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.
Now come up with a prediction based on your explanation. Bet you can’t.
colewd,
What, not even in forensic DNA fingerprinting or within-species genealogy? Don’t you think you ought to before spouting off about how everyone is wrong?
The cause of sequence identity is primarily template-based copying of DNA. This occurs every time a cell replicates, and also more locally during homologous repair, the related process of crossover formation in meiosis, or during transposition events.
The cause of sequence differences in general is mutation, from various sources. Splicing code differences and gene expression differences are irrelevant here. There is a distinction between genotype (underlying sequence) and phenotype (things that sequences cause to happen in lives). The thing being compared in molecular phylogeny is the former.
Mung,
Seems pretty clear to me.
If no members of population A can interbreed with any member of population B, even when placed together, that is complete reproductive isolation. There are of course other mechanisms – such as a physical barrier, on removal of which the populations are no longer reproductively isolated because there is no physical or genetic incompatibility. It should be clear I wasn’t wondering whether the physical barrier can evolve …
So, armed with this pretty unnecessary clarification, can a single population get to become two populations, none of the members of A being capable of interbreeding with any from B even if located in the same area, though evolution?
(hey, let’s argue about what ‘evolution’ means again … no, let’s not. You do know what I mean by it).
CharlieM,
You could usefully forget your pet taxon for a moment and look at invertebrates, fungi, plants or bacteria … the explanation you have come up with applies to a sequence ultimately leading to … ta-dah! … Charlie! The more general explanation, hardly based upon ‘beliefs’, works for any group.
Allan Miller,
*through evolution, soz.
Dude, I wrote a post on this very subject. Didn’t you see it? Brady is wrong.
But as far as I can tell we’re both coming up with the same explanation. You just add some mystical nonsense on top of it that doesn’t actually have anything to do with explaining the pattern.
We don’t use our belief in common descent to justify the nested hierarchies we observe. Well at least I don’t. Once again: common descent is a conclusion, not an assumption. You and Erik make the same consistent error.
And that makes me curious: what gives you your belief in common descent? What sort of evidence if not that nested hierarchy?
Well, not so much wrong as not making the claim you seem to think. Brady is just saying that the nested hierarchy can be discovered without prior reference to evolution, which is certainly true. And then he quibbles about how “homology” should be defined, which is in fact irrelevant to his point, and that’s where he’s wrong. But I agree with his main point, and that in fact argues against your claims, not for them. As he says, common descent is the explanation of nested hierarchy, a conclusion, not a prior assumption.
Allan Miller,
This is true when you have a direct paternal relationship but how about when you don’t?
How can they be irrelevant? You do not believe that gene expressions differences and splicing differences effect phenotype? How would you demonstrate that the differences come solely from mutation?
Gene expression and splicing differences do affect (note spelling) phenotype. And differences between species in gene expression and splicing do come solely from mutation. That’s what you find when you investigate the causes of those differences, which result from differences in DNA sequences. Where do you think they come from? And how are they relevant to the causes of nested hierarchy in genomic data?
colewd,
So you think one generation of DNA copying accounts for sequence identities, but not two or more?
Of course they affect phenotype, and I said as much. But sequence-based analysis does not take account of phenotype, and hence they are irrelevant to it.
If you have something beyond the known causes, you are the one who needs to demonstrate the difference, not I.
You must accept the logical possibility that all differences between 2 sequences are accounted for by known mechanisms of generation of variation occurring incidentally during the cell cycle, surely? I don’t see any requirement to import any other cause. Let’s not forget the differences are embedded in vast seas of identity, indicating genetic relationship.
Allan Miller,
I think this conclusion is highly unlikely. The cell cycle minimizes variation in order to keep its repeatable function.
The logical conclusion that we understand the cause of similarities and differences of the DNA sequences between different species is almost certainly wrong. There is little experimental evidence that would allow a real scientific conclusion here.
Do you believe that we can explain the diversity of life solely from reproduction originating from a UCA?
colewd,
It is absolutely, 100% observably clear that mutation happens, along with all the other sources of variation I’ve mentioned. You think I’m making them up?
