cursuswalker wrote:

Therefore they could be argued to represent to ends of a ring species, could they not?

It's a tough one. It is physically impossible for them to mate, yet they can still receive gene flow between intermediary sized dogs like a ring species. However, they are interfertile, unlike ring species.

Dunno - I will pass that one to Susu!

cursuswalker wrote:

Therefore they could be argued to represent to ends of a ring species, could they not?

Assuming the answer is yes (ie that dogs represent a ring species ranked simply by size, with the two extremes being unable to interbreed naturally), can anyone indicate two populations of humans that are also unable to interbreed naturally and have demonstrably not done so when placed in geographical proximity?

No, all modern human populations are interfertile and have sufficient similarity in their tackle to interbreed.

An example that springs to mind is the progeny of Tasmanian women raped by colonists.

In contrast to the dogs, here is an example of a woman of child bearing age from the most genetically isolated human population from Europe.

http://www.slv.vic.gov.au/pictoria/a/0/9/im/a09296.jpg

Anyone care to make out that no european man would want to get to know her better?

Spearthrower wrote:

cursuswalker wrote:

Therefore they could be argued to represent to ends of a ring species, could they not?

It's a tough one. It is physically impossible for them to mate, yet they can still receive gene flow between intermediary sized dogs like a ring species. However, they are interfertile, unlike ring species.

Dunno - I will pass that one to Susu!

They are interfertile if artificial means are used, but I would argue that they could not, in fact, mate.

cursuswalker wrote:

Spearthrower wrote:

cursuswalker wrote:

Therefore they could be argued to represent to ends of a ring species, could they not?

It's a tough one. It is physically impossible for them to mate, yet they can still receive gene flow between intermediary sized dogs like a ring species. However, they are interfertile, unlike ring species.

Dunno - I will pass that one to Susu!

They are interfertile if artificial means are used, but I would argue that they could not, in fact, mate.

Stretching the imagination, it is presumably possible for the Great Dane bitch to crouch like a lioness and the chihuahua to climb aboard and enjoy the ride.

Stretching the imagination, it is presumably possible for the Great Dane bitch to crouch like a lioness and the chihuahua to climb aboard and enjoy the ride.

In the Ancestors Tale Dawkins tells of two species of cricket that will mate successfully if the mating call of one of the species is played to them. The offspring are fertile. Yet they are still classed as two species.

On that definition I would definitely class the Great Dane and the Chihuahua as two different species.

I think dog breeds are extremely close geneticaly, far more then you'd expect.

Tyrannical wrote:I think dog breeds are extremely close geneticaly, far more then you'd expect.

That is irrelevant. The accepted definition of a species is a group of organisms who interbreed successfully under natural conditions.

Could a Great Dane and a Chihuahua do so?

Could a north European and a Tasmanian aborigine do so?

In the former case, I suspect not. In the latter case:

cursuswalker wrote:

Tyrannical wrote:I think dog breeds are extremely close geneticaly, far more then you'd expect.

That is irrelevant. The accepted definition of a species is a group of organisms who interbreed successfully under natural conditions.

Could a Great Dame and a Chihuahua do so?

Could a north European and a Tasmanisn aborigine do so?

In the former case, I suspect not. In the latter case:

There are numerous definitions of species, and in fact, the ring species you cited clearly challenges the traditional definition of a species.

Could a Great Dane and Chihuahua interbreed, yes they probably could if they could overcome the size difference, as per the example I already gave. As another way of explaining it, I already mentioned that gene flow continues between the 2 breeds via intermediary sized dogs, so, unless the 2 groups are kept in strict breeding isolation, they will never truly become another species.

Note that the term 'ring species' is actually singular, as in, they are all members of the same species.

http://en.wikipedia.org/wiki/Ring_species

In biology, a ring species is a connected series of neighboring populations that can interbreed with relatively closely related populations, but for which there exist at least two "end" populations in the series that are too distantly related to interbreed.

Neighbouring populations, not neighbouring species.

Segundo wrote:
Relatedly, I have come across people who think zoological classification is "wrong" and that species are "human inventions" because ring species exist and I think these people are badly mistaken.

I don't think that species are a human invention because of ring species, but they most certainly are a 'human invention' in the sense that they are a means of drawing lines in nature where lines do not exist. A species is a population at a point in time. All individuals could breed with their parent's generation back forever, so we are the ones who decide, based on morphological characteristics, what one species is and what another is. That doesn't make it 'wrong', but people should be aware of the way a species is constructed.

Segundo wrote:My opinion is that classifying all domestic dogs as one species is dumb. I do not know why it is done but I would guess it has something to do with convenience.

It's because they are extremely similar genetically and interfertile.


As for the intuition, I will look forward to seeing your answers to Tyrannical's next competition.

cursuswalker wrote:

Tyrannical wrote:I think dog breeds are extremely close geneticaly, far more then you'd expect.

That is irrelevant. The accepted definition of a species is a group of organisms who interbreed successfully under natural conditions.

Could a Great Dane and a Chihuahua do so?

