What is the standard for evidence in biology?

Specifically, what is the evidence for common descent?(Not quite) famously, Darwin mused about the similarities of taxonomic hierarchies in linguistics and biology and asserted that the hierarchies must ultimately point to common descent. (Chapter XIV, On the Origin of Species) That’s common descent as distinguished from microevolution.

The linguistic equivalent is the single origin of all languages (eminently unproven and deemed unprovable) as distinguished from a language family (with demonstrable relevant organic shared features).

Darwinists are welcome to present their evidence. From Rumraket, we have the observation that all organisms can reproduce, “Nesting hierarchies are evidence of common descent if you know that the entities sorted into hierarchies can reproduce themselves. And that particular fact is true of all living organisms.” Good start.

From Joe Felsenstein we have the doubt that the border between micro- and macroevolution can be determined, “OK, so for you the boundary between Macro/Micro is somewhere above the species level. How far above? Could all sparrows be the same “kind”? All birds?” Not very promising.

From Alan Fox, “Darwin predicted heritable traits. Later discoveries confirmed his prediction.” Questions: Which heritable traits specifically? Was there a principled improvement over Mendel? And how does this lend credence to common descent?

Thanks to all contributors.

324 thoughts on “What is the standard for evidence in biology?”

  1. Tom EnglishTom English

    colewd: How do you explain contradictory evidence like convergent evolution?

    It may be a while before I return to this thread. But I don’t know why you think that convergent evolution is evidence against common ancestry. I’d say there’s a pretty good chance I’m not the only one who doesn’t know. So you might want to spell it out.

  2. Neil Rickert

    Allan Miller: I think, ultimately, Erik might be displaying his faith to God.

    It seems more likely that it is a confusion between process and history.

    For language evolution, one builds a tree based on history. And then presumably one infers process of evolution from the history using that tree.

    With biology, we have good knowledge of process. And then, using that known process and its production of one or more trees, we can build a history using relatively sparse historical data.

  3. colewd

    Tom English,

    I’d say there’s a pretty good chance I’m not the only one who doesn’t know. So you might want to spell it out.

    As an example convergent evolution is flight evolving in different animals that don’t share a near common ancestor like birds and bats. The evolution of flight is complex and hard to explain by blind processes. Having flight evolve more than once is quite a challenge. Other examples are sight and echo location.

  4. Adapa

    Erik: Why “imperfect” rather than “permitting variation within the limits of species” as actually observed?

    What limits would those be? We’ve only been watching species for a few hundred years out of the 3.5+ billion years life has been on the Earth.

    If you watched 10 seconds of a marathon would that indicate it’s impossible for a human to run more than 50 meters at a time?

  5. Adapa

    colewd:
    Tom English,

    As an example convergent evolution is flight evolving in different animals that don’t share a near common ancestor like birds and bats.The evolution of flight is complex and hard to explain by blind processes.Having flight evolve more than once is quite a challenge.Other examples are sight and echo location.

    Evolution isn’t a completely blind process. It has a feedback component in the form of selection provided by the environment.

    Why do you think flight, sight, or echolocation are particularly hard to evolve? All provide great benefit in the environments of the creatures that possess them. Evidence shows all three have evolved independently multiple times too.

  6. colewd

    Adapa,

    Why do you think flight, sight, or echolocation are particularly hard to evolve? All provide great benefit in the environments of the creatures that possess them. Evidence shows all three have evolved independently multiple times too.

    This is true but the advantage is not reached until a very complex system comes together. Selection needs the complex system to evolve before it can fix it in the population.

    You need material that is aerodynamic (feathers) to evolve, a muscle system that matches with the aerodynamic material, navigational systems etc. Until all this comes together the advantage of flight cannot be selected for.

  7. John HarshmanJohn Harshman

    colewd: How do you determine how well the data fits the common descent hypothesis?

    I invite you (for the nth time) to read my ratite paper I keep bringing up for you, or even the Theobald paper, for examples of how that’s done. Why won’t you just do that?

  8. John HarshmanJohn Harshman

    colewd: You need material that is aerodynamic (feathers) to evolve, a muscle system that matches with the aerodynamic material, navigational systems etc. Until all this comes together the advantage of flight cannot be selected for.

