scholarly journals Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis

2019 ◽  
Author(s):  
Marc HE de Lussanet
Keyword(s):  
Bilateral Symmetry ◽  
Optic Chiasm ◽  
Early Embryo ◽  
The Body ◽  
Head Region ◽  
Evolutionary Selection ◽  
Left Handed ◽  
Secondary Feature ◽  
Half Turn ◽  
Axial Twist

The contralateral organization of the forebrain and the crossing of the optic nerves in the optic chiasm represent a long-standing conundrum. According to the Axial Twist Hypothesis (ATH) the rostral head and the rest of the body are twisted with respect to each other to form a left-handed half turn. This twist is the result, mainly, of asymmetric, twisted growth in the early embryo. Evolutionary selection tends to restore bilateral symmetry. Since selective pressure will decrease as the organism approaches symmetry, we expected a small control error in the form of a small, residual right-handed twist. We found that the mouth-eyes-nose (rostral head) region shows a left-offset with respect to the ears (posterior head) by up to 0.8° (P<0.01, Bonferroni-corrected). Moreover, this systematic aurofacial asymmetry was larger in young children (on average up to 3°) and reduced with age. Finally, we predicted and found a right-sided bias for hugging (78%) and a left-sided bias for kissing (69%). Thus, all predictions were confirmed by the data. These results are all in support of the ATH, whereas the pattern of results is not explained by existing alternative theories. As of the present results, the ATH is the first theory for the contralateral forebrain and the optic chiasm whose predictions have been tested empirically. We conclude that humans (and all other vertebrates) are fundamentally asymmetric, both in their anatomy and their behavior. This supports the thesis that the approximate bilateral symmetry of vertebrates is a secondary feature, despite their being bilaterians.

scholarly journals Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7096 ◽  
Author(s):  
Marc H.E. de Lussanet
Keyword(s):  
Bilateral Symmetry ◽  
Optic Chiasm ◽  
Early Embryo ◽  
The Body ◽  
Head Region ◽  
Evolutionary Selection ◽  
Left Handed ◽  
Secondary Feature ◽  
Half Turn ◽  
Axial Twist

The contralateral organization of the forebrain and the crossing of the optic nerves in the optic chiasm represent a long-standing conundrum. According to the Axial Twist Hypothesis (ATH) the rostral head and the rest of the body are twisted with respect to each other to form a left-handed half turn. This twist is the result, mainly, of asymmetric, twisted growth in the early embryo. Evolutionary selection tends to restore bilateral symmetry. Since selective pressure will decrease as the organism approaches symmetry, we expected a small control error in the form of a small, residual right-handed twist. We found that the mouth-eyes-nose (rostral head) region shows a left-offset with respect to the ears (posterior head) by up to 0.8° (P < 0.01, Bonferroni-corrected). Moreover, this systematic aurofacial asymmetry was larger in young children (on average up to 3°) and reduced with age. Finally, we predicted and found a right-sided bias for hugging (78%) and a left-sided bias for kissing (69%). Thus, all predictions were confirmed by the data. These results are all in support of the ATH, whereas the pattern of results is not (or only partly) explained by existing alternative theories. As of the present results, the ATH is the first theory for the contralateral forebrain and the optic chiasm whose predictions have been tested empirically. We conclude that humans (and all other vertebrates) are fundamentally asymmetric, both in their anatomy and their behavior. This supports the thesis that the approximate bilateral symmetry of vertebrates is a secondary feature, despite their being bilaterians.

scholarly journals Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis

2019 ◽  
Author(s):  
Marc HE de Lussanet
Keyword(s):  
Bilateral Symmetry ◽  
Optic Chiasm ◽  
Early Embryo ◽  
The Body ◽  
Head Region ◽  
Evolutionary Selection ◽  
Left Handed ◽  
Secondary Feature ◽  
Half Turn ◽  
Axial Twist

