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.
Christ, Erik. Do some reading:
Thanks for putting the OP up, Erik.
Regarding my comment:
What I meant by this remark is that Darwin predicted some heritable element that could pass from parent to offspring. We now refer to this heritable element as a gene and we know that these genes exist as sequences of nucleic acid residues in chromosomes.
So, basically, organisms transfer genes to offspring, therefore common descent of all organisms? Am I getting it right?
Do Indo-European languages make much sense except in the light of language evolution? Of course not. As far as the evidence goes, wtf is Erik doing here without knowing hardly any of the copious evidence that has been presented? No one is here to spoon-feed someone who won’t even find out the basics of what he is opposing.
The huge number of cognate words in Indo-European languages make sense largely through vertical inheritance, although horizontal transfer is both possible and occasionally large (English). But biologic evolution also has the kind of record that is missing from most language evolution (of course there are texts, but only to a few thousand years ago), the fossil record, which is gappy but highly supportive of evolution (even Wells admitted that it looked good for evolution, then pretended that it made sense with creationism as well).
Erik’s doing about as well with this as he did with his claim that people didn’t believe in a flat earth in the second millenium BC.
Glen Davidson
It’s the most parsimonious explanation. At the biochemical level, all living organisms show an amazing similarity. The universality of the genetic code is one example.
And in what light would the relation of Indo-European and Semitic languages make sense?
Who cares?
Why don’t you deal with the evidence of relatedness rather than throwing in red herrings to cover your incompetence at discussing these matters?
Glen Davidson
Looks like a key passage is this (my emphasis),
What are those “firm evolutionary arguments”? Being evolutionary (i.e. apparently presupposing common descent), do they really justify the method? Is Hennig’s relevant work (objections to criticism) openly available?
This was what I wrote for the “Evolutionary Turing Test”:
It was a “paragraph,” and covers the evidence for evolution reasonably well for a short piece. It’s not like the evidence hasn’t been given.
Glen Davidson
Erik,
You said there is no evidence different species are related to each other. What is your theory of how they arose? Once we know that we can compare that theory to other theories that deal with the same evidence and decide which is the best supported.
What’s your idea?
What you seem to be missing, is the trivially obvious evidence of common descent. Every known organism descended from its parent(s). This is very different from the situation in linguistics.
So the only question is how many trees are there. There could be one for each species at one extreme, or a single tree at the other.
My assumption is that many people originally thought there might be one tree for each major phylum. In any case, that was my own original assumption when I first heard of evolution. Note, though, that I did not immediately jump to accepting evolution.
The effectiveness of the Linnaean classification system seemed to be pretty good evidence for common descent within a phylum. Pretty good, but not enough to convince me. I did consider it a reasonable possibility, but I did not consider it certain.
But the Watson-Crick work, together with known similarities in the DNA of all organisms, seemed to make it likely that there was but single tree. It was Watson-Crick that settled the issue for me.
And note that I am not a biologist, so I cannot actually speak for biologists.
keiths,
From http://www.talkorigins.org/faqs/comdesc/section1.html#fundamental_unity
This is fallacious. The theory is, specifically (in the first sentence), that all current variety of species descends from a single one. The “prediction” (intended as proof of the theory) is stated to be that all living organisms should share the common nature of living organisms.
This is as bad as: All languages share the necessary feature of serving as a communication tool, therefore they all descend from a single origin.
No. Being a tool of communication is, among other things, what language is, nothing to do with where it came from. Similarly, reproduction, heritability, catalysis and metabolism is what it means to be a living organism, nothing to do with what other species it descended from, if any.
If the standard for proof of common descent of living organisms is, minimally, this list of characteristic features shared by all living organisms, where none of the features distinctly indicates the origin of the species, it’s not enough. Sub-standard.
Looks like there is just one possible serious argument for common descent: Genetics. Provided that genes can functionally enable species to evolve into another (rather than restrict reproduction to within species, which seems to be the actual case) and leave the relevant tracks while doing it.
