“Species”

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On the thread entitled “Species Kinds”, commenter phoodoo asks:

What’s the definition of a species?

A simple question but hard to answer. Talking of populations of interbreeding individuals immediately creates problems when looking at asexual organisms, especially the prokaryotes: bacteria and archaea. How to delineate a species temporally is also problematic. Allan Miller links to an excellent basic resource on defining a species and the Wikipedia entry does not shy away from the difficulties.

In case phoodoo thought his question was being ignored, I thought I’d open this thread to allow discussion without derailing the thread on “kinds”.

1,428 thoughts on ““Species””

  5. “A simple question but hard to answer. Talking of populations of interbreeding individuals immediately creates problems when looking at asexual organisms, especially the prokaryotes: bacteria and archaea.”

    The concept of a species is just the result of man’s obsession with categorizing everything. If evolution is real, we would expect to see many instances where the devisions between these man-made categories are not as clear as with others. And that is exactly what we see. How does Phoodoo and the other ID supporters explain this?

  6. It sounds like a lot of people are saying there is no such thing as species delineation.

  7. phoodoo:
    It sounds like a lot of people are saying there is no such thing as species delineation.

    As I mentioned, “species” is a concept, not an objective reality. We are comfortable saying that a horse and a dog are different species. They cannot inter-breed. But what about a horse and a donkey? They can breed but the offspring is sterile. And what about a lion and a tiger? They can inter-breed and produce viable offspring, yet we classify them as different species, although this is done very rarely in the wild. And dogs and wolves. We classify them as different species yet they inter-breed at a frequency much higher than lions and tigers.

  8. Acartia,

    Well, it sorts of makes John Harshman’s question: “Can a kind encompass more than one species?” a pointless one then.

  9. phoodoo,

    Well, it sorts of makes John Harshman’s question: “Can a kind encompass more than one species?” a pointless one then.

    If so, it is not merely because of the ‘species’ element, is it? What is a kind? Is it more rigorously bounded than species?

  10. phoodoo:
    Acartia,

    Well, it sorts of makes John Harshman’s question: “Can a kind encompass more than one species?” a pointless one then.

    According to Sal’s “ring species” a kind can in fact encompass more than one species

  11. Genetically similar organisms with a set of characteristics that are used to survive specific environmental niche.

  12. Creationism is animal-centric. Plants are more promiscuous, and the concept of species doesn’t really make much sense for most living things, since most things clone themselves.

  14. phoodoo:
    Allan Miller,

    Hard to say since we still don’t know how rigorously bounded a species is.

    Species can’t be “rigorously bounded” dimwit, or else it would be of no use as a concept in a theory that postulates descent with modification like evolution.

  15. dazz: Species can’t be “rigorously bounded” dimwit, or else it would be of no use as a concept in a theory that postulates descent with modification like evolution.

    Even beyond our use for the term, it would be silly to think of “species” as rigorously bounded since nature doesn’t reflect such (except, perhaps, as measured in terms of chunks of human lifespans, but even within this caveat there are ton of exceptions that would make such a criteria dubious.) The fact is, the very essence of sexual reproduction is messy from a “biologically similar” standpoint. What would constitute a “species” for the mallard (Anas platyrhynchos) given its promiscuity and myriad hybrids? What’s a “breed” in such a rigorous definition? This is why the definition I put forth above doesn’t even reference “viable mating”, “reproduction”, “group”, or any such similar terms. As others have noted above, “species” is a term to allow humans to characterize some level of understanding of the fluid nature of the characteristics that denote genetically similar organisms surviving within (or across) some niche environment. As the environment changes, so too do the “species” within and across it.

    ETA: The one concept people really need to get past is the idea of species as some fixed, interbreeding, homogeneous group. That, to me, is just plain inaccurate.