I’ve been through the care with which one needs to interpret LUCA before, to no avail.
Still … if one substitutes nucleic acid replication for reproduction, recognises that LUCA is not the first ever organism, and adds in the population resampling processes of drift and selection, a dash of LGT up to full-organism symbiosis, then … yeah, pretty much.
Allan Miller,
We have common ground. Mutations happen 🙂 Your faith on what they can create has to be admired.
colewd,
Jeez. You just said they don’t because the cell cycle has error correction. Make your mind up.
My faith is neither here nor there. As far as I can see, the thing you doubt – common ancestry of lineages with more differences – has the potential to be accounted for by the same basic cause as the thing you don’t doubt – common ancestry of lineages with fewer differences. Naturally, the longer lineages are separated, the more differences will accumulate, regardless what strange magic you’d like to invoke besides. Given the reasonable expectation of time-proportionality, ‘more differences’ is not a reliable counterfactual to common descent.
You still haven’t made clear why the inference of common ancestry in the many-differences case is circular, but not the comparatively-few.
Allan Miller,
To say they are minimized by DNA repair is not to claim they don’t happen. Do you really believe that my claim was that no mutations happen?
This has continually been a problem claim you have made. You are comparing something that is backed up by evidence (common ancestry of lineages) vs common ancestry across lineages. The latter is contradicted by the evidence that species variation stays inside a tight band. There is also no reason to believe that random change can find unique advantageous functional capability like flight, breathing or digestion.
The evolutionary canard is to claim that evidence of small adaptions is evidence that the diversity of life can be explained solely by reproductive variation.
You are clearly hiding behind ambiguity. Not only do mutations happen, but their observed frequency is after all mechanisms of DNA repair have already operated. Direct parent-child sequence comparisons show us that not only do they happen, they accumulate between generations. Comparisons of conspecific populations show that they accumulate in those populations. It shouldn’t be a big jump from that to comparisons between recently diverged species, for example humans and chimps. And yet it’s a non-jump you are not prepared to make. Why?
It’s the same eivdence.
What evidence is that? I don’t know of any.
That’s an entirely separate question, irrelevant to common descent. You keep trying to confuse the two. And there are good reasons to believe that random mutations followed by natural selection can do all that stuff. But it’s still irrelevant.
Again, irrelevant to the question of common descent. But unless you have evidence that small adaptations can’t accumulate indefinitely, I don’t see why you would consider it a canard.
colewd,
Hard to see the relevance otherwise. I’d said differences are caused by mutation, you’d said dubious because of error correction. Why even mention it?
What does that even mean? Common ancestry is common ancestry is common ancestry. Lineages diverge, some – possibly all – have common ancestry. There is no common ancestry of lineages that don’t have common ancestry. Are you taking the extremist view that NO non-interbreeding species have common ancestry? It would be nice to know. But even on that view, I don’t see why circularity comes into it at that boundary, if it isn’t there inside it.
I don’t know what that means either. Obviously, species don’t become completely different in a matter of weeks; that is not evidence of a barrier, but of a low rate of mutation and fixation.
We are talking about the evidence for common descent. That is held within the similarities, not the differences. (Well it’s also, strictly speaking, held in the branching patterns of multiple independent character states, but since I can’t seem to get past the conceptual issues around individual nodes, there’s little hope of getting there).
What are you aiming for here? Are you trying to persuade me that you are doubtful of evolution? Great. I am persuaded.
“What is the standard for evidence in biology?”
The standard for evidence in biology is pretty standard…
The first standard is: Evolution is true whether it fits any evidence or not.
The second is a pretty similar standard: If evidence doesn’t fit the first standard; namely it doesn’t support evolution, then it is false.
Example: So-called junk DNA.
The standard for evidence in biology: Evolution predicts a lot of junk DNA in human genome.
Evidence: Biologist have uncovered so far that about 80% of human genome could be functional, if not more, possibly even 100%.
