Speciation - what exactly is it?

[shadron]

I am a bit of a dilettante in biology. I've read Asimov in my earlier years, watched innumerable videos by Ken Miller, Aron Ra, cdk007, and others, and read lots of articles. I'd like to find out whether my notion about speciation is correct.

Species are usually defined as groups of animals who can interbreed and produce potent offspring. At the chromosome level, I presume it means that no critical genes have moved their site from one place to another on the chromosomes, and chromosomes have neither fused nor split apart. It seems to me that simple movement of a gene site would not itself be a problem, since it likely doesn't make much functional difference where on a chromosome a gene is located, but that gene shuffling between the mother's and father's chromosomes would make a hash of genes which have moved sites, rendering the proteins created from those sites to be inappropriate for the jobs they were intended to fulfill, and rendering offspring unviable, or at a minimum, sterile (what exactly is the mechanism for that, and why should it seem to be the result of a "close" match, BTW?).

Is there any good materials on the internet that explain how speciation occurs at the genetic level? Thanks for your help.

[kuroyume0161]

I'm no biology expert either, just a bit well read in the evolution/creationist debate. Speciation is defined about as you suggest - when two closely related organisms can no longer procreate in order to create viable offspring. I'd start with talkorigins.com and see what they provide (usually good general to very specific material is provided).

As an offshoot to the topic, speciation is such a vague term (as is species and all of the categorization). What made me think about this is that when one considers when the 'first' human appeared one is a bit confounded. If there was a 'first' human, with whom did it mate to make the next human? In other words, the species drift (ecological or geologic separation) is within the so-called species that is drifting. There was no 'first' human. There was just a set of hominids which procreated towards our line of animals distinctly from other hominids. In other words, which came first, the chicken or the egg? Neither. :)

[shadron]

As an offshoot to the topic, speciation is such a vague term (as is species and all of the categorization). What made me think about this is that when one considers when the 'first' human appeared one is a bit confounded. If there was a 'first' human, with whom did it mate to make the next human? In other words, the species drift (ecological or geologic separation) is within the so-called species that is drifting. There was no 'first' human. There was just a set of hominids which procreated towards our line of animals distinctly from other hominids. In other words, which came first, the chicken or the egg? Neither. :)

As for that, what I understand is that you have mutations happening all the time - up to 150 heritable ones in an average human's life, if I understood what I was reading properly. Most, of course, occur in junk DNA, or they are transpositions in real DNA that do not affect the active locations on the proteins that the gene codes for, or they don't change the triggering of other genes. These are neutral markers. Then there are the ones that will change an active area on a protein, or cause the protein to be truncated leaving the active area unattainable. These would usually be debilitating, depending on how necessary to vital function the protein is, but occasionally they will change the protein in such a way as to make it more useful to the animal, say, by acting with the HOX genes to change its skin camouflage.

So, any subpopulation of a species will simultaneously have any number of ongoing neutral or positive mutations. The positive ones will propagate through the subgroup, carrying along others with it, including those which are gene transpositions/splits/merges. If they, together, overtake and replace the subgroups existing genetics, then the subgroup will become a separate species. My 2 cents worth, anyway.

The skepticwiki (due to the writing efforts of Dr A) discuss this to some extent, but I haven't actually found anything that directly addresses either my question or yours. TalkOrigins also has some info, but not detailed enough for what I want.

[Raze]

Is there any good materials on the internet that explain how speciation occurs at the genetic level? Thanks for your help.

I do not believe so, since species are not defined on the genetic level in the first place. Furthermore, no species is ever static anyway. Things are always changing in the long run.

[Dogdoctor]

I would say species (as far as animals are concerned) are populations of animals who do interbreed. Geographical separation is probably the start of a new species. Within that population is a wide variety of genes not shared by each individual. These genes can have a positive negative or neutral effect on the animals with them. If there is sufficient pressure on a species then the percentage of the various genes that survive are not the same as those present before and if enough pressure is put on the group it changes enough to be called a new species (or the group may die off and become extinct). The exact point that a new species develops is debatable since this happens over long periods of time.

[Eos of the Eons]

Most biologists basically accept the biological species concept, but argue that it is really an idealized concept, since only rarely is an actual test for reproductive compatibility performed. Thus, in practice, nearly all biologists think of species as morphologically distinct groups of organisms.

