It will be rather difficult.

In the mean time, an old rule I had to install for coffee&sci and dloale is back and this time it is applied in a wider scale. Vincent Fleury’s comments will not be accepted in any of my blogs except if there is a copy sent by e-mail previously, CCed to his boss ; nowadays Jean-Marc di Meglio. As it is all about science Dr di Meglio should be interested.

It is not that I don’t want his comments to appear here, I’ll be happy to see his replies and answers to comments and questions. Usually it’s fun stuff and it would be sad to miss it.
It’s just necessary to refrain his childish ways to behave and oblige him to focus on the subject rather than desperately trying to change it.

So Dr Fleury, your comments are to be moderated by your boss, not by me Whatever he accepts I’ll accept.
By the way, I wonder, is he aware of the content of your website?

I opened The Mechanisms Underlying Primitive Streak Formation in the Chick Embryo, by Manli Chuai and Cornelis J. Weijer¹ for inspiration and of course Fleury’s webpage with his english short presentation.

Chuai & Weijer propose a simple model fitting their observations.

This is a rearrangement of elements from figure 1 (left panels) showing the transient vortices observed at the first stages of gastrulation at the epiblast level, bright field and epifluorescence, the marker being GFP expressed post-transfection and figure 3 (right panels) presenting a schema of their chemotactic model and the analogy with a hydrodynamic flow.

This is what Fleury describes as:

The usual picture of a development oriented in the antero-posterior direction is wrong. The recent dipolar description by Chuai, Weijer and co-workers is also wrong.

By saying so, he implies that the model don’t fit reality.
Maybe he failed to observe that the model proposed above include an area where V_x=V_y=0 at the center of Koller’s Sickle (KS)

How Fleury’s model fit reality? One may think that it must be better.

Let’s see:

The left panels as previously described, the right panel from Fleury’s model, tilted to align the axis to the one of the microscope images, the lower one being a superposition with the actual data. Pretty much the same frame of Weijer’s et al. time-lapse movie as the one Fleury used to position the missing vortices two years ago [fr but the images are international].

That would place the hindlimbs, according to Fleury’s, behind the KS!

A larger picture with the missing vortices annotated L2/R2:

not only “no L2/R2 – no hindlimbs” but also “if L2/R2, then hindlimbs behind the embryo!”

That doesn’t bother Fleury who prefers his model, coming out from the platonician space of forms, with the two invisibleimaginary vortices, instead of one quite realistic.

Make your mind. My preference goes to the one that stand reality check.

And if your name is Vincent Fleury and you are a theoretical physicist try to explain that.

Welcome guys.

Feel comfortable but be afraid, I’m the one manipulating the Master!
Using noodly appendages of course.

This one is from An Elasto-Plastic Model of Avian Gastrulation, Vincent Fleury, Organogenesis 2:1, 6-16, 2005.

[p13, col1, §4]

The extraordinary fact is that this equation is exactly the equation for two magnetic dipoles located at +a and -a near the caudal pole.⁸

Where 8 is given as: Bershadsky AD, Balaban NQ, Geiger B. Adhesion-dependent cell mechanosensitivity, Annual rev. oc Cell and Dev Biol 2003; 19:677-95.

OK, there is a small typo. But that’s not the problem.

Bershadsky et al. paper have just nothing to do with “two magnetic dipoles”! or any “caudal pole”. This is cell biology they are discussing there (abstract and full reference below).

Fast check:

• equation, absent,
• magnetic, absent,
• dipole, absent,
• caudal, absent,
• pole, absent

Slow check, I read the paper, nothing that could be confused with Fleury’s statement.

There are just 12 references in that paper, the first one I’m checking is wrong.

So,

The extraordinary fact is that this equation is exactly the equation for two magnetic dipoles located at +a and -a near the caudal pole.⁸

Either the reference is wrong or Fleury’s assertion. Or both.