The contralateral organization of the forebrain and the crossing of the optic nerves in the optic chiasm represent a long-standing conundrum. According to the Axial Twist Hypothesis (ATH) the rostral head and the rest of the body are twisted with respect to each other to form a left-handed half turn. This twist is the result, mainly, of asymmetric, twisted growth in the early embryo. Evolutionary selection tends to restore bilateral symmetry. Since selective pressure will decrease as the organism approaches symmetry, we expected a small control error in the form of a small, residual right-handed twist. We found that the mouth-eyes-nose (rostral head) region shows a left-offset with respect to the ears (posterior head) by up to 0.8° (P<0.01, Bonferroni-corrected). Moreover, this systematic aurofacial asymmetry was larger in young children (on average up to 3°) and reduced with age. Finally, we predicted and found a right-sided bias for hugging (78%) and a left-sided bias for kissing (69%). Thus, all predictions were confirmed by the data. These results are all in support of the ATH, whereas the pattern of results is not explained by existing alternative theories. As of the present results, the ATH is the first theory for the contralateral forebrain and the optic chiasm whose predictions have been tested empirically. We conclude that humans (and all other vertebrates) are fundamentally asymmetric, both in their anatomy and their behavior. This supports the thesis that the approximate bilateral symmetry of vertebrates is a secondary feature, despite their being bilaterians.

scholarly journals The geometry of insect pairing

1922 ◽  
Vol 94 (656) ◽  
pp. 1-11 ◽  
Keyword(s):  
Median Plane ◽  
Bilateral Symmetry ◽  
Ventral Side ◽  
Dorsal Side ◽  
The Body ◽  
Anal Orifice ◽  
The One ◽  
Special Points ◽  
Asymmetrical Condition ◽  
Axial Twist

In insects bilateral symmetry is practically universal, except in some minor matters, as, for example, the slight overlap of the elytra exhibited by many beetles. In the females the symmetrical condition may be taken to be almost universal, but the males in certain families exhibit asymmetry, which in some cases is very extreme, in the terminal segments of the abdomen. It is with this condition that the present paper deals, and the simplest course to pursue is, first to state the case as shown by some species of Diptera, that being the Order most familiar to the author and one in which an asymmetrical condition is comparatively common, then to outline a possible explanation of the phenomenon, in the course of which certain terms will be defined in order to clear the ground of existing ambiguities. Certain statements made in the course of the argument will then be justified as far as possible, and, finally, a few special points will be discussed. In most insects, excluding such aberrant forms as the dragon-flies, the genital tube opens on the under side of the 9th abdominal segment, and the anal orifice is in the 10th. Let us trace a line in the vertical median plane of the insect, beginning on the dorsal side of the abdomen and proceeding round to the ventral side. On such a peregrination we shall first encounter the anal orifice and subsequently the genital one; this is true for all females and for most males, but there are some remarkable exceptions. Thus, it was shown by Snodgrass that in the Asilid genera Dascillis and Laphria a different condition exists. On referring to the figures in that paper, it will be seen that on tracing such a line round the insect in its median plane the genital orifice is met before the anal one ; the hypopygium is then said to be “inverted.” The term “hypopygium” will be used for the combination of the 9th and 10th segments, which are commonly fused into a single complex in flies, so that no movement of the one segment relative to the other is possible, and the two segments must always behave kinematically as a single body. This inversion is produced by the presence of a twist of 180° about the main axis of the body between the 6th segment and the hypopygium; the 8th segment is quite unsymmetrieal and has an axial twist of about 150°; the hypopygium has the complete twist of 180°, but nevertheless it is practically symmetrical about the median plane which still bisects it. The result of this twist is to produce a true asymmetry, although it may not be very apparent on casual examination; in fact, not until the relative positions of the orifices are looked into.

scholarly journals An ancestral axial twist explains the contralateral forebrain and the optic chiasm in vertebrates

2012 ◽  
Vol 62 (2) ◽  
pp. 193-216 ◽  
Author(s):  
Marc H.E. de Lussanet ◽  
Jan W.M. Osse
Keyword(s):  
Common Ancestor ◽  
Ventral Side ◽  
Optic Chiasm ◽  
The Body ◽  
Molecular Evidence ◽  
Trochlear Nerve ◽  
Inner Organs ◽  
Axial Twist ◽  
Migratory Movements ◽  
The Brain

Among the best-known facts of the brain are the contralateral visual, auditory, sensational, and motor mappings in the forebrain. How and why did these evolve? The few theories to this question provide functional answers, such as better networks for visuomotor control. However, these theories contradict the data, as discussed here. Instead we propose that a 90-deg turn on the left side evolved in a common ancestor of all vertebrates. Compensatory migrations of the tissues during development restore body symmetry. Eyes, nostrils and forebrain compensate in the direction of the turn, whereas more caudal structures migrate in the opposite direction. As a result of these opposite migrations the forebrain becomes crossed and inverted with respect to the rest of the nervous system. We show that such compensatory migratory movements can indeed be observed in the zebrafish (Danio rerio) and the chick (Gallus gallus). With a model we show how the axial twist hypothesis predicts that an optic chiasm should develop on the ventral side of the brain, whereas the olfactory tract should be uncrossed. In addition, the hypothesis explains the decussation of the trochlear nerve, why olfaction is non-crossed, why the cerebellar hemispheres represent the ipsilateral bodyside, why in sharks the forebrain halves each represent the ipsilateral eye, why the heart and other inner organs are asymmetric in the body. Due to the poor fossil record, the possible evolutionary scenarios remain speculative. Molecular evidence does support the hypothesis. The findings may shed new insight on the problematic structure of the forebrain.

