Des « miasmes » et « germes » du XIXᵉ siècle au Covid-19, ces controverses historiques sur le mode de transmission des épidémies

Source: The Conversation – in French – By David Simard, Docteur en philosophie, Université Paris-Est Créteil Val de Marne (UPEC)

Une mise en perspective historique éclaire la position initiale prise par l’Organisation mondiale de la santé lors du déclenchement de la pandémie de Covid-19. L’agence de l’ONU avait d’abord minoré la transmission par voie aérienne, mode de propagation majoritaire du SARS-CoV-2.


Quelques semaines après l’apparition de la pandémie de Covid-19, début 2020, une controverse majeure avait émergé concernant les modes de transmission du virus SARS-CoV-2. Le virus se transmet-il principalement par contact rapproché entre individus et par l’intermédiaire d’objets et surfaces (fomites), ou bien par voie aérienne sur de plus longues distances ?

L’Organisation mondiale de la santé (OMS) avait d’abord rejeté l’idée de la transmission aérienne. Puis, elle avait progressivement modifié sa position, reconnaissant finalement cette voie comme la principale forme de propagation du coronavirus.

Cette controverse ainsi que l’évolution de la position de l’OMS s’inscrivent dans un contexte historique plus large, marqué par des débats séculaires sur la nature des épidémies.

Au début du Covid-19 : prédominance du modèle de la transmission par contact

En février 2020, après quelques hésitations en interne, l’OMS a statué officiellement sur les voies de transmission du SARS-CoV-2. Selon elle, le virus se transmet alors directement par les grosses gouttelettes émises par une personne infectée qui tousse ou éternue, et qui sont respirées par une autre personne se trouvant à proximité. Il se transmet également indirectement par l’intermédiaire d’objets ou surfaces contaminées par les gouttelettes émises par les personnes infectées. Ces voies de transmission caractérisent le modèle dit de contact (médiat ou immédiat).

Toutefois, exception faite de certaines procédures en milieu de soins générant des aérosols (intubation endo-trachéale, bronchoscopie…), la voie aérienne n’est pas retenue comme un facteur majeur de transmission. Fin mars 2020, l’agence de l’ONU rejette même catégoriquement cette dernière possibilité, à travers une communication sur les réseaux sociaux.

Une controverse immédiate sur la transmission et les mesures sanitaires

Déclinée par la plupart des autorités politiques et sanitaires à travers le monde (l’U.S. Center for disease control and prevention ou CDC aux États-Unis, l’European Centre for Disease Prevention and Control ou ECDC en Europe…), la minimisation de la transmission dite « aéroportée » (airborne en anglais) a rapidement donné lieu à controverse au sein de la communauté scientifique. En particulier, de nombreuses et nombreux scientifiques et ingénieur·es du domaine de la dynamique des fluides et des aérosols ont mis en avant la transmission aéroportée du Covid-19, mais aussi d’autres infections respiratoires, privilégiant ainsi le modèle dit de l’air.

Ce débat se traduit en pratique par la promotion de mesures sanitaires différentes :

  • pour le modèle du contact, la distanciation sociale (se tenir à un ou deux mètres les uns des autres), la désinfection des surfaces et le lavage des mains, ainsi que le port d’un masque anti-projections de type chirurgical, en particulier par les personnes infectées, lorsque la distance entre les personnes ne peut être respectée ;

  • pour le modèle aérien, le port d’un masque de protection respiratoire individuelle de type FFP2 par les personnes infectées ou non, particulièrement dans des lieux clos, et la désinfection de l’air dans ces mêmes lieux, par l’aération et/ou la ventilation filtrée.

Les mesures soutenues par le modèle du contact se fondent sur la théorie selon laquelle les contaminations s’opèrent essentiellement par l’intermédiaire des grosses gouttelettes émises par les personnes infectées. Ces gouttelettes sont porteuses de particules pathogènes, dont la trajectoire est semi-balistique : leur poids les fait tomber rapidement sur le sol à proximité du lieu de leur émission. Pour être contaminé, il faut alors se trouver physiquement proche de la personne infectée, ou toucher des surfaces ou objets (poignée de porte, stylo, téléphone…) où se sont déposées des gouttelettes, et porter ensuite ses mains au visage.

En revanche, les mesures soutenues par le modèle de l’air reposent sur la théorie d’une transmission des particules infectieuses par l’intermédiaire de gouttelettes beaucoup plus fines et légères, appelées microgouttelettes, dont la trajectoire est dynamique, c’est-à-dire répondant aux lois de la mécanique des fluides : elles peuvent être transportées par les mouvements de l’air à plusieurs mètres de leur lieu d’émission (on parle alors d’aérosols).

L’enjeu de santé publique est d’importance : si la théorie de l’aéroportage est correcte, les mesures promues par le modèle du contact sont inadaptées et donc inefficaces. De plus, si un confinement drastique, comme ce fut le cas en 2020, interrompt les transmissions interfoyers, l’absence de prise en compte de l’aéroportage contribue aux contaminations au sein des foyers par les personnes infectées avant la mise en œuvre du confinement.

Un héritage historique

La position initiale de l’OMS en faveur du modèle du contact s’est inscrite dans la suite de la prédominance depuis plus d’un siècle de ce modèle à propos des infections respiratoires. Autour des années 1910, le médecin de santé publique américain Charles Chapin a soutenu le modèle du contact entre les corps individuels pour la plupart des maladies infectieuses, y compris respiratoires, en insistant en outre sur le rôle prépondérant des porteurs asymptomatiques dans les dynamiques épidémiques. Il a tenu pour négligeables les transmissions par fomites (par des objets et surfaces) et par l’air.

Charles Chapin a exercé une très grande influence sur la santé publique du XXᵉ siècle au niveau international, et on considère qu’il a inauguré « une troisième phase révolutionnaire du mouvement moderne de santé publique », après l’assainissement urbain (nettoyage des rues, réseaux d’égouts…) et la lutte contre les maladies infectieuses à partir de la théorie microbienne (isolement des malades, vaccination…).

Mais Chapin a élaboré sa conception sur les modes d’infection selon deux biais majeurs :

  1. il l’a avant tout fondée à partir des infections sexuellement transmissibles et des maladies de l’appareil digestif, en insistant pour ces dernières sur la transmission directe (poignées de main) ou indirecte (alimentation) de matière fécale par les mains non lavées ;

  2. ses considérations sur le rôle des gouttelettes dans les infections respiratoires reposaient uniquement sur des expériences réalisées avec des bactéries, alors que, si l’existence de microbes plus petits que celles-ci était soupçonnée, aucun virus au sens restrictif du terme n’avait été observé. Certaines maladies virales, telles que la grippe, étaient d’ailleurs faussement considérées comme bactériennes.

Comme pour les infections digestives, Chapin a mis en exergue la transmission par les mains pour les infections respiratoires, celles-ci étant souvent portées à la bouche et au nez, et touchant de nombreux objets. Sur le plan épidémiologique, il considérait que le manuportage des microbes contenus dans les sécrétions nasales et buccales suffisait à rendre compte des épidémies respiratoires, y compris de tuberculose pulmonaire, sans faire appel à d’autres mécanismes.

En particulier, il a rejeté la théorie des microgouttelettes élaborée à la fin du XIXᵉ siècle par l’hygiéniste et bactériologiste allemand Carl Flügge, collègue de Robert Koch : sans contester l’émission de telles gouttelettes, il considérait qu’elles étaient très peu porteuses de microbes, contrairement aux plus grosses gouttelettes.

Pourtant, avec l’émergence de la bactériologie dans la seconde moitié du XIXᵉ siècle, la théorie de la transmission des microorganismes infectieux, alors appelés « germes », incluait la voie aérienne, notamment pour la tuberculose pulmonaire (alors appelée « phtisie »). Non seulement Flügge, mais également Koch, Pasteur, etc., soutenaient l’idée de l’air transportant des microbes. Comment, alors, expliquer un tel revirement au début du XXᵉ siècle ?

Un air inquiétant de théorie des miasmes

Si la seconde moitié du XIXe siècle a établi que les maladies infectieuses ont pour cause biologique des microorganismes qui se reproduisent, deux grandes théories étaient auparavant en concurrence : la théorie des germes se transmettant de personne à personne, et la théorie des miasmes se transmettant par l’air. Cette dernière trouve ses racines dès l’Antiquité dans la médecine hippocratique, tandis que la première a surtout commencé à être développée à la fin de la Renaissance par le médecin et philosophe italien Jérôme Fracastor.

