Tsk

Genetic tests on bacteria, plants and animals increasingly reveal that different species crossbreed more than originally thought, meaning that instead of genes simply being passed down individual branches of the tree of life, they are also transferred between species on different evolutionary paths. The result is a messier and more tangled \”web of life\”.

There\’s a good reason why at one time the definition of \”species\” was a group that was capable of breeding into fertile offspring.

We\’ve rather changed that definition in recent years/decades: which leads to this particular conclusion.

Donkey/horse crosses are mules or hinnys. Which are almost always infertile. But not quite always. So whether donkeys and horses are actually different species under that old definition is, umm, debateable.

Lions and tigers produce ligers and tigons. Always (I think?) infertile: thus they are different species.

Wolves and dogs produce fertile puppies: they\’re the same species.

This new finding is really a result of the way we\’ve changed our definition of species.

26 comments on “Tsk

  1. It’s a bit like the problem of what is or isn’t a planet: the classification itself is faulty, based on incomplete understanding. Species are just snapshots of a process of continuous change, they’re not really meaningful categories at all.

  2. Peter Risdon – “Species are just snapshots of a process of continuous change, they-re not really meaningful categories at all.”

    So you would not be upset at the loss of, say, Blue Whales as a species? Or pandas? As there is no such meaningful category?

  3. Matthew L – “That-s not at all what he said, you twit.”

    You do not know and in fact you cannot know. Let us wait and see what he says. I suspect you might be right. But it is a logical consequence of what he said. So either he thinks this or he has not thought through the implications of his claims.

    Either way, a response should be interesting.

    Unlike your comment.

  4. To interpret his comment that way you’d either have to be functionally illiterate or deliberately ignorant to the point of retardation. Which one is it in your case?

  5. Matthew L – “To interpret his comment that way you-d either have to be functionally illiterate or deliberately ignorant to the point of retardation. Which one is it in your case?”

    I am quite enjoying Napoleon Chagnon-s new book. It is quite remarkable how stupid some academics can be.

    Either species are a meaningful category or they are not. If they are not, then their loss is utterly irrelevant. Either the loss of the individual is a tragedy or the loss of, I am not sure, all life on this planet, I guess, is, or perhaps the loss of over all genetic diversity is. But the loss of pandas qua pandas cannot be as they do not exist as a meaningful category.

    That is, if you refuse to accept the existence of any group between the individual and all life forms (or perhaps all vertebrates or whatever), you should understand the consequences of that position.

    You cannot claim that species do not exist and yet that they do when it suits you in another argument. Well you can. But you should not.

  6. SMFS
    It is a question worth asking. Why should we be concerned about the loss of the blue whale or panda? Neither species is likely around in a few million years irrespective of homo sap.
    Panda, particularly, is an overspecialised evolutionary dead end. Pandas will become extinct whatever happens. They’ll go the same way of all overspecialised species. Or they’ll evolve out of the evolutionary trap. And won’t be pandas anymore.

  7. But that article does have a rather awkward implication. There’s a hell of a lot invested in homo sap being one single species. Be a bit unwelcome casting doubt on that one & the possibility we’ve got evolutionary divergences.

  8. bloke in spain – “It is a question worth asking. Why should we be concerned about the loss of the blue whale or panda? Neither species is likely around in a few million years irrespective of homo sap.”

    No species is likely to be around in a few million years. But I am happy to say that I hold a quasi-religious position on this. It is an article of faith that the natural world, as it was before people started messing with it, has a unique value all of its own. We should do all we can to preserve it.

    Although admittedly quite how I manage to hold this view along with a strong defence of open cut mining, nuclear power and logging is a mystery even unto myself. But at least, unlike most of my fellow believers, I recognise this as a quasi-religious position based on faith and not on any objective logic at all.

    “Panda, particularly, is an overspecialised evolutionary dead end. Pandas will become extinct whatever happens. They-ll go the same way of all overspecialised species.”

    That is a little over-stated and perhaps even a tad prejudicial. A lot of overspecialised species have been around for a long time. I can think of dozens of species that have successfully filled very narrow niches for a very long time indeed. Slime eels for instance.

    “Or they-ll evolve out of the evolutionary trap. And won-t be pandas anymore.”

    Not sure it is possible to evolve fast enough to escape both encroaching Chinese peasants and the clumsy cack-handed efforts of the Chinese government to help. They are almost certainly doomed.

