The Species Problem

[Techne]

There are at least 24 different species concepts and none of them can be applied to all organisms that have ever lived (Hey, J. 2001). The Species Problem is a philosophical problem of biology that can be divided into two important questions that need to be addressed. Before giving a proper definition of the term "species", the ontological status of the concept needs to be addressed and this is the first important question. Once the ontological status is cleared, the second question is how to adequately define the term "species" so that is can be used to properly catalogue all the different life-forms. In order to answer the first question, one needs to clarify whether the term "species" firstly refers to either individuals or classes (kinds) (1a) and secondly whether universals (classes being a kind of universal) are real or not (1b)?

Most species concepts refer to a group or population of individuals as a species.

The Individuality Thesis is supported by Michael T. Ghiselin. The argument is that modern evolutionary theory supports the notion that species are individuals. It can be summed up by Ghiselin’s comment that "If species were not individuals, they could not evolve. Indeed, they could not do anything whatsoever. Classes are immutable, only their constituent individuals can change." (Michael Ghiselin, "Species Concepts, Individuality, and Objectivity," Biology and Philosophy 2 (1987): 129-43.). Ghiselin’s argument can be rewritten in deductive form e.g.

1) Individuals change
2) Classes do not change, they are immutable
3) Modern evolutionary theory describes how species evolve or change over time
4) Therefore species are individuals

Ghiselin’s argument depends on at least two important aspects. Firstly, the argument depends on the view that there is a fundamental dichotomy between individuals and classes and/or kinds (which is reasonable) and that the concept of "species" is either one or the other. Secondly, the argument depends on a clear analysis of what it means to evolve or change.

The Species Problem is of course relevant to biology in order to understand the process of speciation. Without a proper concept of the term species, speciation is unintelligible.

How would you answer the following questions?
1) Does the term "species" refer to either individuals or classes?
2) Is "species" real or or not? In other words, does "species" have an objective existence outside our intellectual abstractions or is it just a useful delusion?
3) How do you define species so that it adequately catalog all the different life-forms?

 

[James R]

Interesting questions.

1) Does the term "species" refer to either individuals or classes?

Groups of individuals make up a class, do they not?

I don't think it is correct to say that classes are immutable. For example, I can consider the class of all people currently waiting at a particular bus stop. Clearly, the individual members of that class will change over time, but it is still meaningful to talk about the class.

Whether you say that the class itself has changed when its composition changes is a semantic question.

2) Is "species" real or or not? In other words, does "species" have an objective existence outside our intellectual abstractions?

Biologically, species are not usually defined so explicitly that any given individual can be definitely ruled into or out of a species. Since individual members of a species are typically genetically unique, the concept of species cannot specify a particular genome. Therefore, the definition of a particular species must be coarse-grained enough to roughly mirror common-sense notions of "kinds" of animals/plants/whatever, but fine-grained enough to be able to distinguish allopatrically separated groups that cannot interbreed (for example).

3) How do you define species so that it adequately catalog all the different life-forms?

I don't think a single definition will work for everything. For example, many lifeforms are asexual, so any definition implicating sexual reproduction won't work for them.

 

[Techne]

Groups of individuals make up a class, do they not?

I don't think it is correct to say that classes are immutable. For example, I can consider the class of all people currently waiting at a particular bus stop. Clearly, the individual members of that class will change over time, but it is still meaningful to talk about the class.

Whether you say that the class itself has changed when its composition changes is a semantic question.

The first question can be argued to be related tot the question of universals or particulars. Is "species" a universal or a particular?

Biologically, species are not usually defined so explicitly that any given individual can be definitely ruled into or out of a species. Since individual members of a species are typically genetically unique, the concept of species cannot specify a particular genome. Therefore, the definition of a particular species must be coarse-grained enough to roughly mirror common-sense notions of "kinds" of animals/plants/whatever, but fine-grained enough to be able to distinguish allopatrically separated groups that cannot interbreed (for example).

I think a certain amount of vagueness goes with every concept of "species".

I don't think a single definition will work for everything. For example, many lifeforms are asexual, so any definition implicating sexual reproduction won't work for them.

Certainly not the 24 or so in use today.

 

[Enmos]

I don't think a single definition will work for everything.

Why not? You could define 'species' as a group of beings so closely related that they have at least 99.9% of their (functional) genome in common with each other. The percentage is fictive as I'm not clear on what it should be, but that should work.
You can then go on to define 'genus', 'family', 'order', etc. in the same manner.
I think they are using molecular phylogenetics to class organisms nowadays, which is basically what I describe above.

For example, many lifeforms are asexual, so any definition implicating sexual reproduction won't work for them.

I don't think there are any species out there that are only capable of asexual reproduction.

 

[chimpkin]

I don't think there are any species out there that are only capable of asexual reproduction.

Bacteria?
But they swap DNA with other bacteria, the slutty buggers.

 

[Enmos]

Bacteria?
But they swap DNA with other bacteria, the slutty buggers.

Yup.

 

[Fraggle Rocker]

I don't think there are any species out there that are only capable of asexual reproduction.

I started with the Kingdom of Fungi and within fifteen seconds I discovered the Glomeromycota, an entire phylum that only reproduces asexually. Based upon that good luck I'll assume there must be many more.

 

[Enmos]

I started with the Kingdom of Fungi and within fifteen seconds I discovered the Glomeromycota, an entire phylum that only reproduces asexually. Based upon that good luck I'll assume there must be many more.

I stand corrected Thank you, Fraggle.
However, classification of species based on genetic similarity does not require the organisms to reproduce sexually.


Edit: Here's an interesting article on "The Evolutionary Biology of Parthenogenesis": http://eebweb.arizona.edu/faculty/birky/Readings/Birky07AsexualSpecies.pdf

 

[spidergoat]

There can be no universal definition of species. It's an artificial attempt to categorize that which in reality has no defined boundaries, like trying to name all the colors of the rainbow.

 

[James R]

I don't think there are any species out there that are only capable of asexual reproduction.

There are entire kingdoms of them, are there not?

 

[Enmos]

There are entire kingdoms of them, are there not?

I wasn't thinking when I said that. But Fraggle already set me straight.
Have you read the article? It's about speciation in asexual organisms.

 

[Hercules Rockefeller]

There can be no universal definition of species. It's an artificial attempt to categorize that which in reality has no defined boundaries, like trying to name all the colors of the rainbow.

Precisely.

 

[iceaura]

I started with the Kingdom of Fungi and within fifteen seconds I discovered the Glomeromycota, an entire phylum that only reproduces asexually.

As far as is known.

It's not safe to presume a complete absence of genetic exchange among the members of a "species" - especially a little known group of spore producers.

But that would not much affect this discussion, except in the note that in the past (and still?) the various life stages of some of the more complicated beings on this planet have been classified as different species - or even higher taxa - and this has always been universally regarded as misclassification, without argument.

We do have criteria, related to genetic heritage and future, and a useful concept. The arguments are not at the center.

 

[Techne]

A Scholastic approach to the species problem is described here.

Thoughts?

 

[iceaura]

A Scholastic approach to the species problem is described here.

Thoughts?

There is no "species problem", outside of such efforts themselves.

If someone is interested in Scholasticism, its approach to the scientific employment of classification by species might be of interest.