Talk:Recapitulation theory/Archive 1

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Comments

Unfortunately all texts about evolution written by authors widely quoting from popular Creation "Science" websites hold no credibility -- even if the text is nicely structured.

This immediately brings to mind the weakness of Wikipedia. It takes no vandal or hooligan to ruin it! It takes one zealous Evolutionist and one zealous Creationist to pick up a fight against each other and confuse thousands of readers on the way. They can edit and reedit their materials ad infinitum!

Of respect for human creative effort and out of rudimentary need for tolerance, I do not embark on investigations and wasteful reediting. However, using Wikipedia as a soap box for one's own religious convictions is not fair either.

Piotr Wozniak

I have simply removed the offending text, and urge whoever put it there to leave it off. What creationists think on the relationship between ontogeny and phylogeny is necessarily irrelevant, since they do not believe in the second, and the claim that the similarities of ontogenies and phylogenies do not provide evidence for evolution is false, whether you believe in the theory or not. -- Josh Grosse

Did I strike a nerve? :-)

That would be me who "put it there." I'll heed Piotr's lament by avoiding an "edit and reedit" feud; however, I find the accusation that I "widely quot[ed] from popular Creation 'Science' websites" to be misleading. Let's examine the quotes:

The work of Haeckel "was the culmination of the extremes of exaggeration which followed Darwin." "Haeckel's doctrines were blindly and uncritically accepted," and "delayed the course of embryological progress." Oppenheimer, J. 1967. Essays in the History of Embryology and Biology, p. 150, MIT Press. Cited at http://www.gennet.org/Metro06.htm.

"The so-called basic law of biogenetics is wrong. No buts or ifs can mitigate this fact. It is not even a tiny bit correct or correct in a different form. It is totally wrong." -- embryologist Dr. E. Blechschmidt Cited at http://emporium.turnpike.net/C/cs/ontogeny.htm.

Piotr, I quoted Oppenheimer and Blechschmidt because they both seemed to be reputed by the creationist Web site as "hostile witnesses" to creationism. I thought that with my bias (and all scientists have a bias -- see the work of Michael Polanyi), it was fair to quote hostile witnesses. Other than URLs, which I merely used because they showed up in a quick and simple Google search, there is no evidence to substantiate your ad hominem attack that I used the article as "a soap box for [my] own religious convictions." I challenge you to show me where I was being unfair to Haeckel or his ideas in the text (uninformed, perhaps, but not unfair), and I challenge you to show me the link to religion on a page about a historical scientific embarrassment.

I see from your signature page that you have an interest in the creationist/evolutionist debate. So do I -- at the hazard of being pejoratively labeled a creationist simply because I prefer contrarian evidence to toeing the party line. It's a thankless job, but someone has to call the evolutionists to task when they stoop to junk science.

You call yourself "a science maniac." So am I. It's just that I don't swallow all the claims of evolutionary theory as indisputable fact. G.K. Chesterton said, "The object of opening the mind as of opening the mouth is to close it again on something solid." I strive to follow that advice.

<>< Tim Chambers

Dear Tim. I have no doubt that you are a very nice person and open to honest discussion that would enrich you and me and perhaps those who would bother to read. There are two limitations though:

By choice, I NEVER get involved in creationism-evolutionism debates (this is personal, I will then explain at Piotr Wozniak then)
I got lots of work to do before vacation so I gotta de-Wikify my brain IMMEDIATELY!!! :)

Thank you for an invitation and hope to read more of you in early September 2001 -- Piotr Wozniak

"For instance, humans historically evolved from fish whose gills evolved into lungs; every human embryo passes through a phase with gills, which then turn into lungs."

Sorry, it's going to take more than AxelBolt's authorship to convince me of this. <>< Tim Chambers

Via phone conversation in June 2001 a molecular biologist specializing in the Genome Project genetic databases and I discussed this subject. The PHD mentioned this Ontogeny theory is taught, but not given academic support any longer. ~BF the New Age person and closet scientist =)

So when Irwin says at http://www.utm.edu/~rirwin/391OntogPhylog.htm that embryos have gills, she says that in spite of the evidence?