scholarly journals The Psycho-Physiological Theory of Right-handedness [Théorie Psycho-Physiologique de la Droiterie]. (Revue Philosophique, June and July, 1916.) Mlle. Ioteyko

1917 ◽  
Vol 63 (263) ◽  
pp. 596-598
Author(s):  
J. Barfield Adams
Keyword(s):  
Biological Sciences ◽  
Bilateral Symmetry ◽  
Point Of View ◽  
The Body ◽  
Natural State ◽  
Left Brain ◽  
Left Handed ◽  
Normal Human ◽  
Normal Man ◽  
The Right

The writer commences her article by enunciating the doctrine that the normal human being is asymmetrical. “In 1903,” she says, “I expressed the opinion that the normal man is asymmetrical. The principle of the bilateral symmetry of the organism, established until recently in biological sciences, is replaced to-day by the idea of asymmetry, which, far from being an abnormal or pathological phenomenon, is, on the contrary, the expression of the natural state. One of the halves of the body is more developed than the other from an anatomical and physiological point of view. In the case of the right-handed man, it is the right side which is favoured; in the case of the left-handed man, it is the left. Now, each half of the body being dependent on the hemisphere of the opposite side, one sees that in the case of the right-handed man it is the left brain which is most developed, whilst in the case of the left-handed man a greater development of the right brain is assumed.” This thesis is supported by references to the works of many observers.

scholarly journals Aetiological factors in left-handedness

2005 ◽  
Vol 133 (11-12) ◽  
pp. 532-534 ◽  
Author(s):  
Sanja Milenkovic ◽  
Goran Belojevic ◽  
Radojka Kocijancic
Keyword(s):  
Genetic Factors ◽  
The Body ◽  
Intrauterine Environment ◽  
Foetal Development ◽  
Ultrasound Exposure ◽  
The Past ◽  
Left Handedness ◽  
Left Handed ◽  
Efferent Pathways ◽  
Genetically Determined

Lateralisation associates the extremities and senses of one side of the body, which are connected by afferent and efferent pathways, with the primary motor and sensory areas of the hemisphere on the opposite side. Dominant laterality denotes the appearance of a dominant extremity or sense in the performance of complex psychomotor activities. Laterality is manifested both as right-handedness or left-handedness, which are functionally equivalent and symmetrical in the performance of activities. Right-handedness is significantly more common than left-handedness. Genetic theory is most widely accepted in explaining the onset of lateralisation. According to this theory, the models of brain organisation asymmetry (anatomical, functional, and biochemical) are strongly, genetically determined. However, the inability to clearly demonstrate the association between genetic factors and left-handedness has led researchers to investigate the effects of the environment on left-handedness. Of particular interest are the intrauterine environment and the factors influencing foetal development, of which hormones and ultrasound exposure are the most significant. It has been estimated that an extra five cases of nonright-handed lateralisation can be expected in every 100 males who were exposed to ultrasound in utero compared to those who were not. Socio-cultural pressure on left-handed individuals was much more severe in the past, which is confirmed by scientific findings that left-handedness is present in 13% of individuals in their twenties, while in less than 1% of individuals in their eighties.

scholarly journals Intra-specific morphological and morphometric variability of Radopholus similis (Cobb, 1893) Thorne, 1949

2018 ◽  
Vol 10 (3) ◽  
pp. 841-846 ◽  
Author(s):  
S. Roy ◽  
K Roy ◽  
S. Sarkar ◽  
A Rathod ◽  
J. Hore
Keyword(s):  
The Body ◽  
Radopholus Similis ◽  
Body Width ◽  
Head Region ◽  
Morphometric Characters ◽  
Lateral Field ◽  
Oesophageal Gland ◽  
Morphometric Features ◽  
Basal Bulb ◽  
Stylet Length