Taxonomy - Definition Of Species http://science.jrank.org/pages/6703/Taxonomy-Definition-species.html#ixzz0Zob1rWUa


a branch of biology that deals with the form and structure of animals and plants
http://www.merriam-webster.com/dictionary/morphology


http://www.talkorigins.org/faqs/faq-speciation.html


On a genetic level, if the gonad gene counts differ, then no offspring can even start. http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

If they are too different on a genetic level, then the sex cells won't ever get together, so to speak.

[shadron]

Oh, Eos, I completely agree that the definition for speciation that I gave is only one of several, and that they are all vague in that they either allow what is graded by biologists as separate species to be one, and vice versa. Furthermore, as noted in http://skepticwiki.org/index.php/Species , species aren't even transitive (A can mate with B, B can mate with C, does not imply A can mate with C).

On a genetic level, if the gonad gene counts differ, then no offspring can even start. http://en.wikipedia.org/wiki/List_of_organisms_by_chromosome_count

If they are too different on a genetic level, then the sex cells won't ever get together, so to speak.

So it's strictly a matter of behavior and gross anatomy? You could, artificially, join human and chimpanzee and get a viable offspring? After all, Leakey says there is less difference between a human and a chimp than between a horse and an ass.

[kuroyume0161]

As for that, what I understand is that you have mutations happening all the time - up to 150 heritable ones in an average human's life, if I understood what I was reading properly. Most, of course, occur in junk DNA, or they are transpositions in real DNA that do not affect the active locations on the proteins that the gene codes for, or they don't change the triggering of other genes. These are neutral markers. Then there are the ones that will change an active area on a protein, or cause the protein to be truncated leaving the active area unattainable. These would usually be debilitating, depending on how necessary to vital function the protein is, but occasionally they will change the protein in such a way as to make it more useful to the animal, say, by acting with the HOX genes to change its skin camouflage.

So, any subpopulation of a species will simultaneously have any number of ongoing neutral or positive mutations. The positive ones will propagate through the subgroup, carrying along others with it, including those which are gene transpositions/splits/merges. If they, together, overtake and replace the subgroups existing genetics, then the subgroup will become a separate species. My 2 cents worth, anyway.

The skepticwiki (due to the writing efforts of Dr A) discuss this to some extent, but I haven't actually found anything that directly addresses either my question or yours. TalkOrigins also has some info, but not detailed enough for what I want.

A bit more explanatory than I could provide offhand, but yes. Any populations that are mating and producing viable offspring have variations in these offspring (mutations and variant combinations) which have variable success rates of procreation themselves (with a dab of 'bad luck' spread amongst all of them). Many archaeologists talk about this first step towards human or that (Lucy et al). Although they most likely understand this as more of a representative of a diverse population with many individuals all stepping towards 'human' (and others not), the popular portrayal can be misleading so as to say that Lucy was the first and only proto-human at this stage (which is bullocks obviously). The adaptations will be shared generation to generation so that the gene pool is slowly acquiring the successful adaptations and adding new ones. As Raze said, there is no static species (at least at the genomic level - maybe in a gross categorization level). And species individuals are not clones - they are variations on a theme which is slowly changing over time*.

*I'll put a word in about Gould's punctuated equilibrium hypothesis as a possibly good explanation for quicker changes over time under periods of environmental duress.

[shadron]

I do not believe so, since species are not defined on the genetic level in the first place. Furthermore, no species is ever static anyway. Things are always changing in the long run.

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

[biomorph]

I'm no biology expert either, just a bit well read in the evolution/creationist debate. Speciation is defined about as you suggest - when two closely related organisms can no longer procreate in order to create viable offspring. I'd start with talkorigins.com and see what they provide (usually good general to very specific material is provided).

Good advice.



As an offshoot to the topic, speciation is such a vague term (as is species and all of the categorization).

I'm not sure were the vagueness is in can or can't breed, providing of course that "breeding" is involved.

Mules come to mind.

What made me think about this is that when one considers when the 'first' human appeared one is a bit confounded. If there was a 'first' human, with whom did it mate to make the next human?


Sort of.

common ancestry means some species at some time was the common ancester.

I think if you define "human" there's your answer.


In other words, the species drift (ecological or geologic separation) is within the so-called species that is drifting.

Can be, however geo/eco seperation has to prevent breeding to effectively get speciation.

Drift within an active population occurs, sure, without eco/geo seperation but the species still breeds. In fact there's no drift without it.