Last I checked, scientists who have studied human embryos have proven that this is not the case. Wikipedia should not put with such junk science. Let's get to the bottom of this! <>< Tim Chambers

Please cite a reference for this proof. --AxelBoldt

It is my impression that the general consensus among modern biologists, who are all dedicated Darwinists, is that Haeckel's work was in fact a wild extrapolation and was just wrong, and they were in fact blindly accepted and uncritically accepted by many. "Ontogeny recapitulates phylogeny" is a great example of what happens when individual scientists fall in love with ideas that don't hold water. Basically, Haeckel observed things like the gill-stage through which human embryos pass (that's a very well-known thing Tim, just watch any film on human embryonic development and see for yourself--though they are just gill-like things, not actually functioning gills), and elevated these simple observations to a "law" with no justification. True, the observations are very suggestive, and more responsible biologists currently studying embryonic development have better explanations, but Haeckel was just a crackpot.

Including the Oppenheimer or Blechschmidt quote above I think is entirely appropriate (both is kind of redundant; either is a good example of the disdain modern biologist have toward the idea). My belief in evolution is certainly not affected by the fact that one of its early proponents was an idiot--why whould it be? I believe it because of the evidence, not the personailties or social history. Of course Josh is right that the claims of Creationists beyond the immediate subject have no place here, and their lies (such as that the observations mentioned--if not the theory behind them--do not provide evidence for evolution) have no place anywhere. --Lee Daniel Crocker

The main article claimed that Irving teaches Haeckel's theory to be correct; in fact she says "It turns out that for some characterstics the ontogeny of the trait does go through stages much like the adult forms of the ancestors of the species with the trait-- that is, ontogeny does recapitulate phylogeny. But there are also many examples where this does not occur." I therefore removed the claim about Irving. --AxelBoldt

Here's another quote that might be useful:

"The theory of recapitulation was destroyed in 1921 by Professor Walter Garstang in a famous paper; since then no respectable biologist has ever used the theory of recapitulation, because it was utterly unsound, created by a Nazi-like preacher, named Haeckel."-*Ashley Montagu, debate held April 12, 1980, at Princeton University, quoted in L.D. Sunderland, Darwin's Enigma, p. 119.

I warn, though, that though I like the above quote and Ashley Montagu is a respectable scientist, I got the quote from a creationist site that has many outright lies, so it may be misquoted or edited, and I don't have time right now to verify the quote with a respectable source. --LDC

The main article claimed that Irving teaches Haeckel's theory to be correct; in fact she says "It turns out that for some characterstics the ontogeny of the trait does go through stages much like the adult forms of the ancestors of the species with the trait-- that is, ontogeny does recapitulate phylogeny. But there are also many examples where this does not occur." I therefore removed the claim about Irving. --AxelBoldt

Tbc, another reference for gill-like structures in human embryos is EB's article about evolution, in the "Embryonic development and vestiges" section. I'm not going to list that one as a reference though :-) --AxelBoldt

In my opinion the key issue here is not the fact that there do appear gill like appendages on human embryos during a specific developmental phase, but that the general theory of ontogeny recapitulating phylogeny actually impeded research into the actual purpose of these "gill like flaps" for many years. And as soon as people looked into the matter, it became apparent that do have a purpose, and that the purpose (IIRC the formation of certain glandular systems) would have occurred far later in the human evolutionary system than they do in human phylogeny.

I don't understand this. Under what condition would what have occured later? --AxelBoldt

Another, far more serious problem with the theory is that many closely related species have widely divergent processes of embryonic development.

One of the cited references of the main article claims just the opposite: often closely related species differ dramatically in appearance, but once you look at their ontogeny, it becomes clear that they must be related. If you say "many", what percentage are we talking about? Keeping in mind that in biology all statements are probabilistic, I would rephrase the above as "it is possible but highly unlikely that closely related species differ dramatically in their ontogeny". --AxelBoldt

Anyway, As far as I can tell, the theory is junk science, and the important points to make about it come from a historical and sociological perspective. One of these points is that biologists specializing in embryonic development rejected the notion long before a) textbooks stopped repeating it as evidence for evolution, and b) the "creationist" movement started using it in their arguments against evolution.

