sphenisc
Philosopher
- Joined
- Jul 14, 2004
- Messages
- 6,233
Evolution: the Facts.
- Thread starter The Atheist
- Start date
yomero
Graduate Poster
- Joined
- Jul 31, 2009
- Messages
- 1,222
On the ''Naturalistic alternative to neo-darwinism''thread, Randman has brought again the subject of Haeckel's drawings. I'd like to clear some uncertainties that I have on this. Instead of posting there, I decided to do it in this thread to avoid derailment by creationists.
I understand that Haeckel altered his drawings a bit and that his concept of ''ontogeny recapitulates phylogeny'' has been in great part discarded. I have some lingering doubts. Is the theory of recapitulation completely invalid? Early forms of modern embryos do look like ancestral forms. I understand that the theory of evolution does not imply that there are ''higher'' and ''lower'' species, that all have evolved in their own way. Ancestral species had themselves evolved to suit their ecological needs, therefore I do not consider them ''lower'' either.
It seems logical to me that if there is going to be an evolutionary change in morphology, the major part of the change would happen during the embryological stage. That embryos start relatively similar to each other and to their common ancestors. From this general body plan, variations occur as gestation proceeds. Closely related species mantain their similarities for longer periods and that we should be able to see the branching-off of different groups (could the term ''clades'' be used here instead of ''groups''?) A chimpanzee fetus looks more like a human one than a pig does.http://www.flickr.com/photos/97793800@N00/3823605287/
What have I got wrong? Is there a generalized rejection of Haeckel's theory or is it accepted within limitations? Did Haeckel invoke a supernatural guiding force for recapitulation? Is the apparent rejection just an exagerated backlash in response to his cheating with his drawings? I'm confident that several posters here will help clear my doubts.
I understand that Haeckel altered his drawings a bit and that his concept of ''ontogeny recapitulates phylogeny'' has been in great part discarded. I have some lingering doubts. Is the theory of recapitulation completely invalid? Early forms of modern embryos do look like ancestral forms. I understand that the theory of evolution does not imply that there are ''higher'' and ''lower'' species, that all have evolved in their own way. Ancestral species had themselves evolved to suit their ecological needs, therefore I do not consider them ''lower'' either.
It seems logical to me that if there is going to be an evolutionary change in morphology, the major part of the change would happen during the embryological stage. That embryos start relatively similar to each other and to their common ancestors. From this general body plan, variations occur as gestation proceeds. Closely related species mantain their similarities for longer periods and that we should be able to see the branching-off of different groups (could the term ''clades'' be used here instead of ''groups''?) A chimpanzee fetus looks more like a human one than a pig does.http://www.flickr.com/photos/97793800@N00/3823605287/
What have I got wrong? Is there a generalized rejection of Haeckel's theory or is it accepted within limitations? Did Haeckel invoke a supernatural guiding force for recapitulation? Is the apparent rejection just an exagerated backlash in response to his cheating with his drawings? I'm confident that several posters here will help clear my doubts.
Last edited:
Lowpro
Philosopher
- Joined
- Jan 1, 2011
- Messages
- 5,399
Haeckel basically altered the drawings to support his pet theory of "Ontogeny Recapitulating Phylogeny" (Ont Recap Phyl) that is to say all vertebrate embryos actually go through the adult stages of its "evolutionary tree" more or less, like fish to whatever to whatever until it itself is its adult form. This is not the case.
However there is definite homology among vertebrate embryos. Randman had made an issue of texts using the term "gill slits" which are referring to the pharyngeal slits present on most, if not all vertrebrate embyros. These slits develop into different things though; they are not a part of Ont Recap Phyl when described this way, but creationists want to warp it and say that it's being taught as such.
It is commonly understood that gill slit = pharyngeal slit and to call it a gill slit does not imply that it must develop into functional gills or have to be homologous to gills of an adult fish.
I suggest that if you want to understand embryology and homology you need to understand what HOX genes are. During fetal development there are completely different molecular pathways occurring which need to be understood.
