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.
I would ask: Who is their common ancestor? I see you replied in the other thread: None, as far as you know. You can of course say that this does not necessarily lead to the conclusion I like, but it doesn’t lead to the conclusion you like either. So we’re even.
Erik,
We have data – genomic data. Which way do you think it points? 50/50? I realise it’s possible to just stick your fingers in your ears and deny, deny, deny. But you seem to be trying to persuade someone. So what would cause one to prefer the ‘conclusion you like’? (Which bizarrely seems to be that the Common and Spotted Sandpipers were separately created with almost identical genomes).
You tell me how “50/50” and “None, as far as I know” can live together just fine in your head.
Obviously, we don’t disagree about the data. We only disagree about how to interpret it and this is a point that easily gets philosophical and ideological. Necessarily so when the data is insufficient.
To make our agreement broader, let’s explicitly agree that the data is insufficient to establish common descent, certainly universal common descent, which is the topic of the OP.
Erik,
‘None, as far as I know’ refers to the question on whether a given fossil has been shown to have descendants in the present. It would also be the answer to the question ‘How many fossils of the Common/Spotted Sandpiper common ancestor are there?’.
’50/50′ refers to your apparent belief that the genomic data on those sandpipers is silent on whether they are related or not.
So, like that.
Erik,
“To scuttle away with the goalposts, ‘cos I’m obviously on shaky ground with the Sandpipers, let’s talk about something else”.
First things first. Look to the Sandpipers, and consider their ways.
The topic was there in the OP from the get-go. It’s you making the target as small as possible.
So, who was the common ancestor of sandpipers and how does that have any relevance to universal common descent? You like genomic data. Lay it out.
Erik,
If you can’t even get your head round the case on two closely related species, the rest will be a waste of time.
Universal common descent (if it were the case) would include all lower-level relationships, such as those very Common and Spotted Sandpipers. You really have to understand how relationships and evidence at that level work first. You seem strangely resistant.
You want the actual genome sequences in full?
Typically, for practical reasons people use a sample of genes, rather than entire genomes. If one doubts the sample, one can always sample more genes. There comes a point where it would seem pointless to keep sampling – if the info doesn’t change, you’ve got reasonable coverage.
We don’t disagree about the data. We disagree about the interpretation.
Give as much data as you deem necessary, but the crucial point is that it must be accompanied with your analysis and how it leads to your conclusion.
Erik,
Let’s just try a hypothetical first. If one 3-billion base pair genome was identical to another in 99.99% of positions – an average 1 difference per 10,000 bases – what would be the most robust conclusion as to the cause of that extensive identity: common descent or ‘something else’?
If something else, what is it?
Note that at this point all you have are the sequences.
Yep, and that’s why it’s inconclusive. It’s not enough to have plenty of similar sequences. We must know what they are sequences of and what those sequences do. Otherwise it would be like the similarity of a huge cup and a small vase: Let’s say they are 99.99% identical, so common descent must be the most robust conclusion, right?
Looks like all evidence points to that the theory of common descent was not posited based on biological evidence at all. It’s an assumption on some other grounds and it’s held at least as long as the data is not perceived too incongruous with it.
Erik,
You here confuse digital character states with analogue ones. A better example, in line with your linguistic obsession, would be two books that differed in just 1 in every 10,000 letters. What more would we need to make a perfectly justifiable contention that, on the evidence, these had a common origin? We don’t need to know what any of the letters do.
So to ask again: what is your ‘something else’ – the alternative hypothesis against which you are evaluating common descent? Common descent (template DNA copying) produces closely related sequences. The error rate of DNA polymerase guarantees some differences. We find two sequences that are mostly similar, with some difference. That is precisely predicted by template copying of DNA. Why do we discard this as an explanation?
On the book analogy: Perhaps copies from the same printing press, except that somebody tampered with the printing press meanwhile.
On genes, there’s variation sure enough. Children are very much like their parents, but not perfect copies. The variation stays within the same species though. It gets odd when there’s disagreement on this empirically observable point.
Erik,
ie Common Frigging Descent! Jeez, it’s like pulling teeth.