    I can’t see why you need any more navigational system to evolve flight than you need to find your way around on foot. The muscle system and the feathers, as you really ought to know by now, evolved before flight. The old technical term is “pre-adaption”, and the newer one is “exaptation”. Of course bats don’t have that aerodynamic material and have to make do with flaps of skin, the sort seen in a host of mammalian gliders.

    Further, even if flight can’t be explained by “blind processes”, that has nothing to do with common descent. Consider Michael Behe, for example, who accepts universal common descent but doesn’t think any natural processes can account for some unknown number of adaptations.

  9. Adapa

    colewd:
    Adapa,

    This is true but the advantage is not reached until a very complex system comes together.Selection needs the complex system to evolve before it can fix it in the population.

    You need material that is aerodynamic (feathers) to evolve, a muscle system that matches with the aerodynamic material, navigational systems etc.Until all this comes together the advantage of flight cannot be selected for

    That is demonstrably false. A stubby proto-wing that allowed its possessor to jump a small bit farther between tree branches is enough evolutionary advantage to get selected for.

    A light/dark sensing eyespot is better that zero light sensing capability and will be selected for.

    Even a tiny bit of echolocation that gives its owners a 1% advantage in catching its dinner will be selected for.

    The claim an entire modern flight system had to evolve before it could be of any use (the “what good is half an eye” argument) is one of the dumber claims out there. 1% functionality is better than 0%. 2% is better than 1%. You can figure it out from there.

  10. GlenDavidson

    colewd:
    Tom English,

    As an example convergent evolution is flight evolving in different animals that don’t share a near common ancestor like birds and bats.The evolution of flight is complex and hard to explain by blind processes.Having flight evolve more than once is quite a challenge.Other examples are sight and echo location.

    Why convergent evolution? Because evolution doesn’t know anything about evolution that occurred in other lines of descent.

    Why not homologous flight adaptations in separate lines, if there is a Designer responsible? Bats, birds, and pterosaurs all have homologies, but not in flight capabilities. Why? They all evolved from a common ancestor, but they all evolved flight after diverging from a common ancestor.

    Evolution doesn’t know, the Designer should, but apparently didn’t. I always wondered why believers think they’re doing their God a service by making it no brighter than evolutionary processes are.

    Glen Davidson

  11. colewd

    John Harshman,

    Further, even if flight can’t be explained by “blind processes”, that has nothing to do with common descent. Consider Michael Behe, for example, who accepts universal common descent but doesn’t think any natural processes can account for some unknown number of adaptations.

    John, I accept some level of common descent also as you have shown with some flightless birds in your paper. The evidence in your paper showed strong similarity among all flightless except for the ostrich. I would hold my final conclusion based on analysis of additional DNA segments but at this point I have no reason to doubt your claim.

    I agree with Michael Behe and consider evolving flight once is beyond known natural process let alone several times.

    As Eugene Koonan said in his paper supporting neutral theory as the current default hypothesis: ” Its time to get rid of the adaptionists just so stories” This includes all the transitional stories without transitional evidence.

    I agree with Eric that Universal Common Descent is a monster claim with very little supporting evidence. It stumbles right out of the block with the evolution of the spliceosome, chromosome structure and the nuclear pore complex which lack evidence for precursors.

  12. Adapa

    colewd:

    I agree with Michael Behe and consider evolving flight once is beyond known natural process let alone several times.

    Behe has never opined flight is beyond known natural processes to evolve. Where did you get that turd?

    I agree with Eric that Universal Common Descent is a monster claim with very little supporting evidence.

    More than a few people have shown you plenty of evidence to support evolution. Pretty much every dumb claim you’ve made has been beaten into the proverbial fine pink mist. That you choose to remain such a willfully ignorant knob on the subject is a sad reflection on your desire to educate yourself, a desire which seems nonexistent.

  13. John HarshmanJohn Harshman

    colewd: John, I accept some level of common descent also as you have shown with some flightless birds in your paper. The evidence in your paper showed strong similarity among all flightless except for the ostrich. I would hold my final conclusion based on analysis of additional DNA segments but at this point I have no reason to doubt your claim.

