What is your definition of a species?

[29apples]

This is a more complex question than you think. I think it is very hard to come up with a definition that is practical.

I will start off with an example. So domestic dogs are supposed to be one species, but a great dane and chihuahua cannot hybridize naturally. Are they the same species?

So what do you think?

 

[Pwnzerfaust]

From Wikipedia:

A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring.

I think that's a pretty good basic definition of species, but of course that is hardly sufficient for all cases. Ring species are a favorite example of mine which throw it for a loop. Classification of organisms is certainly anything but straightforward/simple.

 

[Washington]

I will start off with an example. So domestic dogs are supposed to be one species, but a great dane and chihuahua cannot hybridize naturally. Are they the same species?

Not too long ago the American Society of Mammologists reclassified the domestic dog as Canis lupus familiaris (making it a subspecies of wolf). However, I don't believe this reclassification has been universally adopted. Your point about the physical incompatibility among breeds does nothing to the classification because breeds are artificially created variants, and therefore have no bearing on the validity of the species designation. So the great dane and chihuahua most definitely belong to the same species.

I think that's a pretty good basic definition of species, but of course that is hardly sufficient for all cases. Ring species are a favorite example of mine which throw it for a loop. Classification of organisms is certainly anything but straightforward/simple.

That's a pretty dated definition, at least 30-40 years old. Since then many others have been proposed. The one I favor is that of Ernest Mayr who contends a species is a "reproductively isolated aggregate of populations which can interbreed with one another because they share the same isolating mechanisms."
[The Growth of Biological Thought: Diversity, Evolution, and Inheritance (Cambridge, Mass,: Belknap, 1982), 311]

 

[29apples]

^^^ but your criteria fits my example. Being a product of human domestication does not disqualify them from pushing the limits on the definition of a species.

Another fun fact: It is thought that 1/3 of all plants can hybridize with another species (oaks are notorious).

The same is beginning to be thought of animals, although there are far less examples.

 

[CACTUSJACKmankin]

we need to get away from definitions that include sexual reproduction. bacteria & protists & countless asexual organisms need to be included in the definiton of a species. i think that the way around this is a genetic standard, since that is something that can be attributed to any organism. if two populations have so much genetic distance then they are different species. the obvious problem is that it is going to be plagued with being relatively arbitrary. different pairs of organisms may be equidistant genetically to be different species but have the classical signs of being the same species. human definitions and boundaries will never be without exceptions to the rules, there will always be gray areas.

 

[Washington]

^^^ but your criteria fits my example. Being a product of human domestication does not disqualify them from pushing the limits on the definition of a species.

Domestication has nothing to do with the creation of hybrids. It's the taming of wild organisms to suit human purposes.

The same is beginning to be thought of animals, although there are far less examples.

Unless the result is unsterile offspring (both sexes) it isn't meaningful.

 

[29apples]

They do form fertile hybrids. 1/3 of all species can form fertile hybrids (according to my evolution professor)

Also my point was the the great dane and chihuahua cannot form fertile hybrids, yet are considered by most to be the same species

 

[Washington]

They do form fertile hybrids. 1/3 of all species can form fertile hybrids (according to my evolution professor)

I strongly suggest you verify that you heard correctly.

Also my point was the the great dane and chihuahua cannot form fertile hybrids, yet are considered by most to be the same species

Out of curiosity, just what reputable source doesn't consider them to be of the same species?

 

[Bombila]

What educational facility has an 'evolution professor' anyway? Do you mean a biology prof?

 

[29apples]

I do not have a source for the formation of fertile hybrids of animals constituting 1/3 of all animal species. It is partially hearsay at this point, but yes that is what my professor has stated.

Off the top of my head I can think of a dismal list at best: Orioles, Darters (small stream fish), and Dogs (with wolves). Im sure you guys can come up with others (keep in mind this is the ability to form fertile hybrids, even if that is a very slim chance i.e. 1/1000 so a donkey and horse would apply as well).

My professor teaches evolution. I have only seen him teach ecology/ evolution classes. I am currently taking a graduate course in evolution. He specializes in the specization of orioles. The class is actually taught by 4 professors who each specialize in their own particular portion based on their research.

And for the dane/chihuahua example, I doubt there is any reputable statements about them being different species. It was just a discussion we had in one of the classes. The bottom line was it all depends of how you define a species (based on strict/loose defined biological species concept or strict/loose defined phylogenetic species concept).

If you define a species by the statment: "they are different species if they can't naturally hybridize, either due to prezygotic or postzygotic limitations," then by your definition you would have to classify the great dane and chihuahua as different species because they cannot naturally form hybrids due to a prezygotic barrier.

This thread was made just to get everyone thinking

Does anyone else know any species that can hybridize with other species?

 

[Washington]

do not have a source for the formation of fertile hybrids of animals constituting 1/3 of all animal species. It is partially hearsay at this point, but yes that is what my professor has stated.

Now you're saying that 1/3 of all animal species are hybrids, whereas you previously stated that "1/3 of all species can form fertile hybrids." Hardly the same thing, all of which makes me believe there's a good chance you haven't really understood what your professor said.

