In the broad sense it is not a discredited theory. 

Paddy:

There is no reason why Ernst Haeckel's hypothesis be discredited despite inherent deficiencies and controversies. Charles Darwin's Natural selection hypothesis does not deserve to be discredited either as Biological sciences are not governed by a set of discrete and well defined laws as in physical sciences.

Best

Syed

Syed;

Thank you Syed. My question arose because Wikipedia, usually a good first reference, describes the statement as ‘discredited’, which is unfortunate.

While it may be philosophical time well spent to distinguish between physical and biological science, do all biological sciences lack scientific discipline?

It makes no sense to ignore the biochemical complexity of living as it is involved in evolution (genetics), pregnancy (ontogeny) and childhood and adult life (cellular development, healthy operation, sickness and death).  Nor does it make sense to use other disciplines to try and understand mental illness rather than acknowledging our poor understanding of this biochemistry at every level.

Best

Paddy

Dear Colleagues,

Thank you for these contributions !

I checked the original Wikipedia page (a short explanation of the Recapitulation theory from 30 October 2001). Its 2nd alinea wisely states : "Connections between ontogeny and phylogeny can be observed in most species." Now this is exactly how I successfully used it, while teaching (comparative) anatomy and embryology in the past 40 years.

Furthermore, a dogma can also (literally) be a presentation or a principle, so to my experience the Recapitulation theory is still  very useful while presenting and explaing some Principles of Anatomy and Embryology !

Wishing you success, with kind regards,

Koos Jaap van Zwieten

Dear Paddy,

Again, for explanatory reasons, we can also refer to these inspiring phrases written by Elisabeth Mann Borgese (in The Drama of the Oceans) : “Every woman’s womb is a micro-ocean, the salinity of its fluid resembling that of the primeval waters; and every microcosm restages the drama of the origin of life in the gestation of every embryo, from one-celled protozoa through all the phases of gill-breathing and amphibian, to mammalian evolution.”  (From: Glimpses of the Blue Caribbean, UNESCO, 2000).

While introducing / explaining human embryology, according to our experience over the years, it can be most helpful to cite references like this ! Therefore I agree with you, that speaking about the principles of recapitulation as being discredited, is at least pedantic.

With best wishes,

Koos Jaap van Zwieten

It is discredited from the perspective that we most certainly do not recapitulate our phylogeny. Where, for example, is our reptilian stage? It is undoubtedly true that there are elements of our ancestry embedded in our development, like the "gill slits" present in a fetus. However, Haeckel took this to an extreme, assuming it to be completely true, and either intentionally or unintentionally altering his drawings of fetuses to more explicitly resemble the forms he claimed were being recapitulated. This is not pedantic - he made a claim, and manipulated observational data (drawings, the best technology of the age), to support that claim.

Of course, like with many scientific claims, there was some truth in what he was saying. He simply carried it too far. Today we would not say that ontogeny recapitulates phylogeny, but rather that animals (and plants, fungus, and probably all of life, for that matter) often share patterns of development with other, related groups. The more closely related, the more developmental patterns and processes tend to be shared.

Dear Koos Jaap , Alex et al

Thank you for you comments. I think it matters not how literally you understand 'recapitulates'. Clearly the fetus experiences development through a nine month period of change that encompasses many of the stages characteristic of its evolution.

I raised the issue because the current understanding of stressor-related disorders and mental illness and the 'risk factor' the role of fetal responses to the stresses it may experience during pregnancy, demands some consideration of the consequences of  these primitive responses.

How this can be studied presents enormous problems but until we do it seems unlikely that we will properly understand the response to adult stresses or the development of mental illnesses.

With best wishes,

Paddy

The reason that ontogeny often recapitulates (parts of) phylogeny is that mutations early in ontogeny tend to be very disruptive, whereas mutations late in ontogeny have smaller (finer) results.

Not only does ontogeny often recapitulate phylogeny, but phylogeny is in fact a succession of 1000s or millions of ontogenies.

The concept of 'ontogeny recapitulates phylogeny' cannot be disregarded.Of course one should not expect the entire evolutionary process to be repeated in human development.However,it is obvious that quite a few congenital anomalies are in fact normal functional structures or organ systems in  earlier forms.The teachers in comparative anatomy,human anatomy or embryology have to refer to the concept quite often.Regards.

For a modern summary of the status of the theory of recapitulation, a good source is the online supplement for Scott Gilbert's textbook, Developmental Biology (10th edition).  This is better than the Wikipedia article and it is written by a leader in the field of evolutionary developmental biology, informed about both the history and the modern state of the subject. There he says:  "A disastrous union of embryology and evolutionary biology was forged in the last half of the nineteenth century by the German embryologist and philosopher, Ernst Haeckel...". In Ontogeny and Phylogeny, Gould gives a much longer overview of the history of the subject and why the rediscovery of Mendelian genetics made the theory untenable. There is still some debate among historians about what led to the demise of the theory, as well as about how destructive the theory was to efforts to unify genetics, development and evolution. What may be responsible for the sense that the theory of recapitulation is useful, especially in comparative anatomy and medicine is that evolutionary biology in general, and evolutionary developmental biology, in particular, are useful for those field. 