Mais en l’absence d’identification des microorganismes, la théorie des germes contagieux n’était pas moins spéculative que la théorie des miasmes supposés émaner, par phénomène de génération spontanée, de la matière en putréfaction et des marécages viciant l’air.

Pour autant, dès Fracastor, l’idée d’une transmission de personne à personne n’excluait pas l’air comme vecteur. Mais, pour Chapin et d’autres, cette idée évoquait trop la théorie des miasmes, tombée en désuétude. De plus, elle était généralement considérée comme plus inquiétante et susceptible d’effrayer les populations, en rendant invisible la voie de transmission par des microgouttelettes plutôt que par de grosses gouttelettes visibles (crachats, postillons…).

Enfin, persistait l’idée issue de la théorie des miasmes selon laquelle, si les maladies sont transmises par l’air, alors la médecine se trouve dans une forme d’impuissance pour les combattre sur le plan prophylactique, ou doit recourir à des mesures considérées comme beaucoup trop contraignantes et complexes.

Malgré l’appropriation de la transmission aérienne par la théorie microbienne dans la seconde moitié du XIXᵉ siècle, sa proximité avec la théorie des miasmes a ainsi favorisé le modèle de la transmission par contact, plus rassurant en ce qu’il écarte le risque volatil.

Épilogue : en 2024, le modèle de transmission du SARS-CoV-2 révisé

Mais tout au long du XXᵉ siècle, et ce dès les recherches sur le virus de la grippe dans les années 1930, des recherches expérimentales ont été menées sur la transmission des infections respiratoires virales par l’air.

Celles publiées sur le Covid-19 ont conduit l’OMS à infléchir sa position, jusqu’à publier en 2024 deux documents qui proposent une révision du modèle de compréhension de la transmission du SARS-CoV-2 en particulier et des maladies respiratoires transmissibles en général. Ils mettent en exergue la transmission aéroportée en milieu intérieur et proposent un nouveau modèle de gestion du risque, en précisant la terminologie afférente en conséquence (aéroporté, transmission aéroportée, transmission par aérosols…). Reste à savoir dans quelle mesure l’héritage historique, profondément ancré dans les pratiques médicales et paramédicales, pourra être dépassé.

Alors que les infections respiratoires sont récurrentes, que le Covid-19 sévit plusieurs fois par an, et que de nouvelles pandémies respiratoires sont probables, l’enjeu de santé publique s’avère fondamental.

The Conversation

David Simard est membre du Comité d’Orientation et de Dialogue de Santé Publique France, ainsi que du Collège des Humanités Médicales.

ref. Des « miasmes » et « germes » du XIXᵉ siècle au Covid-19, ces controverses historiques sur le mode de transmission des épidémies – https://theconversation.com/des-miasmes-et-germes-du-xix-siecle-au-covid-19-ces-controverses-historiques-sur-le-mode-de-transmission-des-epidemies-275290

Barbie, figure d’émancipation féminine ?

Source: The Conversation – France (in French) – By Sophie Renault, Professeur des Universités en Sciences de Gestion et du Management, Université d’Orléans

Une partie de la collection Barbie Fashionistas, qui se veut plus inclusive. Mattel

Longtemps critiquée pour enfermer les fillettes dans des carcans stéréotypés, Barbie s’affirme désormais comme un symbole de l’émancipation féminine. Effectivement, Mattel a entièrement révisé sa stratégie : diversité des origines, des hobbies et professions, représentation des handicaps… Mais Barbie est-elle pour autant devenue un levier d’émancipation ou présente-t-elle un féminisme compatible avec les ambitions commerciales ?


Créée en 1959, Barbie apparaît comme une innovation majeure dans l’univers du jouet. À une époque où les poupées proposées aux fillettes sont essentiellement des bébés à pouponner, Barbie incarne une femme adulte, indépendante, dotée d’une maison, d’une voiture et susceptible d’épouser une pluralité de métiers. Elle ouvre ainsi un espace de projection inédit, permettant aux enfants d’imaginer des trajectoires féminines affranchies du seul horizon domestique. Cette promesse d’autonomie s’accompagne toutefois de critiques. La silhouette de Barbie, aux proportions irréalistes, devient un symbole de la pression exercée sur les corps féminins. Comme l’indique Bazzano dans son ouvrage intitulé la Femme parfaite : histoire de Barbie :

« Si Barbie, au lieu de ses quelque trente centimètres, mesurait un mètre soixante-quinze, ses mensurations poitrine-taille-hanches seraient : 95-53-83. »

Selon l’auteure, il s’agit de proportions peu crédibles avec un buste trop court, une poitrine trop forte, sur une taille trop fine, avec des hanches trop étroites, sur des jambes trop longues se terminant par des pieds trop cambrés. De nombreuses recherches montrent que l’exposition répétée à cet idéal corporel contribue à l’intériorisation de normes de beauté susceptibles d’affecter l’image corporelle dès le plus jeune âge.

L’univers esthétique de la poupée, centré sur la mode, la consommation et une féminité très codifiée, renforce cette critique. Barbie représente une femme indépendante, certes, mais tenue de rester belle, mince et désirable.

Représenter pour rendre possible

Afin de répondre aux transformations sociétales et de mieux coller à la diversité du réel, Mattel a engagé une évolution progressive de la poupée. Comme le signifie Rogers dans son ouvrage intitulé Barbie Culture, bien que Barbie ait des amies racisées depuis les années 1960 et qu’elle ait elle-même été commercialisée en version afro-américaine, asiatique et hispanique, elle demeurait dans l’esprit collectif blonde, blanche et élancée.

L’introduction de la gamme Barbie Fashionistas en 2009 constitue une étape décisive. Mattel élargit la gamme des carnations, de types de cheveux et coiffures, tout en mettant l’accent sur une diversité des styles, hobbies et professions. Il faut attendre 2016 pour que la marque franchisse une étape supplémentaire en introduisant des morphologies alternatives en termes de taille et corpulence engageant ainsi une remise en question plus directe de l’idéal corporel historiquement associé à la poupée.

Barbie incarne également une diversité de carrières, avec un message clair : « You can be anything » (« Tu peux être qui tu veux »). Sur le plan symbolique, cette logique se fonde sur un principe qui postule que tout ce qui est visible devient susceptible d’être pensé. Les jouets jouent un rôle actif dans la socialisation genrée et la formation des aspirations. Évidemment, une poupée astronaute, paléontologue, médecin ou rock-star n’évoque pas les mêmes rêves qu’une poupée confinée au milieu domestique. Ici, l’émancipation se manifeste par le jeu, la redondance et la normalisation de figures féminines qui ont été longtemps mises en marge. Ainsi, Barbie permet aux enfants d’explorer une variété de scénarios professionnels. Pourtant, cette influence sur le réel reste complexe.

L’étude menée par Sherman et Zurbriggen a montré que les fillettes qui jouaient à Barbie, même dans sa version docteur avec blouse blanche, otoscope et stéthoscope, indiquaient qu’elles avaient moins d’options de carrière futures que les garçons. En revanche, celles qui jouaient avec Monsieur Patate signalaient une différence moins importante entre leurs propres carrières futures possibles et celles des garçons, suggérant que la sexualisation de la poupée pèse plus lourd que son uniforme.

Présentée comme célibataire, malgré l’omniprésence de Ken, son éternel prétendant relégué au second plan, Barbie met en scène une indépendance qui passe aussi par ce qu’elle possède. Les objets qui l’entourent participent à la construction d’une image de femme libre et ambitieuse. L’empowerment se transforme alors en promesse individualisée, esthétisée et compatible avec les logiques de consommation de masse, plutôt qu’en un processus collectif de transformation sociale. Par ailleurs, malgré les efforts de diversification, certaines normes persistent. Même lorsqu’elle est scientifique ou pilote d’avion, Barbie reste conforme aux standards de désirabilité dominants. Son évolution demeure ainsi régie par les normes du marché. Il s’agit in fine de provoquer l’acte d’achat.