The homology will be traced to how these HOX genes assist development; not through phenotypic homology otherwise you'll make inaccurate comparisons. With as much as is understood about molecular biology and embryology, phenotypic homology is not accurate to describe the evolutionary processes seen.
miRNA expression, which I study, plays one of the most crucial roles in tissue development of developing embryos BTW.
yomero
Graduate Poster
- Joined
- Jul 31, 2009
- Messages
- 1,222
Thank you, Lowpro. Let's see if I have it right.
In my search for HOX genes, I found that an entire field of biology, Evo-Devo, engages in studying the embryological developement of organisms and the evolutionry relationships revealed by that. HOX genes determine where a structure will grow along the body. Other genes encode for enzymes that will switch the mechanisms on, and other enzymes will switch them off. The delicate regulation of these processes result in a horse having horse's legs and a person, human legs. I understand that this applies even to fruit flies, although the HOX genes in all 3 are very similar or even identical. It is the regulation of where, when and for how long that those genes will be expressed that determine morphological differences. I assume that other genes specify the presence of tissues such as bone that are particular to some organisms.
But I can't see yet why the theory of recapitulation must be completely discarded. As I understand it, HOX genes operate on a general body plan for invertebrates. The enzymes responsible for regulation should be more similar in closely related species. Those ''regulators'' operating at the early stages of gestation could be almost identical. As embryological developement proceeds, the ''regulators'' will progressively vary, morphological differences will follow and by that, evolutionary distances between species will be marked. Am I correct in my assumptions? Can some part of the recapitulation theory be salvaged? Is this a case of throwing out the baby with the bath water?
I will appreciate it if Lowpro or other biologists in this forum point out errors in the above paragraphs and direct me to links or books where I can find the information I need. I mean lay-man friendly links and books.
In my search for HOX genes, I found that an entire field of biology, Evo-Devo, engages in studying the embryological developement of organisms and the evolutionry relationships revealed by that. HOX genes determine where a structure will grow along the body. Other genes encode for enzymes that will switch the mechanisms on, and other enzymes will switch them off. The delicate regulation of these processes result in a horse having horse's legs and a person, human legs. I understand that this applies even to fruit flies, although the HOX genes in all 3 are very similar or even identical. It is the regulation of where, when and for how long that those genes will be expressed that determine morphological differences. I assume that other genes specify the presence of tissues such as bone that are particular to some organisms.
But I can't see yet why the theory of recapitulation must be completely discarded. As I understand it, HOX genes operate on a general body plan for invertebrates. The enzymes responsible for regulation should be more similar in closely related species. Those ''regulators'' operating at the early stages of gestation could be almost identical. As embryological developement proceeds, the ''regulators'' will progressively vary, morphological differences will follow and by that, evolutionary distances between species will be marked. Am I correct in my assumptions? Can some part of the recapitulation theory be salvaged? Is this a case of throwing out the baby with the bath water?
I will appreciate it if Lowpro or other biologists in this forum point out errors in the above paragraphs and direct me to links or books where I can find the information I need. I mean lay-man friendly links and books.
Last edited:
Lowpro
Philosopher
- Joined
- Jan 1, 2011
- Messages
- 5,399
Well Ont Recap Phyl says much more than that the initial embryo will start with homologous structures, it goes MUCH further. In its time, it was assumed that the embryo would actually develop THROUGH the stages of its ancestors all the way up to the adult stage. THAT is just wrong.
Almost all vertebrate embryos share homology, including pharyngeal slits, tails, somites, and how neurulation develops (because neurulation is highly highly highly conserved) so yes there are homologous structures, but they don't necessarily HAVE to develop into the same thing along the ancestors evolutionary path that Ont Recap Phyl says.
SO really Ont Recap Phyl isn't completely discarded, but its main theory, which was to be used in the hourglass model, is.
First off, there should be no real reason that HOX genes SHOULD be different among invertebrates or invertebrates. Predictably HOX genes should pretty highly conserved at least in sequence. How they are regulated will probably be more different than the sequence of the genes themselves.
I had used miRNA before because I study it, but it is very important to understand that there is a good grasp on embryology but it's not complete yet either. miRNA regulates protein expression during somite development in embryos, yet miRNA are nothing more than 18-22nt long RNA strands coded from introns. All they do is block protein coding by binding to the 3'URT of mRNA, but that's essential to the regulation. But they're extremely weird because one miRNA can bind to many different mRNA, and one mRNA can hold more than 10 different miRNA's which means there are many many many many redundancies and particulars to protein regulation. We don't yet know how it fits into the evolutionary pathway in embryology because of these redundancies.