  16. Some instructive reading for anybody interested:

    – the “unified” species concept:
    http://sysbio.oxfordjournals.org/content/56/6/879.long

    The issue of species delimitation has long been confused with that of species conceptualization, leading to a half century of controversy concerning both the definition of the species category and methods for inferring the boundaries and numbers of species. Alternative species concepts agree in treating existence as a separately evolving metapopulation lineage as the primary defining property of the species category, but they disagree in adopting different properties acquired by lineages during the course of divergence (e.g., intrinsic reproductive isolation, diagnosability, monophyly) as secondary defining properties (secondary species criteria). A unified species concept can be achieved by treating existence as a separately evolving metapopulation lineage as the only necessary property of species and the former secondary species criteria as different lines of evidence (operational criteria) relevant to assessing lineage separation. This unified concept of species has several consequences for species delimitation, including the following: First, the issues of species conceptualization and species delimitation are clearly separated; the former secondary species criteria are no longer considered relevant to species conceptualization but only to species delimitation. Second, all of the properties formerly treated as secondary species criteria are relevant to species delimitation to the extent that they provide evidence of lineage separation. Third, the presence of any one of the properties (if appropriately interpreted) is evidence for the existence of a species, though more properties and thus more lines of evidence are associated with a higher degree of corroboration. Fourth, and perhaps most significantly, a unified species concept shifts emphasis away from the traditional species criteria, encouraging biologists to develop new methods of species delimitation that are not tied to those properties.

    – Integrative taxonomy: a multisource approach to exploring biodiversity:
    http://www.ncbi.nlm.nih.gov/pubmed/19737081

    Good alpha taxonomy is central to biology. On the basis of a survey of arthropod studies that used multiple disciplines for species delimitation, we evaluated the performance of single disciplines. All included disciplines had a considerable failure rate. Rigor in species delimitation can thus be increased when several disciplines chosen for complementarity are used. We present a flexible procedure and stopping rule for integrative taxonomy that uses the information from different disciplines separately. Disagreement among disciplines over the number and demarcation of species is resolved by elucidating and invoking evolutionary explanations for disagreement. With the identification of further promising study organisms and of new questions for in-depth analysis, evolutionary biology should profit from integrative taxonomy. An important rationale is clarity in researcher bias in the decision-making process. The success of integrative taxonomy will further increase through methodological progress, taxonomic training of evolutionary biologists, and balanced resource allocation.

  17. As Acartia and Robin have noted, all this hang-wringing arises from a peculiar desire to have some categorizing rule that has the transitive property: if a=b and b=c, then of necessity a=c.
    Reality is not so tidy. This fact presents a problem for biblical inerrantists. For evolutionists, not so much.

  18. Perhaps the concept of species should be replaced by degrees of cousinship. that seems to be what Dave’s post is doing.

  19. Allan Miller,
    Evidence for speciation

    Speciation in action?
    In the summer of 1995, at least 15 iguanas survived Hurricane Marilyn on a raft of uprooted trees. They rode the high seas for a month before colonizing the Caribbean island, Anguilla. These few individuals were perhaps the first of their species, Iguana iguana, to reach the island. If there were other intrepid Iguana iguana colonizers of Anguilla, they died out before humans could record their presence.

    Iguana iguana Evolutionary biologists would love to know what happens next: will the colonizing iguanas die out, will they survive and change only slightly, or will they become reproductively isolated from other Iguana iguana and become a new species? We could be watching the first steps of an allopatric speciation event, but in such a short time we can’t be sure.
    A plausible model
    We have several plausible models of how speciation occurs — but of course, it’s hard for us to get an eye-witness account of a natural speciation event since most of these events happened in the distant past. We can figure out that speciation events happened and often when they happened, but it’s more difficult to figure out how they happened. However, we can use our models of speciation to make predictions and then check these predictions against our observations of the natural world and the outcomes of experiments. As an example, we’ll examine some evidence relevant to the allopatric speciation model.

    I pulled the part out that looks like circular reasoning.

    We have several plausible models of how speciation occurs — but of course, it’s hard for us to get an eye-witness account of a natural speciation event since most of these events happened in the distant past. We can figure out that speciation events happened and often when they happened, but it’s more difficult to figure out how they happened.