If an ongoing process of small change continued indefinitely, past the point at which dividided subpopulations could interbreed, we would simply have more of the same. But you seem to regard speciation as a lineage leaping out of one bath (in which variation can occur) and then into another (in which variation can occur). Why do you exclude the possibility that it is simply continuous change with branching, no containers required?
Somebody making copies at the printing press and tampering with it occasionally is just as much common descent as it is special creation. So you are basically saying the two are the same.
In discussing with somebody else here, we arrived at the same conclusion. So be it.
It’s a hypothetical possibility against any and all observations. Need more data.
Erik,
‘Special Creation’ is the same as whatever you want it to be. My brother and I were both specially created. I defy any paternity test to say different.
How do you envisage the ‘genetic’ process working, when it’s not actually mediated by DNA polymerase? Why would a designer need to do anything other than use DNA polymerase?
Erik,
Nope. It is a prediction of descent with modification. There are clearly possible observations that would lead one to discard it, for real data.
I’m not sure if you’re just typing random words at this point.
Somebody more evolution-minded would make his analogies more specific to evolution. Your book analogy is indistinguishable from Paley’s watchmaker.
I don’t even know what “mediated by DNA polymerase” means, so I am not denying anything here. The relevant point is whether “mediated by DNA polymerase” means what is necessary and sufficient to make your point. Specifically, does it mean that a species can evolve into another as opposed to being doomed to breed the same species indefinitely. The latter seems to be the case rather than the former, based on observable data, if that still matters to you.
If he needed to do just that and nothing else, then does it follow that there was no designer? (It’s not a concept I would use, but you keep bringing it up. It’s getting less and less clear why.)
Erik,
Non sequitur. But rather proves my point about analogies being a pointless distraction. Let’s screw them, shall we? Let’s talk about the actual process of genetic inheritance.
DNA polymerase is the enzyme responsible for faithful copying of a DNA sequence. It is imperfect, hence there is a source of difference in the sequences.
You are wishing to deny that two near-identical sequences, which are potentially a product of a physical process of sequential template copying of DNA (by DNA polymerase), actually result from a process of sequential template copying of DNA. So if it isn’t that, what could account for the sequence identity we observe in closely related (I’d ‘say ‘related’ but for the Mung sitting on my shoulder misunderstanding why) species?
Why “imperfect” rather than “permitting variation within the limits of species” as actually observed?
The fact that speciation usually happens over time-frames longer than what humans can observe would only be a problem for the epistemic status of evolutionary theory if we were to institute a more general principle: that we are never warranted in making claims about processes that unfold over time-frames larger than what a normal human being can be expected to observe over his or her life-time.
But on that more general principle, we would have not only reject paleontology but also archeology, cosmology, astronomy, geology. We would end up shrinking our knowledge of the universe to fit the narrow glimpses we can acquire with our unaided mammalian senses.
The principle is that even given enormous time-frames, remain grounded, not haphazard in your claims. In scientific terms, be evidence-based. Should not be too hard.
Regardless of the scale we are talking about, there are warranted claims and unwarranted claims. Warranted based on something and unwarranted because not based on anything. No amount of time frame or distance changes this.
Indeed, and it is not. The evidence you’re asking for has already been presented in this thread and others at TSZ. Why an intelligent person such as yourself is having difficulty seeing this is a mystery to the rest of us.
I imagine Erik believes that he’s simply holding evolutionism to the same rigorous standards that his own field hews to. No more and no less.
The supposed evidence is unwarranted and usually proves too much. Among the very first given was exactly your excuse: Very Long Time. Given that, absolutely anything can be said, such as God created stuff and is now resting. Same result.
No evidence has been given to conclude evolution specifically, instead of special creation, alien/designer intervention or whatever.
For example, if evolution is slow and gradual, then there should be attested direct ancestors to current species. Yet I have been told that there are none. This doesn’t compute with Darwinian macroevolution. It’s evidence against it.
So why are the patterns those predicted of evolution, and are not what we see in manufactured goods? In vertebrates, it’s pretty much just vertical derivation in functional sequences, limited to that by the means of DNA transmission.