Seperation can take other forms, too maybe. social, tribal, etc. However hypothetically the next valley might be enough, given a few generarions. You might not get speciation in a linear manner, either. I',m not entirely sure its a one way street all the time.



There was no 'first' human.

see above

There was just a set of hominids which procreated towards our line of animals distinctly from other hominids. In other words, which came first, the chicken or the egg? Neither. :)

The egg. Maybe your question is rhetorical,:p

the common ancestor, but "first", well, first of what?

Look, the word "human" includes a set of definitions you have about a set of animals which is us..

I'm not saying humans cannot perhaps be uniquely defined, whoever I consider the line one draws where you consider "human" or not, to be perhaps more flexible maybe?

[biomorph]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

I'd agree, tho I guess its just the reproductive system that needs to work.

I guess the genetic mutation might not have to be much.

Just enough.

i think the breeding habits of ducks, (i think?) outline this well, from memory.

[Eos of the Eons]

Oh, Eos, I completely agree that the definition for speciation that I gave is only one of several, and that they are all vague in that they either allow what is graded by biologists as separate species to be one, and vice versa. Furthermore, as noted in http://skepticwiki.org/index.php/Species , species aren't even transitive (A can mate with B, B can mate with C, does not imply A can mate with C).



So it's strictly a matter of behavior and gross anatomy? You could, artificially, join human and chimpanzee and get a viable offspring? After all, Leakey says there is less difference between a human and a chimp than between a horse and an ass.

Um... Most separate species can't produce offspring via mating anymore, and I just posted the reason why. The main reason is that they are too different genetically anymore. The very definition of a species is that animals have enough different traits to make them separate from one another, and then on a genetic level (at their gametes) they are even too different to produce offspring anymore.

Having to artificially join animals to produce offspring is just more evidence of how different they are.


The process of becoming different is called speciation. You had one interbreeding population at one point. Then some animals got separated. Over time traits that allowed for survival become more and more dominant compared to the original population generations ago. One group has these traits over time, and the other has those. Both have changed over time, enough so that they can't even breed any longer. It's genetics, at the base level, and then we see the traits that are a result of those genes.

[kuroyume0161]

Good advice.

Thanks. :D

I'm not sure were the vagueness is in can or can't breed, providing of course that "breeding" is involved.

Mules come to mind.Definitely. But there are some cases of designation wherein we are just guessing - mainly with extinct 'species' since we cannot observe them engaging in "breeding". I think that my mistake here is in using 'speciation' which is more well-defined (esp. for extant lifeforms) when 'species' isn't (esp. when including non-extant lifeforms).

Sort of.

common ancestry means some species at some time was the common ancester.

I think if you define "human" there's your answer.

What I mean is that there was probably some distinct population from which we evolved, not a single individual in particular. I cannot imagine a single individual within a population being so isolated or the opposite (spreading all of its genes to all members of the population which would lead to homo sapiens sapiens). It is more likely that these genes and others were combined and recombined with others so that the population was generally evolving towards humans rather than a string of singular ancestors. We certainly do not see humans procreating so as to preserve a single ancestral lineage but rather a continual ad hoc mixture.

Can be, however geo/eco seperation has to prevent breeding to effectively get speciation.

Drift within an active population occurs, sure, without eco/geo seperation but the species still breeds. In fact there's no drift without it.

Seperation can take other forms, too maybe. social, tribal, etc. However hypothetically the next valley might be enough, given a few generarions. You might not get speciation in a linear manner, either. I',m not entirely sure its a one way street all the time.

I guess my point is that the drift starts and continues once two groups are separated (in some way) so that they are no longer inter-procreating. One group is going to favor variations that are advantageous to their circumstances while another is going to favor different variations advantageous to their circumstances. The common idea of hominid speciation is the rift valley where the group on one side of the rift drifted one way whereas the group on the other side drifted in another way. Whether the drift occurs in both groups or just one group probably depends upon the need for adaptation. Either way, the group that is adapting is drifting (or both are drifting because both are adapting from previously conducive conditions when they were not separated).

The egg. Maybe your question is rhetorical,:p

the common ancestor, but "first", well, first of what?

Look, the word "human" includes a set of definitions you have about a set of animals which is us..

I'm not saying humans cannot perhaps be uniquely defined, whoever I consider the line one draws where you consider "human" or not, to be perhaps more flexible maybe?

