DARWIN'S MACROEVOLUTION: Why Unscientific?

[Angrboda]

In biology, a ring species is a connected series of neighboring populations, each of which can interbreed with closely sited related populations, but for which there exist at least two "end" populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each "linked" species. Such non-breeding, though genetically connected, "end" populations may co-exist in the same region thus closing a "ring".

Ring species provide important evidence of evolution in that they illustrate what happens over time as populations genetically diverge, and are special because they represent in living populations what normally happens over time between long deceased ancestor populations and living populations, in which the intermediates have become extinct. Richard Dawkins observes that ring species "are only showing us in the spatial dimension something that must always happen in the time dimension."

Ring species also present an interesting case of the species problem, for those who seek to divide the living world into discrete species. After all, all that distinguishes a ring species from two separate species is the existence of the connecting populations - if enough of the connecting populations within the ring perish to sever the breeding connection, the ring species' distal populations will be recognized as two distinct species.

Ring species are living examples of transitional forms. They are speciation in action.

Greenish warblers

Another ring species that has provided valuable insights into speciation consists of the greenish warblers (Phylloscopus trochiloides). These small, insect-eating songbirds breed in the forests of central and northern Asia and eastern Europe. In the center of Asia is a large region of desert, including the Tibetan Plateau and the Taklamakan and Gobi Deserts, where the warblers cannot live. Instead, they inhabit a ring of mountains surrounding this region, as well as the forests of Siberia to the north. The warblers have remarkable geographic variation:

• In Siberia, two distinct forms of greenish warblers coexist, one in the west and one in the east, their distributions narrowly overlapping in central Siberia, where they do not interbreed. These forms differ in color patterns, the songs that males sing to attract mates, and genetic characteristics. Also, males of each form usually do not recognize the song of the other form, but respond strongly to their own.
  
• The traits that differ between the two Siberian forms change gradually through the chain of populations encircling the Tibetan Plateau to the south.
  
• Thus two distinct species are connected by gradual variation in morphological, behavioral, and genetic traits.
  

Claude Ticehurst, who during the 1930s studied variation in museum specimens of greenish warblers, hypothesized that the present pattern of variation arose when an ancestral species in the south, perhaps in the Himalayas, expanded northward along two pathways, one on the west side of Tibet and the other on the east. The two expanding fronts gradually became different, resulting in two distinct Siberian forms. More recently, studies of genetic variation and song variation have strongly supported this view.

The pattern of song variation is particularly interesting:

• Songs are short and simple in the south, but to the north songs become gradually longer and more complex along both pathways into Siberia.
  
• However, songs have also become different in structure, resulting in distinct differences in songs between the Siberian forms.
  

The birds distinguish between these differences; males respond aggressively to tape recordings of their own songs, thinking that another male has invaded their territory, but they do not respond to songs of the other form. In most species of songbirds, songs play an important role in mate choice; usually, only males sing, and females listen to songs when deciding which male to choose as a mate. Speciation is essentially the evolution of reproductive isolation between two populations, and song differences can cause reproductive isolation. Hence, the geographical variation in songs of greenish warblers provides a rare illustration of how gradual change in a trait can cause speciation.

— Ring Species: Unusual Demonstrations of Speciation, Darren E. Irwin,

[Mister Agenda]

Um, no. I appreciated and understood your point.

Ah, fair enough. Its just that rainbow paragraph took alot of effort.
I'm very proud of it.

As well you should be. It was loverly.

[libalchris]

Ring species are so freakin cool. So many places today we can see the different stages of speciation occuring. It's like the life of a star, we can document the different stages of it by observing different stars in the different stages, even if we can't observe the whole process. With life you can see the very beginning with different sub-species (domestic dogs and wolves), then as separation occurs more and more we see ring species, as apophenia gave examples of, then speciation becomes more definite. The species can make offspring, but the offspring is sterile, as is the case with donkeys and horses. And finally species that are very similar today that interbreed but cannot produce offspring.

[Phil]

Ring species are so freakin cool. So many places today we can see the different stages of speciation occuring. It's like the life of a star, we can document the different stages of it by observing different stars in the different stages, even if we can't observe the whole process. With life you can see the very beginning with different sub-species (domestic dogs and wolves), then as separation occurs more and more we see ring species, as apophenia gave examples of, then speciation becomes more definite. The species can make offspring, but the offspring is sterile, as is the case with donkeys and horses. And finally species that are very similar today that interbreed but cannot produce offspring.

One ring to rule them all

Check out my thread Evolution In Action for a few examples of speciation that is taking place over a human lifetime.

[Mister Agenda]

She just has a very small and rigidly calcified mind. She offers no rebuttals, just assertions to the contrary, back by well poisoning. A very small mind stuffed full of biblical crap, and lacking the flexibility to expand even a tiny little bit, even in defense of her bible. My dog can come up with better trick to get his food.

If you think god couldn't work a miracle and make a creationist dumber than Statler Wordorff, you are proven wrong.

I don't think it's so much of a dumbing (she may be fully functional in other areas) as a blinder on her imagination. I keep running into creationists mystified by things that only take a few moments thought. 'What good is half a wing?' Gee, I don't know, maybe you should ask a flying squirrel, fish, lizard, or lemur. 'What good is half an eye?' You know I DO wonder what good half an eye is to a tapeworm or Nautilus. Why, theyd be better off blind!

[Anomalocaris]

Yeah, think of ring species as the Latin language family. There was once on single mutually almost completely intelligible population of speakers, gradually speakers dispersed, local dialect evolved, until today, when one could go from Portugal to Spain, to France, to italy, to Romania, and never find a single break in the mutural intelligblilith of adjacent dialects in the continuum of the Latin language family, yet portuguese and Romanian on either end are mutually unintelligible despite the Latin origin of both, and are now definitively different languages.

[Epimethean]

Of course, the language that became Latin was itself a fusion of Osco, Umbrian, Etruscan and many other root languages by the time it cohered into the monster that colonized the world.