The evidence is of evolution. You just can’t handle it.
Glen Davidson
Erik,
What sort of evidence could be produced that could also not be faked by the devil?
None so blind. That’s part of phrase you probably already know, as a linguist. Can you complete it?
Really? So evidence of transitional stages in organisms closely related to the actual ancestor (shown to exist by genomic evidence) is actually evidence against evolution? Or are you just nattering away in your ignorance of the fossil record (far from complete) and your lack of understanding of how evolution must and does occur?
So far, I’ve seen a lot of denial and very little understanding in your creationist nonsense.
Glen Davidson
Nope, nothing like that has ever been found. We wish, eh! That’d sure show them…
Such as? Are you saying newly-found species find their place in the taxonomy without difficulty?
Anyway, if evolution is essentially random, then difficulties in classification should be very much expected and evolution would really NOT be predicting any specific patterns, but more like making it up as one goes along, in the spirit of Darwin. Because, you know, you have to survive and circumstances for survival change all the time so the course of evolution should be ever-shifting.
Then again, classification difficulties would be true given special creation too. This point does not confirm anything one way or the other.
What is that even supposed to mean?
The fact is that species inherit their genes, and cannot deviate greatly from those in a short period of time, hence recently diverged species must be quite close genetically.
Are you just shotgunning away? Do you have any idea of what role randomness plays in evolution, vs. the commonalities occurring via descent (and in some cases, horizontal gene transfer)? It really won’t do for you to come in with no knowledge about evolution, thus using terms in a very incorrect manner.
IOW, that’s too ignorant a view to address, except to say that you need very much to begin to understand evolution, rather than using bits and pieces as slogans in your propaganda against it.
Unless you know something about evolutionary theory. Which you need to begin to do.
Glen Davidson
Thanks, picture says more than a thousand words. Particularly when the words are “None” which is the answer I have gotten earlier to the same question.
That said, some words are still telling, “Hyracotherium (/ˌhaɪərəkoʊˈθɪəriəm, -kə-/[1][2] HY-rək-o-THEER-ee-əm; “hyrax-like beast”) is an extinct genus of very small (about 60 cm in length) perissodactyl ungulates which was found in the London Clay formation. This small, dog-sized animal was once considered to be the earliest known member of Equidae before the type species, H. leporinum, was reclassified as a palaeothere, a perissodactyl family basal to both horses and brontotheres….” https://en.wikipedia.org/wiki/Hyracotherium
Should not be happening if the line of descent is as straightforward as in the picture.
Well, I can say stuff like this about Darwin too. Yet I am making my best effort to address his ideas.
What I am getting here is that there’s no clear evidence for evolution. Intelligent people (KN’s term) are laboring under misconceptions that do not deserve an illuminating response.
This goes both ways. Nobody on the side of evolution displays even the remotest understanding about what the claim of universal common descent entails and what it takes to prove it. Instead they expect they can just say stuff or align pics of similar animals. Yeah, I’ve noticed that leaner pigs resemble horses somewhat. So what? If this is good evidence, then it’s okay for Mormons too to say that tapirs *are* horses and this proves that Book of Mormon is true.
This indicates a pretty serious misunderstanding of what “randomness” in evolution actually means. Evolution is not “random” in the sense of not conforming to any predictable pattern at all. (In that sense, evolution is not “random” in the same sense that atomic decay is “random”.)
The supposed “randomness” of evolution consists solely of the claim that there is no empirically detectable mechanism that first anticipates what traits will be adaptive and then causes those traits to come about. (This is how Eliot Sober, one of the foremost philosophers of evolutionary theory, puts it.)
That depends on what the standard for “clear evidence” amounts to.
If you demand that “clear evidence” requires that we have direct observation of speciation, well, we do have for some very short-lived animals (also for plants that can evolve quite differently from how animals evolve). And there are no empirically detected mechanisms that prevent speciation events from accumulating into larger macroevolutionary changes. (Behe was trying to show that there are, in Edge of Evolution, but his claims have been debunked by Kenneth Miller and others.)