If'n you want you can read the first slide of this PP I made (selfless of me, I know
) if you want to know a little more on miRNA but also it shows why they're REALLY important AND so damned confusing because conserved miRNA in both human AND mouse don't regulate the same thing anymore! They're just redundant but they're STILL present and transcribed!
http://www.scribd.com/fullscreen/74702753?access_key=key-4fa2wjclrn2wkyadeai
Almost all vertebrate embryos share homology, including pharyngeal slits, tails, somites, and how neurulation develops (because neurulation is highly highly highly conserved) so yes there are homologous structures, but they don't necessarily HAVE to develop into the same thing along the ancestors evolutionary path that Ont Recap Phyl says.
SO really Ont Recap Phyl isn't completely discarded, but its main theory, which was to be used in the hourglass model, is.
First off, there should be no real reason that HOX genes SHOULD be different among invertebrates or invertebrates. Predictably HOX genes should pretty highly conserved at least in sequence. How they are regulated will probably be more different than the sequence of the genes themselves.
I had used miRNA before because I study it, but it is very important to understand that there is a good grasp on embryology but it's not complete yet either. miRNA regulates protein expression during somite development in embryos, yet miRNA are nothing more than 18-22nt long RNA strands coded from introns. All they do is block protein coding by binding to the 3'URT of mRNA, but that's essential to the regulation. But they're extremely weird because one miRNA can bind to many different mRNA, and one mRNA can hold more than 10 different miRNA's which means there are many many many many redundancies and particulars to protein regulation. We don't yet know how it fits into the evolutionary pathway in embryology because of these redundancies.
If'n you want you can read the first slide of this PP I made (selfless of me, I know
) if you want to know a little more on miRNA but also it shows why they're REALLY important AND so damned confusing because conserved miRNA in both human AND mouse don't regulate the same thing anymore! They're just redundant but they're STILL present and transcribed!http://www.scribd.com/fullscreen/74702753?access_key=key-4fa2wjclrn2wkyadeai
Last edited:
http://www.ncbi.nlm.nih.gov/pubmed/12475051
Interesting that the guy that stated Haeckel's drawings were "scientific fraud" that made him "angry" just 5 years later writes the faked data is actually "evidence for evolution."
How is that?
Most of the drawings were useful. Some were fraudulent and discarded. The theory he created the fraudulent drawings to support was discarded.
The rest of the drawings were repeatedly drawn and later photographed by other scientists and are useful in embryology.
Also, ETA to include Lowpro's comment which does correctly assign the hourglass model to Haeckel.
Has the hour-glass model been discarded? Maybe by some but it hasn't gone away.
http://www.biomedcentral.com/1741-7007/5/1/
It just won't go away. My suggestion is when you see even peer-reviewed journals publish that known faked data is "evidence", one needs to take a step back and consider what's going on. Why are evos clinging to Haeckel's ideas and theories and data so much?
Does embryology really offer specific support for evolution or is this a myth that got planted so deeply they are having trouble freeing their minds from a biased view of data based on fakery?
Last edited:
The idea that ontogeny recapitulates phylogeny has been so completely discredited that, as Gould noted, many scientists shied awway from discussing phylogenetic implications of embrionic development for fear of the APPEARANCE of agreeing with Haeckel's idea. Gould outlined this in one of his books. This shows 2 things that randman refuses to undrestand: first, science threw out Haeckel's ideas. This is rather unfortunate on Randman's part because the truth is more damning for us evolutionary scientists--we didn't just throw out the idea that ontogeny recapitulates phylogeny, we threw out Haeckel's ideas--which included some really good ones. Science is not kind to members that commit fraud. The second issue is how long ago it was. I'm sure you can still dig up some textbook that includes a copy of his drawings, but I serously doubt it'd be complimentary (teaching the errors of science is a good way to demonstrate the process) and at any rate textbooks are not, nor have they been for at least 50 or 75 years, representative of the current state of evolutionary biology. Simply put the field moves too fast for textbooks to keep up, and textbooks tend to be reviewed by publishers rather than scientists (remember, publishing is a business--and a rather competative one).