Erik does not believe species are related in any way. So common descent does not seem to be possible in that regard.
Do we really have to cite this again?:
Theobald D.L. A formal test of the theory of universal common ancestry. Nature 2010; 465:219-223.
Note, by the way, that Darwin wasn’t actually referring to universal common descent. Even in the Origin he said “breathed into a few forms or one”. And for a person who refuses to believe that different species are related (except, paradoxically, different species of sparrow), it seems odd to demand that it be universal descent or nothing.
As for somewhat less than universal descent, I offer at random this:
Harshman J., Braun E.L., Braun M.J., Huddleston C.J., Bowie R.C.K., Chojnowski J.L., Hackett S.J., Han K.-L., Kimball R.T., Marks B.D., Miglia K.J., Moore W.S., Reddy S., Sheldon F.H., Steadman D.W., Steppan S.J., Witt C.C., Yuri T. Phylogenomic evidence for multiple losses of flight in ratite birds. Proceedings of the National Academy of Sciences 2008; 105:13462-13467.
You should be able to find PDFs easily online.
OMagain,
This claim assumes that Erik does not understand the definition of species. Do you think that is the case?
Based on his sparrow comments, that seems very likely.
Common ancestry implicitly indicates fewer ancestral forms. If 2 species share a common ancestor, there are obviously fewer ancestors than descendants. That doesn’t necessarily mean that fewer forms existed, but that fewer have left descendants. The ‘fewer’ does not have to be 1, extended back to an origin for all extant life. Evolution could be entirely true and the number still not be 1 – evolution does not depend on it. But it turns out that 1 is indicated by the data.
To me, there is an apparent genetic continuum linking all of life. We see this unarguably within a species (complicated slightly by sex). It should also be pretty non-controversial in closely ‘related’ species. There’s the sparrows, or my own ‘type’ example, the Common and Spotted Sandpipers. So I guess the first task is to determine the level at which controversy arises for the person asking.
The evidence of commonality in the sandpipers is morphological, but is also writ large in the genes. If one could travel along the DNA, sliding one hand along Common and the other along Spotted, there would be enormous stretches where there was absolutely no difference. If we were alerted by a ‘bleep’ every time there was a difference, there’d be a hell of a long wait between bleeps. We wouldn’t know, unless we’d been told, whether we were looking inside or outside a species.
Now I’d say being actually related is a strong candidate for the cause of this commonality. I can’t think of a better. What say you, Erik?
No, as usual you aren’t.
Organisms transfer genes to offspring with mutations in them. That process produces nesting hiearchies. The longer that process is allowed to continue, the more divergence will happen.
We observe lots of diversity. And we observe that all of that diversity can be sorted into objective nesting hierarchies. There is no other observed process operating on living organisms, known to produce nesting hierarchies. So we infer that the process known to produce nesting hierarchies, did so in the past too and produced the patterns we see. There’s more to it than that, but that is basically enough.
That’s all perfectly true and should be enough to settle the issue decisively.
However, I think that Erik is also taking issue with the analogy from languages. That seems quite right.
For one thing, are there objective criteria that allow us to from nested hierarchies of languages?
For another, the nested hierarchies that we observe in biology are distinctive in terms of the relation between time and complexity. Generally speaking, the further back we go in the history of life, the less complexity we observe. (This is a contentious claim, because it’s hard to know which measure of complexity is the best one to use.)
By contrast, I’m not aware of any evidence to suggest that any natural language is more or less complex than any others.
So I’m inclined to agree with Erik that it’s the analogy between biological evolution and linguistic change is a poor analogy. But the preponderance of evidence in favor of evolution does not depend on that analogy.
In both biology and language the inferences are probabilistic. Reinforced by the fact that we can observe the underlying processes. And in the case of language, we have a couple thousand years written record of the transitions.
No. That is one aspect of one of the predictions. Which is necessary, but not sufficient, to infer common descent.