La représentation du handicap : entre reconnaissance et simplification

Parmi les avancées les plus notables figure la récente représentation du handicap dans l’univers de Barbie. Mattel a en effet déployé des poupées en fauteuil roulant, dotées de prothèses de jambe, touchées par le vitiligo, l’alopécie, la cécité ou bien encore la trisomie 21. Élaborées en partenariat avec des personnes concernées ou spécialistes (professionnels de santé, associations…), ces poupées ont le plus souvent été saluées pour leur aptitude à représenter des vérités longtemps négligées dans le monde du jouet. Elles permettent aux enfants concernés de se reconnaître et aux autres d’intégrer la différence comme une composante ordinaire du monde social. Le jeu devient alors un espace de familiarisation et de déstigmatisation.

La commercialisation, en 2025, d’une Barbie atteinte de diabète de type 1, équipée d’un capteur de glucose et d’une pompe à insuline, marque une étape importante dans la politique inclusive de la marque. Ce lancement ouvre un nouveau chapitre en déplaçant la question de la représentation vers le terrain des handicaps dits « invisibles », longtemps absents de l’univers du jouet. Dans cette mouvance, une Barbie autiste est commercialisée depuis janvier 2026. Ici aussi, la représentation s’opère principalement par l’utilisation d’accessoires. La Barbie est en effet équipée d’un casque antibruit, d’un hand-spinner et d’une tablette de communication. Ces évolutions posent alors la question de la capacité du jouet à offrir un véritable espace d’identification, sans réduire le handicap à une série de signes ou d’objets immédiatement reconnaissables.

Barbie, miroir de nos contradictions

À mesure que l’inclusion devient un argument central du discours de marque, une tension se dessine entre reconnaissance symbolique et logique commerciale, au risque de relever d’une forme d’habillage éthique. Dans cette perspective, l’inclusion est envisagée comme une stratégie de marque, consolidant la crédibilité de Barbie sans remettre en question les hiérarchies esthétiques et commerciales qui structurent son succès.

Barbie cristallise certaines des contradictions contemporaines : la reconnaissance d’une diversité plus visible s’accompagne d’une vigilance face à une stratégie marketing bien maîtrisée. Cette ambivalence a été mise en évidence par le film Barbie (2023) qui oscille entre satire populaire et analyse métaféministe. Le film met en effet en exergue les paradoxes d’un féminisme soutenu par une icône commerciale.

En définitive, Barbie ne génère pas l’empowerment, elle le soutient, le reformule et parfois le simplifie. Elle exprime, dans le langage accessible du jouet, des problématiques complexes. La trajectoire de Barbie illustre que l’émancipation dépend des conditions socio-économiques et culturelles qui peuvent transformer ces représentations en expériences concrètes.

The Conversation

Sophie Renault ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d’une organisation qui pourrait tirer profit de cet article, et n’a déclaré aucune autre affiliation que son organisme de recherche.

ref. Barbie, figure d’émancipation féminine ? – https://theconversation.com/barbie-figure-demancipation-feminine-274678

Manger ou ne pas manger d’huîtres ?

Source: The Conversation – France (in French) – By François Lévêque, Professeur d’économie, Mines Paris – PSL

L’huître est clivante : elle séduit les amateurs gourmets et dégoûte ses détracteurs. Mets de fête, longtemps réservées aux mois en « r », les huîtres ont échappé à leur destin depuis que l’humain s’est mêlé de leur génétique. Aliment naturel, ce mollusque est réputé pour être sain, si l’on survit à ce qui pourrait être le plus grand des dangers : ouvrir sa coquille.


Noël est passé, la consommation d’huîtres a chuté. La France se retrouve coupée en deux : les amateurs qui en mangent toute l’année et les mangeurs occasionnels qui rejoignent alors les rangs de celles et ceux qui n’en avalent jamais. La France du littoral contre celle de l’intérieur.

Examinons sérieusement, mais dans la bonne humeur, cette fracture française trop ignorée dans notre monde, pourtant si friand d’oppositions binaires. Quel que soit votre camp, renforcez ou questionnez vos comportements en découvrant les causes de ce fossé séparant les Français.

Deux positions bien tranchées

Traçons tout d’abord le profil des uns et des autres. Si vous ne consommez pas d’huîtres, sachez que vous êtes loin d’être seuls. Un tiers de la population française n’en mange jamais. Vous en avez peut-être goûté un jour mais vous n’aimez pas cela. Ou même pas essayé, rebuté par l’idée d’ingérer un animal ou par conviction religieuse. Souvent, vous craignez aussi que les huîtres ne conviennent pas à toute la famille.

Si vous êtes un consommateur occasionnel, vous en avez mangé à Noël ou au Nouvel An ; éventuellement aussi lors d’autres repas festifs. Vous formez le plus grand bataillon des consommateurs d’huîtres. Vous les achetez au supermarché et vous manquez d’expertise pour les choisir. Vous n’aimez pas trop les ouvrir.




À lire aussi :
Huîtres et algues : partenaires pour le meilleur et pour le pire dans un océan en mutation


Enfin, si vous êtes un consommateur régulier, comme 20 % des Français, vous habitez le plus souvent près de la mer et en consommez toute l’année. Vous achetez vos huîtres auprès d’un ostréiculteur ou d’un écailler du marché. Vous savez faire la différence entre les huîtres numéro 2, 3 ou 4, les fines et les spéciales. Vous éprouvez même un certain plaisir et de la fierté à les ouvrir.

De La Fontaine à Maupassant

Trouvez-vous les huîtres délicieuses ? Comme Maupassant qui décrit les huîtres d’un souper dans Bel-Ami (1885) « mignonnes et grasses, semblables à de petites oreilles enfermées en des coquilles et fondant entre le palais et la langue ainsi que les bonbons salés ». Ou bien dégoûtantes, comme ce personnage d’une nouvelle de Tchekhov, un enfant pauvre de Moscou, forcé à manger des huîtres. Il les découvre « hideuses, aux yeux brillants et à la peau visqueuse ».

Il est vrai que ce coquillage se mange vivant. À ma connaissance, c’est le seul animal ainsi ingurgité sous nos latitudes. Piquez de la pointe de votre couteau le bord d’une huître, elle se rétractera à moins qu’elle se soit endormie sous la glace. Âmes sensibles, s’abstenir. Ou manger les huîtres cuites – il y a pléthore de recettes. Renonciation aussi des végétariens, au moins tant que la chair d’huître végétale n’a été inventée, à partir d’algues par exemple.

Dans les enquêtes, l’aspect cru et vivant ainsi que le mauvais goût et l’odeur sont invoqués en premier par les non-consommateurs. À l’inverse, les mangeurs d’huîtres soulignent leurs qualités gustatives et leur parfum iodé.

Naturelle peut-être, mais plus très sauvage

L’huître fait partie des fruits de mer, d’où le côté naturel que les consommateurs lui associent spontanément. Mais, contrairement à la coquille Saint-Jacques ou à la crevette grise, elle a quitté son caractère sauvage. Bel-Ami mangeait des huîtres plates cueillies sur l’estran et les compères qui, chez Boileau et La Fontaine, se disputent une huître qu’avalera finalement un troisième larron l’ont trouvée sur une plage. La découverte d’une huître sur l’estran suggère qu’une exploitation ostréicole n’est sans doute pas loin. Surexploitée au dix-neuvième siècle, l’huître plate sauvage, native de nos côtes, a quasiment disparu.

Si l’huître est un fruit de mer, elle est le produit de l’aquaculture. Une aquaculture que l’on serait néanmoins tenté de qualifier de douce, de quasi-naturelle, puisque l’huître, contrairement au saumon, croît sans aliments industriels ni médicaments vétérinaires.

Tout dépend cependant si l’huître est née en écloserie ou en mer ainsi que de son nombre de chromosomes. Reproduite en mer, elle aura vécu sa vie larvaire au gré des courants et des vagues avant de se fixer aux collecteurs posés par les ostréiculteurs. Aux branchages, pierres, coquilles et tuiles d’autrefois, les naissains sont désormais captés dans des assemblages de coupelles ou de tubes en PVC, plus rarement en plastique biosourcé. Née à terre entre quatre murs, elle aura connu un début de vie en milieu contrôlé, vie qu’elle poursuivra un temps en nurserie dans des bacs alimentés en eau de mer avant de découvrir enfin la vie marine.

France 3 Nouvelle-Aquitaine, 2022.