All that evolutionary theory says (and needs to say) is that hereditable variation (which can be caused by several mechanisms) and differential reproduction due to varying degrees of fitness can explain the observed consilience across multiple lines of evidence: genetics, paleontology, ecology, embryology, comparative anatomy, and biogeography.
Of those, genetics was the only one unavailable to Darwin.
Firstly, there’s some ambiguity in what “universal common descent” means in the hands of biologists and non-biologists.
There’s a difference between saying (1) “for all species, that species evolved from some previous species” and (2) “there exists one species from which all other species evolved”. (With a bit of symbolic logic with quantification, one can see that the two claims are logically distinct — and also, with a bit of work, it can be shown that the (1) does not entail (2).)
Secondly, the difference between evolutionary theory and Mormonism (for example) is that we have empirical verification of some of the mechanisms that drive the patterns we observe in the fossil record. Mormons have nothing comparable.
You seem to be laboring under the impression that all just-so stories are created equal. That’s simply not the case. There are multiple lines of evidence that strongly support evolution, and nothing yet that undermines it.
Kantian Naturalist,
What empirical verification do we have?
Erik,
It’s amusing to see it phrased like that. In reality there is only one “side” of evolution, the reality based side. There may be disagreements, but it’s reality based disagreements. The only people who think there are two sides are the people who don’t understand anything about it.
Yeah, people just “say stuff” and expect to be taken seriously. Laughable, I know
It’s a picture from wikipedia. It’s caption says: This image shows a representative sequence, but should not be construed to represent a “straight-line” evolution of the horse.
https://en.wikipedia.org/wiki/Evolution_of_the_horse
Feel free to have a read. And it prompts me to ask, what independant research have you yourself done on the evidence for common descent? Or are you just simply asking the question here and waiting to be spoon fed?
I see. Sort of self-defeating pic then.
And the crucial point here that I failed to understand is…..?
It’s already awkward that I have to demand anything. In science, it should be straightforward – evidence in proportion with and as per the nature of the claims.
Or we could do what some people here do: Extraordinary claims require extraordinary evidence, specifically empirical evidence, no matter what the nature of the claim. Universal common descent is an extraordinary claim.
Short-lived why? And in what sense were they different species? Oddly the definition of species here has been no better than the definition of design in IDism.
Without looking any further, my hunch is: The evidence involved was nothing but some statistical model. At best it was on genetic data.
So how did Behe try to prove his claim and how was he debunked?
Another thing interests me, though I haven’t brought it up before: Can species devolve? E.g. why say Humans came from Australopitecus (or whatever) rather than the other way round?
Common descent says quite a bit more than this.
The topic has not been unclear at all. Some have been trying their best to make it unclear and they have been unclear themselves.
Yes, the two claims are distinct, which is why a common ancestor of, say, finches has no bearing on the actual topic.
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?
And could you describe what you think the actual topic is?
Erik,
Yes, the picture illustrates nothing of use nor of interest to anyone whatsoever. Nothing in the fossil record can be shown scientifically to be related to anything else in the fossil record.
You are missing something that is central to how science evaluates theories: they are judged on how well they explain the evidence. “Explain” means something slightly different in science than it does in common speech — in science, to “explain” something is to explain why it is the particular way it is (and not some other way), not just to explain how it could happen to be that way. Thus, explanation in science is essentially equivalent to prediction of future observations and retrodictions of past observations.
Let’s take a simple historical example: whether the motions of the planets are better explained by Newton’s theory of gravity, or by angels pushing them around the Sun. Newton’s theory makes a number of specific predictions about the planets’ motions: they’ll follow elliptical orbits with the Sun at (or very near) one of the ellipse’s foci; their speed will vary such that their angular speed WRT the Sun is inversely proportional to their distance from the Sun; and their orbital periods will be proportional to the 2/3rd power of the semi-major axes of their orbits. These are known as Kepler’s laws, and were known before Newton developed his theory of gravity. Newton’s theory provided an explanation for these laws.
It is important to understand that the “angels” theory (which is not a scientific theory) is also entirely compatible with Kepler’s laws. Angels could move planets however they wanted to, and there’s no reason at all that they couldn’t move them according to Kepler’s laws. But they could also move them in completely different ways. Thus, the “angels” theory cannot explain (in the scientific sense) why planets move in these particular ways.