    That’s so very open-minded of you. I bet you could google up a few additional segments if you tried just a little bit.

    I agree with Michael Behe and consider evolving flight once is beyond known natural process let alone several times.

    Are you agreeing with him on something he actually said? If so, where?

    As Eugene Koonan said in his paper supporting neutral theory as the current default hypothesis: ” Its time to get rid of the adaptionists just so stories” This includes all the transitional stories without transitional evidence.

    Ah, quote-mining. So much easier than making an actual argument.

    I agree with Eric that Universal Common Descent is a monster claim with very little supporting evidence. It stumbles right out of the block with the evolution of the spliceosome, chromosome structure and the nuclear pore complex which lack evidence for precursors.

    Damn, and you were so very close before that last paragraph. You seemed to understand that the evidence for common descent doesn’t depend on the source of the changes, but I guess that was just me seeing what I wanted to see. And you’ve already completely forgotten Theobald 2010.

  14. Erik Post author

    Neil Rickert: For language evolution, one builds a tree based on history. And then presumably one infers process of evolution from the history using that tree.

    No. The evolution of language is observed, not assumed. A single generation is enough to effect a specific change and it’s usually irreversible, unless a norm is fixed by some authoritative diktat, but this only slows it down, instead of blocking it.

    Neil Rickert: With biology, we have good knowledge of process. And then, using that known process and its production of one or more trees, we can build a history using relatively sparse historical data.

    See, it’s precisely in biology where both the process and the history are assumed.

    Linguists can build trees too (many places where you can draw trees, this by itself proves nothing about history), based on all sorts of linguistic data, but from the direct observation of the actual process it’s known that e.g. broad typological, syntactic and lexical phenomena are easily borrowed and thus deceptive, whereas core vocabulary, morphology and lawful phonetic correspondences demonstrate organic relatedness. These are conclusions made from observations, such as how things have gone from Latin to its modern descendants.

    In biology you seem to have assumptions projected on the data, no observation of the process. I know it’s by necessity, and this is precisely the problem. With some imagination one can make all sorts of assumptions compatible with the data, even more parsimonious than evolution.

  15. Erik Post author

    Adapa: What limits would those be?

    Such as no turtles come from rabbits. Breeding is consistently an intra-species thing.

    This of course fails to impress you. Similarly, it should be understandable why your Very Long Time argument fails to impress me.

  16. Erik Post author

    John Harshman: I thought the actual topic was the standard of evidence in biology. Why does the standard of evidence for two species of finches having a common ancestor have no bearing on that?

    The way you prove a common ancestor to finches would illustrate your standard of evidence. The further conclusions you draw from it, baseless or otherwise, illustrate it further.

    John Harshman: And could you describe what you think the actual topic is?

    Which is why it’s lucky that I made the OP short.

  17. Erik Post author

    Tom English: It bugs me to see something like phylogenetic inference detached from all the rest, and treated as though the theory of evolution depends on it entirely.

    You can fix the problem, I hope. Instead of arguments like “things breed with tiny changes over Very Long Time, therefore common descent” please bring all the relevant lines of evidence together.

    However, from what I’ve seen, the distinct lines of evidence are in fact radically disconnected. For example, a few attested ancestors (which are conspicuously not there) would not prove universal common descent, but would be good for macroevolution, if it’s beyond species.

  18. Allan Miller

    Erik,

    Instead of arguments like “things breed with tiny changes over Very Long Time, therefore common descent” please bring all the relevant lines of evidence together.

    That’s a fine summary of the arguments you have been presented on common descent there, Erik. You are quite the scholar.

  19. OMagain

    Allan Miller: That’s a fine summary of the arguments you have been presented on common descent there, Erik. You are quite the scholar.

    Erik seems to be playing the role of an erudite Joe G but with the same underlying misconceptions.

  20. Erik Post author

    Gordon Davisson,

    Thanks, but your post does not explain anything. Given your peculiar definition of “explain”, this is all that I should say, but I will say more. I will really explain how your post does not explain anything.