La vérité est dans les chromosomes

L’essor des écloseries a été favorisé par l’invention de l’huître triploïde, rencontre d’un gamète à 10 chromosomes et d’un autre qui en compte 20. Souvenez-vous de vos cours de biologie ou d’éducation sexuelle : les gamètes n’embarquent qu’une moitié des chromosomes de chacun de leurs parents. L’huître triploïde est donc issue du mariage d’une huître diploïde normale (deux fois 10 chromosomes) et d’une huître tétraploïde (quatre fois 10 chromosomes) fabriquée en laboratoire. Évidemment, cela fait peur et renforce le camp des non-consommateurs. L’huître serait devenue un être transgénique, un OVM (organisme vivant modifié) !

Mais soyons rassurés. On dispose d’un temps de recul suffisamment long pour établir solidement l’absence de contamination des zones de captage naturel des huîtres normales. Manger des huîtres triploïdes n’entraîne pas non plus de risques pour la santé humaine. L’Agence nationale de sécurité sanitaire (Anses) a tranché la question. En outre, l’élevage de l’huître diploïde est majoritaire. Il couvre les trois quarts de la production ostréicole.

Diploïde ou triploïde ?

Il est vrai que l’origine diploïde ou triploïde des huîtres est rarement communiquée aux consommateurs. Il n’y a pas d’obligation légale en la matière. Pas de signes faciles à déceler non plus. En revanche, si vos huîtres consommées l’été ne contiennent pas de laitance, il s’agit à coup sûr de triploïdes. Ces huîtres étant stériles, elles ne produisent pas cette substance blanchâtre visqueuse principalement composée de gamètes. C’est d’ailleurs ce qui explique l’intérêt commercial et économique de la triploïde. Pas de reproduction, pas de laitance qui rebute les consommateurs et cantonne la consommation aux mois de l’année en « r ». L’huître triploïde peut se consommer toute l’année. Par ailleurs, sans dépense d’énergie de l’animal pour se reproduire, le cycle d’élevage peut être ramené à deux ans au lieu de trois.

Quant au goût différent entre les huîtres modifiées et celles non modifiées, la question reste ouverte. La composition chimique présente bien quelques différences objectives. Mais il n’est pas évident d’en saisir les effets sur le plan olfactif et gustatif. Le seul test à l’aveugle dont j’ai connaissance n’est pas convaincant faute d’un protocole scientifique digne de ce nom.

Blessures et intoxications

Pompant plusieurs litres d’eau chaque heure pour se nourrir de plancton, l’huître est tributaire de la qualité de l’eau qu’elle filtre. Microalgues toxiques, virus et bactéries sont ses ennemies mais aussi les nôtres quand nous les dégustons. Un risque d’intoxication entraînant diarrhées, nausées et vomissements est bien réel. La France dispose cependant d’un réseau efficace de surveillance sanitaire et d’alerte pour le réduire à de faibles proportions. Les autorités n’hésitent pas à interdire la commercialisation des huîtres s’il le faut. Ainsi, en décembre 2023, les huîtres du bassin d’Arcachon ont raté les repas de fêtes.

Le vrai danger est plutôt de se blesser en ouvrant les huîtres ! Les Français semblent d’ailleurs ne pas s’y tromper comme le suggèrent leurs réponses aux sondages. Ils sont 87 % à avoir confiance dans la production d’huîtres en France ; les craintes sanitaires sont peu évoquées alors que la très grande majorité des sondés reconnaissent l’existence de ce risque.

Ainsi, la mention de ces craintes vient très loin derrière les images négatives ayant trait au dégoût, que ce soit pour les Français dans leur ensemble ou pour les non-consommateurs. Pour ces derniers, la difficulté à ouvrir les huîtres est citée juste après la crainte de tomber malade comme raison justifiant le choix de ne pas en consommer. Dans une autre enquête portant sur un plus faible échantillon, elle est même placée devant.

L’huître innocentée faute de preuves

Ce faisceau de présomptions n’apporte pas la preuve que l’ouverture des huîtres est bien objectivement le plus grand danger. Il faudrait pouvoir comparer le nombre de personnes intoxiquées à celui d’ouvreurs d’huîtres blessés. Des données manquantes dans les deux cas. En outre, déclarer que les huîtres sont difficiles à ouvrir ne signifie pas forcément que l’on s’est entaillé la peau de la main en tentant l’opération.

L’ouverture des huîtres est en tout cas un frein à leur consommation. Pour la faciliter, de nombreuses méthodes, plus ingénieuses et cocasses les unes que les autres, ont été inventées. Citons le fil à couper l’huître consistant à passer un cordon en inox dans l’huître en la faisant bâiller dans une eau saturée en sel. Refermée, il suffira ensuite à la maison de tirer ce fil pour provoquer l’ouverture. Ou encore le cachet de cire alimentaire fermant un trou percé exprès, laissant plus facilement entrer la pointe du couteau. Ou enfin, l’ouv-huître, un outillage ad-hoc, créé par un ostréiculteur de Pontivy, Michel Lannay. Il a remporté le concours Lépine et a même été couronné au concours mondial des inventeurs. Sa prestation vidéo vaut le détour.

Actu 2024.

Vous n’allez sans doute pas modifier votre habitude alimentaire à l’issue de cette lecture. J’espère qu’elle vous aura seulement rendu plus tolérant à l’égard de ceux qui ne font pas comme vous. Que mangeurs et non-mangeurs d’huîtres puissent partager la même table, les uns dégustant leurs mollusques marins, et les autres une autre entrée qu’ils trouveront délicieuse.

The Conversation

François Lévêque ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d’une organisation qui pourrait tirer profit de cet article, et n’a déclaré aucune autre affiliation que son organisme de recherche.

ref. Manger ou ne pas manger d’huîtres ? – https://theconversation.com/manger-ou-ne-pas-manger-dhuitres-274679

Water in the dams, but South Africa’s taps are dry: essential reads on a history of bad management

Source: The Conversation – Africa – By Caroline Southey, Founding Editor, Africa, The Conversation

It’s become a common refrain in South Africa: there’s no drought, dams and reservoirs are full, but the taps are dry.

The ongoing crisis has been decades in the making. South Africa is a water-scarce country, yet it has failed to take even basic measures to preserve water supplies. These include:

The chronic crisis is underscored by the fact that the challenges – and what needs to be done about them – have been known for some time, as these articles from our archives show.


Johannesburg’s water crisis is getting worse – expert explains why the taps keep running dry in South Africa’s biggest city

Cape Town’s sewage treatment isn’t coping: scientists are worried about what the city is telling the public

The right to water is out of reach for many South Africans: case study offers solutions

South Africans flush toilets with drinkable water: study in Cape Town looked at using seawater instead

South Africa’s sewage crisis: official reports don’t include millions of litres of leaking wastewater

Is my water safe to drink? Expert advice for residents of South African cities

How to make sure water is safe to drink: four practical tips

The Conversation

ref. Water in the dams, but South Africa’s taps are dry: essential reads on a history of bad management – https://theconversation.com/water-in-the-dams-but-south-africas-taps-are-dry-essential-reads-on-a-history-of-bad-management-275832

How to get away with mass murder: 4 tactics Ethiopia used to hide Tigray atrocities from the world

Source: The Conversation – Africa (2) – By Teklehaymanot G. Weldemichel, Lecturer in Environment and Development, University of Manchester

The Tigray region in Ethiopia’s north has endured one of the world’s deadliest armed conflicts of the 21st century. Between 2020 and 2022, as many as 800,000 people were killed (out of a regional population of about 7 million). This rivals estimates from recent major conflicts, including those in Ukraine, Yemen, Sudan and Syria.

The war was fought between Tigray’s security forces and the allied forces of Ethiopia and Eritrea, along with ethnic militias from different regions of Ethiopia.

This period was marked by organised massacres. There was also systematic sexual violence and mass displacement. Ethnic cleansing and prolonged siege conditions devastated civilians.

Despite its unparalleled scale, the Tigray crisis remained largely invisible to the world. Factors such as race and the peripherality of the region made the Tigray conflict a blind spot in global geopolitics. But these explanations are not sufficient.

I have studied Ethiopia’s politics, and closely followed developments in Tigray since the outbreak of the war. In a recent article, I examined the steps taken by the Ethiopian government and its allies to conceal atrocities from global scrutiny.

I analysed government statements, media coverage and reports from local and international human rights organisations shortly before and during the war. I found that the war and its associated human rights and humanitarian crises were not hidden by accident. They were actively rendered invisible.

The Ethiopian government and its allies employed four major tactics to create a “zone of invisibility” – a deliberate effort to obscure what was happening:

These measures allowed atrocities to unfold with limited external scrutiny.