Which is why it isn’t the only requirement for the inference of common descent. It is necessary but not sufficient. Technically, you need both prediction 1.1 and prediction 1.2, to infer common descent.
The additional predictions 1.3 and 1.4 are pretty much icing on the cake. But no, prediction 1.1 alone is not enough.
It isn’t.
From the section on prediction 1.2, we get this:
And more follows on that point. Perhaps Erik should read more than the first two subsections of the first prediction.
Kantian Naturalist,
Like all analogies, it breaks down somewhere. You seem to think it poor because it breaks down over issues of complexity. But I don’t see complexity as a particularly central component of evolution – certainly not one that an apt analogy must capture.
It succeeds as an analogy because it contains the components of divergence between separated sub-populations, cross-transfer between such isolated lineages, hybrid zones and introgression. It think it actually has these things – they are not merely analogous; they are essentially the same in the two systems, at ‘string’ level. Of course it doesn’t greatly matter whether it succeeds or fails – nothing is rendered more or less true by the aptness of any analogy one chooses. But I think it a good one.
I’d say it’s a contentious claim because there seems to be no measure of complexity under which it’s actually true. Would you care to support that claim?
I’d say the analogy is pretty good, and would be even if your claims about complexity were true. The analogy doesn’t depend on them. All it depends on is that there is descent with modification and branching. Granted, violations of linear descent happen more often with language than with life, at least eukaryote life, but the pattern remains clear enough.
Yes. Thank you. There are folks who tune in irregularly, and folks who regularly forget. I’m a member of both groups.
Good thread. What is the standard for evidence in biology???
I say its a poor one relative to evolutionism as follows.
All these common descent conclusions are entirely based on comparative anatomy or comparative genetics. the operative word is comparative.
They build a entire paradigm on mere comparisonism.
So i say that if there is another option for likeness then its not just another option but nullify’s the comparisonism as a claim for biological evidence.
There is no biological evidence for common descent.
Now another problem.
Common descent could be a minor operation but this is not evidence for everything..
Micro does not equal macro!!
To claim biology bacvks up common descent, in macro things, demands that no other option can explain likeness.
Creationists say its an option God created on creation week all creatures with eyeballs and in exactly the same way. The same blueprint.
its not demanding biologal evidence that like eyeballs equals a common descent from a original critter with these eyeballs.
This includes they would have the same dna.
In short its an issue of science philosophy about evidence.
evolutionism has no biological evidence or I’ve never seen a evolutionist present it and prove it was biological and not something else.
Yes Indo european males sense without evolution in language.
What came first was the segregation of tribes, then the confusion of languages at babel, and all in a logical march.
So japhet is the great indo european family but the languages did not, no evidence, evolve from some original tribe.
It was instantly changed slightly for many.
Born from parents does not prove common descent except for that kind. its not proving evolution of body types to other body types.
In fact parent/kids doesn’t do this but only, they say, a selection action on some marginally different trait on one of the kids.
since there are admitted types or kinds, before ideas of origin, then finding like traits between these kinds is no evidence of common descent. Even if they were from common descent.
It would also be from a creator that like traits would be given unlike kinds.
Its an option for a thinking creator.
Likewise dna simply would shadow this. Like traits etc equals like dna but not because creatures are from common descent.
Man has like dna with apes but its only because we have the same body type.
Its just lines of reasoning to say like bodies equals like descent.
Yet God easily would do this too.
So common descent is not proven biologically or by genetics merely because of sameness.
Thats not scientific evidence but only philosophical evidence.
Another philosophy easily trumps it or equals it.
Allan Miller,
Based on this what is you’re working definition of Evolution?
The evidence for common descent involves evidence from biogeography, development, fossils, present-day morphology and molecules. It is not just an inference from Darwin’s discussion of linguistics.
Starting in the mid-1700s, biologists (who were largely creationists then) noticed the concordance in the hierarchical classification, reflected in many kinds of characters. By the time Darwin wrote, most biologists were ready to accept that this reflected genealogy.