    First, you make the target small. Second, you make the claims minimal. Third, along with it, you make the definitions of “explain” and “predict” ridiculous.

    Common descent, for you, is just the ability to build trees. Since there are two independent lines of data (morphological characters vs. cytochrome c) that yield a similar-looking tree, you take it that the tree represents history and there should be no objection. Moreover, you call the ability to build the tree a prediction, even though the human ability to connect similarities is ubiquitous, universal, not specific to Darwin’s theory of evolution and not a prediction in any relevant sense.

    Unfortunately for you, the tree was there long before Darwin’s grandfather, even before Linnaeus. Linnaeus only systematized it successfully. So the tree was “predicted” long before Darwin. Darwin’s contribution was to project the “origin of species” on it. It is this projection that is at issue. The tree itself is not at issue. I never denied that the tree can be built. The issue is whether it represents the history of the species a la “ontogeny recapitulates the phylogeny” or if it is just the building blocks of natural life put together systematically.

    Since living beings are made of the same building blocks, of course we can build a tree based on the building blocks. Instead of implying whether some or all of the species have a common ancestor, it could just as well imply a common maker and this is the more parsimonious explanation better in line with the observed evidence because

    (1) Breeding is observed to be an intra-species thing
    (2) Species gradually morphing into other species is not observed
    (3) Ancestor species to modern species are not observed, i.e. the Darwinian theory even fails to project the past, not to mention the future

    Thus the tree is not a prediction, certainly not specific to the Darwinian theory of evolution and it fails to explain anything relevant to what the theory actually claims. The actual claim of the theory is universal common descent – all species come from a single one. It’s not “we should be able to build a tree”. There are tons of non-evolutionary things we can build trees from. All this has already been covered in this thread many times. You have added nothing to the discussion.

    Fourth, to mix things up and to answer your question, I actually agree with something like evolution. For balance, my theory involves devolution. Just like consciousness (souls) can climb up along the ladder of species, there must be descent also. This climbing occurs in the dark side, during death, which has its own laws of nature. On the physical side, which is the only side that the Darwinian theory considers, my theory would “predict”

    (1) Fixity of species – some variation when the species settle new ecological niches, but not beyond the limit of species
    (2) Hierarchy of species according to levels of consciousness
    (3) Rough correspondence of expansion and extinction of species – when a species or group multiplies and commands many ecosystems, other species go extinct, because the number of souls should remain roughly the same
    (4) The actual origin of the species lies beyond the material and the arrangement of the building blocks; the tree of life would illustrate something like the plan of creation, but the material does not arrange itself, it is being arranged according to the plan, a.k.a. laws of nature

    Feel free to mock and criticize, but make it relevant to actual observations and human experience. Because actual observations and human experience are the points where your post was weak. It was even weak in terms of specific to Darwin’s theory of evolution.

  21. Allan Miller

    OMagain,

    Erik seems to be playing the role of an erudite Joe G but with the same underlying misconceptions.

    It’s a syndrome. When you see such hopelessly off-the-mark paraphrases of concepts, time to get a new hobby.

  22. Allan Miller

    colewd,

    The evidence in your paper showed strong similarity among all flightless except for the ostrich. I would hold my final conclusion based on analysis of additional DNA segments but at this point I have no reason to doubt your claim.

    Drop everything, Bill Cole wants greater coverage of the ratites, in case the ostriches aren’t related at all. To the laboratory!

  23. GlenDavidson

    Allan Miller:
    OMagain,

    It’s a syndrome. When you see such hopelessly off-the-mark paraphrases of concepts, time to get a new hobby.

    Erik’s obtuse, therefore evolution lacks evidence. Oh, and Bill Cole believes him, for the same reason.

    Being without understanding is its own sort of freedom, I guess. Bliss, some say.

    Glen Davidson

  24. RumraketRumraket

    Rofl. He really doesn’t get it and it seems he never will.

    Turtles and squirrels can’t interbreed. That’s the level he’s stuck at intellectually. All this stuff about why that pattern and not another? About explanatory power, prediction and retrodiction? Comparative hypothesis testing? No, fuck all that, because “it’s just the same species”.

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