You have to be careful though: biology rejects the notion that evolutionary history is replayed in ontogeny, but it also holds that very often ontogeny recapitulates embryonic stages of evolutionary ancestors. This fact is indeed a strong argument for evolution. Creationists often state that Haeckel's law has been discredited, which it has, but then they deliberately misstate Haeckel's claim, trying to discredit any connection between ontogeny and embryonic forms of evolutionary ancestors. --AxelBoldt

I think the fact that ontogeny does not recapitulate phylogeny in any real sense is something we should all be able to agree about, that said, I hope we can turn our attention to characterizing the history of the issue fairly. MRC

Sure, that should be added. But I still think it is also important to give the proper reason why there are gills and tails and webbed fingers in human fetuses. It's not just a random coincidence. It makes sense. --AxelBoldt

This is clearly not my area, but... The gills are not functional gills

Neither are the gills in fish embryos --AxelBoldt

and are visible results of the development of glandular development. The "tail" is part of the development of the spine, and is also not a "real" tail. I seem to recall that there is a functional element to the webbed fingers. Both you and I are out of our area here, but I seem to remember talking about insect species that were very closely related with vastly different ontogeny. As far as I know there's no clearly defined biological mechanism behind the theory -- what specifically makes ontogeny recapitulate phylogeny?.

Ontogeny does not recapitulate phylogeny, as we all know, but the common appearance of embryonal forms of evolutionary ancestors in ontogeny is not just an accident: it is explained on the main article page and also in the references there. Briefly: evolution has to modify a developmental program and it is easier to modify it at its later stages than to mess with a step in the middle. --AxelBoldt

Moreover, there’s strong disconfirming evidence visible in nature, there are functional explanations for the apparent recapitulation of phylogeny in human embryonic development, and leading embryologists say the theory is outdated and incorrect -- but as I said I am no expert in embryology, and it is possible that all of these objections could be overcome and the theory could be saved.

However, I think with the available evidence, there is just no reason to think there’s a biological law, which states that there is a necessary relationship between ontogeny and phylogeny.

There are no laws in biology; everything has exceptions. Some things are more likely than others, and there are reasons for the higher likelihoods. It's not just an accident that all vertebrate embryos have gills but insect embryos don't. --AxelBoldt

Come on now, there are law like phenomenon in biology. Put a fish on land and it'll die. Ask a human to breathe water and she'll die. Breed two fireflies with different spotting characteristics, and the spotting on their offspring will follow Mendel's law.

Except that some fish can live on land (most can't, and there are good reasons for it), and some traits don't follow Mendel's laws (most do, and there are good reasons for it). The fact that humans can't breathe water and firefly spottings behave Mendelian are not laws, just isolated facts about certain species. --AxelBoldt

There may be quite a few accidental similarities but they don’t mean anything -- in the same way that there quite a few surface similarities between a duck and a platypus, but these similarities don’t indicate a close evolutionary relationship, they just represent the functional utility of webbed feet, and a certain shape of "bill."

And having a tail helps the human embryo exactly how? --AxelBoldt

It is part of the developmet process of the spine. Without the "tail" the spine would either have to develop latter in the process, or not develop at all.

I would be interested in seeing if there has been any evidence collected about the very strong probability relationship you mention, I have not seen such evidence and if it were conclusively demonstrated that there is a high probability that ontogeny reflects the actual phylogeny of a large number of species, we’d obviously need to re-think the whole issue. MRC

Check out the references cited on the main page. --AxelBoldt

We sure that lungs evolved from gills? From what I know, lungs evolved as a modification of the swim bladder, but I could be mistaken.

You are correct; I'll change it. --AxelBoldt

Is the inverse perhaps more interesting here? Phylogeny recapitulates Ontogeny. That would be a new idea for the "science guys", a la Dr. Michio Kaku's writings on http://www.mkaku.org/ superstring theory. Ahem.