If you define a species by the statment: "they are different species if they can't naturally hybridize, either due to prezygotic or postzygotic limitations," then by your definition you would
have to classify the great dane and chihuahua as different species because they cannot naturally form hybrids due to a prezygotic barrier.

And just who defines species this way? Moreover, hybridization can occur within the varieties (subspecies, infrasubspecies, races, breeds, and forms) of species---typically, intra-specific hybrids. And, hybridization can sometimes (rarely) take place between different species---usually interspecific hybrids. So perhaps this is the source of the confusion. When used in discussions such as this your use of "hybridization" should best be defined.

The bottom line was it all depends of how you define a species (based on strict/loose defined biological species concept or strict/loose defined phylogenetic species concept).

By "strict/loose defined biological species concept" are you referring to the old and discarded phenetic concepts? And, exactly what definition are you using when you speak here?

 

[Bombila]

I do not have a source for the formation of fertile hybrids of animals constituting 1/3 of all animal species. It is partially hearsay at this point, but yes that is what my professor has stated.

Off the top of my head I can think of a dismal list at best: Orioles, Darters (small stream fish), and Dogs (with wolves). Im sure you guys can come up with others (keep in mind this is the ability to form fertile hybrids, even if that is a very slim chance i.e. 1/1000 so a donkey and horse would apply as well).

My professor teaches evolution. I have only seen him teach ecology/ evolution classes. I am currently taking a graduate course in evolution. He specializes in the specization of orioles. The class is actually taught by 4 professors who each specialize in their own particular portion based on their research.

And for the dane/chihuahua example, I doubt there is any reputable statements about them being different species. It was just a discussion we had in one of the classes. The bottom line was it all depends of how you define a species (based on strict/loose defined biological species concept or strict/loose defined phylogenetic species concept).

If you define a species by the statment: "they are different species if they can't naturally hybridize, either due to prezygotic or postzygotic limitations," then by your definition you would have to classify the great dane and chihuahua as different species because they cannot naturally form hybrids due to a prezygotic barrier.

This thread was made just to get everyone thinking

Does anyone else know any species that can hybridize with other species?

If your prof specializes in orioles, it is possible he is an ornithologist - are you not curious to know what degrees your professors have?

Along with Washington, I suspect you have misunderstood whatever point your prof was trying to make.

 

[corvus_corax]

To the point-
There is no unversally accepted definition of species
There is only closer and closer definitions which must take into condideration
One day, there may be a scientifically accepted defnition of species (and since science depends on observable facts, that day may be in the near future)

And, if this is a metaphor for "kinds"..............just give it up now.
Biblical "kinds" will never (NEVER) be defined.

 

[AV1611VET]

Biblical "kinds" will never (NEVER) be defined.

But I'll bet you guys will keep asking though, won't you? Over and over and over and over and over.

 

[[serious]]

But I'll bet you guys will keep asking though, won't you? Over and over and over and over and over.

Yes, we will. The definition of species may be somewhat impercise in the grey areas that nature seems to so love presenting us with, but it gets the job done with the vast bulk of comparisons we have to make. The definition of "kinds" as a classification system is nonexistent. There is no discernible way to tell where to draw the line between kinds. Are fruit flies the "fruitfly kind" the "fly kind" the "insect kind" hexapod, arthropod, animal, eukaryote? Where is the line drawn?

 

[juvenissun]

To the point-
There is no unversally accepted definition of species
There is only closer and closer definitions which must take into condideration
One day, there may be a scientifically accepted defnition of species (and since science depends on observable facts, that day may be in the near future)

And, if this is a metaphor for "kinds"..............just give it up now.
Biblical "kinds" will never (NEVER) be defined.

If species could be defined, then the kind could also be defined based on the definition of species.

 

[[serious]]

If species could be defined, then the kind could also be defined based on the definition of species.

How so?

 

[Washington]

If species could be defined, then the kind could also be defined based on the definition of species.

But didn't god, whom the writers chose to quote, and those that claim to be able to interpret such quotes, have something in mind for the word, "kind"?

Genesis 7:1 The LORD then said to Noah, " . . . Take with you seven of every kind of clean animal, a male and its mate, and two of every kind of unclean animal, a male and its mate, 3 and also seven of every kind of bird, male and female, to keep their various kinds alive throughout the earth.

​

Why should god's meaning of "kind" depend on our meaning of "species"? I assume he knew what he was talking about regardless of how we classify his organisms.

 

[CACTUSJACKmankin]

If species could be defined, then the kind could also be defined based on the definition of species.

kind is derived from the bible. the problem with kind is all were represented on the ark and there are many millions of species. creationists get around this by suggesting that there werent lions and tigers and leopards and jaguars, just one big cat. this doesnt alleviate problems either because it makes for an incredibly imprecise definition that has no internal consistency. furthermore it leads to the problem of hyperevolution, since millions of varieties (species) must derive from several orders of magnitude smaller number of kinds in a few thousand years.

 

[Washington]

creationists get around this by suggesting that there werent lions and tigers and leopards and jaguars, just one big cat. this doesnt alleviate problems either because it makes for an incredibly imprecise definition that has no internal consistency. furthermore it leads to the problem of hyperevolution, since millions of varieties (species) must derive from several orders of magnitude smaller number of kinds in a few thousand years.

Reminds me of a graphic I created awhile ago.