Cause of speciation observed

[truth above all else]

Yes, I agree, defining species is not that easy.

But it is easy to see that in observed instances speciation is not arbitrary.

what about the polar bear and the grizzly bear, your definition suggests they are a specie since they can mate and produce offspring yet they are classified as separate species

 

[Mocca]

Oh really? Care to provide a source?

And also, is the offspring fertile?

 

[truth above all else]

Oh really? Care to provide a source?

And also, is the offspring fertile?

grizzly ursus arctos horribilis
polar ursus maritimus
recognised as separate species yet capable of producing fertile offspringhttp://http://www.grizzlybear.org/bearbook/bears_of_the_world.htm

 

[Mocca]

Then they should be defined as subspecies.

 

[truth above all else]

Then they should be defined as subspecies.

hence you agree with the arbitrariness of the term species
it would seem that these two species are but different varieties within one of the original created kinds

 

[Mocca]

hence you agree with the arbitrariness of the term species
it would seem that these two species are but different varieties within one of the original created kinds

Actually, I'm agreeing with the objective definition by stating they should be considered subspecies.

Anyway, would you like to provide any evidence that they're different varieties of these original created kinds you speak of?

 

[rmwilliamsll]

The idea that members of a species living side by side can split into two species is controversial. Some scientists have presented evidence that the process has produced several species of plants and animals, but their ideas have met with intense skepticism.

Two new studies in the journal Nature — one on the kentia palm and a second on fish in a Nicaraguan lake — are impressing some leading skeptics, however.

One reason for the skepticism is that another way for forming new species is well supported by evidence. When a population becomes isolated by a geographical barrier, it can evolve into a new species.

from: http://www.nytimes.com/2006/02/21/science/21spec.html

a short popularized article on the issues.

 

[MewtwoX]

Allopatric and Sympatric Speciation...

Your point? Speciation is still dependent on the definition of species as populations that can no longer interbreed.

In fact, one of the problems in this is that classical divisions of species can carry over, even though the species are now defined as the ability to interbreed.

I think the bear species is one example of this. It's similar to Chemical Nomenclature. A lot of people use Fromaldehyde insted of the correct IUPAC term, but that doesn't mean you call IUPAC terminology into question as accepted in scientific circles...

 

[Dr.GH]

All I have read in this thread is that some people don't have a good grasp of what a species is. I recommend reading What is a Species, and What is Not? by ERNST MAYR.

As Mayr observed, short of doing actual taxonomic studies, it is hard for most people to really grasp the idea. Darwin made a similar observation in a letter to Huxley (Mayr quoted one by Darwin to Hooker) and it was a reason that Darwin devoted years to the taxonomy of barnacles. At least the experience of keying out many species of many groups will provide the needed experience. It is like swiming- you won't understand until you get into the water.

The species concept is typically under attack by philosopher type people, and biologists without any field work experience with real organisms.

 

[Tomk80]

Then they should be defined as subspecies.

No, they shouldn't. The ability to interbreed in different species, not only reflects whether such things can happen genetically, but also whether they can happen naturally. Extra criteria, such as location, are important in that respect also.

What is important is whether there is a constant gene flow between the populations.

 

[Late_Cretaceous]

What people need to appreciate is that the concept of species is an artificial man made construct. It makes for a convinent definition, but somehow nature just doesn't want to comply with our attempts at segregation. The lines between species can be blurred. Species is not a concrete concept, and that is what a lot of people have a hard time understanding. Look up the word "cline" and you will understand more.

From Wikipedia, the free encyclopedia CLINE

http://en.wikipedia.org/wiki/Cline#searchInput
In population genetics, a cline is a gradual change of a character or feature (phenotype) in a species over a geographical area, often as a result of environmental heterogeneity. The change in phenotype does not result in different species as long as the geographically spread populations can interbreed with one another. This meaning of cline was introduced by Sir Julian Huxley.
A ring species is a special kind of cline where the geographical distribution in question is circular in shape, so that the two ends of the cline overlap with one another, giving two adjacent populations that rarely interbreed due to the cumulative effect of the many changes in phenotype along the cline. The populations elsewhere along the cline interbreed with their geographically adjacent populations as in a standard cline.
A "cultural cline" is a gradual change of a cultural characteristic or feature over a geographical area. Source of definition unknown.
In linguistics, the term cline refers to a list of words dealing with the same concept, arranged in order of intensity. For example a list could be made with words like "freezing", "cold", "cool", "tepid", "warm", "hot", and "scorching".

 

[Late_Cretaceous]

The RING SPECIES gives us the most compelling evidence of evolution and speciation, while giving an example of the fuzziness of the term species to begin with

The Ensatina salamander complex in California