That's my point. There was no 'first chicken' (or 'first egg') unless one can define a chicken so precisely - but then does that definition include all animals that we designate as chickens. One can probably define all chickens due to their now spacious species gap to other relative. But at some time there was a set of avians which weren't chickens. Some may have become turkeys or pheasants or peacocks but there would have been a blurry time where the groups were not yet distinct yet 'speciating'. This is my point about a 'first human'. Speciation is a process - and not one where one day you have hominid A and the next you have hominid B. I hope that is vaguely clear. :)

[William Parcher]

Both have changed over time, enough so that they can't even breed any longer.

That is a recurring theme in this thread but there is another way to look at species. Rather than say this animal and that animal can't breed - instead it is often more practical to say that this animal and that animal do not breed. The distinction is that the former suggests attempts with futility, while the latter refers to no attempts at all. This is what really happens in nature. The speciation causes animals to be reproductively incompatible before the point of copulation. Their appearance and behavior keeps them from even trying when and if they encounter each other. It's not foolproof but it is what has allowed scientists to differentiate species long before modern genetics. Otherwise we might be inclined to artificially mate every animal with every other animal to see what happens in order to decide what species is what.

Having strict rules about can't breed gets complicated because we have set up situations where what are considered separate species do breed and produce viable offspring. We can't rightfully force ourselves to declare them the same species because these animals do not breed in nature.

Well, maybe that's all I can add to the conversation. I understand that there is more than one definition of species and speciation.

[kuroyume0161]

That is a recurring theme in this thread but there is another way to look at species. Rather than say this animal and that animal can't breed - instead it is often more practical to say that this animal and that animal do not breed. The distinction is that the former suggests attempts with futility, while the latter refers to no attempts at all. This is what really happens in nature. The speciation causes animals to be reproductively incompatible before the point of copulation. Their appearance and behavior keeps them from even trying when and if they encounter each other. It's not foolproof but it is what has allowed scientists to differentiate species long before modern genetics. Otherwise we might be inclined to artificially mate every animal with every other animal to see what happens in order to decide what species is what.

Having strict rules about can't breed gets complicated because we have set up situations where what are considered separate species do breed and produce viable offspring. We can't rightfully force ourselves to declare them the same species because these animals do not breed in nature.

Well, maybe that's all I can add to the conversation. I understand that there is more than one definition of species and speciation.

Well said *and* definitely!

There are two general (and probably artificially categorized) reasons where species do not breed (successfully - as in 'ability to produce viable offspring').

1) Two local but incompatible groups don't breed. As a forced example, snakes and skunks that inhabit the same region. They might try as they may but it is unlikely that it will work in many ways. :)

2) Two groups which were once interbreeding, separated long enough to 'speciate', and then re-integrated into a common region (possibly due to foraging, migration, following prey, etc.).

It is very probable that attempts are made in futility due to differences in sexual organ mechanics, genetics, mating rituals, mating periods (seasonal, solar, lunar, etc.).

Nonetheless, it goes without saying that my original definition stands: procreation without the ability to create viable offspring (minus the 'closely related'). ;)

[William Parcher]

Grey wolves and coyotes can breed and produce fertile hybrid offspring. The thing is, they almost never do this in nature even though they live in the same environment. If we were strict about the can't breed rule - we would have to call them the same species. They are the same genus but different species. They fall under the species concept/definition I mentioned. Besides having distinct morphologic differences, they don't naturally breed with each other in the wild.

[kuroyume0161]

Grey wolves and coyotes can breed and produce fertile hybrid offspring. The thing is, they almost never do this in nature even though they live in the same environment. If we were strict about the can't breed rule - we would have to call them the same species. They are the same genus but different species. They fall under the species concept/definition I mentioned. Besides having distinct morphologic differences, they don't naturally breed with each other in the wild.

Horses and donkeys were mentioned. These are two clearly different species. Yet when they are 'artificially' bred we have viable offspring we call 'mules' (which are infertile! which bespeaks a particular issue of 'viability'). So, yes, there is something to be said about the ability of two species to create viable offspring but it seems to be rare. What can we say about this in respect to the definition of species (since you have removed 'can't reproduce' and 'don't reproduce')? :D

[Raze]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

If so that is coincidence. Species were originally defined by morphological similarities and the ability to breed. Over the long haul what is there that really differentiates species? It's simply a human convention based entirely on human time scales.

Tigers and Lions can breed, but they are defined as different species.