Today we would describe this evidence differently — by pointing out that different sets of characters produced evidence for the same (or very similar) phylogeny. As molecular sequences have become available, the same pattern is seen. We can predict that if we take a new set of (say) 10 loci, and infer a phylogeny from it, it will largely support the conclusions from other loci.
Doug Theobald, who knows this evidence well, has described it in his paper on 29 Evidences for Macroevolution.
Darwin could be completely wrong about linguistics, and that wouldn’t have the slightest effect on the conclusion that organisms are connected by a genealogy reflecting descent with modification. Sure, there are other processes like hybridization and horizontal gene transfer, but that is the main signal in eukaryotes.
colewd,
It is summarised by ‘descent with modification’. Of course you’d like to invoke 1 extra cause for the ‘Modification’*** part. That does not change the fact that the evidence is for Descent.
*** Originally I’d made a typo there – ‘Nodification’. I quite like that. Evolution is Descent with Nodification.
Well, my overall point is not that the analogy between linguistics and biology is poor. My overall point is that, having now taken a look exactly in what way the analogy is poor, linguistics seems to have a far more rigorous standard for evaluating the evidence. Therefore, let’s see “the preponderance of evidence in favor of evolution [actually, universal common descent]” that you mention.
When Darwin mentioned linguistics, he was not inferencing from linguistics. He was inferencing from morphology and other observable similarities, like linguists do. Except that linguists do it with caution and care, taking due note of differences and knowing that features can converge easily to similar appearance due to contact or even by pure chance and even be the same all along with no justification to posit a common ancestor. Darwin failed to take note of that part. Darwin posited primary common source as if giving a reason, but it’s the wrong reason, and declared all the current variety secondary.
The same book, the same chapter (too bad he didn’t write in a briefly quotable way), “I believe [the element of descent] has been unconsciously used [in grouping species under genera, and genera under higher groups]; and thus only can I understand the several rules and guides which have been followed by our best systematists. As we have no written pedigrees, we are forced to trace community of descent by resemblances of any kind… We care not how trifling a character may be – let it me the mere inflection of the angle of the jaw, the manner in which an insect’s wing is folded, whether the skin be covered by hair or feathers – if it prevail through many and different species, especially of those having very different habits of life, it assumes high value; for we can account for its presence in so many forms with such different habits, only by inheritance from a common parent.”
In contrast, linguists pay a lot of attention to how “trifling” a character is as opposed to *relevant to tracing the ancestry*. The word “internet” may be common to all languages, the letters/sounds “i” and “n” and “t” may be common to all languages, it does not follow that these particular shared features can be accounted for only by inheritance from a common parent.
Darwin is not only wording things badly here. He is reasoning on totally false grounds, on no ground whatsoever I’d say. He stepped into the territory of metaphysics without having a capacity of orientation.
Openly available? Link?
I hope I have demonstrated by now that Darwin was wrong about something decisively fundamental, relevant to everyone who classifies stuff.
Erik, there must be genomes that you accept are commonly descended, and others where you consider the inference less secure. It might help focus discussion if you would indicate what evidence causes you to accept descent yourself (where you do), and the taxonomic level at which you think this inference breaks down.
No, there aren’t, because I know nothing about genetics. However, I have already acknowledged above that the debate has effectively narrowed down to genetics. All other arguments for common descent, such as “all organisms reproduce” or “shared morphology here and there”, fail totally. Maybe arguments from embryology and atavisms and such have some slim chance too.
I know, which is why it would have been important for the text to have stated so. Instead, the text says, “At a very minimum, these four functions are required to generate a physical historical process that can be described by a phylogenetic tree.” Without nothing further required, it very much leaves the impression that they are saying that those functions are minimally sufficient for common descent.
Erik,
It might help if you did before bloviating about how slack biologists are compared to linguists.
It hasn’t really. It is just the most incontrovertible arena of evidence – one of which Darwin was completely unaware. It has confirmed his arguments in spades, while providing powerful tools to resolve relationships on which coarser tools are silent.