All the root inhabiting migratory endoparasitic nematode populations of Radopholus procured from banana crop of Vellayani, Thiruvananthapuram, Kerala were identified as Radopholus similis. Heat killed females were straight to slightly ventrally curved posteriorly. Female’s head was low, rounded, continuous or slightly setoff with the body contour. Females were 500-660 µm long and were comparatively longer than males. Males had button shaped head set off by a constriction; female with three to five lip annuli, four crenate and areolated lateral incisures, stylet 14-18 µm long with rounded knobs, vulva post-equatorial (58%), sometimes with slight protuberant lips, ovary paired and equally developed, oesophageal gland overlapped the intestine dorsally, tail elongate-conoid with narrowly rounded terminus. The stylet length (µm), width of stylet knob (µm), distance of excretory pore from anterior end (µm), distance from head to basal bulb (µm), lateral field structure, shape of stylet knob, head region, position of phasmid, tail shape with its terminus, morphometric values like m%, o% and v% and a, c and c´ ratios of females were stable (CV<12%) features. There is an existence of intra-specific variability in the morphological and morphometric features of R. similis. The main morphological diversity was observed with P% of male and female, b ratio of female and stylet length, distance of DEGO from stylet base, o% and T% of male. All the root inhabiting migratory endoparasitic nematode populations of Radopholus Thorne, 1949 procured from banana of Vellayani, Thiruvananthapuram, Kerala were identified as Radopholus similis (Cobb, 1893) Thorne, 1949. A high degree of intra-specific morphometric variability was observed with regard to the total body length (µm), body width (µm), stylet length (µm), distance of dosrsal oesophageal gland orifice (DEGO) from stylet base (µm), number of lip annuli, lip height (µm), distance from head to basal bulb (µm), distance of anus from anterior end (µm), tail length (µm), anal body width (µm), distance of phasmid from tail terminus (µm), number of lateral lines, width of lateral field (µm), b ratio and P % among females of R. similis. Morphometric features like m%, o% and v% of females of R. similis showed least variability. These can be considered as the stable morphometric characters for discrimination of females of R. similis. Ratios like ‘a’ and ‘c’ of females of R. similis were found moderately variable. The morphometric feature and of male i.e. distance from head to basal bulb (µm) was found least variable; while number of lip annuli and spicule length (µm) were moderately variable.  

scholarly journals Plastid-Localized EMB2726 Is Involved in Chloroplast Biogenesis and Early Embryo Development in Arabidopsis

2021 ◽  
Vol 12 ◽  
Author(s):  
Chuanling Li ◽  
Jian-Xiu Shang ◽  
Chenlei Qiu ◽  
Baowen Zhang ◽  
Jinxue Wang ◽  
...  
Keyword(s):  
Chloroplast Development ◽  
Developmental Process ◽  
Higher Plants ◽  
Critical Role ◽  
Elongation Factor ◽  
Early Embryo ◽  
The Body ◽  
Insertion Mutant ◽  
Cell Stage ◽  
Dna Insertion

Embryogenesis is a critical developmental process that establishes the body organization of higher plants. During this process, the biogenesis of chloroplasts from proplastids is essential. A failure in chloroplast development during embryogenesis can cause morphologically abnormal embryos or embryonic lethality. In this study, we isolated a T-DNA insertion mutant of the Arabidopsis gene EMBRYO DEFECTIVE 2726 (EMB2726). Heterozygous emb2726 seedlings produced about 25% albino seeds with embryos that displayed defects at the 32-cell stage and that arrested development at the late globular stage. EMB2726 protein was localized in chloroplasts and was expressed at all stages of development, such as embryogenesis. Moreover, the two translation elongation factor Ts domains within the protein were critical for its function. Transmission electron microscopy revealed that the cells in emb2726 embryos contained undifferentiated proplastids and that the expression of plastid genome-encoded photosynthesis-related genes was dramatically reduced. Expression studies of DR5:GFP, pDRN:DRN-GFP, and pPIN1:PIN1-GFP reporter lines indicated normal auxin biosynthesis but altered polar auxin transport. The expression of pSHR:SHR-GFP and pSCR:SCR-GFP confirmed that procambium and ground tissue precursors were lacking in emb2726 embryos. The results suggest that EMB2726 plays a critical role during Arabidopsis embryogenesis by affecting chloroplast development, possibly by affecting the translation process in plastids.

