Café des sciences

[Alchimi]

On a mis les pieds sur la lune et y'a pas une autre espèce de mammifères qui peut tous nous bouffer à mort.

Ça doit marcher, quelque part.

[Alchimi]

Bon on a aussi inventé l'autotune, ça marche pas tout le temps non plus.

[Tramp]

il y a 2 minutes, Alchimi a dit :

Ça doit marcher, quelque part.

Ça a plus que marché. Quelles sont les espèces qui ont le plus de succès ? Humains, chien, chat, poulets, vaches, cochons, etc. 

[Alchimi]

il y a 1 minute, Tramp a dit :

Ça a plus que marché. Quelles sont les espèces qui ont le plus de succès ? Humains, chien, chat, poulets, vaches, cochons, etc. 

That was the joke.

[Riffraff]

Le 12/06/2025 à 19:36, Tramp a dit :

Ça a plus que marché. Quelles sont les espèces qui ont le plus de succès ? Humains, chien, chat, poulets, vaches, cochons, etc. 

Je crois que le poulet est le vertébré terrestre avec le plus d'individu.

 

Side note, les chauve-souris représentent 1/4 des espèces de mammifères.

[Mathieu_D]

On 6/12/2025 at 6:36 PM, Rincevent said:

Réduction du volume crânien (et du cerveau), raccourcissement des mâchoires (avec parfois un encombrement excessif des dents), amollissement des tissus que le collagène est censé rigidifier (on pense évidemment aux oreilles tombantes du bétail, mais ça entraîne aussi des problèmes articulaires), engraissement facilité, stratégie reproductive de plus en plus r et de moins en moins K (y compris plus faible "pair bonding" ou maturité sexuelle arrivant plus tôt), plus grande sensibilité aux pathogènes et aux parasites, modifications hormonales (baisse de la testostérone et hausse du cortisol, mais là c'est évident puisque ça va dans le sens d'une plus grande "soumettabilité")... tout n'est pas nécessairement présent simultanément ni au même degré, mais tout ça tend quand même à converger.

Tiens avant de lire j'étais persuadé que tu allais évoquer l'augmentation du volume mammaire.

[Rincevent]

il y a 42 minutes, Mathieu_D a dit :

Tiens avant de lire j'étais persuadé que tu allais évoquer l'augmentation du volume mammaire.

Pas nécessairement (la présence de mammelles apparentes toute l'année chez l'être humain n'est pas encore expliquée avec certitude, peut-être est-ce plutôt lié à l'œstrus cryptique chez la femme). Par contre j'aurais pu évoquer aussi la gracilisation des os.

[Mégille]

Ca y est, on a une idée de la tronche du denisovien (l'hypothèse de l'homme dragon denisovien est confirmée) : https://www.nature.com/articles/d41586-025-01899-y

[Hugh]

Bien, le 3I/Atlas:

 

Citation

Comet 3I/ATLAS is the third known object from outside our solar system to be discovered passing through our celestial neighborhood. Astronomers have categorized this object as interstellar because of the hyperbolic shape of its orbital path. (It does not follow a closed orbital path about the Sun.)

Comet 3I/ATLAS poses no threat to Earth and will remain far away. The closest it will approach our planet is about 1.8 astronomical units (about 170 million miles, or 270 million kilometers). 3I/ATLAS will reach its closest point to the Sun around Oct. 30, 2025, at a distance of about 1.4 au (130 million miles, or 210 million kilometers) — just inside the orbit of Mars.

 

https://science.nasa.gov/solar-system/comets/3i-atlas/#:~:text=3I%2FATLAS will reach its,by astronomers around the world.

 

[Freezbee]

En parlant de 3I/Atlas, beaucoup de vidéos essaient de faire le buzz en ce moment. Michio Kaku y ajoute son grain de sel :

 

 

[Hugh]

Il y a une pétition pour:

 

Citation

We call for a prohibition on the development of superintelligence, not lifted before there is

1. broad scientific consensus that it will be done safely and controllably, and
2. strong public buy-in.

 

https://superintelligence-statement.org/

 

Bien, beaucoup de non-conservateurs qui veulent du conservatisme?