The tactics could easily be replicated by Ethiopia – or by other authoritarian regimes elsewhere – which makes understanding the Tigray case crucial.

The Tigray war demonstrates how modern authoritarian states can combine military force, information control and narrative framing to obscure mass atrocities.

When mass violence is rendered invisible, it is rarely resolved. Instead, it is reproduced. And when accountability is deferred, the conditions that enabled atrocities remain intact.

Manufactured invisibility

The production of a “zone of invisibility” in Tigray was the result of deliberate political and military strategies. The Ethiopian government and its allies systematically limited what could be seen, documented and understood about the war.

1. Communication shutdowns: Immediately after the war began, the Ethiopian government imposed a near-total communications blackout. This lasted over two years. It happened alongside widespread disruptions of telecom, media and power infrastructure. These measures isolated Tigray and prevented information about violence from circulating.

2. Restrictions on journalists and humanitarian organisations: Access to the region was tightly controlled. Journalists and humanitarian organisations were denied entry or restricted in their movements. This removed independent witnesses who could document events and convey civilian suffering to global audiences.

3. Physical blockades: Road closures, territorial occupation and blocked aid routes physically isolated the region. Tigray became a space where violence was difficult to observe or escape, allowing atrocities to unfold largely beyond international scrutiny.

4. Narrative framing: The federal state promoted narratives that made the violence in Tigray appear legitimate and necessary. Official discourse and allied media portrayed Tigrayans as “rebels”, “weeds” and a “cancer in the body politic”. This language dehumanised the population and normalised collective punishment. Such framing dampened calls for intervention and accountability. Additionally, the Tigray war was presented as a “law enforcement operation”. It was often addressed as a domestic conflict. This is despite the full-scale involvement of the Eritrean army. Foreign states also supplied weapons, including the United Arab Emirates, Israel, Turkey and China.

Taken together, these patterns suggest that the violence was structured, targeted and sustained.

Large-scale fighting in Tigray formally ended with the Pretoria Cessation of Hostilities Agreement in November 2022. However, the aftermath has not brought justice or security.

Instead, violence has persisted in Tigray – and spread across Ethiopia.

Accountability mechanisms have been weakened or dismantled. Survivors of the 2020–2022 war continue to live under conditions of profound insecurity, humanitarian deprivation and ongoing human rights violations.

Evading justice and accountability

Following the ceasefire deal in 2022, the Ethiopian regime effectively undermined and ultimately dismantled international investigative mechanisms into crimes committed during the Tigray war.

In 2023, both the UN-mandated International Commission of Human Rights Experts on Ethiopia and an African Union commission of inquiry were terminated. This left no independent international body to pursue accountability.

The dismantling of these mechanisms partly resulted from a sustained campaign by the regime and its allies. However, international actors also allowed themselves to be persuaded by promises made by Ethiopian authorities to establish domestic transitional justice processes.

These commitments amounted to what the UN Commission of Human Rights Experts on Ethiopia has described as “quasi-compliance”: symbolic gestures rather than genuine efforts to ensure accountability.

This is evident in the absence of meaningful attempts to prosecute perpetrators, protect survivors or halt ongoing violence in the post-ceasefire period.

Instead, the Ethiopian state has used the ceasefire agreement to rehabilitate its international image. It has re-established diplomatic and trade relations with regional blocs such as the European Union. These ties had been strained by human rights violations in Tigray.

What happens when atrocities go unnoticed, unpunished, or even tacitly accepted? Impunity does not end violence; it perpetuates it.

After a relative pause over the past three years, active war has flared up again in Tigray in 2026.

This has raised the prospect of a renewed full-scale siege. This is evidenced by recent drone attacks and the suspension of flights to the region.

Further, since late 2025, the federal government has seemed to be moving toward a potential war with Eritrea. This would severely impact Tigray once again. Any confrontation is likely to be fought over Tigrayan territory.

Ethiopia is invoking Eritrea’s occupation of Tigrayan territories – as grounds for confrontation.

In an address to the federal parliament in February 2026, Prime Minister Abiy Ahmed further acknowledged that the Eritrean army killed civilians on a large scale in Tigray, and dismantled and looted civilian infrastructure.

With rhetoric hardening on both sides, war appears increasingly likely.

Diffusion of violence beyond Tigray

The enduring consequences of invisibility and impunity are evident across Ethiopia.

Since the signing of the ceasefire in 2022, the Ethiopian regime and its former allies have fractured and turned their weapons against one another.

In the Amhara region, south of Tigray, is the Fano. This is an ethnic militia accused of ethnic cleansing in western Tigray and other grave crimes alongside the federal army. It’s now been engaged in armed conflict with that same army for nearly three years.

Meanwhile, violence in the Oromia region, which began long before the Tigray war, has continued unabated.

Tactics that were tested and refined during the Tigray war are now being redeployed against civilians in both Amhara and Oromia.

Rather than marking a transition to peace, the post-ceasefire period in Tigray has led to the diffusion and normalisation of violence across Ethiopia’s political and geographic landscape.

The Conversation

Teklehaymanot G. Weldemichel does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. How to get away with mass murder: 4 tactics Ethiopia used to hide Tigray atrocities from the world – https://theconversation.com/how-to-get-away-with-mass-murder-4-tactics-ethiopia-used-to-hide-tigray-atrocities-from-the-world-275298

History with a human face and voice: how museum theatre gets kids to care about the past

Source: The Conversation – Africa – By Stephanie Jenkins, Post-doctoral researcher, University of Pretoria

The facts of history are important, but try telling that to a classroom full of bored youngsters. One way to liven up the subject is to show that real people lived through historical events. Drama academic Stephanie Jenkins argues that learning becomes fun when learners care about what they are asked to remember. And one way to encourage caring is to perform the stories of the past, using museums as theatre spaces. Here she explains the idea, using an example from her work in South Africa – where the past is painful but shapes current social issues and future citizens.

What is museum theatre and how does it bring history to life?

Museum theatre is a form of performance that uses acting and other theatrical techniques within a museum, gallery or historical space (such as a historical building) to bring the exhibitions “to life”.

Performers act out historical people and narratives that have been researched. It’s a way for people to encounter the past through experience rather than just facts.

Bringing the past into the museum space through performance offers an opportunity to gain attention and foster potential for further engagement with the historical topic.

How have you used museum theatre to teach South African history?

One example was a play I developed called Beer Halls, Pass Laws and Just Cause, which was performed at the KwaMuhle Museum in Durban, South Africa, during March 2020. It was connected to the Grade 11 history syllabus with the aim of connecting what was learnt in class to the historical site of the museum.

The building this museum is housed in used to be the Native Administration Department. Under the apartheid system of racial segregation, black people had to carry a passbook (also referred to as a dompas) which gave them permission to be present in certain areas of a city for work. They had to apply for it and get it approved at this building, which would often mean waiting in long lines in the Durban heat.

The performance dramatised some of those people’s experiences, in the place where they’d had them. The actor guides spoke the recorded words of actual historical people, many of whom had stood in the spaces where the audience was standing. Their words had been recorded in various texts, newspaper articles and interviews conducted by officials at the museum in the early 1990s. (The pass system was abolished in 1986.)




Read more:
Alcohol and colonialism: the curious story of the Bulawayo beer gardens


Part of the experience for learners was to interact with objects, using all their senses, to spark creative thought processes and dialogue.

For example, they had to hold a replica passbook during the performance. Some reported that it felt “demeaning”, “stressful”, “oppressive”, or “scary”. The passbook “prop” helped them to experience how surveillance and fear can be used to control people.

In museum theatre like this, learners interact with the characters and learn about the past by observing, and often participating in, the performed action. By encouraging the learners to be part of the action, and surrounded by the exhibitions to which the performance is speaking, the learners are encouraged to be more active in their learning.




Read more:
Fun with fossils: South African kids learn a whole lot more about human evolution from museum workshops


The use of actors provides the opportunity for the learners to personally connect to the history and to care about the characters. Historical people are given a “face”, a three-dimensional body and a voice, making history look human and less removed from the present. Empathy, putting yourself in someone else’s shoes, is an important skill to learn. And it connects what is taught with the learner’s own life, making it relevant and easier to remember.

What did you learn from this performance?

The performance was used to challenge both notions around what learning about history is like (in terms of classroom and book learning) and what a run-of-the-mill museum visit is “supposed” to evoke. The performance attempted to encourage learners to be part of the historical experience rather than just “absorb facts”.