    This is from the UC Berkeley link: This definition is based on something that has not been experimentally validated or observed, and that is an obvious source of confusion. The lack of observation and experimental validation moves the definition in the direction of circular reasoning. I think I see the same problem in the creationist version that John posted.

  20. colewd: I pulled the part out that looks like circular reasoning.

    We have several plausible models of how speciation occurs — but of course, it’s hard for us to get an eye-witness account of a natural speciation event since most of these events happened in the distant past. We can figure out that speciation events happened and often when they happened, but it’s more difficult to figure out how they happened.

    Seriously? What circularity do you see there?

    colewd: This definition is based on something that has not been experimentally validated or observed, and that is an obvious source of confusion.

    How many times do we need to tell you that “experimentally validated” or “observed” don’t mean that one needs to be there to actually see something happen?

  21. colewd,

    Cole, you really, Really, R E A L L Y need to learn what circular reasoning actually means. It has nothing to do with whether something has been established through experimentation. For example, Newton’s principles of gravity were not based on circular reasoning before we used them to land some clown on the moon. Similarly, that Einstein’s Theory of General Relativity implied black holes, this did not mean they were therefore based on circular reasoning until we began to confirm the implicating elements. Even the concept of “god” is not, in and of itself, a circular concept simply because such can never being experimentally supported. It’s when folks attempt the demonstrate the validity of the concept by using the concept that makes it circular.

    For example, saying the bible is true because it’s written by God and God never lies according to the bible is a pretty straight-forward example of circular reasoning.

    Here’s the definition: “A is true because B is true; B is true because A is true.”

    That’s it.

    And note: none of the examples you’ve provided for circularity have been examples of circularity.

  22. Robin,

    We have several plausible models of how speciation occurs — but of course, it’s hard for us to get an eye-witness account of a natural speciation event since most of these events happened in the distant past. We can figure out that speciation events happened and often when they happened, but it’s more difficult to figure out how they happened.

    How would you validate the above models? or

    Universal common decent is true therefor speciation is true. Speciation is true because Universal common decent is true. Not circular?

  24. colewd:
    Robin,

    How would you validate the above models?or

    Universal common decent is true therefor speciation is true.Speciation is true because Universal common decent is true.Not circular?

    No, because speciation could be true AND universal common descent could be false at the same time.
    Even as a creationist you have to concede this, since presumably you believe there were a smaller number of basic created “kinds” that later speciated into a greater diversity of species, such as all the species of “cats”, all the species of “bears”, all the species of “birds” and so on.

    In such a scenario, UNIVERSAL descent would be false, but common descent “within kinds”(however you may want to define that) could be true. The original single “kind” speciated into many closely related cat-kinds, for example. Then there would be many smaller “bushes” of life(one for each “kind”), that are not connected, unlike the single big Tree Of Life of evolution by universal common descent.

    The several small bushes-of-kinds is actually the view pushed by creationist institutions such as AiG and ICR.

  25. colewd: Universal common decent is true therefor speciation is true. Speciation is true because Universal common decent is true. Not circular?

    If anyone actually thought like that, yes, that would be circular.

  27. I was just going to publish a link here to Kevin de Queiroz’s masterly review of species concepts and species delimitation, but thought to scan the comments — and found Dave Carlson had already linked to it (and it’s a free article).

  28. colewd:
    Robin,

    How would you validate the above models?or

    They gave you the validation in the UC Berkley article. To wit:

    Scientists have found a lot of evidence that is consistent with allopatric speciation being a common way that new species form:

    Geographic patterns: If allopatric speciation happens, we�d predict that populations of the same species in different geographic locations would be genetically different. There are abundant observations suggesting that this is often true. For example, many species exhibit regional “varieties” that are slightly different genetically and in appearance, as in the case of the Northern Spotted Owl and the Mexican Spotted Owl. Also, ring species are convincing examples of how genetic differences may arise through reduced gene flow and geographic distance.

    Spotted owl ranges
    Spotted owl subspecies living in different geographic locations show some genetic and morphological differences. This observation is consistent with the idea that new species form through geographic isolation.