Unfortunately, the standard for evidence in biology is that evolution is true and takes precedence over any evidence against it. So it follows that 90% of human genome must be junk.
What is the standard for this evidence in this biology?
90% of human genome is not under selection, therefore it must be junk.
And there we go… Evolution is the standard over any evidence in biology!
This is what the standard for evidence in biology means…The standard for evidence if biology is that Evolution is true and any evidence against must be false…
As famous Doolittle once wrote about junk DNA teleology:
“…Selected effect is the form of teleological explanation allowed, indeed required, by Darwinian theory…”
http://biophilosophy.ca/Teaching/6740materials/6740-2013-reflection7.pdf
Who can argue with the standard of evidence in biology that is nothing else but teleology?
I must confess I was not aware of this. My reading is that the percentage of DNA for which some function has been identified varies widely with species, with some species having a great deal of it, and others none. If there is a pattern, so that one can predict this percentage for a given species in advance of testing, I’m not aware of it. So I don’t see how any theory could reasonably be said to predict anything along these lines.
What I find more interesting is that bits and pieces of “jumping genes” get scattered through the genome, where occasionally one snippet might get co-opted into another gene, changing its function. Kind of like a big flea market, where one gene’s junk is another’s treasure. I didn’t read that this possibility is a theoretical prediction, but it’s not too surprising.
You can read about the so-called C-Value paradox and genetic load.
Yes, there are some organism that have none or very little so-called junk DNA, such as the puffer fish.
J-Mac,
All you have to do is come up with something that makes better predictions. We can then test those predictions.
I’d rather have something that was incomplete and partially wrong then nothing at all. And so far you’ve offered precisely that as an alternative.
Yes I’m looking at the general trend, not the particulars. The standard account of vertebrate evolution tells us that mammals evolved from reptiles, reptiles from amphibians, and amphibians from fish.
When I say that some animals remain relatively fixed in earlier forms, I mean that this is what is indicated by the fossil record. Out of the four groups referred to above the age of fishes is the earliest, They had the form of fish then and we still class extant animals as fish today because they have the features which we recognise as fish. Fish have fish in their history and remain fish, amphibians have fish in their history but have developed further, reptiles have amphibians and fish in their history, mammals have reptiles, amphibians and fish in their history and so have passed through more developmental stages than the others. Why do you not think that this is a line of progression? If you do not like the term “line of progression”, I am happy to call it radiating out from the centre, where the centre is the origin of earthly life.
It’s lucky we have knowledge of the fossil record then, isn’t it?
Because first, it isn’t a line unless you happen to concentrate your attention on one particular line (again, yours) and ignore all the other lines. Second, any other line is also an equally valid “line of progression”. “Fish remain fish” is a biologically absurd claim. Modern fish are quite different from Devonian fish, just not in ways that make them more similar to you. And so with amphibians and reptiles. Have you ever seen a frog?
Yes, that’s much better. And it destroys your supposed point. Every species has some primitive features and some derived features. There is no line of progression.
The above quote is actually CharlieM 🙂
I doubt anyone was confused, though I wonder how it got attributed.
Vertebrate evolution from fish takes the path through amphibians and reptiles to birds and mammals. Humans are the mammals which have developed the largest array of features which have become highly developed in unique ways. Some of these features are: Endothermy and the ability to manipulate relationship to the environment: Bipedalism and an upright posture which allows the forelimbs to be extremely dexterous: The transmission and receiving of sound in such an intricate way which allows for not only feelings to be communicated but also the sharing of concepts. The ability to be able to learn and remember these concepts.
If we look at these features and their relationship to the vertebrates along the path, what do we see.
Fish. They are exothermic although some have developed antifreeze which allows them to survive extremes of cold. Bipedalism doesn’t apply to fish, but some have assumed a vertical position (seahorses). Fish are mute. Learning and memory are not something we associate with fish.
Amphibians. Also exothermic. We can see a beginning on the path to bipedalism in the difference in posture between newts and frogs, but because of the structure of their limb attachment they still tend to rest on their bodies when not moving. They transmit and recieve basic sounds for mating and territorial purposes. Again amphibians are not renowned for their learning abilities.