Further, what about ring species?


The point being that differentiation by species is a completely human convention that only approximates what is going on in nature, mainly because human beings define things like species based upon things that are familiar and easily quantifiable by them. Species were defined long before genetics were even known about, so IF there is ONE exact genetic reason (which I find unlikely), we'd have to change our definition of species anyway.

But that's me, what can I say?

[William Parcher]

There is some interesting reading at the Wiki page on species (http://en.wikipedia.org/wiki/Species).


It is surprisingly difficult to define the word "species" in a way that applies to all naturally occurring organisms, and the debate among biologists about how to define "species" and how to identify actual species is called the species problem.

Most textbooks follow Ernst Mayr's definition of a species as "groups of actually or potentially interbreeding natural populations, which are reproductively isolated from other such groups".

Various parts of this definition serve to exclude some unusual or artificial matings:

* Those which occur only in captivity (when the animal's normal mating partners may not be available) or as a result of deliberate human action.

* Animals which may be physically and physiologically capable of mating but do not normally do so in the wild, for various reasons.

* Animals whose offspring are normally sterile.

It is Mayr's "biological species concept" that I was trying to describe in my posts.

[Eos of the Eons]

I didn't mean that 'can't breed' was some rule. They just simply don't have gametes that can mix in any way to produce offspring. Think dogs and cats.

Some still can breed, but viable offspring that can have offspring themselves is doubtful (mules).

Grey wolves and coyotes can breed and produce fertile hybrid offspring

Cool.

All in all, my point though, was that everything is genetically determined, and species are classified by traits that are genetically determined. Genes are involved whether a different species can breed or not.

[shadron]

I found a page that I think answers the question that I posed in the OP, its in Understanding Evolution: History, Theory, Evidence, and Implications by R. G. Price:

http://www.rationalrevolution.net/articles/understanding_evolution.htm

The answer is that I was right, and Eos was right and William Parcher and Kuroyume and Raze and Biomorph are all right. It makes the following points:

- Linnaean species is a wrong concept and should be shelved, but is, unfortunately so woven into biology that such an excision will be very traumatic.
- Biological species are different from Linnaean; too bad they share the same word. This definition is much better but still has problems of ambiguity, transposition and attempting in general to make a gray situation black and white.
- Boundaries separating interspecies breeding include:
Pre-mating boundaries:


Geographic isolation
Mating preferences (organisms choose mates based on certain characteristics, such as color, song, size, smell, etc.)
Physical incompatibility of sex organs (penis does not pair with vagina, etc.)
Different mating schedules (different timed release of gametes among things like corals, plants, etc.)

Post-mating boundaries include:


Different numbers of chromosomes
DNA from one parent is not able to fully pair with other parent DNA during fertilization and mitosis

The article is much, much longer than just this one small section ("Species and Speciation"), and it has a ton of biology in it, easily enough, I think, for a 3 sem-hour college course on evolution, and may well be just that. I plan to take a week or so to look through it thoroughly. There are some spectacular (and gruesome) photos and lots of discussion in areas such as religion, social darwinism and creationist trickery.

I found it, BTW, from one of Dr. Adequate's skepticwiki pages, so thanks for that, Dr. A.

Appropos to the last few postings, look up also the Cama, a cross between a llama and a dromedary camel.

[Taffer]

I am a bit of a dilettante in biology. I've read Asimov in my earlier years, watched innumerable videos by Ken Miller, Aron Ra, cdk007, and others, and read lots of articles. I'd like to find out whether my notion about speciation is correct.

Species are usually defined as groups of animals who can interbreed and produce potent offspring. At the chromosome level, I presume it means that no critical genes have moved their site from one place to another on the chromosomes, and chromosomes have neither fused nor split apart. It seems to me that simple movement of a gene site would not itself be a problem, since it likely doesn't make much functional difference where on a chromosome a gene is located, but that gene shuffling between the mother's and father's chromosomes would make a hash of genes which have moved sites, rendering the proteins created from those sites to be inappropriate for the jobs they were intended to fulfill, and rendering offspring unviable, or at a minimum, sterile (what exactly is the mechanism for that, and why should it seem to be the result of a "close" match, BTW?).

Is there any good materials on the internet that explain how speciation occurs at the genetic level? Thanks for your help.