I belive that the current convention is to use photos in biology textbooks for embryology. Haeckel's diagrams presented the pictures in a logical fashion, even if the drawings themselves weren't factual, so a similar arangement is nearly universally used, which leads to randman's constant attacks that we're still using Haeckel.
What I've often wondered is how much embryo development contributes to channelization. I mean, if you're a sponge it doesn't mater how you develop--there's not enough specialization in a sponge to create real tissues. If you're a human, it's a different story. You need to develop certain things at certain times--you have to have certain structures in place in order to grow limbs, or jaws; you need certain hormones to grow certain parts, and those hormones require certain glands to be in place in order to produce them; and I can only imagine the structural issues involved! I assume that as organisms increase in complexity (however you decide to measure that--not going down THAT rat hole here) more parts rely on other parts, making dramatic shifts much harder to accomplish, evolutionarily speeking. And how things show up in our development is going to be a major part of that.
I belive that the current convention is to use photos in biology textbooks for embryology. Haeckel's diagrams presented the pictures in a logical fashion, even if the drawings themselves weren't factual, so a similar arangement is nearly universally used, which leads to randman's constant attacks that we're still using Haeckel.
What I've often wondered is how much embryo development contributes to channelization. I mean, if you're a sponge it doesn't mater how you develop--there's not enough specialization in a sponge to create real tissues. If you're a human, it's a different story. You need to develop certain things at certain times--you have to have certain structures in place in order to grow limbs, or jaws; you need certain hormones to grow certain parts, and those hormones require certain glands to be in place in order to produce them; and I can only imagine the structural issues involved! I assume that as organisms increase in complexity (however you decide to measure that--not going down THAT rat hole here) more parts rely on other parts, making dramatic shifts much harder to accomplish, evolutionarily speeking. And how things show up in our development is going to be a major part of that.
you drunk or is spellcheck off there Dinwar?yomero
Graduate Poster
- Joined
- Jul 31, 2009
- Messages
- 1,222
Here is what I have learned so far:
The hour glass model of embryonic development applies at a molecular, gene level as it does at the macroscopic morphological level. The earliest and the latest stages of gestational development are more diverse across species than the middle ''phylotipic stage.'' Extensive morphological similarities are seen during the middle of development, and less at the beginning or at the end. Pavel Tomancak found that gene expression is also more similar in different species during the ''phylotipic stage'' than in other periods. Other researchers found that the ancestral oldest genes are expressed during this stage and newer genes are active before and after. Even in adults, older genes are expressed progressively as the individual ages. There lies one of my errors. I had assumed that genes would be expressed serially according to their antiquity. I don't completely understand how the hour glass model ''...demonstrates that parallels exist between ontogeny and phylogeny''(Diethard Tautz). Perhaps it means that finding such great genetic similarity during the ''phylotipic stage'' points to a common ancestor and that variations occur during the earlier and later periods according to the relatedness of the species considered.
In post # 1445 Lowpro explains that the apparent similarities in body structure in embryos does not mean that the embryos will go through all the adult stages of their ancestors. Pharyngeal slits in mammals look like fish gills, but they are not gills.
Lowpro also mentions microRNA and the importance it has in gene expression. This proved a difficult subject for me. What I gathered is this: MiRNA's are short strands of RNA that bind to messenger RNA and repress (or sometimes activate) mRNAS translation. Genes that code for activities common to all cells are usually not targeted by miRNA. However, miRNAs act on those genes responsible for specific activities of certain cells. To me, this means that miRNA determines how cells from different organs and different tissues do their particular activities under miRNA's regulation. Also, that miRNA's determine how embryonic cells differentiate from an original fertilized egg.
As usual, I welcome any corrections needed.