What you are forgetting, is that it is unnatural conditions that led to dog breeds, and it is only through continually enforcing these conditions through selective breeding that breeds continue to exist. Without human intervention, you'd have a bunch of mutts

Tyrannical wrote:

cursuswalker wrote:

Tyrannical wrote:I think dog breeds are extremely close geneticaly, far more then you'd expect.

That is irrelevant. The accepted definition of a species is a group of organisms who interbreed successfully under natural conditions.

Could a Great Dane and a Chihuahua do so?

What you are forgetting, is that it is unnatural conditions that led to dog breeds, and it is only through continually enforcing these conditions through selective breeding that breeds continue to exist. Without human intervention, you'd have a bunch of mutts

In the documentary series "Earth after people" they demonstrated exactly that. They said that the scavenger "wolf" gene in dogs is still strong enough for them to become exactly like wolves within a few months of having to find their own food and that all 'pure' breeds would disappear very quickly once they had to fight for the fertile females and they'd be feral because of having to fight for food within weeks. Anyone who's ever seen a litter of puppies scrapping over a bowl of food would understand that.

And yet if humans disappeared those two breeds would not be able to interbreed. Of course it wouldn't matter as they could breed with their neightbours on the size scale and those differences would even out.

But a feral Great Dane and a feral Chihuahua (there's a scary thought!) would not interbreed.

cursuswalker wrote:And yet if humans disappeared those two breeds would not be able to interbreed. Of course it wouldn't matter as they could breed with their neightbours on the size scale and those differences would even out.

But a feral Great Dane and a feral Chihuahua (there's a scary thought!) would not interbreed.

What I find interesting is that morphological differences was a barrier to natural breeding far faster than genetic differences.

Spearthrower wrote:

Segundo wrote:
Relatedly, I have come across people who think zoological classification is "wrong" and that species are "human inventions" because ring species exist and I think these people are badly mistaken.

I don't think that species are a human invention because of ring species, but they most certainly are a 'human invention' in the sense that they are a means of drawing lines in nature where lines do not exist. A species is a population at a point in time. All individuals could breed with their parent's generation back forever, so we are the ones who decide, based on morphological characteristics, what one species is and what another is. That doesn't make it 'wrong', but people should be aware of the way a species is constructed.

It as though you are putting two species concepts together there. If you consider only contemporaneous populations then species are discrete populations (in their idealized form) and not a human invention. If considering lineages over deep-time then things change, and in that case I would accept that the concept of the species is a little artificial.

EDIT: Populations which have a zero tendency to out-breed are real and not human inventions.

Segundo wrote:

Spearthrower wrote:

Segundo wrote:
Relatedly, I have come across people who think zoological classification is "wrong" and that species are "human inventions" because ring species exist and I think these people are badly mistaken.

I don't think that species are a human invention because of ring species, but they most certainly are a 'human invention' in the sense that they are a means of drawing lines in nature where lines do not exist. A species is a population at a point in time. All individuals could breed with their parent's generation back forever, so we are the ones who decide, based on morphological characteristics, what one species is and what another is. That doesn't make it 'wrong', but people should be aware of the way a species is constructed.

It as though you are putting two species concepts together there. If you consider only contemporaneous populations then species are discrete populations (in their idealized form) and not a human invention. If considering lineages over deep-time then things change, and in that case I would accept that the concept of the species is a little artificial.

EDIT: Populations which have a zero tendency to out-breed are real and not human inventions.

Your last sentence was the point I was making - we chop them arbitrarily based on a schematic that is a product of the way our mind works, not the way nature works - that doesn't eliminate its usefulness. Also, in your edit you have adopted 'populations', which are certainly real things.

cursuswalker wrote:And yet if humans disappeared those two breeds would not be able to interbreed. Of course it wouldn't matter as they could breed with their neightbours on the size scale and those differences would even out.

But a feral Great Dane and a feral Chihuahua (there's a scary thought!) would not interbreed.

The feral Chihuahua might not partake in your disbelief!

Oh, and this is a rather explicit example of what I was talking about earlier! Anyone who has a taboo about watching inter-specie sex, avert your eyes!

[youtube]http://www.youtube.com/watch?v=3TmSwF0mejg[/youtube]

The title really should read: Tiger TRIES to mate with dog, dog too sleepy to perform.

Amazing that the tiger doesn't try to eat the dog.

I had two Maltese once when my cats were in season, they tried to do the cats, the kids thought that was funny.

Since the discussion centered on dogs so much, the following was posted a couple of months ago and is very relevant. If you have little time, skip to the last couple of paragraphs describing what stray dogs in Moscow are evolving into.

http://observationsofanerd.blogspot.com/2010/01/evolution-curious-case-of-dogs.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+observationsofanerd+(Observations+of+a+Nerd)&utm_content=Google+Reader

cakrit wrote:Since the discussion centered on dogs so much, the following was posted a couple of months ago and is very relevant. If you have little time, skip to the last couple of paragraphs describing what stray dogs in Moscow are evolving into.

http://observationsofanerd.blogspot.com/2010/01/evolution-curious-case-of-dogs.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+observationsofanerd+(Observations+of+a+Nerd)&utm_content=Google+Reader

That is so interesting, thanks.