    Experimental results: The first steps of speciation have been produced in several laboratory experiments involving “geographic” isolation. For example, Diane Dodd examined the effects of geographic isolation and selection on fruit flies. She took fruit flies from a single population and divided them into separate populations living in different cages to simulate geographic isolation. Half of the populations lived on maltose-based food, and the other populations lived on starch-based foods. After many generations, the flies were tested to see which flies they preferred to mate with. Dodd found that some reproductive isolation had occurred as a result of the geographic isolation and selection for different food sources in the two environments: “maltose flies” preferred other “maltose flies,” and “starch flies” preferred other “starch flies.” Although, we can’t be sure, these preference differences probably existed because selection for using different food sources also affected certain genes involved in reproductive behavior. This is the sort of result we’d expect, if allopatric speciation were a typical mode of speciation.

    That is validation for the models right there.

    Universal common decent is true therefor speciation is true.

    As I have pointed out three times now, this is a strawman. No biologist or even anyone who understands evolution makes this claim. UCD is a conclusion derived from the observed existence of nested hierarchies.

    Speciation is true because Universal common decent is true.

    That would be another strawman. No one who understands evolution makes that claim either. Speciation is true because we’ve observed it.
    The conclusion of UCA is simply derived from extending the models of speciation events to their logical conclusion.

    Not circular?

    Well, you’re strawmen could be considered circular, but since those don’t represent anything from the actual science, your question is rather moot.

  29. colewd:
    dazz,

    Can you lift from the paper the evidence that supports your argument?

    I’ll be glad to spoon feed you provided that you lift from any paper or evolutionary biology source evidence that supports your claim that “Universal common decent is true therefor speciation is true.Speciation is true because Universal common decent is true” is not another of your pathetic strawmen

  30. Rumraket,

    No, because speciation could be true AND universal common descent could be false at the same time.
    Even as a creationist you have to concede this, since presumably you believe there were a smaller number of basic created “kinds” that later speciated into a greater diversity of species, such as all the species of “cats”, all the species of “bears”, all the species of “birds” and so on.

    I did not know the real creationist position until John posted it and I have not had time to look at the creationist position closely. If we limited our analysis to claims that are made from observation and testing then how would we build these relational trees? My brief look at the creationist baramins is that they make claims beyond observation and experiment.

  31. Robin,

    That would be another strawman. No one who understands evolution makes that claim either. Speciation is true because we’ve observed it.
    The conclusion of UCA is simply derived from extending the models of speciation events to their logical conclusion.

    I read your evidence. Do you think this is an observation of speciation happening? Can you take me through the logical conclusion that leads to UCA?

  32. Acartia: The concept of a species is just the result of man’s obsession with categorizing everything.

    What I see as the problem of species is the inescapable fact we observe the categories as real things. Try as we might we can’t get around it. Darwin’s whole mission in life was to try and explain away this curious inference. That’s why the book is called “Origin of Species” and not something like “Origin of novel traits”

    Why would we have this experience if it is false? What is the evolutionary reason for this deception?

    If we can’t trust the universal experience of humanity when it comes to something like this what justification do we have for trusting anything we believe?

    peace

  35. fifthmonarchyman: What I see as the problem of species is the inescapable fact we observe the categories as real things. Try as we might we can’t get around it Darwin’s whole mission in life was to try and explain this curious inference. That why the book is called “Origin of Species” and not something like “Origin of novel traits”

    Why would we have this experience if it is false? What is the evolutionary reason for this deception?

    It isn’t false in sexual species. Mostly, such species are fairly discrete. This is because organisms aim for successful reproduction, and no longer fertilize (much, anyway) organisms that wouldn’t produce very viable offspring. It’s rather more arbitrary with asexual species, although there’s nothing false about them being in clades, despite more frequent HGT.

    If we can’t trust the universal experience of humanity when it comes to something like this what justification do we have for trusting anything we believe?

    In fact, in sexual organisms like birds, scientific species map quite well with human recognition of “different birds.” There are any numbers of exceptions, unsurprisingly, given that we’re bound to find “species in the making.”