In scientific terms, this difference in explanatory capability between gravity vs angels means that the motions of the planets are considered evidence supporting Newton’s theory over angels. This doesn’t necessarily prove that Newton’s theory of gravity is right (it isn’t), but that it’s a better theory than the angels. It also means that any theory that seeks to replace it will also have to explain the planets’ motions as well as Newton’s theory does (as general relativity does).
(BTW, I’m oversimplifying things a bit here. Anything you can read in an afternoon on about any nontrivial topic is necessarily an oversimplification. Get used to it.)
Now, let’s look at how this applies to the phylogenetic evidence. I’ll pick out two specific things: that the patterns of similarity between different (contempurary) species should form a nested hierarchy, and that this same pattern should appear across different features (e.g. the congruence between trees inferred from morphological characters vs. cytochrome c that keiths cited).
Branching common ancestry explains (/predicts) this, because species with more recent common ancestors share more evolutionary history, and have had less time to develop different features, and therefore will tend to be more similar. With an ancestral tree, you’ll inevitably have a nested hierarchy of groups descended from various ancestors. And since this grouping applies to the species as a whole, it’ll apply across all features of the organisms (although there may also be other things influencing some features, which complicates the picture).
(Note: you appear to be having some trouble understanding how these predictions works out. This is exactly as relevant to the predictions’ validity as whether you can work out the calculus to derive Kepler’s laws from Newton’s theory has to those predictions, i.e. none at all. The theories work the same whether you understand them or not.)
Design (without common anestry) is consistent with this pattern of similarity, but does not predict or explain it. Look at cars, for example: if you were to group them by manufacturer and model, you’d find very different engines, transmissions, body styles, etc under the same model and/or manufacturer, and very similar engines, transmissions, body styles, etc under completely different model lines. Depending on what feature you pick, you’ll get wildly different patterns of similary.
And the cars’ individual features don’t fall particularly well into nested groups either. Here’s a test: try arranging the different common body styles into a nested hierarchy. Seriously, try it. I’m pretty sure you’ll find that while it’s entirely possible to arrange them in a nested hierarchy, that hierarchy won’t do a very good job of grouping similar designs together.
Thus, this pattern of similarity is evidence for common ancestry. And as with Newton’s theory, it means that any theory challenging common ancestry will have to explain the pattern at least as well as common ancestry does. Design does not do this (unless you add common ancestry to it). Nothing else I’ve seen even comes close to explaining it as well as common ancestry does.
If you want to challenge common ancestry, you need an alternative that actually explains (as in prediction and retrodiction) the pattern, not something that’s merely consistent with it. So far you have nothing.
Erik isn’t so much interested in explanation and evidence, as he is in taking another opportinity to put his capacity for staunch denial on display. It’s a kind of creationist virtue-signaling. It’s pretty much the only thing IDcreationists ever do around here. They don’t so much discuss and debate the subjects as they just find new and inventive ways to express the mere fact of their disbelief.
Gordon Davisson,
Nicely done, Gordon. Good to see you.
I’ll add the remark that critics of the theory of evolution often play divide-and-conquer. The greatest strength of the theory has always been that support comes from multiple, dissimilar lines of evidence. 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.
Shouldn’t read threads in reverse order, should I?
John Harshman,
I think it’s ‘give evidence for universal common descent without any reference to evidence at non-universal levels’.
I think, ultimately, Erik might be displaying his faith to God. “See how I withstood their arrows. Reward Me”. I guess that’s a rule-breaking observation, but I see no better explanation for denying even the most trivial of common descent evidence.
Gordon Davisson,
How do you determine how well the data fits the common descent hypothesis? How do you explain contradictory evidence like convergent evolution?
Tom English,
Fair point, but it’s that or Gish Gallop ISTM. I’ve been trying to pin things down to one trivial observation in one species pair. The wriggling response has been quite illuminating, but also illustrates the pointlessness of going anywhere else with someone hell-bent (pun half-intended) on denial.