  9. Species are species because we can see them and this species is blatantly obviously different from that species. To paraphrase some great quote the source of which escapes me, “I can’t tell you what an X is but I know one when I see it”. There will probably never be a universal biological definition that covers all eventualities. Especially when we get down to bacteria and other organisms that do not reproduce sexually, not to mention the whole debate about whether viruses are even living organisms.

  10. In other words the definition of a species is best made in reference to other species. As in “this group of organisms is clearly/less clearly not the same species as that group of organisms”. What you do with infertile reproductive dead-ends like tigons or donkeys doesn’t really matter, since you aren’t going to get any more of them.

  11. To jump from “the definition of species is blurred” to “their loss is utterly irrelevant” is ridiculous. Here’s an example.

    A can interbreed with B.
    C can interbreed with D.
    B can interbreed with C.
    A cannot interbreed with D.

    Which of A, B, C and D are the same species?

    B and C die off. A and D are now unambiguously different species because there is no path for genes to flow between them. By your argument, logically they weren’t worth preserving at the start but they are now.

    I agree with you that we should preserve as much genetic diversity as possible. The labels we put on that diversity don’t change that necessity. If those labels are inadequate we need to recognise their limitations and work around them. Trying to put a black and white definition of “species” and saying that one side should be preserved and the other doesn’t matter is silly.

  12. Either species are a meaningful category or they are not. If they are not, then their loss is utterly irrelevant.
    Nice non-sequitur you have there. It seems doubtful to me that the value we put on say blue whales, depends on there being a coherent definition of the term ‘species’.

  13. Female tigons and ligers are actually interfertile with both species, but male hybrids are usually infertile.

    There haven’t been enough quarter-breeds (titigons and liligers) to know their fertility to be sure, but their males may well be fertile with pure-breeds of the species they are 3/4 a member of.

    There are historic records of wild ligers, but not tigons (ligers, which are huge, are far easier to identify in the wild than tigons) when the species’ territories overlapped (in modern Iran and Pakistan) in the historic past.

  14. What Matthew describes at 13 is how species speciate. B& C did die off. So A&D are separate species.
    “and so it goes” (Kurt Vonnegut)

  15. bloke in spain: Yes, but consider the case before B & C die off. A & D still can’t interbreed, but they can exchange genes through B & C – are they the same species?

  16. Matthew L – “To jump from [the definition of species is blurred] to [their loss is utterly irrelevant] is ridiculous.”

    I am curious, do you know you are making an asinine mistake or has your self-righteousness simple made you blind to the ass you are making of yourself?

    1. The previous poster did not say the definition was blurred. He said species as a category was meaningless. That was a much stronger statement.

    2. I did not even hint that the loss of a single species is irrelevant. In fact I have made my views very clear about that. I simply asked a question about how the previous poster felt about it.

    So all in all, that is an entirely content-free reply. Are you trying to challenge Arnald for the position of, well, whatever the hell is Arnald-s deal?

    “Here-s an example.”

    Of what? Nothing to do with anything I said.

    “Which of A, B, C and D are the same species?”

    Which is an interesting question but not one even remotely relevant to your demonstration of whatever it is you think you are demonstrating.

    Yes, I am perfectly aware of ring species. Yes, the former definition of a species as an inter-breeding community has problems. That does not mean we have a better definition. Or that we should throw away the definition of a species. And it certainly does not mean the concept of a species is meaningless. Just not quite right. Even blurred.

    “By your argument, logically they weren-t worth preserving at the start but they are now.”

    I made no such claim. But that is how it would work in present environmental law. Which is why the splitters tend to be more vocal than the clumpers these days.

    “I agree with you that we should preserve as much genetic diversity as possible. The labels we put on that diversity don-t change that necessity.”

    Yes but suppose Ecuador has limited funds and they have a choice of saving half the finches on the mainland – where genetic diversity is high – or half a dozen finch species on some off shore islands – where genetic diversity is low – which should they choose?

    “If those labels are inadequate we need to recognise their limitations and work around them.”

    By all means. Explain to us what better definition we have of a species.

    “Trying to put a black and white definition of [species] and saying that one side should be preserved and the other doesn-t matter is silly.”

    Let me know when you find someone who has said so.

    14Eddy – “Nice non-sequitur you have there. It seems doubtful to me that the value we put on say blue whales, depends on there being a coherent definition of the term [species].”

    What value do you put on the Blue Whales as a group if in fact the group does not exist?