Adhesion-Dependent Cell Mechanosensitivity

Alexander D. Bershadsky, Nathalie Q. Balaban, and Benjamin Geiger

Annual Review of Cell and Developmental Biology Vol. 19: 677-695 2003, doi:10.1146/annurev.cellbio.19.111301.153011

The conversion of physical signals, such as contractile forces or external mechanical perturbations, into chemical signaling events is a fundamental cellular process that occurs at cell–extracellular matrix contacts, known as focal adhesions. At these sites, transmembrane integrin receptors are associated via their cytoplasmic domains with the actin cytoskeleton. This interaction with actin is mediated by a submembrane plaque, consisting of numerous cytoskeletal and signaling molecules. Application of intrinsic or external forces to these structures dramatically affects their assembly and triggers adhesion-mediated signaling. In this review, we discuss the structure-function relationships of focal adhesions and the possible mode of action of the putative mechanosensor associated with them. We also discuss the general phenomenon of mechanosensitivity, and the approaches used to measure local forces at adhesion sites, the cytoskeleton-mediated regulation of local contractility, and the nature of the signaling networks that both affect contractility and are affected by it.

4.1 Tetrapod origin

If we turn to paleontology, we find a description of tetrapods appearance into three main steps. Appearance of chordates, segmentation of lateral fins, appearance of tetrapods.

That’s the shortest version one can get except “pouf they appeared”. Interesting nevertheless the second step, the “segmentation of lateral fins“. This is one of three hypothetical, not exclusive, working models. Not to be used as a granted fact (see below).

Good news, bad news.

Good news are that Fleury abandonned the idea it appeared in one of his conferences announcement, and promoted in fora, that the tetrapods may have appeared suddenly, with all there attributes, specifying suddenly as “in a single generation“.

But he still think that:

These early tetrapods have well formed complex limbs apparently almost “right away”.

Almost right away being an estimate of the time-lapse between Haikouichthys ercaicunensis, presenting a single median fin-fold and tail, to the tetrapodomorph Tiktaalik roseae; almost right-away corresponds to 100 millions years. At least we are not anymore at the “single generation“level.

Progressive modifications are problematic for a model which is based on a suddenly appearing bauplan.

4.2 About pentadactily

Well, certainly the bests Oops of this subsection. You can read about it here.

The idea to connect somites to fingers was not bad, but it doesn’t stand scrutiny, unless it’s Fleury who compares whatever to whatever (mixing mutants) forgetting or not caring to check the controls, and finally draws false conclusions.

This is not anymore about ignorance but rather about lousy methodology, not particularly connected to biology or physics. Of the general kind.

Reality check says that limb buds facing the same number of somites develop to pentadactylous limbs in wt embryos and nonadactylous embryos to double mutants.

The idea was interesting, but it doesn’t fit reality, so down the drain it goes (an old idea when it comes to Fleury’s theories).

And we find here also one of Fleury’s exact calculations, the “possible period doubling“, with 2*5={8,9,10}, a new kind of arithmetics.

And a second major Oops in the same subsection with the misrepresentation of fig. 21, wrong reference, wrong description.

Fleury wrote a few time ago [source: #63]:

To answer your comment [#50], yes, It was a physics paper, intended for physicists in a physics journal, so it makes little sense that somebody like Prof. Myers tries to review it, and then complain about the lengthy and tedious introduction. I find it weird that Prof. Myers should not be able to understand that a text is always intendend for a certain audience, it was not for people like him.

I wonder what that does mean. Because the expected audience was physicists that means that Fleury can serve them BS because they will not understand what they are served? And an embryologist’s opinion make little sense?
He is certainly right to think so, the referees didn’t understood what they were served after all. That doesn’t mean nobody will understand and explain them.

4.3 Fold extension

All fin-like appendages, be it anal, pelvic, pectoral or dorsal seem to be progressive extensions of superficial folds.

Not. Not folds, morphogenic fields (in the embryologist’s sense) which produce buds. There is probably shear stress acting as a positional cue integrated with other ones and participating in the morphogenetic events. But what specifies the morphogenetic field and produce the buds is cellular differentiation, that is differential genetic expression; that’s how folds are produced and what determines where and when they will be produced during the developmental process.

The AER is a typical example of an anatomic structure not being a fold, but an outgrowth of differentiated cells. But then Fleury may consider it as a fold, falsely believing (from a patently ignorant point of view) that in the normal case the AER is the junction of ectoderm and endoderm.

The discussion about the chorio-amniotic fold of the amniotes is interesting. Nothing to do with paleontology, no references concerning the timeline of its development to help connect the embryos curling with the fold‘s formation, an hypothesis out of thin air, expressed as an assertion (“The chorio-amniotic fold is analogous to a fin fold, except that the topology of the edge is a circle which closes up progressively like an iris, to form a hollow bag, and not a flat veil.“).
At least when it comes to the genetic components specifying its development he express his opinion as a belief (“I believe that a genetic analysis of the amniotic edge would give similar genetic inductions as a tail (see data base GEISHA [97]“). It could be, did he checked out the available data that could support this hypothesis? Or does he cite GEISHA just to bring false credibility to the hypothesis?