The hour glass model of embryonic development applies at a molecular, gene level as it does at the macroscopic morphological level. The earliest and the latest stages of gestational development are more diverse across species than the middle ''phylotipic stage.'' Extensive morphological similarities are seen during the middle of development, and less at the beginning or at the end. Pavel Tomancak found that gene expression is also more similar in different species during the ''phylotipic stage'' than in other periods. Other researchers found that the ancestral oldest genes are expressed during this stage and newer genes are active before and after. Even in adults, older genes are expressed progressively as the individual ages. There lies one of my errors. I had assumed that genes would be expressed serially according to their antiquity. I don't completely understand how the hour glass model ''...demonstrates that parallels exist between ontogeny and phylogeny''(Diethard Tautz). Perhaps it means that finding such great genetic similarity during the ''phylotipic stage'' points to a common ancestor and that variations occur during the earlier and later periods according to the relatedness of the species considered.
In post # 1445 Lowpro explains that the apparent similarities in body structure in embryos does not mean that the embryos will go through all the adult stages of their ancestors. Pharyngeal slits in mammals look like fish gills, but they are not gills.
Lowpro also mentions microRNA and the importance it has in gene expression. This proved a difficult subject for me. What I gathered is this: MiRNA's are short strands of RNA that bind to messenger RNA and repress (or sometimes activate) mRNAS translation. Genes that code for activities common to all cells are usually not targeted by miRNA. However, miRNAs act on those genes responsible for specific activities of certain cells. To me, this means that miRNA determines how cells from different organs and different tissues do their particular activities under miRNA's regulation. Also, that miRNA's determine how embryonic cells differentiate from an original fertilized egg.
As usual, I welcome any corrections needed.
Last edited:
Lowpro
Philosopher
- Joined
- Jan 1, 2011
- Messages
- 5,399
Hmm, gene's don't have to be expressed serially according to antiquity and if you think about it, there's no reason they should and to suppose as much I think is a gestalt issue. I can try describing the process of neurulation or somite development, both of which are highly highly highly highly conserved processes using effectively the same genes and similar expression, which can be identified as "homology" among the embryos of various species of vertebrates and good evidence for a common ancestry, but it doesn't really give "good" proof because the demands of good proof include the molecular biology, not just morphology. This is why HOX genes are more reliable if you want to understand evolution and embryology; facts are facts if you wanna do evolution you're going to need to understand molecular biology now. Oh, and I totally know that gets under the skin of every field biologist who envies my air conditioning.
That's one of the reasons I introduced miRNA, and if you don't understand it that's fine. You won't even find it in most textbooks. The point is that common ancestry is now being more accurately understood through molecular biology than just morphology.
Now this is a weird issue and I say it's weird because it's borderline lying sometimes when I've seen it here. Gill slits is the colloqial term for pharyngeal arches, present on most, if not all vertebrate embryos. They are morphologically homologous. HOWEVER they do NOT all develop into the same thing. Now, Haeckel's theory, taken to an extreme, would have said something along the lines of "these arches first develop into the ancestral gills, then THOSE develop into whatever terrestrial functional thingy our ancestors had, and then THAT develops..." and so on and so forth. This isn't the case. We KNOW it's not the case. In Haeckel's own time it was discovered not to be the case, and Haeckel even corrected his own self.
BUT! It's still a colloqialism to mean pharyngeal arches. It does not invoke Haeckel's theory, and those who demand it must (you know who you are) are just lying and it's pathetic.
That's one of the reasons I introduced miRNA, and if you don't understand it that's fine. You won't even find it in most textbooks. The point is that common ancestry is now being more accurately understood through molecular biology than just morphology.
Now this is a weird issue and I say it's weird because it's borderline lying sometimes when I've seen it here. Gill slits is the colloqial term for pharyngeal arches, present on most, if not all vertebrate embryos. They are morphologically homologous. HOWEVER they do NOT all develop into the same thing. Now, Haeckel's theory, taken to an extreme, would have said something along the lines of "these arches first develop into the ancestral gills, then THOSE develop into whatever terrestrial functional thingy our ancestors had, and then THAT develops..." and so on and so forth. This isn't the case. We KNOW it's not the case. In Haeckel's own time it was discovered not to be the case, and Haeckel even corrected his own self.
BUT! It's still a colloqialism to mean pharyngeal arches. It does not invoke Haeckel's theory, and those who demand it must (you know who you are) are just lying and it's pathetic.