Reptiles. Similar to amphibians but some do run bipedally.
Birds. These animals have representative which have attained much of the features that humans have. They are endothermic but they cannot control their body temperatues as efficiently as humans. They are certainly bipedal but this has not freed their forelimbs to give them dexterity. And as for sound, here to they excel, but they come no where near humans in their ability to communicate concepts. Again they use their songs for mating and terretorial purposes.
Mammals. When it comes to all the features mentioned humans are the supreme representative of mammals. And these atributes makes humans stand well above any other mammal.
At each stage we see species which have radiated out in all sorts of directions, but as we progress through the line we see the later stages going further than the previous ones.
Now what I’d like you, or anyone else who is willing, to do, is to take this or any other line of evolution that takes their fancy, from any domain of life, show us the progression of features and the way that the latest species in the line have become unique and have surpassed their ancestors, or indeed have not.
No it doesn’t. That’s one path, the path that leads to mammals. There are other paths that don’t lead to mammals. Once more you take one lineage, yours, call it special, and ignore everything else as a side branch. And by the way, “fish” refers to a paraphyletic group that, if considered as a clade, includes you. In the modern sense, amphibians are monophyletic and don’t include you, while “reptiles” are not considered a group at all, but if they were they wouldn’t include you but would include birds.
You can’t support that, but thanks for trying below. Once more you define “highly developed in unique ways” as “having the characteristics we associate with humans”. Why those characteristics and not different ones? Why, because you are the pinnacle of creation, and that’s all. If you just give up this Charlie-centric perspective, you will have a better appreciation for the true diversity of life.
These aren’t even human characteristics in particular, except possibly for language, which is what I suppose you mean by your convoluted description.
You may not associate them, but fish do both. And some fish are endothermic too. There’s a lot you don’t know about biology.
You seem to be claiming some kind of pathway from newt to frog to human. What? I also point out you are addicted to some kind of scala naturae to which you force-fit everything you know.
What is the source for your claim that birds can’t control their body temperatures as efficiently as humans? And don’t birds completely contradict your ideas on bipedalism? Bird vocalizations, incidentally, have many purposes other than the two you describe. Again, your ignorance shows through your force-fitting. I’ll pass over the reptiles without comment.
Not above giraffes, certainly. Nor “all the features mentioned”, since humans exceed other mammals only two of the characteristics that are important to you: being bipedal and having language. Why, though, are those the important characteristics? Simply because you choose human characteristics as the basis of comparison and ignore everything else. If you were a giraffe, I’m sure you would extoll height or length of neck over everything.
The line itself is in your imagination. Extant species are not arranged in a line, and none are later than others. Extinct species aren’t in a line either. Once more you concentrate on the human lineage (or what you imagine is the human lineage) as if it were the main trunk of evolution. That’s your central fallacy, I think.
One could do that with any line whatsoever. All that’s required is that you take the extant species as a pinnacle and count all its differences from its ancestors as the goal of evolution. Since every species has some unique character or other, there is no problem. Consider the giraffe, for example, much longer legs and neck than its ancestors. And its superior length of tongue, perfectly suited to manipulation, and its superior spots. Surely the giraffe is the goal toward which all evolution has been probing since the dawn of time.
One prediction would be that there are constraints to the directions of evolution so we would see evidence of convergence throughout life.
In this video Dominique Bergmann has the following to say:
Something to consider is that we can look at invertebrates, fungi, plants and bacteria. We can carry out all sorts of experiments on them. We can classify them and allot them places in nested hierarchies. They can do none of these things to us.
Could you give me a link to this?
No need for a link: Just look at Jonathan Wells and Homology, right here at TSZ.
Sorry, but that’s a prediction of ordinary evolutionary theory, so it won’t distinguish your ideas from the standard ones. It might if you fleshed it out a bit more and explained what sort of convergence you would expect or not expect. But there are physical constraints to organisms, constraints on what would be advantageous, constraints on what would be advantageous given a particular starting point, and biases in the sorts of mutations that happen. These constraints come from interactions between organisms and environment, mostly. Convergence happens when a given adaptation is advantageous in multiple species. Thus we get wolves and thylacines, Equus and Thoatherium, innumerable evolutions of the tree habit in plants, etc.