No mention of the neural fold, in plain sight (fig. 18), which doesn’t fit with the idea of proximo-distally extension.

Charles Darwin is wrongly cited here too. Maybe “scaffold” sounds better in Fleury’s ears, but it wasn’t used by Darwin.

This is also true of other edge-like organs, such as ears, nostrils or lips, which are well known to be observed in nature with almost “arbitrary” lengths, a word often used by Darwin.

Not very often, and never in association with “lenght”.

Citing Darwin doesn’t validate hypotheses, citing him (or anybody else) inappropriately, disrupts the argument.

So,

In the case of the pectoral and pelvic fins, they are believed to originate from a uniform fin present along the body; in the centre of this fin, an area was interrupted or somehow inhibited.

Again, no reference.

There is a quite interesting and relevant to the specific question paper (and for further discussion), by Yonei-Tamura et al.¹, addressing the presence of competent stripes for diverse positions of limbs/fins in gnathostome embryos, presenting three, non exclusive, work models:

Fig. 5. Model for the diversification of appendage morphology and its position in gnathostomes. Top: basic body plan for appendage formation with distinct features as a conserved developmental program; light blue indicates the lateral and dorsal competence for formation of limb/fin buds. Middle: appendages in early gnathostomes are formed by species-specific selection of limb/fin positions from the entire general competent region. Bottom: basic morphology and diversification of appendages in extant gnathostomes had evolutionally been established under the competence. Note that the animal retains competence in the dorsal and flank regions as shown in light orange.

One of them, middle/left of fig.5, fits with the hypothesis favored by Fleury. The authors compared msx1 expression in dogfish, skate and chicken, supporting the model by restricted gene expression domains between the three kinds of embryos (from fig. 2, panel Q¹ :

Schematic representation of msx1 expression in dogfish, skate, and chick embryos. Light and dark orange bars represent msx1 expression in the mesenchyme and ectoderm, respectively.

The skate embryo expressing msx1 in a way that gives an “8-shape” when observed from a dorsal or ventral point of view.

A very interesting information one can draw from this paper is that competence for limbs/fins is conserved to actual gnathostomes’ embryos and it comes in stripes rather then buds restricted at the limbs/fins morphogenic fields. And this information gathered by experimental data, confirming previous observations (including ref [65]).

Thus, the assertion

This is to say that it is not the regulatory loops of the genetic expressions which actually induced the splitting of the fin into limbs, but some “contraction”, which remains to be understood.

was obsolete before cteappv’s acceptation by EPJAP, the contraction being the one of of the limbs/fins morphogenic fields specifying genetic expression. One could have anticipated that this would be the case, from data available through the relevant scientific literature, Yonei-Tamura et al. paper being a systematic confirmation of previous results (which was necessary and is welcome), more than a revolutionary inout.

4.4 Limb extension

The fourth subsection starts quite badly.

Therefore, the situation in this field is not quite clear. It seems again that the same genes, already present prior to limb appearance, may serve to make a tail, a fin, or a limb, depending on where they are expressed, i.e., depending on the local geometrical context, and physical twists which occurred before genetic expression, in addition to chemical differences. This reminds of the fact that cnidarians and vertebrates have similar gene regulatory networks.

Hox genes where co-opted for specification of limbs, the central nervous system, the vertebral column, the gut, the genitals, the excretory apparatus and the hematopoietic system. They produce DNA binding proteins which act either as activators or repressors of transcription, depending of the differentiation state of the concerned cells and the integration of signaling events.
They indirectly (via the genes which expression they regulate) define geometrical context and in turn may be influenced by it as it specifies positional cues. Their role is evidenced by loss and gain of function experiments, limited by the pleiotropy of action of these genes (mutants development may be arrested before the onset to the developmental stage to be studied, e.g. limb development).

For the higher-then-the-cell level, genetic expression always precede geometrical variations, providing the molecular effectors and the energy necessary to produce them. Abrogating transcription (for tetrapods also mRNA maturation) and/or translation (i.e. gene expression) inevitably results in cell death; the single resulting mechanical effect observed being the cell’s collapse and desegregation.