The issue is that the concept of a species in biology is an artificial category which often fits, but doesn't always. Things are easy when we deal with fairly large animals, but start looking at bacteria and plants, for example, and things start to become slightly more arbitrary.

A perfect example: A native New Zealand bird, the Black Stilt (Himantopus novaezelandiae) is taxonomically a separate species from the Pied Stilt (H. himantopus), but readily hybridizes with it to such an extent that this behaviour is threatening the black stilt's existence. Should we consider them a single species, or two separate species?
Another example is that of the mule, wherein sometimes female offspring of a male horse and a female donkey can, rarely, be fertile. Are they different species most of the time? All of the time. Never?

While the above examples are not the most controversial (both are explained by a species definition which simply states that most offspring be infertile), you get the idea.

Concerning the genetic modes of speciation, there is more to it than chromosomal number, etc. You mention that a gene's location should have no affect, but quite the contrary. The human genome, for example, has recently (http://www.sciencedaily.com/releases/2009/10/091008142957.htm) been shown to be fractaline in nature. In this case, the physical location of a gene can directly affect its regulation. Not to forget the affects of epigenetics (http://en.wikipedia.org/wiki/Epigenetics), in which genomic imprinting (http://en.wikipedia.org/wiki/Genomic_imprinting) directly affects the viability of the offspring.

Basically, biology, and genetics in particular, are really complicated. :)

[biomorph]

The issue is that the concept of a species in biology is an artificial category which often fits, but doesn't always.

I'm having problems with your "artificial" tag.

Although there are what appear to be exceptions, I venture to say that the emergence, divergence and perhaps convergence of the non breeders perhaps brings about some crossbreds, occasionally that might be fertile for some generations too.

Probably over a more extended period, for example the drift of diverging breeds, within species, that are "close enough" to bear viable future generations of offspring
might be seen to be actually diverging. Or not.

Things are easy when we deal with fairly large animals, but start looking at bacteria and plants, for example, and things start to become slightly more arbitrary.



I'm not sure about that.

Maybe.

.

A perfect example: A native New Zealand bird, the Black Stilt (Himantopus novaezelandiae) is taxonomically a separate species from the Pied Stilt (H. himantopus), but readily hybridizes with it to such an extent that this behaviour is threatening the black stilt's existence.

that's not a plant, or bacteria. ahem...

See above re divergence , convergence etc. maybe


Should we consider them a single species, or two separate species?

Well, for this case measure the drift in the breeding pairs over enough time, and eventually you might see a drift, one way or another. There might be a very long period of stasis even, if conditions permit.




Another example is that of the mule, wherein sometimes female offspring of a male horse and a female donkey can, rarely, be fertile. Are they different species most of the time? All of the time. Never?


See above

While the above examples are not the most controversial (both are explained by a species definition which simply states that most offspring be infertile), you get the idea.

Yup, did I make sense, ? am wrong?


Concerning the genetic modes of speciation, there is more to it than chromosomal number, etc. You mention that a gene's location should have no affect, but quite the contrary. The human genome, for example, has recently (http://www.sciencedaily.com/releases/2009/10/091008142957.htm) been shown to be fractaline in nature. In this case, the physical location of a gene can directly affect its regulation. Not to forget the affects of epigenetics (http://en.wikipedia.org/wiki/Epigenetics), in which genomic imprinting (http://en.wikipedia.org/wiki/Genomic_imprinting) directly affects the viability of the offspring.

Basically, biology, and genetics in particular, are really complicated. :)

Yup, that is true.

several billion years of time to get that way, eventually..lol

[biomorph]

I found a page that I think answers the question that I posed in the OP, its in Understanding Evolution: History, Theory, Evidence, and Implications by R. G. Price:

http://www.rationalrevolution.net/articles/understanding_evolution.htm

The answer is that I was right, and Eos was right and William Parcher and Kuroyume and Raze and Biomorph are all right. It makes the following points:

- Linnaean species is a wrong concept and should be shelved, but is, unfortunately so woven into biology that such an excision will be very traumatic.

Yes, I'd agree, but the truth is worth the trauma, this science after all.



- Biological species are different from Linnaean; too bad they share the same word. This definition is much better but still has problems of ambiguity, transposition and attempting in general to make a gray situation black and white.

Yes. it's hard.

- Boundaries separating interspecies breeding include:
Pre-mating boundaries:


Geographic isolation
Mating preferences (organisms choose mates based on certain characteristics, such as color, song, size, smell, etc.)
Physical incompatibility of sex organs (penis does not pair with vagina, etc.)
Different mating schedules (different timed release of gametes among things like corals, plants, etc.)