Last edited:
shadron
Philosopher
- Joined
- Sep 2, 2005
- Messages
- 5,918
Would I then be correct in assuming that the appearance that ontology kinda recaps physiology is that the early structures are required to be in place so that later adaptation of those structures can build upon them? For example, the gill arches form because if they didn't the later uses for those arches, such as for the lower jaw, are built upon the earlier framework physically? If a mutation suppressed the arches then the jaw wouldn't be able to form?
Lowpro
Philosopher
- Joined
- Jan 1, 2011
- Messages
- 5,399
Well yes more or less, but that's not true in all cases either, as in the digits of birds which START with what appears to be five digits but then apoptosises and loses "digits I and V" and then continues on; there is an appearance of some early homology between common ancestors of birds to the 5 digit tetropod of which we are all evolved from, but the truth is far stranger too.
Interestingly, if anyone wants to know, birds do a weird "frame shift" where the developing digits (not called digits, but called "condensations") start off, Condensations I through V (using roman numerals if you haven't caught on) however I and V go away and Condesation II "becomes" Digit I, condensation III is digit II, and so on.
What's REALLY bleepin' cool is that there's NOTHING new! There's no new genes for this either (at least, no new genes of staggering significance), they're the same homeoboxes of almost all species, certainly the same, if almost exactly similar as those of its ancestors, doing this! It's just the regulation is different, which is why there is different morphology as development continues. The homology more accurately described rests within the homeoboxes, the HOX genes. THAT'S the more accurate homology, THAT is proof of evolution.
miRNA is probably, within my lifetime, going to become the HOX gene study of our generation. Or it totally won't, I have no idea. They're really really really weird. Seriously, if I didn't have a sense of humor, they'd drive me to kill myself.
Interestingly, if anyone wants to know, birds do a weird "frame shift" where the developing digits (not called digits, but called "condensations") start off, Condensations I through V (using roman numerals if you haven't caught on) however I and V go away and Condesation II "becomes" Digit I, condensation III is digit II, and so on.
What's REALLY bleepin' cool is that there's NOTHING new! There's no new genes for this either (at least, no new genes of staggering significance), they're the same homeoboxes of almost all species, certainly the same, if almost exactly similar as those of its ancestors, doing this! It's just the regulation is different, which is why there is different morphology as development continues. The homology more accurately described rests within the homeoboxes, the HOX genes. THAT'S the more accurate homology, THAT is proof of evolution.
miRNA is probably, within my lifetime, going to become the HOX gene study of our generation. Or it totally won't, I have no idea. They're really really really weird. Seriously, if I didn't have a sense of humor, they'd drive me to kill myself.
Last edited:
I've just been talking about the data here but you make a very good point that I've often considered. The hourglass model, imo, doesn't even appear to be evidence for evolution. I think it's overstated in that there isn't so much of an hourglass model, but if there was, seems to me that'd be pretty strong evidence against evolution, not for it, since development is progressive and if the divergence occurs at the earliest stages, how is there an evolutionary explanation for less divergence in the middle.
This is one reason I don't see embryology as good evidence for evolution. I may be overstating it to say it is evidence against it, but just looks like to me that evos jumped on this VERY early and have not been able to excorcise themselves from the argument and vestiges of the biogenetic law.
It was a mistake and shouldn't still be resurrected and relied on as some evidence for evolution since frankly, the hourglass model itself, even if it were true, seems to contradict what one would expect based on evo models. Just looks like a glaring fact that doesn't match up, but one could perhaps just say, well, it's just not evidence for evolution and is neutral in that, of course, once creatures have evolved and diverged evolutionary, their embryonic development has as well, and the suggestions of more conserved stages are a fluke since clearly the embryonic development had already diverged; that this must be a developmental constraint that is needed at those stages; that it's evidence for that and nothing more.
Except the very earliest stages had already widely diverged. Maybe there is a developmental reason, of course, for these things and maybe evos are being fooled a bit by superficial appearances, but the idea there is this unfolding and indication of a past evolutionary past is made moot by the earliest differences in development.
yomero
Graduate Poster
- Joined
- Jul 31, 2009
- Messages
- 1,222
I guess we will have to add to Mark Twain's phrase that ''The only 2 certainties in life are death and taxes.'' A third certainty is that in any honest discussion on evolution, an ID/Creationist will try to spoil it.
Apparently, Benjamin Franklin originated the phrase. Twain repeated it.