That’s basic biology textbook knowledge and it’s really weird to have to introduce these basic notions while reviewing an already published paper. And they directly contradict the notion of geometrical context and pysical twists occurring before genetic expression.

And facts concerning the similarity of GRNs between cnidarians and vertebrates should be adequately revised.

Later during evolution limbs disappeared from some tetrapod lineages which became aped, such as snakes.

Adult tetrapods may be limb-less because limbs don’t develop. The natural pattern of tetrapods is just tetrapod. If some species doesn’t conform with it’s just not a tetrapod. Easy to grasp, even for physicists. The adult of some species are limbless.
Fleury rightly concludes that for a species to be considered as tetrapod it must be a tetrapod! Puzzling, right?

The fact that hindlimbs form first [...]

is just one (more?) of the authors fantasies and certainly not a general fact, the forelimb-hindlimb developmental timing changes across tetrapod phylogeny. BIBO rule applies here, also.

4.5 Limb flexion

Articulations of the zygo- to auto-pode and stylo- to zygo-pode have being demonstrated to be sensible in respect to their orientation to ectopic gene expression which is able to change them.

This is a huge problem for the model Fleury propose, and his effort to minimize experimental results is ridiculous, and some ensuing statements are quite curious:

If this experiment would be confirmed, it would be an uncommon case of a chirality, directly induced by a scalar non-chiral field. This would suggest that Tbx5 codes for a chiral molecule.

If one needed an additional proof that the author really don’t understand what he is talking about, he got it. I really don’t find what to say about the degree of ignorance showcased here, except once more suggest that Fleury should RTFM and avoid talking about transcriptions factors before doing so.

Concerning limb flexion and Fleury’s model:

1. Limbs grow in a reverse way than the model predicts,
2. but this isn’t really important as the limbs flexion is represented by the model falsely, the third dimension lacking, and no mechanism is proposed for the instruction of the direction of flexion of the limbs, between the assumed vortices and the orthogonally growing limb.

This is the second predicted feature of the model, after limb positioning and is patently flawed.

Last in this subsection, one more display of Fleury’s poor understanding of biological literature, the way he reports the work of Liao & Collins, unable to make the distinction between an intoxication (reality) and a mutation (Fleury’s point of view) and correctly report on the “duplication of the entire body axis” which the authors report as lethal beyond gestation day 9 (reality) and are here considered necessary for the apparition of additional limbs (Fleury’s point of view).

1. Competent stripes for diverse positions of limbs/fins in gnathostome embryos, Sayuri Yonei-Tamura, Gembu Abe, Yoshio Tanaka, Hiromasa Anno, Miyuki Noro, Hiroyuki Ide, Hideaki Aono, Ritsu Kuraishi, Noriko Osumi, Shigeru Kuratani, and Koji Tamura, Evolution & Development 10:6, 737–745 (2008)

My very first objection concerning Fleury’s model¹ was that he described the epiblast cells as contained between two extracellular membranes. When I pointed that his only response was that if there is a single basal membrane that doesn’t affect his model, the flow would be just faster. From that point on you can’t trust the guy with any description.

Assuming, once more for argument’s sake, that there would be four vortices on the center of which the limb fields develop, could that explain, as Fleury presents the flexion of the limbs ? I asked one question which is still unanswered by Fleury more than ten days later.

His description doesn’t fit with his description. We have here an inner contradiction of his model that gone under his radar. The limbs growth doesn’t follow the vortices flow. That’s sad, but it’s not the worse part of it. Let’s add an new-dimension.

Fleury so much like to consider embryos as rather flat entities that he forgotten the third dimension. Not completely. In Fig 37, panel a, he present us a stage 4 embryo of Eleutherodactylus coqui, with a personal annotation showing the vortices:

On the left the original from Richardson MK et al.² paper, on the right Fleury’s interpretation of the positioning of the vortices. As we have see, when it come to limbs flexion, this third dimension vanish and the schemas of fig. 38 are flat.

The growth of the limb bud is orthogonal to the plane of the vortex, let’s represent it as below:

the vortex in yellow, rotating clockwise and the bud growing upwards.