I’ve never seen the first advanced as an argument. I agree it would be a weak one, if offered. And the second expressed in such a lily-livered way is also weak, which might incline one to express it thus, if one were determined to remain a critic. But to do so would be to attack a strawman. Morphology is not useful beyond certain taxonomic ranks – not least because there are (apparently) multiple transitions to multicellular morphologies.
Cell morphology is certainly shared, but again this breaks down at the prokaryote-eukaryote boundary. Nonetheless, these take us one hell of a way towards universal common descent, even as they stand, without genetics.
Have you read Darwin? It might have helped him if he had done some study before bloviating anything about linguists…
And this is supposed to help him out how?
Rumraket in the OP.
This is the “all living organisms are cellular, therefore common descent” argument. About as good as “all languages have vowels and consonants in them, therefore common descent.” Not good enough.
All you have is genetics. Maybe, because genes might not work the way you expect. Namely, instead of enabling evolution from species to other, their function could be to restrict reproduction to within the same species.
Erik,
You’re doing it yet again — galumphing into an area in which you have no expertise or even aptitude, declaring that the entire community of experts is wrong about something fundamental.
The problem here is not with the biological community. It’s with you. You’re in full crackpot mode again.
Erik,
Christ, yes! I read the original 1st edition back in 1860. I jest, but what on earth makes you think I haven’t read Darwin? Regardless, evolutionary theory did not start and finish in 1859.
It’s a fact that something of which he was unaware provides posterior confirmation for his arguments – and, indeed, a mechanistic basis for the patterns he could use. So, like that.
You have misunderstood his point. Organisms that reproduce do not prove universal common descent. A branching pattern of descent is, nonetheless, an expectation of a reproducing lineage, back to the origin of that lineage. Multiple reproducing lineages of independent origin are a possibility. ‘All organisms reproduce’ is not intended to disprove that possibility.
No it isn’t. You are just strawmanning it again. I referred to cellular morphology. That is much more than the mere existence of cells, if you would just trouble yourself to peer down a goddamned microscope!
What is the vowel or consonant in this analogy?
The way I expect is that, given reasonable replication fidelity, genomes are copied in their entirety through the generations. This is a potential source of genetic commonality that can hardly be ignored.
If you divide a population, such that gene flow between the parts ceases, how is that restriction to be effected, across the boundary?
Oh, so his argument was actually irrelevant to the point. I misunderstood, my bad.
The analogy with linguistics can be easily extended, “All languages have vowels and consonants that appear in pronounceable sequences. They form words and sentences. The words and sentences have meanings. It’s amazing how languages can borrow words from one to another as if they were a single species, regardless of synchronic typology. Surely given all this wealth of evidence, it must follow that they must trace back to a single common parent!”
Nope. All this does is list the kind of phenomena that occur given certain environmental conditions where the phenomena can occur. It does not follow that the environmental conditions at first occurred in a single given place.
If “replication fidelity” means that the offspring has the same features as the parent(s) and cannot deviate beyond a certain point, then this is an argument against common descent, not for it. There must be evidence that genome can, under favorable conditions, “naturally” stretch so that a species transforms into another, and that there is really no boundary to that stretching.
And even that would not properly prove universal common descent, just like the easily observable flexibility of language structures does not.
Erik,
Please define “species”.
Erik,
Do you think there is an argument that could be made that you should have done them same regarding biologists?
Erik,
http://lmgtfy.com/?q=29+Evidences+for+Macroevolution.
Hope that helps.
Let’s follow Darwin, shall we? Chapter II.
“No one definition (of species) has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species. Generally the term includes the unknown element of a distinct act of creation. The term “variety” is almost equally difficult to define; but here community of descent is almost universally implied, though it can rarely be proved.”
Oops, he said “act of creation” and “community of descent is almost universally implied, though it can rarely be proved.” Let’s try elsewhere.