So? What does that have to do with the question? Charliecentrism is a biologically senseless philosophy.
Picture this: Two advanced alien blobs, Jane and Joe (I’ve changed their names to protect their identity) have been watching earth for some time and are having a bit of a disagreement. Jane thinks that among the vertebrates humans stand out as being the most advanced but Joe thinks it is giraffes that should have this honour.
Jane asks Joe to explain his reasoning and so he lists the main attributes of giraffes which sets them apart.
1. They are very tall and have longer legs and necks than any other extant vertebrate.
2. They also have a very long prehensile tongue.
3. And their markings. Have you ever seen spots like those!?
“Okay” says Jane, “Let’s see if humans can beat that, here is my list:”
1. They can communicate their thoughts and feeligs to each other from one end of the planet to the other in a instant.
2. They have the ability to travel all over the earth, some have even gone as far as the moon.
3. They have produced what they call musical instruments with which they can use singly or together to make harmonious sounds for their mutual pleasure.
4. They are aware of the stars and galaxies beyond the earth and of the inner workings of their own bodies.
5. They have developed the means to cure or aleviate the effects of a vast range of maladies.
6. They have invented powerful weapons of mass destruction with which they can and have done much damage.
7. Some of their activities can be seen from space.
8. They are aware that they have a history, life has a history, and the universe has a history.
9. They blush and they cry.
10. They wear clothes.
11. They use fire.
12. They plan in advance, sometimes years ahead.
13. They make sport of killing the most fearsome of beasts just for the fun of it.
14. They…
Joe, “Okay, I get the picture.”
I wonder why they didn’t start by defining what they mean by “advanced”. If they don’t have their definition in common, they’re talking past each other.
I also wonder why the list of giraffe attributes was so short. For example under humans Jane lists crying and blushing as somehow being “advanced” human attributes. Are we supposed to think Giraffes have no body language for social signaling of their mental states? I find that hard to believe. I think if you were to list in an objective manner all the attributes of humans and Giraffes, they’d honestly look much more a like than you like to think about.
My mom and my siblings all have dogs (I have 2 birds). It is obvious to me that these dogs can instantly sense each other’s mental states in ways that take hours to days to dawn on me. And I’m absolutely perplexed about how birds signal each other (besides the superficial fact that they probably do it through their movements and vocalizations). They clearly communicate with and understand each other, yet I am patently clueless about what they’re saying.
CharlieM,
I will agree that humans are much more like humans than are giraffes or any other species, and if your criterion for “advanced” is “like humans”, well then of course we are advanced. I will note that this is the first time, in this thread at least, that the word “advanced” has appeared.
I don’t know why you can’t see that this is nothing more than Charliecentrism. Charlie is the measure of all things. Jane and Joe are just Charlie in disguise. Yes, you are very, very special. Even the giraffes worship your specialness.
So as you say, we are “fish”. And modern fish are “fish” . But we are also something which modern fish are not, we are synapsids and we are mammals. How can you call this anything but an advancement. We were once fish but we have moved on from there. Modern fish have radiated from primeval fish but they still remain trapped in their watery environment as fish.
If I said that birds hold a similar position among the sauropsida that humans do among the synapsids would you call me bird-centric?
It is not so much that the characteristics are unique, although as you have admitted some of them are, it is the combination of characteristics in the one organism that makes humans stand out.
Well its all a matter of relativity. Generally fish are exothermic. And can the learning and memory of fish really be compared with that of humans, crows, dogs or dolphins?
No, I am claiming a pattern in the radiation of vertebrates within clades.
I did read it but I can’t find the ref. at the moment. I will have another look to see if I can find it.
No, bipedalism is part of the pattern of the separate radiations.
No doubt bird vocalization is more varied than in the examples I gave. But do you really think that bird vocalization is as highly developed and nuanced as human speech?