When it come to define the flexion at the junction between the stylo- and zeugo-pode what would be the mechanical mechanism that would instruct a particular direction for the bending ? I represented below the development of the limb with the stylopode in blue, the zeugopode in green and the articulation (elbow or knee) as a pale blue sphere. (four directions in color, plus four as gray ghosts, and infinity of case not represented)

None presented, despite the role Fleury attribute to limbs flexion.

Let’s see what that would give us if we try to map it to the four vortices model:

(here the vortices are in red to improve visibility) The AnteroPosterior and DorsoVentral directions are annotated, along with the cartesian (orthogonal) coordinates system. The latter is just represented to show how much inappropriate it may be to confound the embryos axes to it.

There is no relation between the vortices and the limbs flexion, limbs proximodistal axes being parallel between them and to the Z axis.
The real stuff in almost the same orientation as the above schema:

with the direction of growth of the limbs in white (insert, original).

Both papers freely available
1. An Elasto-Plastic Model of Avian Gastrulation, Vincent Fleury, Organogenesis 2:1, 6-16, 2005
2. Limb development and evolution: a frog embryo with no apical ectodermal ridge (AER), Richardson MK, Carl TF, Hanken J, Elinson RP, Cope C, Bagley P. J Anat. 1998 Apr;192 ( Pt 3):379-90, doi: 10.1046/j.1469-7580.1998.19230379.x.

Limbs positioning and global orientation is attributed by Vincent’s model to four vortices. For argument’s sake¹ let’s assume that such vortices exists and have something to do with limbs .

In the legend of Fig. 38 there is an explanation of the global orientation of the limbs.

Unfortunately the vortices are not represented but it’s easy to add them. Hindlimbs are represented so the hypothetical L2/R2 are in play. Two counterrotating vortices flanking the anteroposterior axis, centered (?) to the hindlimbs fields.

I hope I positioned them correctly according to the model, based on Fleury’s sketches in his personal university’s website. L2 in the left turning clockwise and R2 on the right, turning anti-clockwise.

Two step further from the third panel of fig. 38 you get which curiously represent an already developing autopod instead of the limb bud, with five rays probably representing the future fingers. Probably a residue of the misconception described in Oops 090616. Not really important here.

The hiatus is visible when we continue to panel five of the figure, where the stylo- and zygo-pods become apparent.The proximal point is depicted by a round, the distal one by an arrowhead. The limbs “rotation” is inverse in respect to the vortices, counter-clockwise for the left limb and clockwise for the right limb.

Here L2 in detail: L2 turns clockwise, the limbs counter-clockwise. Is this correct Dr Fleury?

By the way “I can has L2/R2″ is not a sentence

Aha! this is not a sentence. I was waiting for this one since I read the paper.

For Dr Fleury first step here, and second one here, both necessary to get the flavor.

For everybody else, a puzzle served below [p22 col2 §1]:

The significance of the reversed flexion of the hindlimb in 10% of the experiments reported in reference [59] is unclear since the electroporation experiment used to insert Tbx5 in the hindplate prior to hindlimb growth has a polarity in itself. If this experiment would be confirmed, it would be an uncommon case of a chirality, directly induced by a scalar non-chiral field. This would suggest that Tbx5 codes for a chiral molecule.

Maybe Dr Fleury will take the time to provide the solution. Hopefully this will not end as “I can has chirality??“.

While he is visiting lolcats and fails to have an insight about lolchickens I’ll give it a try to prepare a question for him.

Genetic analysis, in relation to evolutionary issues, shows that actually, genes for limbs and for tails are similar, and many are identical ([98] and references above³¹, Ref. [60]). Also, genes which serve to form the true limb skeleton, are actually present in fish fins, in which such skeletal elements are absent [98] (Fig. 21).

³¹ “Not only are the same Hox genes expressed in both developing appendages but they are expressed in identical spatial and temporal patterns” in reference [85].

Where

[98] is An autopodial-like pattern of Hox expression in the fins of a basal actinopterygian fish, Marcus C. Davis, Randall D. Dahn & Neil H. Shubin, Nature 447, 473-476 (24 May 2007) | doi:10.1038/nature05838 and deals with autopodial-like gene expression pattern, not limb in general. [for fig 21 follow the link].

[60] is Hox genes in digit development and evolution, József Zákány & Denis Duboule, Cell Tissue Res (1999) 296:19–25, doi: 10.1007/s004410051262.