From the feedback collected from the learners, it is clear that using performance to re-enact narratives from the past works well in gaining their attention and personal connection to the histories, and to the actual site as well. Many did not know much about this place (in their city) before the performance.

One learner noted that reading about history should feel personal but noted that “this (the performance) felt more personal … I didn’t expect it to”.

Why does it matter?

Performance in museums can be one way that an interest in history, and in turn wider societal issues, is cultivated from a young age.




Read more:
History teaching in South Africa could be vastly improved – if language skills were added to the mix


While the present is vital to our wellbeing, ignoring the past creates citizens who do not have a proper grasp of various historical contexts, which is necessary to better understand where and who we are now. We cannot attempt to change current social issues if we do not understand how the past has influenced these problems.

The Conversation

Stephanie Jenkins does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. History with a human face and voice: how museum theatre gets kids to care about the past – https://theconversation.com/history-with-a-human-face-and-voice-how-museum-theatre-gets-kids-to-care-about-the-past-274664

Cuba is facing an economic and social catastrophe, and not entirely because of Donald Trump

Source: The Conversation – Canada – By Robert Huish, Associate Professor in International Development Studies, Dalhousie University

If you’re planning on a winter break to Cuba, get ready for an adventure rather than a vacation. If you’re wondering if United States President Donald Trump’s oil embargo will shatter Cuba’s Communist government, dig in for a drawn-out slog. And if you’re Cuban, brace for a nightmare.

Cuba is on the brink of one of the worst social and economic catastrophes since the 1959 revolution. Energy sources are sparse. The electrical grid is in tatters.

Inflation is over 15 per cent, with the peso tumbling in value. Tropical diseases like dengue, chikunguny and Oropuche virus are surging, largely because the municipal waste system in Havana ground to a halt in 2025.

As many as two million Cubans have left the country since 2021. Infant mortality spiked from five per 1,000 live births in 2021 to 14 per 1,000 in late 2025.

And now, revenue streams from tourism, international medical co-operation and pharmaceutical production are all but dried up. Some 5,000 Cubans volunteered as mercenaries to fight alongside Russia against Ukraine since 2022. Cuba is hurting.

The U.S. versus Cuba

Cuba’s current pain may not be enough to topple its Communist government, despite the desires of many Cuban exiles. Nor is the current crisis all Trump’s work. Cuba is a victim of the breakdown of the old international rules-based order.




Read more:
Venezuela attack, Greenland threats and Gaza assault mark the collapse of international legal order


The U.S. has long targeted Cuba through various economic weapons dating from the early 1960s. One of the most vicious was the Helms-Burton Act that not only prohibited U.S. companies from doing business with Cuba, but also punished companies in other countries for dealing with both Cuba and the U.S.

In his second term, U.S. President Barack Obama eased travel restrictions for Americans visiting Cuba along with some trade policies, but this was short-lived. Trump restored these measures in his first administration.

Cuban doctors

For decades, Cuba relied on an elaborate network of international solidarity and co-operation with rich and poor countries alike. More than 100,000 Cuban doctors served abroad, often providing medical care in rural and remote locations.

While Cuban doctors working abroad received a salary bump, the government received handsome cash deposits and preferred trade agreements for select products. Venezuela received tens of thousands of Cuban doctors and, later, security personnel in exchange for heavy petroleum.




Read more:
Big Pharma vs. Little Cuba: Why Cubans trust vaccines and how they’re helping vaccinate the world


Cuban doctors served in 103 countries, and as of 2021, they were active in 69 nations. Agreements were also made for other personnel to work abroad, including athletic coaches, teachers and engineers.

The U.S. targeted Cuba’s international solidarity work in 2006 by creating the Cuban Medical Professional Parole program, which essentially regarded Cuban workers as “trafficked.”

The State Department approved an annual US$10 million budget until 2017 to locate and recruit Cuban and Cuban-trained doctors working in poor areas of Latin America and Africa. Diplomats offered them expedited immigration to the U.S. But upon arrival, many had their medical credentials ignored and wound up unemployed or underemployed.

Global support

Against one of the longest economic blockades in history, Cuba has nonetheless positioned itself as an active global player. It’s a diplomatic heavyweight with 139 active embassies and consulates worldwide and well over 100 foreign embassies in Havana.

The United Nations General Assembly routinely denounces the American embargo on Cuba. In 2025, amid shifting political alliances, the assembly voted 165-7 in favour of demanding an end to the embargo.

Many international partnerships have kept Cuba going through hard times in the past. Canada, Italy and Mexico, in particular, have kept business with Cuba going despite the U.S. embargo. In the 1990s, tourism expanded, notably from these countries, helping to stimulate the Cuban economy.

Canadian mining company Sherritt invested heavily in Cuba to extract nickel. When COVID-19 overwhelmed health systems worldwide in 2020, Cuba was the first to volunteer medical services to 19 countries, including affluent states like Italy and Qatar. They even took in a quarantined British cruise ship to offer care.




Read more:
The scene from Cuba: How it’s getting so much right on COVID-19


But in 2026, countries are sending in aircraft to evacuate their vacationing nationals, and companies like Sherritt are grinding to a halt, not because of the U.S. embargo, but because so many professionally trained Cubans have emigrated.

Unlike the 1960s and the 1990s, no brave partners are coming forward to do business with Cuba, which only shows how weak international solidarity is today.

Here are three possible outcomes for Cuba in the coming months in descending order of likelihood:

1. Deals behind the scenes

A backroom deal could be struck between Trump’s White House and Miguel Díaz-Canal’s government in Cuba in much the same way that the Obama administration struck deals with Raúl Castro’s government, working through the Vatican and Canadian diplomats. For example, the Trump administration could permit fuel to be purchased in cash from the U.S., or more tourist real estate may be opened to foreign ownership.

If any deal is in the works, the sticking point will be elections. Unlike Venezuela, with a legitimate opposition in the wings, Cuba has none. Political opponents to the revolution have long been jailed or exiled, and Cuba’s electoral system itself isn’t structured for a multi-party race. Toppling the current government would leave an enormous power vacuum.

2. Martial law

If the fuel embargo remains, Cuba could declare martial law and civil defence to prepare for foreign hostility and to better ration resources.

Díaz-Canal recently hinted at this in what he calls a “war of the people,” which may help explain why Canadian and Russian airlines are now hastily sending in rescue flights for tourists.

Martial law would mean ultra-tight rationing, political volatility and the government acquiring goods through murky channels, which, combined, pose a heightened security risk to the U.S. just 140 kilometres off its shores. Since Dwight D. Eisenhower, most American presidents quickly figured out it was better to have a stable and secure, even though ideologically opposed, neighbour than a politically unstable and vulnerable basketcase.

The situation will grow dire since the well-educated professional class has already left, along with many doctors and nurses. In past crises, the educated, youthful professional class was on hand; this time, they’re already gone.

3. The international community steps in

Third, the world could stand by its sentiment at the United Nations General Assembly and sends much-needed resources and trade to Cuba despite the U.S. bellicosity.

It could be a rallying point for the new era of international order, where bullied countries in the Americas and in Europe defy American pressure and bring lifelines to Cuba.




Read more:
Mark Carney’s Davos speech marks a major departure from Canada’s usual approach to the U.S.


International solidarity could reverse some of the harm and take the pressure off Cubans, including those so desperate they’d choose to fight as mercenaries with Russia.

As the world has seen before, when nations stand up to Trump, he usually backs down. Assistance need not come through foreign aid, but simply by keeping the channels open for business.

But if the international community ignores Cuba today, a humanitarian nightmare will unfold soon.

The Conversation

Robert Huish receives funding from the Social Sciences and Humanities Research Council of Canada

ref. Cuba is facing an economic and social catastrophe, and not entirely because of Donald Trump – https://theconversation.com/cuba-is-facing-an-economic-and-social-catastrophe-and-not-entirely-because-of-donald-trump-275410

Hesitation is costly in sports but essential to life – neuroscientists identified its brain circuitry

Source: The Conversation – USA – By Eric Yttri, Associate Professor of Biological Sciences, Carnegie Mellon University

A split-second pause can make the difference between gold and grief. Marco Bertorello/AFP via Getty Images

At the Winter Olympics, skiers, bobsledders, speedskaters and many other athletes all have to master one critical moment: when to start. That split second is paramount during competition because when everyone is strong and skilled, a moment of hesitation can separate gold from silver. A competitor who hesitates too much will be left behind – but moving too early will get them disqualified.