[Adrian]

Women are better at recognizing illness in faces compared to men, study finds

 

Citation

Most people have either been told that they don't look well when they were sick, or thought that someone else looked ill at some point in their lives. People often use nonverbal facial cues, such as drooping eyelids and pale lips, to detect illness in others, potentially to prevent infection in themselves. A new study, published in Evolution and Human Behavior, finds that women are more sensitive to these subtle cues than men.

[...]

There are two dominant hypotheses as to why women might be capable of detecting illness more accurately. The first is referred to as the "primary caretaker hypothesis," which posits that because, throughout history, women were more often the ones taking care of infants and young children, they evolved to detect illness better. In theory, recognizing the nonverbal cues of illness would help women to detect illness in babies and young children faster. Ultimately, this ability increases the survival of their offspring.

 

Another hypothesis is the "contaminant avoidance hypothesis." This hypothesis states that females experience higher levels of disgust compared to males.

 

The study authors write, "These differences are theorized to result from repeated periods of immune suppression across the reproductive lifespan, occurring both during pregnancy and in the luteal phase of the monthly cycle, in anticipation of pregnancy. Females, therefore, overall, may have had greater selective pressure for disease-avoidance than males."

 

The researchers note that this study was limited to undergraduate students, which may not generalize to broader populations. Also, indicators of sickness, like voice and posture, were not included. The photos in the study were only of stationary, cropped faces. These additional indicators may influence sickness perception to a different degree.

 

[Adrian]

Toddlers expect ingroup loyalty to override personal preferences when outgroups are present

 

Citation

Significance

In the presence of outgroups, adults may set aside their personal preferences to align with perceived ingroup norms, in an outward show of loyalty. In three experiments, we demonstrate that 2-y-old toddlers expect such shows of loyalty. When an individual’s toy preference conflicted with her group’s norm, toddlers expected her to follow the norm when an outgroup member was present, but to act on her own preference otherwise. Thus, by 2 y of age, children already construe individuals as having both a personal and a social identity, they understand that the two identities may suggest opposite actions in different contexts, and they expect the social identity to take precedence in intergroup contexts, presumably in service of ingroup uniformity and cohesion.

Abstract

When outgroups are present, adults may endorse ingroup choices that are at odds with their personal preferences, in an outward show of ingroup loyalty. Here, we examined whether 2-y-old toddlers (N = 108) might already understand such shows of loyalty. In three violation-of-expectation experiments, toddlers watched interactions among a target individual, an ingroup member, and an outgroup member; group memberships were marked with novel labels. In the critical trials, the target individual chose between an ingroup- and an outgroup-associated toy. When the outgroup member was present during this selection process, toddlers expected the target individual to conform to her group’s norm and select the ingroup-associated toy, even when they knew she preferred the outgroup-associated toy. This was true whether or not the ingroup member remained in the scene; as long as the outgroup member was present, toddlers expected the target individual to select the ingroup-associated toy and no other toy. When the outgroup member was absent, however, toddlers expected the target individual to act on her personal preference, if any. They also held this expectation if no information was provided about group memberships. Together, these results indicate that by 2 y of age, toddlers a) construe individuals as possessed of both a personal and a social identity, b) understand that individuals may produce different actions in different contexts depending on which identity has precedence, and c) expect individuals’ social identity to take precedence in intergroup contexts even when it conflicts with their personal identity, in a show of ingroup loyalty.

The “I” in egalitarianism: Hadza hunter-gatherers averse to inequality primarily when personally unfavorable

 

