"Ring Species" - the Inevitable Logic of Flawed Genetic Replication

(George Brooks) #1

This discussion of “Ring Species” floors me - - it’s as though individual links in a chain of Evolution has been delivered to the observer - - but with the individual LINKS in the chain still alive!

"One of the most striking instances of partial or incomplete speciation are the numerous “ring species” (for review see Irwin et al. 2001). Ring species, such as the salamander Ensatina, form a chain of interbreeding populations which loop around some geographical feature; where the populations meet on the other side, they behave as completely different species.

In the case of Ensatina, the subspecies form a ring around the Central Valley of California—the subspecies freely interbreed and hybridize on the east, west, and north sides of the valley, but where they coexist on the south side they are incapable of hybridizing and act as separate species (Moritz et al. 1982; Futuyma 1998, pp. 455-456).

Another example of a ring species is the gull genus Larus. L. argentatus and L. fuscus were originally identified as distinct species in England. However, there is a continuous ring of Larus hybrids extending to the east and west all the way round the North Pole. Only in England are they incapable of interbreeding.

The Great Tit, Parus major, similarly forms a ring species around the mountains of Central Asia, freely interbreeding everywhere except in Northern China (Smith 1993, pp. 227-230).

Many species can hybridize, but the resulting offspring have reduced fertility. One example is the English shrew (genus Sorex) whose hybrids are reproductively disadvantaged due to chromosomal differences. This has also been seen in lab experiments mating Utah and California strains of Drosophila pseudoobscura. Another example are the frogs Bombina bombina and Bombina variegata, whose hybrids have low fitness (i.e. they do not reproduce very successfully) (Barton and Gale 1993).

Many other species can mate and produce viable hybrids, but the hybrids are infertile. This has been observed in species of amphibians (like certain frog species of the Rana genus) and mammals like Equus (where matings of horse and ass result in a sterile mule). Another example is the newt Triturus cristatus and T. marmoratus, in which hybrid infertility is due to unpaired chromosomes (Smith 1993, pp. 253, 264).

Other species are able to mate with successful fertilization, but mortality occurs in embryogenesis. Such is the case with the frog species Rana pipiens and R. sylvatica (Futuyma 1998, p. 460). This phenomenon has also been observed in Drosophila. Additional examples are also found in plants such as the cotton species Gossypium hirsutum and G. barbadense (Smith 1993; Futuyma 1998, ch. 15 and 16)."

The Potential For Falsification (i.e., Disproving):
If all known species were completely genetically isolated from one another, and there were no instances of hybrids, it would be very difficult to reasonably justify the postulation of millions upon millions of gradual speciation events in the past.


(George Brooks) #2

The existence of Ring Species is a FULFILLMENT of the nature of macro-evolution …

These are important developments in the natural order … and they are only explainable using natural selection and genetic mutation!

(Jon Garvey) #3

Jerry Coyne seems less persuaded, George

(Benjamin Kirk) #4

Hello George,

I disagree vehemently with your use of ONLY in this context.

They are FAR MORE explainable using drift and existing polymorphism, neither of which are natural selection and mutation.

(George Brooks) #5


And yet again … your drive to dispute something serves you poorly. The comparison I was attempting to make was between Young Earth Creationism vs. Evolution… not between two sides of the Evolution coin.

When I use the phrase “natural selection and genetic mutation” - - it is my attempt to mean the entirety of evolutionary processes without having to itemize all of them.

I know you are going to accuse me of being an amateur and a know-nothing … but I think that’s just your way of giving a hug.

Maybe I’m just wild-man crazy, but in my view, “Genetic Drift” is just another scenario coming out of your favorite giant bathtub of alleles … so mentioning “existing polymorphism” is a logical corollary.

FORMAL DEFINITION: "Genetic drift (also known as allelic drift or the Sewall Wright effect[1] after biologist Sewall Wright) is the change in the frequency of a gene variant (allele) in a population due to random sampling of organisms. . . .Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation. When there are few copies of an allele, the effect of genetic drift is larger, and when there are many copies the effect is smaller.

Returning to the point I was ATTEMPTING to make - - if you are a Creationist who thinks Macro-Evolution is IMPOSSIBLE … I would think the existence of Ring Species is the most convincing evidence we could ever contrive to show that it IS possible.

(system) #6

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