Though the circumstances are less intense, this paradox of hesitation applies to daily life. Waiting for the right moment to cross the street, or pausing before deciding whether to answer a call from a number you don’t recognize, are daily examples of hesitation. Importantly, some psychiatric conditions such as obsessive-compulsive disorder are characterized by impulsivity, or a lack of hesitation, while excessive hesitation is a crippling consequence of several anxiety disorders.

As a neuroscientist, I have been working to uncover how the brain decides when to act and when to wait. Recent research from my team and me helps explain why this split-second pause happens, offering insight not only into elite athletic performance, but also how people make everyday decisions when the potential outcome isn’t clear.

We found that the key to hesitation is a response to uncertainty. This could be where a dropped hockey puck will land, when a race starts, or placing your order at a new restaurant.

Five rows of Olympic skiiers racing down a hill
Every millisecond counts when the competition is fierce.
Tom Weller/Getty Images

Hesitation and the brain

To understand how the brain controls hesitation, my colleagues and I designed a simple decision-making task in mice.

The task required the mouse’s brain to interpret signals that were predictably good, predictably bad or – most importantly – uncertain, meaning somewhere in between. Different auditory tones indicated whether a drop of sugar water would soon be delivered, not delivered, or had a 50/50 chance of delivery.

How the mice behaved would not affect the outcome. Nevertheless, mice would still wait longer before licking to see whether a reward had been given in the uncertain scenario. Just like in people, unpredictable situations led to delays in response. This hesitation was not the result of vacillating between options in indecision, but an active and regulated brain process to pause before acting due to environmental uncertainty.

When we examined neural activity associated with the onset of licking, we identified a specific group of neurons that became active only when outcomes were unclear. Those neurons effectively controlled whether the brain should commit to an action or pause to gather more information. The degree to which these neurons were active could predict whether mice would hesitate before making a decision.

To confirm that these neurons played a role in controlling hesitation, we used a technique called optogenetics to briefly turn these brain cells on or off. When we activated the neurons, mice hesitated more. When we silenced them, that hesitation faded and their responses were quicker by several hundred milliseconds, in line with their reactions to predictable situations.

Researchers can use optogenetics to turn brain cells on or off.

Daily life, disease and downhill racing

Our findings suggest that, rather than a weakness to overcome, hesitation appears to be a fundamental brain feature that helps people and animals navigate an uncertain world and avoid costly mistakes.

Our study also provides insights into the balance of action and inaction in health and disease. The hesitation neurons are located in the basal ganglia, the same part of the brain affected in Parkinson’s disease, OCD and addiction. While researchers must still determine how much overlap or interaction there is between the cells involved in hesitation and those affected in psychiatric disorders, their overlap in circuitry points to possible targets for treatment.

Our next step is to understand how cells controlling hesitation interact with drugs treating ADHD and OCD, conditions where patients can respond impulsively during volatile or uncertain situations.

We also aim to identify which brain areas provide these cells with information about uncertainty – the environmental signal so critical to hesitation. While researchers have found that several parts of an area of the brain called the prefrontal cortex encode uncertainty, it’s unclear how the brain actually makes use of this information, where the rubber meets the road.

Hesitation is not a flaw – it’s a critical feature for navigating an unpredictable world. Whether you’re a figure skater waiting for the perfect moment to launch your jump or just going about your day, the circuitry behind hesitation plays an important role in figuring out the timing to get the action right.

The Conversation

Eric Yttri receives funding from the National Institute of Health and the Binational Science Foundation.

ref. Hesitation is costly in sports but essential to life – neuroscientists identified its brain circuitry – https://theconversation.com/hesitation-is-costly-in-sports-but-essential-to-life-neuroscientists-identified-its-brain-circuitry-274680

Nearly every state in the US has dyslexia laws – but our research shows limited change for struggling readers

Source: The Conversation – USA (2) – By Eric Hengyu Hu, Research Scientist of Educational Policy, University at Albany, State University of New York

Between 5% and 15% of children have symptoms of dyslexia, but schools are often slow at identifying and responding to it with targeted education. mrs/Stock Photos/Getty Images

Families with children who have dyslexia have long pushed lawmakers to respond to a pressing concern: Too many young students struggle for years to learn to read, before schools recognize the problem.

In response, nearly every state in the U.S. passed some sort of dyslexia laws over the past decade. Most of these laws encourage or require schools to screen young children for reading difficulties, train teachers in evidence-based reading instruction and provide targeted support to students who show early signs of dyslexia.

Families of children with dyslexia, educators and dyslexia advocacy groups widely praised these laws. If schools could identify dyslexia early and respond with evidence-based instruction, reading outcomes would likely improve and fewer children would fall behind.

But what actually happened after these laws passed?

My colleagues and I examined nearly two decades of national student data to answer this question. The results tell a complicated story.

A young girl with dark hair sits with her hands on her head and looks at an open book on a desk.
State laws on dyslexia are less effective without the resources and strategies to implement the laws.
aldomurillo/Stock Photos/Getty Images

An undetected problem

Dyslexia is a brain-based learning difference that makes reading words slow and effortful, even when children have typical intelligence and education.

About 5% to 15% of U.S. children experience persistent reading difficulties consistent with dyslexia. Without early support, these difficulties can have long-term academic and emotional consequences.

Before the 2000s, dyslexia was rarely mentioned explicitly in education policy. Students with dyslexia were typically grouped under a broad learning disability category, often without focused instruction or support.

Parent advocacy groups and dyslexia advocacy organizations began pushing lawmakers in the early 2010s to recognize dyslexia in state education policy. They also lobbied for states to require early screening for reading difficulties and to teach reading with rigorous methods backed by scientific research.

Their advocacy coincided with a growing scientific consensus: Early, explicit instruction in phonics and language structure helps struggling readers, including students with dyslexia.

Research and advocacy also highlighted that many children with reading difficulties were not identified until later in elementary school, after years of academic struggle, when gaps in reading skills are harder to correct.

States respond with dyslexia laws

A few states, like Texas and Arkansas, first passed dyslexia laws in the early 2010s. One central goal was to help schools identify dyslexia in students earlier, rather than waiting until these students experience repeated academic failure.

By the late 2010s, most states had adopted some form of dyslexia legislation.

As of 2025, all states except Hawaii have enacted dyslexia legislation.

While the laws shared similar goals of promoting early screening for reading difficulties, improving reading instruction and expanding support for struggling readers, they varied widely in strength, funding and expectations for schools.

My colleagues and I wanted to examine whether the wave of state dyslexia laws that began in the early 2010s was associated with changes in students’ reading outcomes.

Mixed results

We analyzed fourth grade reading assessments from the National Assessment of Educational Progress, often called the nation’s report card, from 2003 to 2022.

We focused on how often students were identified with reading-related learning disabilities and how well those students performed in reading. We compared trends before and after dyslexia laws were enacted across 47 states.

Two findings stood out:

• First, more than half of the states with these new laws showed no significant shift in identifying learning disabilities related to reading. Some states identified more students, some fewer, but there was no consistent national pattern.

• Second, reading achievement among students identified with learning disabilities often declined, rather than improved, after these laws passed in many states, including Alaska, Maine, Massachusetts, New York, Ohio and West Virginia.

Only four states – Arizona, Mississippi, Nevada and Oklahoma – showed significant gains in reading scores on state assessments, with average increases ranging from 3 points in Oklahoma’s case to 10 points in Arizona’s example. Many other states experienced flat trends or declines over the same period.

Passing a law doesn’t equal classroom change

Our findings suggest that dyslexia laws often raised awareness about dyslexia and early reading difficulties without fully changing classroom practices.

Many states, such as Connecticut, Maine, Massachusetts and North Carolina, required early screening for dyslexia – but did not ensure schools had trained staff, for example, on how to conduct this screening.

Even with enough teachers to screen for dyslexia, screening alone does not help students unless it is followed by high-quality instruction and sustained support.

Funding has been another major challenge. Most dyslexia laws were passed without dedicated funding for teacher training or instructional materials, leaving districts to absorb the costs. As a result, implementation has been uneven, with well-funded districts moving faster than others.

Teacher preparation also matters. Teaching reading effectively, especially for students with dyslexia, requires specialized knowledge that many teachers were never taught in their training programs. Without strong professional development and ongoing coaching, new mandates can be difficult to carry out.