Post-mating boundaries include:


Different numbers of chromosomes
DNA from one parent is not able to fully pair with other parent DNA during fertilization and mitosis

The article is much, much longer than just this one small section ("Species and Speciation"), and it has a ton of biology in it, easily enough, I think, for a 3 sem-hour college course on evolution, and may well be just that.

Um, yup. don't ask.....

I plan to take a week or so to look through it thoroughly. There are some spectacular (and gruesome) photos and lots of discussion in areas such as religion, social darwinism and creationist trickery.

I found it, BTW, from one of Dr. Adequate's skepticwiki pages, so thanks for that, Dr. A.


Dr A is a star...as usual


Appropos to the last few postings, look up also the Cama, a cross between a llama and a dromedary camel.

I will, however timespan is relevant.

As you rightly state, and can be observed often with reality, boundary conditions are the mother of invention.

See chaos theory for example maybe.

glad to have been of help, even if only a little.

[Taffer]

I'm having problems with your "artificial" tag.

Why?

Although there are what appear to be exceptions, I venture to say that the emergence, divergence and perhaps convergence of the non breeders perhaps brings about some crossbreds, occasionally that might be fertile for some generations too.

Probably over a more extended period, for example the drift of diverging breeds, within species, that are "close enough" to bear viable future generations of offspring
might be seen to be actually diverging. Or not.

I have to admit, I have no idea what you're saying. If you're saying that sometimes related species can breed and sometimes they can produce fertile, then I agree.

I'm not sure about that.

Maybe.

.

When bacteria can gather DNA from completely unrelated species, and when they do not reproduce sexually, it becomes difficult to rely on our limited definition of species.

that's not a plant, or bacteria. ahem...

See above re divergence , convergence etc. maybe

What? It doesn't matter how this came about, only that the phenomenon exists, and it challenges the traditional view of a species.

Well, for this case measure the drift in the breeding pairs over enough time, and eventually you might see a drift, one way or another. There might be a very long period of stasis even, if conditions permit.

I am beginning to see the problem is one of language. In evolutionary biology, drift refers to genetic drift, not a change in relatedness between two species. Also, divergence and convergence are related to evolution, in the latter case specifically the evolution of the same phenotype by unrelated species.

See above

Yup, did I make sense, ? am wrong?

My point was not to post concrete proof that species do not exist, only to point out that certain phenomena can challenge the traditional species characterization. I even admitted as much, by giving a possible explanation for the very phenomena I presented as examples.

[biomorph]

Why?

Hard to say....but no big deal..:)


I have to admit, I have no idea what you're saying. If you're saying that sometimes related species can breed and sometimes they can produce fertile, then I agree.


Yes, my point being that at the boundary of interspecies breeding fitness, is where I think most of the few exceptions occur.

I'm postulating some speculative reasons for these uncommon, perhaps what appear to be violations of a real definition of a species.

i'm probably not making that clear., perhaps it is irrelevant to this discussion.




When bacteria can gather DNA from completely unrelated species, and when they do not reproduce sexually, it becomes difficult to rely on our limited definition of species.


Yes. I agree.


What? It doesn't matter how this came about, only that the phenomenon exists, and it challenges the traditional view of a species.



Sorry, I've got the perspective that it adds to the "traditional" view, I guess...


I am beginning to see the problem is one of language. In evolutionary biology, drift refers to genetic drift, not a change in relatedness between two species.


yes, if you like, I can go with that,.

However genetic drift is a driver for the (divergence etc) in the two species you mention isn't it?

Also, divergence and convergence are related to evolution, in the latter case specifically the evolution of the same phenotype by unrelated species.

OK


My point was not to post concrete proof that species do not exist, only to point out that certain phenomena can challenge the traditional species characterization. I even admitted as much, by giving a possible explanation for the very phenomena I presented as examples.

You did, I merely tried to find where those challenges occurred, and if there were perhaps, in an evolved system of divergence, special conditions. I think that perhaps there are.

I think you have raised some interesting points, tho.

It is a very interesting subject..:)

[Taffer]

Yes, my point being that at the boundary of interspecies breeding fitness, is where I think most of the few exceptions occur.