The distribution of E-cadherin during Xenopus laevis development

Development ◽  
1991 ◽  
Vol 111 (1) ◽  
pp. 159-169 ◽  
Author(s):  
G. Levi ◽  
B. Gumbiner ◽  
J.P. Thiery
Keyword(s):  
Xenopus Laevis ◽  
Developmental Stages ◽  
Early Embryo ◽  
The Body ◽  
Gut Epithelium ◽  
A Cell ◽  
Well Differentiated ◽  
Sensory Layer ◽  
Endodermal Cells ◽  
E Cadherin

A vast amount of experimental evidence suggests that cell surface molecules involved in cell-to-cell and/or cell-to-substrate interactions participate in the control of basic events in morphogenesis. E-cadherin is a cell adhesion molecule directly implicated in the control of Ca2(+)-dependent interactions between epithelial cells. We report here the patterns of expression of E-cadherin in developmental stages of Xenopus laevis ranging from early embryo to adult using immunofluorescence microscopy. Although its distribution shares some similarities with those of L-CAM in the chicken and E-cadherin/Uvomorulin in the mouse, the distribution of E-cadherin in Xenopus presents several peculiar and unique features. In early stages of Xenopus development, E-cadherin is not expressed. The molecule is first detectable in the ectoderm of late gastrulas (stage 13-13.5 NF). At this time both the external and the sensory layer of the nonneural ectoderm accumulate high levels of E-cadherin while the ectoderm overlying the neural plate and regions of the involuting marginal zone (IMZ) not yet internalized by the movements of gastrulation are E-cadherin-negative. Unlike most other species, endodermal cells express no or very low levels of E-cadherin up to stage 20 NF. Endodermal cells become strongly E-cadherin-positive only when a well-differentiated epithelium forms in the gut. No mesodermal structures are stained during early development. In the placodes, in contrast to other species, E-cadherin disappears very rapidly after placode thickening. During further embryonic development E-cadherin is present in the skin, the gut epithelium, the pancreas, many monostratified epithelia and most glands. Hepatocytes are stained weakly while most other tissues, including the pronephros, are negative. In the mesonephros, the Wolffian duct and some tubules are positive. During metamorphosis a profound restructuring of the body plan takes place under the control of thyroid hormones, which involves the degeneration and subsequent regeneration of several tissues such as the skin and the gut. All newly formed epithelia express high levels of E-cadherin. Surprisingly, degenerating epithelia of both skin and intestine maintain high levels of the protein even after starting to become disorganized and to degenerate. In the adult, staining is strong in the skin, the glands, the lungs, the gut epithelium and the pancreas, weak in the liver and absent from most other tissues. Our results show that the expression of E-cadherin in Xenopus is strongly correlated with the appearance of differentiated epithelia.

Apical-basal pattern formation in the Arabidopsis embryo: studies on the role of the gnom gene

Development ◽  
1993 ◽  
Vol 117 (1) ◽  
pp. 149-162 ◽  
Author(s):  
U. Mayer ◽  
G. Buttner ◽  
G. Jurgens
Keyword(s):  
Pattern Formation ◽  
Root Formation ◽  
Asymmetric Cell Division ◽  
Early Embryo ◽  
The Body ◽  
Wild Type ◽  
Early Effect ◽  
Normal Number ◽  
Mutant Seedling

gnom is one of several genes that make substantial contributions to pattern formation along the apical-basal axis of polarity in the Arabidopsis embryo as indicated by the mutant seedling phenotype. The apical and basal end regions of the body pattern, which include the meristems of the shoot and the root, fail to form, and a minority of mutant embryos lack morphological features of apical-basal polarity. We have investigated the developmental basis of the gnom mutant phenotype, taking advantage of a large number of EMS-induced mutant alleles. The seedling phenotype has been traced back to the early embryo in which the asymmetric division of the zygote is altered, now producing two nearly equal-sized cells. The apical daughter cell then undergoes abnormal divisions, resulting in an octant embryo with about twice the normal number of cells while the uppermost derivative of the basal cell fails to become the hypophysis, which normally contributes to root development. Consistent with this early effect, gnom appears to be epistatic to monopteros in doubly mutant embryos, suggesting that, without prior gnom activity, the monopteros gene cannot promote root and hypocotyl development. On the other hand, when root formation was induced in bisected seedlings, wild-type responded whereas gnom mutants failed to produce a root but formed callus instead. These results suggest that gnom activity promotes asymmetric cell division which we believe is necessary both for apical-basal pattern formation in the early embryo and for root formation in tissue culture.

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