  17. JamesV – “Species are species because we can see them and this species is blatantly obviously different from that species.”

    Ideally. Some bird species are not obviously different from another species. These days DNA testing is identifying species that look exactly the same but are genetically different.

    “To paraphrase some great quote the source of which escapes me, [I can’t tell you what an X is but I know one when I see it].”

    Justice Potter Stewart said it of pornography.

    “There will probably never be a universal biological definition that covers all eventualities. Especially when we get down to bacteria and other organisms that do not reproduce sexually, not to mention the whole debate about whether viruses are even living organisms.”

    I assume that what the original article meant was the nasty habit of bacteria swapping DNA. Presumably we have just seen the human DNA pool change with HIV. I assume that now we will never get rid of it, but that it will gradually evolve to be less lethal and so in the end, the genes from HIV will just be a normal part of the human gene pool. TW assumed it was all about sex, but it is not necessarily that way.

    But viruses? Ha! Child-s play. Try prions.

  18. Don’t confuse a category with the things in it.

    Planets again: the loss of the word would be fine because a category of ‘objects that could be seen, 2,000 years ago, with the naked eye, from Greece, to move against the stellar background’ isn’t very meaningful. It might be better to talk about rocky objects, gaseous objects, sponge-like objects and to give them names. Even so, in every case it’s an imposition of an artificial classification system on a continuum.

    But getting rid of the category ‘planets’ doesn’t mean blowing up the solar system.

    Similarly, ‘species’ are snapshots of continua, not discrete states that living creatures lurch between. That’s a misunderstanding common to the dumber sort of creationist.

    Dawkins has coined the term ‘the discontinuous mind’ to describe people who who have difficulties with this idea.

  19. Peter Risdon – “Don-t confuse a category with the things in it.”

    I am not. Nor do I see what you are saying here. The loss of one panda is a tragedy but the loss of all of them is not?

    “Planets again: the loss of the word would be fine because a category of [objects that could be seen, 2,000 years ago, with the naked eye, from Greece, to move against the stellar background] isn-t very meaningful.”

    As someone on a stellar object that could be seen, 2000 years ago, to move against the stellar background, I would have to disagree with that. I think the loss of the Earth would be a little bit meaningful. But I do not think that is a good parallel to what you said.

    “Even so, in every case it-s an imposition of an artificial classification system on a continuum.”

    Inter-breeding is not artificial. It is simply not complete. As a rule of thumb it works quite well. Rather like Newtonian physics. It was not complete, but for most purposes, for most of us, most of the time, it worked and works fine. So I still do not follow how it is not a meaningful way of viewing lifeforms.

    “But getting rid of the category [planets] doesn

  20. Peter Risdon – “But getting rid of the category [planets] doesn-t mean blowing up the solar system.”

    No, but if you said that planet are just quasi-random collections of rocks and so not a meaningful way to classify objects in our universe, then some people might think you would not mind the destruction of the Earth because it would just be a re-arrangement of said rocks. Although if you said there were no planets people might not listen for the rest of the argument.

    “Similarly, [species] are snapshots of continua, not discrete states that living creatures lurch between. That-s a misunderstanding common to the dumber sort of creationist.”

    As well as Stephen Jay Gould. However at any one time, like a snap shot of a horse racing, we can say whether all the hooves are off the ground or not. Even if they are also on a continua. So pandas evolved from something and if we were not here to f**k everything up, they might even have evolved into something else. But at this specific time, in this specific snapshot, they are a discrete category of organisms.

  21. “I am not. Nor do I see what you are saying here. The loss of one panda is a tragedy but the loss of all of them is not?”

    Yes, you are.

    The loss of one panda might or might not be a tragedy but the loss of the term ‘panda’ wouldn’t mean the loss of any animals at all.

  22. ‘… at this specific time, in this specific snapshot, they are a discrete category of organisms.’

    Pandas might appear so, but that’s circumstantial. Gulls give a good idea of the real complexity of this.

  23. Peter Risdon – “The loss of one panda might or might not be a tragedy but the loss of the term [panda] wouldn-t mean the loss of any animals at all.”

    Nice but by the same token, we would not know if they became extinct or not. Unless we had another term for them. We need the label. Otherwise their loss would be lost in noise. And thus I assume not much of a tragedy for most people because they would not know.

  24. SMFS, your logic is broken. We can make groupings for conservation purposes even though reality is a continuum.

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