“From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sake of convenience to a set of individuals closely resembling each other, and that it does not essentially differ from the term variety, which is given to less distinct and more fluctuating forms. The term variety, again, in comparison with mere individual differences, is also applied arbitrarily, and for mere convenience sake.”
So there, Darwin’s definition is “arbitrarily given for the sake of convenience”, as if making it up as he goes along. Not my job to help him out.
From the other thread.
So reproduction has nothing to do with proving evolution and the evidence for evolution must be something totally different. Then why did you (and why does Theobald) bring up reproduction as required evidence for common descent? Let’s get relevant. So I’m henceforth justified to ignore your references to reproduction?
Yes, things form patterns when you categorize them. It does not prove common descent though. The similarity of a cup and a vase tells nothing about which one evolved into the other one, and if they did so at all. The relevant proof would be either a direct line of traceable intermediate forms or the general knowledge that those kinds of things morph into each other all the time. This does not quite apply to biological species, does it?
As I have quoted already (emphasis mine),
What are those firm evolutionary arguments? Did they presuppose common descent or did they argue for it and lay out what proves it?
Rumraket already pointed out to that you’re ignoring the differences between evolution and linguistics. We know occasionally words like ‘internet’ transfer from one language to another “horizontally” (loanwords?). This would be analogous to horizontal gene transfer in biology, but I believe HGT is very rare in Eukaryotes. Most of the variation is transmitted vertically, by means of inheritance.
So the problem here is that you’re choosing to focus on the aspects of the analogy between evolution and linguistics that don’t work, and then pretending that what applies to linguistics in those cases should also apply to evolution. That’s just silly.
And Rumraket and you keep ignoring the fact that, by Theobald’s own admission, the standard for classification used by biologists can prove the common descent of anything, even things nothing to do with biology. I will be very grateful for those “firm evolutionary arguments” in support of common descent. Thanks.
Look Erik, I have worked for over half a century on the logic of methods for inferring phylogenies. Since back when there were about 6 people in that field. Up to today, when one of my papers is the 41st most-cited paper in all of science. I wrote the standard book on inferring phylogenies. And I distributed the first widely-distributed package of programs for inferring phylogenies.
So I know how the algorithms for reconstructing phylogenies work. They have gotten steadily more sophisticated and steadily better and better at assessing how conservative or how labile different parts of molecular sequences are. And no, they contain no step that tells the program to make sure to put anything called “chimpanzee” in the tree near anything called human. And yet, they keep doing that. Owing to the evidence.
Take a look at the evidence yourself. Try Orthomam, at
http://www.orthomam.univ-montp2.fr for example, a database of sequence alignments for (now) 14,526 protein-coding loci for 43 completely-sequenced mammalian genomes. And there they have trees, inferred automatically, for each locus. Or you can download the some of the aligned sequences, get one of the free phylogeny programs, and infer the trees yourself. Check out how similar the trees for different loci are. That’s important. Not just that they are trees but which trees they get for different parts of the genome.
If you have problems, ask an expert. Say John Harshman, who is an experienced molecular systematist who is a considerable expert on genomic and morphological evidence on bird and reptile phylogeny, and who uses phylogeny algorithms all the time. My 2004 book contains a section discussing, admiringly, his arguments about using bootstrap sampling with parsimony methods.
There are others here as well who have lots of relevant expertise. Stop lecturing them about how they are making elementary and fundamental mistakes. (In the passage you quote, Darwin didn’t make any mistake either, though you seem to think he did.)
I’m not trying to suppress discussion, just trying to urge you to look at the mass of evidence before making wild statements.
Yeah, I know, it’s always a mistake to “pull rank” and cite one’s own credentials in these discussions. Makes one look like a pompous defensive idiot. We do have to listen respectfully to any argument, no matter how little background the person has who puts it forward.
But in this case Erik is lecturing us about how we have all gone wrong, and when you look at his arguments, it’s like what Gertrude Stein said about Oakland, California: “When you get there, there’s no there there.”
No way, you’re simply stating facts. You earned your stripes. You’re a fucking legend. Period.