Taken together, these factors help explain why dyslexia laws alone have not produced widespread gains.

What distinguishes states that improved

Despite the mixed national picture, students in some states, including Arizona and Mississippi, did better on reading outcomes after their schools adopted dyslexia-related policies. These states shared several features.

First, when young children in these states were flagged as at risk for reading difficulties, schools were expected to provide additional reading instruction – rather than treating screening as an end in itself.

Second, schools in these states invested in practical teacher training, focused on how to teach foundational reading skills – such as phonics and word decoding – that are especially important for students with dyslexia.

Third, these states aligned their dyslexia laws with broader literacy reforms – like using evidence-based reading curricula and providing coaching to teachers – rather than treating dyslexia policy as a stand-alone mandate.

Mississippi is often cited as an example of a state that successfully paired dyslexia policy with a broader overhaul of reading instruction, resulting in a boost in reading achievement scores from 2013 to 2019. This overhaul included more structured reading instruction, teacher training and literacy coaches in schools.

Other states, including Louisiana and Alabama, adopted similar approaches and also saw reading gains for kids with learning disabilities – including dyslexia – after they enacted their dyslexia laws.

The takeaway

Dyslexia laws recognize that struggling young readers deserve early, evidence-based support rather than years of delay. That alone is meaningful progress.

But two decades of national data suggests that legislation by itself is not enough.

If states want dyslexia laws to fulfill their promise, the next step is clear: Move beyond mandates and focus on how schools are supported to carry them out. For children struggling to learn to read, the difference between policy and practice can shape their entire educational future.

The Conversation

Eric Hengyu Hu does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

ref. Nearly every state in the US has dyslexia laws – but our research shows limited change for struggling readers – https://theconversation.com/nearly-every-state-in-the-us-has-dyslexia-laws-but-our-research-shows-limited-change-for-struggling-readers-275202

Polymers from earth can make cement more climate-friendly

Source: The Conversation – USA (2) – By Alcina Johnson Sudagar, Research Scientist in Chemistry, Washington University in St. Louis

Portland cement, widely used for concrete, is responsible for about 8% of global greenhouse gas emissions. Photovs/iStock/Getty Images Plus

Concrete is all around you – in the foundation of your home, the bridges you drive over, the sidewalks and buildings of cities. It is often described as the second-most used material by volume on Earth after water.

But the way concrete is made today also makes it a major contributor to climate change.

Portland cement, the key component of concrete, is responsible for about 8% of global greenhouse gas emissions. That’s because it’s made by heating limestone to high temperatures, a process that burns a large amount of fossil fuels for energy and releases carbon dioxide from the limestone in the process.

The good news is that there are alternatives, and they are gaining attention.

Portland cement: A greenhouse gas problem

Cementlike substances have been used in construction for thousands of years. Architects have found evidence of their use in the pyramids of Egypt and the buildings and aqueducts of the Roman Empire.

The Portland cement commonly used in construction today was patented in 1824 by Joseph Aspdin, a British bricklayer.

Modern cement preparation starts with crushing the excavated raw materials limestone and clay and then heating them in a kiln at around 2,650 degrees Fahrenheit (about 1,450 degrees Celsius) to form clinker, a hard, rocklike residue. The clinker is then cooled and ground with gypsum into a fine powder, which is called cement.

About 40% of the carbon dioxide emissions from cement production come from burning fossil fuels to generate the high heat needed to run the kiln. The rest come as the heat converts limestone (calcium carbonate) to lime (calcium oxide), releasing carbon dioxide.

In all, between half a ton and 1 ton of greenhouse gas is released per ton of Portland cement. Cement is a binding agent that, mixed with water, holds aggregate together to create concrete. It makes up about 10% to 15% of the concrete mix by weight.

Alternative technologies can lower emissions

As populations, cities and the need for new infrastructure expand, the use of cement is growing, making it important to find alternatives with lower environmental costs.

Concrete has seen the fastest growth among commonly used construction materials with rising population between 1950 and 2023
As population has increased, annual global Portland cement production has risen with it.
Hao Chen, et al., 2025, CC BY-NC-ND

Some techniques for reducing carbon dioxide emissions include substituting some of the clinker – the hard residue typically made from limestone – with supplementary materials such as clay, or fly ash and slag from industries. Other methods reduce the amount of cement by mixing in waste sawdust or recycled materials like plastics.

The long-term solution for reducing cement’s emissions, however, is to replace traditional cement completely with alternatives. One option is geopolymers made from earthen clay and industrial wastes.

Geopolymers: A more climate-friendly solution

Geopolymers can be made by mixing claylike materials that are rich in aluminum and silicon minerals with a chemical activator through a process called geopolymerization. The activator transforms the silicon and aluminum into a structure that will look like cement. All of this can happen at room temperature.

The major difference between cement and geopolymer is that cement is mainly made of calcium, whereas geopolymers are made of silicon and aluminum with some possible calcium in their structure.

Geopolymers offer advantages with lower number of steps, lower CO2 emission and lower water requirement over Portland cement
How the production of Portland cement and geopolymers compare.
Alcina Johnson Sudagar, CC BY-NC

These geopolymers have been found to possess high strength and durability, including resilience in freeze-thaw cycles and resistance to heat and fire, which are important requirements in construction. Studies have found that some geopolymers can provide comparable if not better strength than traditional cement and, because they don’t require heat the way clinker does, they can be produced with significantly lower greenhouse gas emissions.

Geopolymers can also be produced from a variety of raw materials rich in aluminum and silicon, including earthen clays, fly ash, blast furnace slag, rice husk ash, iron ore wastes and recycled construction brick waste. Geopolymer technology can be adapted depending on the clay or industrial waste locally available in a region.

A brief history of cement and geopolymers. Geopolymer International.

An added advantage of geopolymers is that changes to the mixture can produce a range of features.

For example, I and my co-researchers at the University of Aveiro in Portugal added a small amount of cork industry waste – the leftovers from creating bottle corks – to clay-based geopolymer and found it could improve the strength of the material by up to twofold. The cork particles filled the spaces in the geopolymer structure, making it denser, which increased the strength.

Similarly, additives such as sisal fibers from the agave plant, recycled plastic and steel fibers can change geopolymer properties. The additives do not participate in the geopolymerization process but act as fillers in the structure.

The structure of geopolymers can also be designed to act as adsorbents, attracting toxic metals in wastewater and capturing and storing radioactive wastes. Specifically, incorporating materials like zeolite that are natural adsorbents in the geopolymer structure can make them useful for such applications as well.

Where geopolymers are used now

Geopolymers have been used in many types of construction, including roads, coatings, 3D printing, coastal environmental protection, the steel and chemical industries, sewer rehabilitation and building radiation shielding and rocket launchpad and bunker infrastructure.

One of the earliest examples of a modern geopolymer concrete project was the Brisbane West Wellcamp airport in Australia.

It was built in 2014 with 70,000 metric tons of geopolymer concrete, which was estimated to have reduced the project’s carbon dioxide emissions by as much as 80%.

The geopolymer market is currently estimated to be between US$7 billion and $10 billion, with the largest growth in the Asia-Pacific region.

Analysts have estimated that the market could grow at a rate of 10% to 20% per year and reach about $62 billion by 2033.

In several countries, greenhouse gas regulations and green-building certifications are expected to support the continued growth of geopolymers in the construction industry.

Expanding the use of cement alternatives

The advantage of using industrial wastes in geopolymers is a double-edged sword, however. The composition of industrial wastes varies, so it can be difficult to standardize the processing methods. The geopolymer components need to be mixed in particular ratios to achieve desired properties.

Producing the activator for the geopolymer, typically done in chemical facilities, can raise the cost and contribute to the carbon footprint. And the long-term data about these materials’ stability is only now being developed given their newness. Also, these geopolymers can take longer to set than cement, though the setting time can be sped up by using raw materials that react quickly.

Developing cheaper, naturally available activators like agricultural waste rice husk with sustainable supply chains could help lower the costs and environmental impact. Also, printing the recipe on the raw material packaging could help simplify the job of determining the mixing ratio so geopolymers can be more widely used with confidence.

Even though geopolymer technology has some drawbacks, these low-carbon alternatives have great potential for reducing emissions from the construction sector.

The Conversation

Alcina Johnson Sudagar has received funding from GeoBioTec.

ref. Polymers from earth can make cement more climate-friendly – https://theconversation.com/polymers-from-earth-can-make-cement-more-climate-friendly-270354