Ernst Haeckle’s hypothesis, I believe offers a gold standard in tracing H.sapiens ancestral lineage.  More specifically, fossil evidence demonstrates calcaneal supinatus in some potential hominins and not others.  I suggest this can be used to determine when foot fossils comes from a H.sapien prototype, and when foot fossils do not.

It is well to note that calcaneal supinatus occurs early in the ontogenetic development of humans and when maintained in newborns is termed PreClinical Clubfoot Deformity.

Professor Rothbart

The supportable conclusion about ontogeny and relatedness is that the earlier stages of development of  different species resemble each other more so than the later stages of  their development.  Another response noted correctly that this is likely due to the more disruptive effects of mutations to genes active in earlier parts of ontogeny. In turn, this can be supported by the likely more pleiotropic effects of those  genes active earlier in ontogeny.

 A nice illustration of this can be found in seedless fruits - they are normal hybrid plants until the end of their ontogenies when reproduction occurs - these late processes have mutated differently in the parents of the two species  thus resulting in  hybrid offspring who are reproductive duds. 

Another example of this can be seen in closely related species of salmon. Adult males of different species have a dull silver color and and look very similar to each other morphologically throughout their ontogenies but, at spawning time, develop different colors and distinct morphologies in body and jaw form.

Prof.Rothbart, yes, if ontogeny +-recapitulates phylogeny, embryological data can be used to reconstruct the evolutionary past of a species. Prof.Coon (The Story of Man) noted that prenatal chimps have feet resembling ours, with long and forward pointing big-toes: "only as it approaches its birth does its foot acquire the appearance of a hand" (S.C.Coon). If chimp ancestors (and therefore probably also the Homo-Pan last common ancestor) had more humanlike feet, this suggests that humanlike feet in fossil hominoids don't prove that the fossil is a closer relative of Homo than of Pan. IOW, a lot of fossils (e.g. australopiths) that are usually attributed to human ancestors or relatives might be closer relatives of chimps (or perhaps of gorillas, if prenatal gorillas also have more humanlike feet).

Thank you all?

My question seems to have been of most interest to those of you studying evolution.

My particular interest is the human foetus’s response to the stresses of pregnancy, which has to be dependant on its stage of development. This suggests different effects on allostasis and  adult consequences.

By 20 weeks the foetus is reported to have its own independantly functioning pituitary and adrenals and a recent study shows that the early-life stress of preterm birth is associated with differential methylation at sites in several protein-coding genes, suggesting that they are promising candidate genes for understanding genetic influences on brain development after preterm birth.

 I wonder if anyone knows if there are any studies comparing the composition of blood in the foetus and its placenta – focused on stress response molecules – in humans or mammals?

Refs. - par

Gitau R, Fisk NM, Teixeira JM, Cameron A, Glover V. Fetal hypothalamic-pituitary-adrenal stress responses to invasive procedures are independent of maternal responses. J Clin Endocrinol Metab 2001; 86: 104-9.

Sparrow S, Manning JR, Cartier J, Anblagan D et al.  2016. Epigenomic profiling of preterm infants reveals DNA methylation differences at sites associated with neural function.

Translational Psychiatry ,(2016) 6, e716; doi:10.1038/tp.2015.210

Paddy:

It is true that development of human embryo could be influenced by external stressful factors, which could adversely affect adult behavior. But how do you relate this to the hypothesis of Ernst Haeckel? Please clarify.

Best

Syed 

Yes Syed:

A stressed mother for a start can influence the development of the embryo and  a difficult birth would  probably, I believe, have a serious effect given that in the last trimester the embryo has an independent HPA axis. Hypoxia and prematurity and no doubt a range of other challenges to its development would also elicit some sort of stress response which would depend on its stage of development. Hence my interest in the essence of Ernst Haeckel's hypothesis. That prebirth experiences may effect adult behavior and mental health is already demonstrated but there is not yet any study, that I am aware of, allowing for the stage of development of the embryo.

 Best

Paddy

Yes Syed:

A stressed mother for a start can influence the development of the embryo and  a difficult birth would  probably, I believe, have a serious effect given that in the last trimester the embryo has an independent HPA axis. Hypoxia and prematurity and no doubt a range of other challenges to its development would also elicit some sort of stress response which would depend on its stage of development. Hence my interest in the essence of Ernst Haeckel's hypothesis. That prebirth experiences may effect adult behavior and mental health is already demonstrated but there is not yet any study, that I am aware of, allowing for the stage of development of the embryo.