[85] is presented as “85. D. Shu, X.-L. Zhang, S.C. Morris Nature (1996)“, probably corresponding to A Pikaia-like chordate from the Lower Cambrian of China, D.-G. Shu, S. Conway Morris, X.-L. Zhang, Nature 384, 157-158 (14 November 1996) doi:10.1038/384157a0, the authors not being presented in the right order. It is their single common paper published in Nature in 1996 and one of the four common (with other co-authors) ever published in Nature, all presenting fossils. At least, some paleontology slipped in this subsection, mistakenly, but…

Citation ³¹ is from [93], Why we have (only) five fingers per hand: Hox genes and the evolution of paired limbs, Clifford J. Tabin, Development 116, 289-296 (1992):

Not only are the same Hox genes expressed in both developing appendages but they are expressed in identical spatial and temporal patterns. The expression of posterior genes in the anterior appendage thus may indicate that the pelvic and pectoral fins evolved by both adopting molecular mechanisms present in a common ancestral posterior fin.

Oh boy! What a mess!

Now, many genes must be commonly expressed at tails and limbs and some differentially expressed specifying features identity.
What’s the point Fleury is trying to make?

This is a completely different dimension from my favorite local (French) crackpot detector, Jean Staune, the very anti-Darwin Secratary General of the Université Interdisciplinaire de Paris, an association heavily financed by the John Templeton Foundation. Whatever Jean likes (in science) becomes immediately suspicious and it was Jean who introduced Fleury in a public forum, where we first meet.

Now, Suzan Mazur, spotted Fleury, and he grabbed the opportunity to explain himself to a larger audience. That’s great, the visibility is much wider then an isolated blogger in France could expect trying to debunk Fleury’s theory.

As I acknowledged, I’m the one who asked PZ Myers’ opinion on Fleury’s paper. The choice of the science blogger to contact at first was easy to make. PZ is an embryologist, have a particular interest for integration of developmental and evolutionary biology, he is a longtime fan of d’Arcy Thompson, is rather outspoken, it’s difficult to influence him, and he have a large audience with a fair proportion of scientists who dare speak their minds in the comments.

I was delighted with PZ’s conclusions which match mines closely, and as a bonus Fleury abundantly commented making his point of view much clearer then in his paper, so people know better where he stands.

In the interview Suzan Mazur stupidly try to make her point that evolutionary biologists, biologists in general, PZ in particular, are worried about some paradigm shift. Paradigms shifts may be a common topic of interest of crackpot detectors and crackpots. PZ took care of that part of the interview.

Fleury’s opinion about PZ is a complex subject:

Flery can make an effort to be consensual in front of fellow crackpot theories, so maybe there is some torus inside the oocyte, Stuart Pivar will be happy to know that; there is some collaboration possible, Mazur could convert herself to a crackpot matchmaker? And Lima-de-Faria could join for a threesome. Except they are not French, so it’s no quite sure they will get those deep concepts.

I would like to thank Suzan Mazur for her excellent idea to interview Fleury, another way to help a fellow hang himself. And Fleury for accepting; quite difficult to translate everything he said in the french press and radio, but now we have an english version of the Big Picture.

---

1. For Fleury “creationism” is a term restricted to YECreationism.
2.

It may be asked how far I extend the doctrine of the modification of species. The question is difficult to answer, because the more distinct the forms are which we may consider, by so much the arguments fall away in force. But some arguments of the greatest weight extend very far. All the members of whole classes can be connected together by chains of affinities, and all can be classified on the same principle, in groups subordinate to groups. Fossil remains sometimes tend to fill up very wide intervals between existing orders. Organs in a rudimentary condition plainly show that an early progenitor had the organ in a fully developed state; and this in some instances necessarily implies an enormous amount of modification in the descendants. Throughout whole classes various structures are formed on the same pattern, and at an embryonic age the species closely resemble each other. Therefore I cannot doubt that the theory of descent with modification embraces all the members of the same class. I believe that animals have descended from at most only four or five progenitors, and plants from an equal or lesser number.

Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide. Nevertheless all living things have much in common, in their chemical composition, their germinal vesicles, their cellular structure, and their laws of growth and reproduction. We see this even in so trifling a circumstance as that the same poison often similarly affects plants and animals; or that the poison secreted by the gall-fly produces monstrous growths on the wild rose or oak-tree. Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.

(Charles Darwin, 1959)

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