The phylogeny of a modern organism is something that has been going on for a billion years, its ontogeny for a year or less. The newer can't recapitulate the older.

Di Stroppo, please explain what specifically you consider to be incorrect in my last edit. Until then, I will restore it. --AxelBoldt 23:05, December 31, 2001 (UTC)

RV26 played down too much the fact that the hypothesis is not hold anymore too much instead of giving an account why the hypothesis is discredited. --Giovanni Di Stroppo 23:38, December 31, 2001 (UTC)

The account of why the hypothesis is discredited is already there, and I didn't remove any of it. What I did was

add the fact of legs in whale embryos
add that creationists use the fact that the theory is discredited as evidence against evolution
add the fact that modern biology recognizes many connections between ontogeny and phylogeny, explains them with evolutionary theory, and sees them as evidence for said theory

Specifically, which of the three do you disagree with, and why? I believe I am entitled to the courtesy of such an explanation since you simply removed my additions instead of adding any material of your own. --AxelBoldt 23:44, December 31, 2001 (UTC)

Well, adding material does not forcefully make an article better. Revision 25 was OK. Actually it blurred the fact the statement ontogeny recapitulates phylogeny cannot be hold any more. That the embryonal development of related species is similar is obvious. The argument has been used for a long time to support the theory of evolution in popular textbooks. Now that's not the case anymore. Full stop. I can understand that creationists point this out as it seems to trickle down slowly. And we don't need to blur this here either. And to connect it still with evidence for evolution backfires considerably as there is no reason why an intelligent beeing designing something would not reuse its design. So let's forget connecting this still in any way with evolution and use version 25 for the time beeing which I actually consider quit OK? --Giovanni Di Stroppo 00:15, January 1, 2002 (UTC)

Since you don't claim that any of the three points I mentioned is wrong, I will add them back in. They could easily be supported with evidence if need be.

To address your points: modern textbooks use the fact that features of embryos of evolutionary ancestors often occur in the embryonal development of species to support the theory of evolution. (e.g. Biology by Campbell, 5th ed. 1999, p.425). Evolutionary theory can easily explain why whale embryos develop legs, but creationism can't.

I am guessing Campbell's text seeks to show that different vertebrates share some stages of development, stages that come about because of combinations of particular genes, many of which are also shared. (We vertebrates share genes with fruitflies and even yeasts.) These shared stages are not proof of any linear development from fish straight to chimp, but our habit of passing through some of the same stages is a hint that we are related. If your father and your son had exactly the same color hair at age 2, you might think that was because they are related, not just chalk it up to coincidence. Here is a good discussion of biogenetics by an excellent embryologist and writer. http://7e.devbio.com/article.php?ch=23&id=219 Eperotao 22:02, 6 January 2007 (UTC)

If you feel that any of my additions are contradicted by evidence or are not believed be a significant group, please add that fact to the article instead of just deleting my additions. --AxelBoldt 20:22, January 1, 2002 (UTC)

Well Axel, as you seem to have been involved in writing this article considerably let me remind you it is about Ontogeny recapitulates phylogeny, an outdated postulate. The article acknowledged this in the beginning but then continues as it still holds somehow. Perpetuating scientific folklore is not helpful, I think. Unfortunatly you happened to be somebody working in this direction. That's why I felt inclined to restore version 25.

As I read that version again I would say the challenge is still here to come up with a well researched article which includes as well the history of the claim. I don't hold a one page quote of a general biology textbook to be sufficient in any way. It's rather poor in fact. After reading again all the things said on this talk page it would surely be worthwile to go through the topics raised here and come up with a comprehensive article which deals with the issues. But that's a considerable amount of work (several days I suppose). I like to invite the people who wrote on this page to contribute. Go to the library; research recent journals and report the findings here. Then we can write a decent article.

