic flow.

    Candidates for Ring Species

    There have been several suggested candidates for Ring Species. The most notable are the:

  • 1) The Ensatina Salamanders surrounding the Central Valley of California
  • 2) The Larus Gulls near the Arctic Circle
  • 3) The Greenish Warbler surrounding the Tibeten Plateau
  • 4) The Crimson Rosella Parrot in Australia
  • 5) The Caribbean Slipper Spurge in Central America.
  • What is Really Observed

    The major downfall of the Ring Species concept is that the end populations, which by definition cannot interbreed, have been found to interbreed even in the wild, typically with fertile offspring. Therefore the species is only showing some variations (as a subspecies) based on the surrounding environment. It remains the same species. The changes that are observed are referred to as Pre-zygotic Barriers which mean characteristics used in choosing a mating partner rather than Post-zygotic Barriers whose characteristics mean successful fertilization cannot occur even when attempted because of genetic dissimilarity. This is further enhanced by recent DNA studies which conclude that the genetics of each population is typically formed by isolation rather than the necessary continuous gene flow.

    For Further Information:

  • 1) Irwin, D., Irwin, J., and Price, T. (2001) Ring Species as bridges between microevolution and Speciation. Genetica 112-113: 223-243, 2001.
  • XXXIIE. Last Updated: 08/01/2016
    Todd Elder

    Todd Elder

    Todd Elder has a deep desire to understand and experience Creation. As a Baraminologist, his current research includes developing the Katagenos Species Concept, the Natanzera Classification System, and the Floral Formula Method of determining Plant Kinds. As an author and speaker, his books and seminar materials are designed to encourage a growing relationship with the Creator.
    Todd Elder

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