Which is exactly my point. You cannot have clear categories without clear boundaries. The broad view is one of discrete species, but upon close examination there is a lot of grey in a world we would all prefer to be black-and-white.

I'm postulating some speculative reasons for these uncommon, perhaps what appear to be violations of a real definition of a species.

There is no "real" definition of species, because species is just a word, made up by humans. It is a category imposed on a area which is not discrete, but is a spectrum.

Think of the colours of the rainbow. There is a clear difference between blue and green, but it is impossible to find the exact border where blue stops being blue, and starts being green. This is like species in nature. The broad view allows for clear divisions, species, genera, etc, but it is at the boundaries where the natural system shows that it is a spectrum of relatedness.

However genetic drift is a driver for the (divergence etc) in the two species you mention isn't it?

No. Genetic Drift (http://en.wikipedia.org/wiki/Genetic_drift) refers to the change in allele frequency in a population over time due to random chance and sampling bias. Genetic drift does drive evolution, but it is not sufficient by itself for evolution to occur in a sufficiently large population. Selection is still required; genetic drift may influence speciation in an isolated population with no migration, however.

You did, I merely tried to find where those challenges occurred, and if there were perhaps, in an evolved system of divergence, special conditions. I think that perhaps there are.

The issue is not if there are special conditions, but that it exists at all. If the traditional distinction of a species truly reflects relatedness in nature, than these situations would never happen.

It is a very interesting subject..:)

Agreed!

[blutoski]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.

Usually. But sometimes they don't interbreed because of geographic isolation.

The species may be able to produce viable offspring if they meet, say, in a zoo or on an ethnocline. (eg: tigers and lions are seperate species from India and Africa respectively, but may interbreed in the Middle East or in the Bronx zoo)


The definition of species is a human system. Like the definition of a planet. Pluto is what it is, and tigers are what they are. How they categorize is up to us.

[blutoski]

All in all, my point though, was that everything is genetically determined, and species are classified by traits that are genetically determined. Genes are involved whether a different species can breed or not.

Ultimately, but genetic differences don't always mean genetic incompatability.

Another example is birds that live in different parts of a tree (high vs low branches, or trunkward vs perimiter). They don't breed with those who live in a different part of the tree.

However, if you move them to an environment with no tree, they interbreed without complaint.

The genetic difference only manifests a speciation in certain environments. In other environments, they could be considered the same species. In this case, genetic difference is necessary but insufficient.

Alternatively, if the only reason for distinction is geographic separation, there is no genetic difference, so it's not even necessary for these limited cases.

[Mojo]

It seems to me that if there is such a thing as a species, and the normally they cannot breed together, then there must be some fundamental (genetic?) reason for it.


Basically just that they are not genetically similar enough to be able to interbreed. All this is a bit circular, because the basic definition (or at least, one basic definition) of a species is a group of organisms that can successfully interbreed.

But the term "species" is a bit nebulous. What we see today as "species" are a snapshot of a population. If we were to come back in a few million years we might well see populations descended from current species that wiould qualify as a new species, but it would never be possible to pinpoint exactly when one species became another.

ETA: check out "ring species".

[kuroyume0161]

Basically just that they are not genetically similar enough to be able to interbreed. All this is a bit circular, because the basic definition (or at least, one basic definition) of a species is a group of organisms that can successfully interbreed.

But the term "species" is a bit nebulous. What we see today as "species" are a snapshot of a population. If we were to come back in a few million years we might well see populations descended from current species that would qualify as a new species, but it would never be possible to pinpoint exactly when one species became another.

ETA: check out "ring species".

Exactly my point about 'first human'. Apply what you said about 'coming back in a few million years...it would never be possible to pinpoint exactly when one species became another' to what I said about hominid speciation towards humans.

There seem to be two types of species designation here:

1) These are the categories that we use to deem individual species at this point in time - current extant biological organisms.

2) These are the categories that we deem individual species in evolutionary terms - extinct or ancestral organisms only evident from fossils.

The first is a bit more 'black and white' (and even then, not really). The second is just opening a can of worms - especially when one is attempting to delineate species in discrete ways under conditions of evolution and speciation which are not discrete. In other words, taking a snapshot makes it easy to employ our categorization system. But when trying to use it over a very long time period of changing organisms, it pretty much fails - not totally, but there are great rents in its applicability. Even Paleontologists still argue over which cladistic representations best represent classification and relationship: monophyletic, paraphyletic, or polyphyletic - and how they should be employed.