The whale leg issue is an interesting topic which deserves an entry of it's own. Whales are an exciting group of animals and it would be nice to generate a lot of entries on them. Cheers! -- Giovanni Di Stroppo 22:39, January 1, 2002 (UTC)

The recapitulation theory is discredited, the article says so, and then it explains what is wrong about it and why it arose and what connections between ontogeny and phylogeny are still recognized and how they can be explained. I don't know what "scientific folklore" you are referring to.

I mentioned the biology textbook to prove my claim that modern biology textbooks still use the phylogeny-ontogeny connection as evolution evidence, which you disputed.

But not, I think, to promote Haeckel's idea of linear, progressive evolution. Eperotao 22:02, 6 January 2007 (UTC)

The fact that human embryos go through a stage with gill-like structures and webbed fingers is well-established; I don't know why you removed it and since you didn't explain yourself here, I'll restore it. --AxelBoldt 04:39, January 2, 2002 (UTC)

If people are going to make controversial changes, they owe it to us to explain why. Why has the following info repeatedly been removed?? (I am paraphrasing the deleted material) "The strong form of this theory has been discredited; a weaker form of this theory, however, is accepted as correct." To the best of my knowledge, this is absolutely correct. Ontogeny is related to phylogeny in many animals; it simply isn't so very strongly linked as it once was thought. This isn't controversial, so why does someone keep removing this? If you have reasons, state them. RK 06:23, January 3, 2002 (UTC)

Removed (which Haeckel could not). The article is fine otherwise. It was a good idea of Axel to factor out the modern view. -- Di Stroppo

I'd better state first that I am a creationist. However, the fact that Recapitulation Theory is erroneous does not, in itself, disprove evolution. Therefore, evolutionists should not be worried about accepting that it is erroneous. Everybody makes mistakes, and evolutionists should not defend an erroneous evidence.

I note that participants will not accept creationist literature on this subject, so I will refer you to a peer-reviewed scientific journal from Germany, Anatomy and Embryology.

Pftaylor 15:19, January 27, 2006 (UTC)

Wow, you people kill me. The embryo forms all structures by enfolding of tissues. The folds of tissue that were called gill slits, in fact form the jaw and other structures that have nothing to do with respiration. The "tail" is merely the coccyx which grows faster than the rest of the body and protrudes for a time. It does not deminish.

Hmm, I'd like to see included here the impact of recapitulation on psychology mentioned as well. The american example is mentioned, but the impact on Freud and Jung are not. Freud's theories are largely based on recapitulation. His oral, anal, and genital stages are a recapitulation of the sexual progress in creatures where sexual union occurs first in the mouth of the creature, then the anus, and lastly at the gentials. Jung believed in a recapitulation of culture. Interesting stuff.

Cutterfl 19:41, 31 March 2007 (UTC) Cutterfl

The section about "Rejection" is imprecise. Biologist do not deny Haeckel ideas. His theory is correct both at the molecular level (modular evolution of reusable parts, like exons and protein domains, is a well proved fact from archaea to humans) and also at the morphology level (embryos do not look like adult species; they should look like the common ancestors of current end forms)

I totally agree with those that mentioned before about vandalism here.

isradelacon 15:11, 6 June 2008 (Central European Time)

I have a BS in biology and this page is incorrect to misleading as it takes the term to a further extreme then its used in modern biology. Currently the idea is used to illustrate the vertebrate embryonic development tends to mimics its evolutionary origins. This does not hold up in some more primitive animals like salamanders. Nor does this literally mean an embryo goes thought literally all of the development of its ancestors, it simply means genetic coding blocks used to create a vertebrate have been reused over the eons as they work just fine and are modified in each spefic species. Here is link from Berkeley one of the top educational institutions in the world to back up everything I have stated. http://evolution.berkeley.edu/evosite/evo101/IIIC6aOntogeny.shtml — Preceding unsigned comment added by 71.217.247.92 (talk) 06:11, 27 December 2011 (UTC)

Picture

I wish we could get this picture into the article. Comments on it come from here. (The relevant study is already cited as a source, it appears.) Jdavidb (talk • contribs) 16:48, 8 February 2006 (UTC)

And this one :-) — Preceding unsigned comment added by 206.191.19.90 (talk) 14:12, February 28, 2006 (UTC)

