Discussion of everything related to the Theory of Evolution.
I've been following the ongoing debate about evolution and, just for the record, would like a simple matter cleared up: if a Great Dane and a Chihuahua were crossed (obviously artificially using IVF, and the resulting embryo placed in the Great Dane bitch for the bitch's comfort) would healthy viable pups result ? If the answer is affirmative then we would be able to say that even though the parents are so dissimilar looking they are really the same species, and that 10,000 years of artificial breeding has not changed the genome; surely this would be of some interest in the discussions about evolution. Natural variation within a species is utilised by three selection agencies (artificial, natural and sexual) to produce individuals that certainly appear to be different; but if they still remain a member of the same breeding pool in what sense have they evolved ? A follow up question would be: It is said that species B has evolved from species A and it is observed that members of the two species do not breed together. Can anyone give real names for A and B and assert that there are no intermediate species, i.e. B has evolved directly from A in one step ?
Yeah, the pups would be viable you don't even need to do some work about that, just keep dogs together...
Maybe that's why they are different breed and not species.
The evolution does not occur in jumps, there are small changes, which, if given chance and accumulate may result either into brand new species or into evolved species...
Cis or trans? That's what matters.
This is an interesting topic in many ways. Wolf and dog can breed and have non-sterile offspring, yet they are considered different species. With the humans' apparently limitless desire to produce odd dog breeds (like chihuahua), I wouldn't be all that surprised if soon different dog breeds were further apart from one another than from a wolf...
As a curious side-note, it is funny how many people find genetic engineering wrong, yet it's completely ok to produce dog mutants that have dozens of genetic illnesses and disfigured appearances and such. Just think of pugs with their eye and respiratory problems, German shepherds and their hip problems and all the myriad other conditions dogs have to suffer. But ain't it grand because it's not called genetic engineering!
Thanks Jackbean. I realise Chihuahua's and Great Danes are breeds of dogs. It's just that variation in dog breeds is often used as an example to demonstrate evolution at work when a selection agency (in this case artificial selection) acts on the natural variation within a species. But for all the variation in form they are still the same species and they haven't "evolved", they just represent different expressions of "dogginess"; microevolution if you will rather than macro evolution. Do you know for a fact that viable offspring will result ? What about my follow-up question ?
Hi Biohazard. The books seem to be a little hazy about the exact definition of species. Most use the "same breeding pool" definition but then go on to refer to exceptions such as the wolf / dog example you mention. If we want to affirm that evolution, in the macro "species to species" form, has occurred then it seems to me that an exact definition of species ought to be used.
I don't quite agree :)
The term "species" is man-made, evolution isn't interested in how we label things. Like JackBean said, speciation happens in such small steps that our methods simply are not precise and definitions conclusive enough to allow us to exactly say where one species ends and another begins. Despite this, in most cases we can clearly tell apart different species and where speciation takes or has taken place. These certain "border cases" just make things difficult for people who want to place everything in strict categories.
And remember, dogs and wolves are a piece of cake if you compare them to, say, the microbial world. That's where the term "species" really becomes blurry!
Yeah, biohazard is exactly right.. Species is man-made, and nature doesn't abide by our rules. So when we think we figured out the line that divides species, nature throws us a curveball.
'micro-evolution' to 'macro-evolution' is in essence only a question of scale, and time. This is easily observed in what we call 'ring species'. Where rings of ranges of a particular animal overlap, and interbreeding occurs, we see 'micro-evolution', or little changes in color/body/behaviour. However when you look at rings that are far enough away from each other, the individuals cannot/do not interbreed, thus 'macro-evolution'. (Example : Ensatina escholtzii)
Dog breeds are kind of similar, in that they've been bred to extract, exhibit, or incorporate features from other breeds, yet not enough isolation has occured yet to make them unable to interbreed. Its obvious 'micro-evolution' has taken place in the breeding of the domestic dogs out of wolves. A wolf's skull and brain is significantly larger then a equal-sized dog, the presence of precaudal glands at the base of the tail, and other physical/behavioural differences exist.
The fact they can interbreed also proves they are indeed, by common definition of the word, of the same species. And dogs are often being labeled as a subspecies of the wolf. However the difference between the dog and the wolf is still roughly twice the difference between breeds of the dog, genetically. ("Genome sequence, comparative analysis and haplotype structure of the domestic dog" Nature Journal 2005).
...with a flick of his wrist, the Devil tossed her picture on the stone table, and pointed at her gravestone.. His eyes squinted, glowing redder then coals from Hell's bosom.. He asked "Will you give me your soul, to save hers from damnation?"
biohazard: actually, e.g. here
is dog considered as form of wolf, not different species
WobertWabbit: as has been mentioned, if you gave it enough time (now are some breeds just like hundreds years old), you would end up with different species.
Cis or trans? That's what matters.
That's what I meant: those are just human definitions. Someone classifies wolves as a different species because of the many differences they have and some classify them as the same species with a dog since they can interbreed. Whatever the case, it doesn't change the reality: these two animals are difficult to categorize by our standards.
Yes, apparently somewhere in the 90's dogs were reclassifed as being sub-species of wolves, but that just supports what I tried to say in my previous posts that by stubbornly sticking to the term "species" we get ourselves into trouble. And make the creationists happy...
Last edited by biohazard on Wed Dec 02, 2009 7:34 am, edited 1 time in total.
I would like to point out that according to Mayr's Biological Species defintion, two populations are considered seperate species if they cannot or do not interbreed in the wild. If you had a population of Great Danes and a population of Chihuahuas living on some island, they would have to be considered seperate species according to this defintion because they would not be able to interbreed.
Good that you mentioned this, this is pretty much how I see the current situation with dogs - if the current dog breeds would live in the wild, it would be quite possible that we'd call them separate species instead of breeds.
Here's an example with a fruit fly species:
An experiment demonstrating allopatric speciation in the fruit fly (Drosophila pseudoobscura) conducted by Diane Dodd. A single population of flies was divided into two, with one of the populations fed with starch-based food and the other with maltose-based food. After the populations had diverged over many generations, the groups were again mixed; it was observed that the flies would mate only with others from their adapted population.
http://commons.wikimedia.org/wiki/File: ... iation.svg
Dodd, D.M.B. (1989) "Reproductive isolation as a consequence of adaptive divergence in Drosophila pseudoobscura." Evolution 43:1308–1311.
Here's another with York Groundsel (Senecio eboracensis)
The York groundsel is a natural hybrid between the common groundsel and the Oxford ragwort, which was introduced to Britain from Sicily 300 years ago. Hybrids are normally sterile, and cannot breed and die out.
But Dr Abbott’s research, published in the journal of the Botanical Society of the British Isles, shows that the York Groundsel is a genetic mutant that can breed, but not with any other species, including its parent species. It thus fits the scientific definition of a separate species.
http://www.timesonline.co.uk/tol/news/u ... 884624.ece
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