I should have said amphibian-like and reptile-like. Then maybe you would had an understanding of my meaning and you would have had less reason to jump on my perceived mistake.
They are important because they are some of the characteristics which allow us to consciously control our interaction with the natural world and not to blindly follow the instinctive nature of their kind which is generally the case with other vertebrates. Maybe endothermy is not unique to humans, but the way we control temperature is. We have taken it well beyond internal bodily temperature control.
Maybe you think that the acquisition of the longest legs is on a par with the acquisition of language in the course that vertebrate life in general has taken?
They didn’t need to start by a definition because they understood and agreed what was meant by it. The more advanced organisms were those who were seen to have climbed out of their local environment and taken a greater control over their individual destinies. They saw that humans had started to take control while giraffes hadn’t.
You are welcome to compile a more complete giraffe list and we can discuss it. Do you not think that humans too have social signalling and body language?
And I suppose on the other hand dogs know and understand all about the communications that go on between humans? In what way do you think that dog or bird communication surpasses human communication?
Interesting. By Charlie’s criterion of “climbing out of their local environment”, aquatic mammals would appear to have humans beat.
Charlie’s “alien blobs” share very Charliecentric values.
OTOH, maybe the alien judges view tool-use and clothing as signs of weakness.
Maybe they view carnivory as utterly depraved. I’m pretty sure the development of weapons of mass destruction won’t appear in the “Pro” column…I mean, WTF, really?
It is fun to see Charlie re-cycle an ancient defense-of-racism argument to bolster his claim that the acme of evolution is, wait for it, Charlie.
But to a flea, he’s just something good to eat.
One alien’s view:
DNA_Jock,
CharlieM’s picture is certainly anthropocentric, for sure.
There are good reasons for why we might take a peculiar interest in human uniqueness. There is something there to be explained about why it’s human beings that have developed culture, technology, art, religion, philosophy, and science — while other primates have not.
My objection to CharlieM’s account is that while there are good reasons to take an interest in human uniqueness, his way of doing so is epistemologically irresponsible. One can construct that narrative only by deliberately ignoring everything that doesn’t fit into it. CharlieM’s anthroopocentrism makes a Procrustean bed out of the history of life.
The more responsible (but far more difficult) approach is to understand human uniqueness from a biological point of view, rather than understand the history of life from the anthropological point of view . But doing that requires understanding a good deal of biology!
Kantian Naturalist,
Agreed.
My highly selective perspective comes from my background in molecular biology: Eukaryotes are a hopeless and confusing mess of jury-rigged kludges. Prokaryotes are smooth, relatively efficient machines. And bacteriophage (viruses that eat bacteria) kick ass! *They* are the acme of evolution.
But I do have a soft spot for Brewer’s Yeast.
Charlie reminds me of warty bliggens
And the pattern you claim doesn’t exist. It only seems to exist if you ignore most of the tree of life and highlight a few carefully chosen bits, chosen because you can force them into your pattern. And even there it works only because you employ vagueness and word play. You ignore endothermic fish because they don’t fit your narrative. You claim humans are more endothermic than other organisms, and then when challenged imply that you were only talking about down jackets and space heaters. And no, birds don’t contradict your Charlie-centrism, because you only mention them because of the few characteristics they share with you. It’s Charlie-centrism all the way down.
The things that make humans (including, of course, Charlie) special are local adaptations to local environment, not the grand scheme and end goal of all nature. Get over yourself.
Publish or perish Charlie….
I meant “climbing out of their local environment” in a metaphorical sense. Wearing clothes, building houses are the sort of things I was talking about.
Weakness is a relative term. Weakness in relation to what?
Why wouldn’t the development of weapons of mass destruction be a sign of advancement in our capabilities. Advancement in taking control and having power does not necessarily go along with advancement in morals and goodness as Hitler, Stalin and the like proved.
I don’t think that humans are the pinnacle of Darwinian evolution. I would say that the honour here should go to bacteria. But maybe that’s just my bacteria-centrism coming out.