Theory

Um... was this ever a scientific theory? Wouldn't it be better to rename it either just recapitulation or at least recapitulation hypothesis? The article itself says it's a hypothesis. Calling hypotheses "theories" causes a lot of confusion. --TheAlphaWolf 03:18, 10 March 2006 (UTC)

wel i dnt av a clue wot this theory is about — Preceding unsigned comment added by 193.192.73.3 (talk) 11:40, March 12, 2006 (UTC)

did u read th articl? —Keenan Pepper 19:18, 12 March 2006 (UTC)

The fact that "Embryology recapitulates Phylogeny" has been well known for some time and accepted by the majority of scientists. Although the initial hypothesises on this topic has been dismissed as too simplistic, the biogenetic hypothesis is now considered a theory. Dilbert 00:02, 17 May 2006 (UTC)

Brennig James Comment

-- Moved this from the main article - Peripitus 14:37, 6 May 2006 (UTC)

"Comment by brennigjames1@msn.com. Haeckels law was proceeded by Von Baers laws admirably praised by Gavin De Beer in 'Embryos and ancestors' This was before the gene was postulated. At their time development was thought to be a continuum,but it is a vast number of discrete steps forming a vast triangular flow chart early alterations will be more disruptive and lethal,so phylogeny will tend to proceed by modifications towards the end of development. So we can restate von Baers Laws as genes will tend to act during development in the same sequence as they arose during the course of evolution. Recapitulation is the strongest evidence for Darwinism and is or best argument against creationism. Haeckels theory was criticised perhaps unfairly because earlier stages in development did not represent adult forms of earlier organisms,it was a generalisation too far perhaps. Von Baers Laws were accurate provided you accept imprecise words like resemble or tend. If you are pedantic Haeckels law is obsolete,but it had its day. After all if Aristotle had said denser rather than heavier Galileos experiment on the leaning tower of Pisa would have failed. We must be kind to the memory of our predeccesors." - Brennig james

Misleading statement about recapitulation theory being used to support evolution

Whoever added the statement at the end of the "Rejection" section that stated that Haeckel's drawings were used to support evolution is sorely confused about both the theory of evolution and Haeckel's own theory of recapitulation. Haeckel's theory was a competitor to Darwin's, not in support of it. Haeckel wanted to suggest that somehow the fact that ontogeny seems recapitulate phylogeny means that there is some inevitable drive toward progress that is manifest in both ontogeny and phylogeny. The inevitable, magical nature of Haeckel's progress was what Darwin was opposed to.

Thus, Haeckel's recapitulation theory could not have been used to support Darwin's theory of evolution. It's like saying that the Catholic dogma of a Ptolemaic solar system was mistakenly used to support Galileo's theory of heliocentrism. (Mavaddat 03:06, 16 August 2007 (UTC))

While I agree wholeheartedly, modern creationists have claimed that recapitulation supports evolution. You are right that it does not, other than perhaps being suggestive. I ~~will edit~~ see you have corrected the mistaken text. ←Ben^B4 20:30, 15 August 2007 (UTC)

Inclusion in modern textbooks

I'll look into the matter a little more closely, but I distinctly remember all of this being presented in my high school biology text book as fact, only a couple of years ago. Something should be said about this. —Preceding unsigned comment added by 68.210.211.188 (talk) 20:11, 5 February 2008 (UTC)

10 years ago, I was being taught in university that the basis of the recapitulation theory is still considered correct, with one vital addition: the ontogenetic development can itself get optimised with evolution. Otherwise it would really be outlandish to suggest that organisms resembling today's insect pupae were the evolutionary link between worm-like and insect-like animals. --Yerpo (talk) 08:23, 17 February 2008 (UTC)

This article appears contradictory. It spends the first 3/4 of time saying that Recapitulation theory is discredited, and then the last 1/4 of time showing examples where it holds well. It cant be both! Fig (talk) 20:33, 18 October 2011 (UTC)