    Glen Davidson

  36. Joe Felsenstein:
    I was just going to publish a link here to Kevin de Queiroz’s masterly review of species concepts and species delimitation, but thought to scan the comments — and found Dave Carlson had already linked to it (and it’s a free article).

    I used to TA a discussion course where the undergrads would read and discuss this paper. They mostly seemed to hate it. I’ll admit that I also had to read it a few times before I really appreciated it, but now I’m certainly glad that I did.

  37. OMagain,

    colewd: Can you take me through the logical conclusion that leads to UCA?

    Um, that’s a joke right?

    I want to see if you can make the logical connection between speciation and UCD without invoking circular reasoning.

  38. OMagain: No it was not. Or, you know, prove it.

    https://en.wikipedia.org/wiki/On_the_Origin_of_Species

    quote:

    Darwin had initially decided to call his book An abstract of an Essay on the Origin of Species and Varieties Through natural selection, but with Murray’s persuasion it was eventually changed to the snappier title: On the Origin of Species, with the title page adding by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

    end quote:

    peace

  39. fifthmonarchyman: https://en.wikipedia.org/wiki/On_the_Origin_of_Species

    quote:

    Darwin had initially decided to call his book An abstract of an Essay on the Origin of Species and Varieties Through natural selection, but with Murray’s persuasion it was eventually changed to the snappier title: On the Origin of Species, with the title page adding by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

    end quote:

    peace

    It is the “favoured races” that is probably more accurate. But not in the way that creationists love to claim.

  40. Acartia: It is the “favoured races” that is probably more accurate.

    In your opinion Is “race” a factual category as apposed to the spurious division implied with “species”?

    peace

  41. fifthmonarchyman: In your opinion Is “race” a factual category as apposed to the spurious division implied with “species”?

    peace

    I’m not sure what you mean by “spurious” here. Clearly, no two individuals are identical, so any group of similar individuals will show various ranges of variation. So by “spurious” do you mean some sort of degree of similarity? Of do you mean that since the term “species” describes a group whose boundaries are shifting and somewhat hazy, the word is therefore meaningless?

    As I understand it, the term “race” was intended to describe some variable aspect-of-interest within the whole group, shared (to the extent that the aspect is “sufficiently similar”) by a subgroup. Perhaps similar to the term “breed”.

  42. I think there are like 7.4 billion species of humans on the planet these days.

    Evolution in action!

  43. phoodoo,

    Hard to say since we still don’t know how rigorously bounded a species is.

    But you accept kinds, right?

    For fuck’s sake.

    Kinds might be complete horseshit, but as long as species are fuzzy, everything is tickety-boo in phoodoo land.

  44. colewd,

    The lack of observation and experimental validation moves the definition in the direction of circular reasoning.

    You continue to demonstrate that you haven’t a clue what circular reasoning is.

  45. Cole would have the evidence provided by a footprint in the sand as circular reasoning if it caused some dissonance with his preferred narrative. If no-one saw the foot fall.

  46. colewd,

    Universal common decent is true therefor speciation is true. Speciation is true because Universal common decent is true. Not circular?

    Circular but not claimed by anybody.

  47. Flint: So by “spurious” do you mean some sort of degree of similarity?

    no by spurious I mean.

    quote:

    not genuine, authentic, or true;

    end quote:

    http://www.dictionary.com/browse/spurious

    Flint: do you mean that since the term “species” describes a group whose boundaries are shifting and somewhat hazy, the word is therefore meaningless?

    According to Acartia the concept is just a result of “man’s obsession with categorizing everything” and does not reflect objective reality. If you disagree perhaps you should take it up with you fellow skeptic.

    peace

  48. Allan Miller,

    We have several plausible models of how speciation occurs — but of course, it’s hard for us to get an eye-witness account of a natural speciation event since most of these events happened in the distant past. We can figure out that speciation events happened and often when they happened, but it’s more difficult to figure out how they happened.

    How do they figure out speciation events happened? Then how do they figure out when they happen?

  49. Again, no surprises. The “Kinds” thread goes into oblivion while creotards fail miserably at grasping the concept of speciation and the implications of gradual change

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