 Best

Paddy

I don't see how Haeckel's theory of recapitulation is even relevant to your question. The theory consists of three laws: (1) the Law of Correspondence, which states that each developmental stage of the species corresponds to an adult stage of an ancestor; the descendant species passes through them in the sequence of ancestral-descendant relationships; (2) the Law of Terminal Addition, which states that each species adds a novel stage at the end of the sequence of those adult ancestors, and (3) the Law of Truncation, which  states that development is shortened (else gestation length would continually increase as each species went through and then beyond the adult stage of its most immediate ancestor). Even when people did believe this, they regarded humans as an exception (proposing that humans undergo the reverse of recapitulation, such that human adults resemble subadult chimpanzees). In effect, we're like axolotls.  I might think that my teenager acted like a subadult chimpanzee, its' hard to take either version of this theory seriously.

Thanks, Miriam. Human adults can resemble young chimps (e.g. prenatal chimps have more hmanlike feet), and at the same time, in other features, adult chimps can resemble young humans (e.g. shorter legs): both species had the same ancestor c 5 Ma. The same examples suggest that the human/chimp LCA had shorter legs & more humanlike feet, as we see in australopiths - which is not surprising: both humans & chimp had (in different directions) more australopith-like ancestors. This implies that some australopiths could have been ancestral to chimps, others to humans, still other to gorillas, or could have been extinct side-branches etc., but it seems to contradict the traditional anthropocentric assumption that australopiths are human ancestors to the exclusion of chimps & gorillas.

Thank you Miriam. I have no argument with you and was unaware  of the laws you detail.  My concern was with the devaluation of the essence of the oft repeated statement (without reference to Haekel's hypothesis / theory) that ontogeny repeats phylogeny.

You seem to miss the point that we cannot ignore the fact that the embryo, at different times in its development, may respond to stresses with primitive responses that will have different consequences for the child / adult.

Thank you Miriam. I have no argument with you and was unaware  of the laws you detail.  My concern was with the devaluation of the essence of the oft repeated statement (without reference to Haekel's hypothesis / theory) that ontogeny repeats phylogeny.

You seem to miss the point that we cannot ignore the fact that the embryo, at different times in its development, may respond to stresses with primitive responses that will have different consequences for the child / adult.

I'm not missing that point because it struck me that the point  of this question is the status of the theory of recapitulation (i.e., whether it is discredited) and if so, why. Those three laws are the essence of the theory so any discussion about whether the theory is, or should be, devalued needs to begin with them. Certainly it would be possible to develop an entirely different rationale for the statement that ontogeny recapitulates phylogeny. The problem is that it doesn't. 

Clearly as ever language is a problem. I never asker about 'the theory of recapitulation'.

Looking at it again I do acknowledge that my original question is badly and incorrectly worded. I note that in elaborating i suggested 'passing through' rather than 'recapitulating' previous stages of the embryo's evolution.  I am sure Haekel defined recapitulation very carefully in his laws but my dictionaries allow a fairly wide interpretation.

My subsequent question remains: "I wonder if anyone knows if there are any studies comparing the composition of blood in the foetus and its placenta – focused on stress response molecules – in humans or mammals?" Ideally this would include different stages of development but I think that is very unlikely.

I'm reading a paper on lumbar numbers in hominoids. Just a thought. There are always 7 cervical vertebrae, usu.12 thoracal vertebrae, but the further we go caudally, the number of lumbar, sacral & coccygal vertebrae vary more. This is probably for the same reason why ontogeny tends to follow phylogeny: a distorsion early (anteriorly) in the vertebral column would distort all the rest caudally, comparable to a distortion early in ontogeny.

Haeckles theory was at best a hypothesis but his work was pure and has been charged with fraud.  There is no evidence that embryology gives any support to evolutionary theory.  This should do little to alter the interest of biologists to study development unless their goal is to force fit such speculation as support for the theory.  Along the study of development, should developmental genes demonstrate homologous control of body development, this would prove interesting and entertaining but is no objective proof of evolution.  The problem with the whole of the theory is that it started out as a speculation and has become a dogmatic assertion still waiting empirical evidence rather than the patchwork of 'evidences' typical of religious fanaticism. As seductive as natural selection is as a working hypothesis, it needs a real mechanism since all natural changes in DNA sequences so far categorized have been demonstrated to be defects or neutral changes.  Only in pretending we can read information from past millennia into the DNA sequence can we "imagine" the unfolding of complexity and change we so dearly seek for belief.  

Thanks  Daniel M for your late interest in this sublect. I was surprised by the vehemence of your contribution. Do you know of any way evolution could be prove or disproved?

While what we know suggests a multifaceted performance and natural selection seems an oversimplification the essence of evolution  is clearly a sensible working hypothesis.

It also seems abundantly clear that in essence gestation follows the pattern of evolution. 

Yes, Haeckel's idea was indeed a hypothesis. It's no strict "law", it's only a tendency: the earlier in fetal life we have a change, the more influential on the further growth this change is.That implies that changes tend to happen later in growth.

Haeckel's "ontogeny tends to follow phylogeny" does support evolutionary theory IMO, but this is not important: evolutionary theory is beyond doubt.

Please, could anyone share an article explaining well what is the recapitulation theory?

Thanks

Hi Umberto, I think you can best google or on Wiki "Haeckel recapitulation".