Um... I just got here, but it really appears that this article presents a loud minority opinion as irrefutable fact. When did growing a set of gills in utero stop being significant? Also: http://www.physorg.com/news/2012-03-baboons-infants-similar-gesturing-behavior.html Slartibartfastibast (talk) 23:12, 21 March 2012 (UTC)

Two questions

Hi, I have two questions on this topic:

Did Haeckel ever propose a mechanism for this theory or did he only report his observations of the embryos? Did anyone after him propose a mechanism?
Generally, if a structure pre-dates another structure in evolutionary terms, then it also appears earlier than the other in the embryo. Species which have an evolutionary relationship typically share the early stages of embryonal development and differ in later stages. What are the current theories on why this happens and does it have a name?

Thanks in advance. --85.145.56.218 (talk) 02:13, 31 December 2008 (UTC)

I absolutely agree that this user's second question needs to be addressed. The introduction describes recapitulation theory as "a discredited biological theory," but while the overarching idea that all embryonic development mirrors evolutionary history has been discredited, the article nevertheless concedes that evolutionary relationships are, in some cases, very well described by embryonic development. I notice the section of the article that notes Darwin's related, but different, view. If this is a separate concept from "recapitulation theory," it deserves to be named or to have its own article. If both Haeckel's and Darwin's hypothesized phenomena qualify as "recapitulation theory," the article should be restructured to reflect their divergent viewpoints, and explain that Haeckel's hypothesis has been refuted while Darwin's has proved, at least in some cases, accurate.66.134.4.226 (talk) 14:44, 22 January 2010 (UTC)

Lead

Other than the obscure-to-me-at-least "ontogeny recapitulates phylogeny," the lead doesn't even try to define what recapitulation theory IS. Anyone willing to take a shot? --John (User:Jwy/talk) 21:24, 23 October 2010 (UTC)

Good point, have given it a go. . . dave souza, talk 22:33, 23 October 2010 (UTC)

copy of removed paragraph from historical influence section--cite needed march 2009

"The maturationist theory of G. Stanley Hall was based on the premise that growing children would recapitulate evolutionary stages of development as they grew up and that there was a one-to-one correspondence between childhood stages and evolutionary history, and that it was counterproductive to push a child ahead of its development stage. The whole notion fit nicely with other social Darwinist concepts, such as the idea that "primitive" societies needed guidance by more advanced societies, i.e. Europe and North America, which were considered by social Darwinists as the pinnacle of evolution.^{[citation needed]}"

Comparative embryology

Maybe what needs to be done is expand the comparative embryology article and then merge the valid parts of this (Recapitulation theory article) into that.--Richard Peterson76.218.104.120 (talk) 10:33, 15 June 2012 (UTC)

A lot of expansion would be needed, and since this is essentially a historical topic Embryology#History of embryology could be a better basis. History of embryology could be a main article on the topic. Improvements are needed in clarifying the extent to which "recapitulation" has some validity, for example in establishing from shared larval forms that barnacles are crustaceans. . . dave souza, talk 11:08, 15 June 2012 (UTC)

Meaning?

Quoting our article:

"However, embryos do undergo a period where their morphology is strongly shaped by their phylogenetic position, rather than selective pressures."

Please, can anyone tell me what this sentence means? Wanderer57 (talk) 22:01, 15 June 2012 (UTC)

That is a pretty awful sentence, but I get what they're saying. It's a common argument in favor of evolution that you will often find an organism that, at some stage in development, has an embryo that more closely resembles a phylogentically close relative than its own adult form. My undergraduate development text argued that since so many critical cell migrations and differentiations occur during early embryonic development, it was simply "easier" for significant changes in body plan to be implemented at later stages in development. And that is what leads to the general phenomenon that the various embryos within a phylogenetic clade are more similar than the corresponding adults, although "similar" here is typically a subjective measure. Someguy1221 (talk) 23:49, 15 June 2012 (UTC)

Thank you both. So if the sentence was being rewritten, should it convey that this statement applies to embryos of some organisms, not to embryos in general? Wanderer57 (talk) 18:02, 16 June 2012 (UTC)