Citation

Many economists contend that humans have strong, universal, other-regarding equality preferences with deep evolutionary roots. Indeed, many hunter-gatherers have endemic food-sharing and proscriptions against accumulation. These “egalitarian” practices appear superficially consistent with intrinsic equality preferences. Previous experiments, involving donating positive endowments to strangers, seldom match the redistributive equality observed in real-world sharing. Such methods ignore the role of taking, and do not capture sharing dynamics among differentially wealthy campmates. This study, instead, uses a one-player “give-or-take” experiment, with real campmates as recipients, better emulating real-world forager food redistribution. We asked 117 Hadza participants, privately, to redistribute food resources between themselves and a campmate after receiving advantageous and disadvantageous endowments. Although few participants were wholly self-interested, most did not seek general equality. Instead, most tolerated inequality when it benefited them but not when it benefited others. Given advantageous endowments, a minority (40.9%) chose to give, while 30% exacerbated inequality by taking more. Given disadvantageous endowments, many took more than necessary to achieve equality. The modal decision across tasks was to take everything. Only when participants could take from others did results approximate real-world sharing patterns. Findings suggest that intrinsic, private other-regarding fairness preferences need not underlie widespread forager food-sharing, which could be maintained by others’ self-motivated demands or extrinsic fairness norms. We also found that men and younger people were more willing to give away advantageous endowments. Further, we found that individuals with greater exposure to cultures outside Hadzaland were more accepting of unfavorable inequality, suggesting that marketization might promote disadvantageous inequality tolerance.

 

[Adrian]

Human populations evolved in similar ways after we began farming
 

Citation

A study combining the growing number of ancient genomes from living people has given us our best picture yet of how humans have evolved over the past 10,000 years or so. It shows that people in different parts of the world evolved in similar – and sometimes even identical – ways after we adopted farming.

 

“Some of the same traits and the same genes are under selection in different populations,” says Laura Colbran at the University of Pennsylvania.
 

Evolution occurs when a genetic variant becomes more common in a population – usually, but not always, because it provides an advantage. By comparing human genomes, then, we can find signs of recent human evolution.

 

The genomes of long-dead people are especially helpful, says Colbran. “Ancient DNA lets us look at genetic history live, as it were, whereas a lot of other methods tend to try and infer that.”

 

Studies of recent evolution have focused on Europe because that’s where researchers have collected the most ancient and modern genomes. But Colbran’s team has taken advantage of the growing number of genomes from outside Europe to take a wider look, based on more than 7000 ancient and modern genomes. The ancient genomes mostly come from within the past 10,000 years, while the modern ones are from living people.

 

The team essentially used the ancient genomes to predict what modern genomes should be like if there were no evolution, and then looked for differences – signals of selection. They found 31 altogether, and many of them were shared – that is, peoples in different parts of the world were evolving in similar ways, most likely because of the independent adoption of farming around the world at around the same time.

 

For instance, less than a quarter of the most ancient people had a genetic variant that boosts the expression of the FADS1 gene. The FADS1 enzyme converts short fatty acids of a kind common in plants into the longer ones common in meat, so making more of the enzyme is thought to benefit people with more plant-based diets. The FADS1-boosting variant is now present in more than three-quarters of people in Europe, Japan and northern China. In Europe, the strength of selection has remained constant over the past 300 generations, the team found, but in East Asia it has increased over the past 100 generations.

 

Then there’s the enzyme alcohol dehydrogenase 1B, encoded by the gene ADH1B. It’s well known that a variant of ADH1B that rapidly turns alcohol into acetaldehyde, producing unpleasant symptoms such as facial flushing, has become common in East Asia. It is thought this variant has been selected for because it discourages drinking. “It’s the strongest signal for selection you see in East Asia,” says Colbran.

 

This variant didn’t exist in ancient Europeans, but her team still found evidence of strong selection involving the ADH1B enzyme. “There’s something that’s changing the amount made, or how it’s responding,” says Colbran. Further work is going to be required to pin down the precise variant involved, and what it does, but it is almost certainly an adaptation to alcohol drinking.

 

The team even looked at traits that are affected by multiple genetic variants, such as the ratio of a person’s waist to their hips. An increase in the waist-hip ratio is linked to higher fertility, so you might think there would be selection for this.

 

Instead, the team found that there appears to be strong selection that keeps the female waist-hip ratio within certain parameters. “It is a really interesting one in that we do see stabilising selection,” says Colbran.

 

The waist-hip ratio does vary in different populations, but the findings suggest there is an optimum value somewhere in the middle, she says. “Population to population, it might shift depending on the precise context.”

 

It’s an exciting study that includes a lot of ancient DNA that hasn’t been analysed before, says Alexander Gusev at Harvard University. “The authors find that variants under selection in one population are significantly enriched for being under selection in other populations,” Gusev says. “I take this to mean that selection is likely to be parallel across populations. This has been hypothesised but not shown before.”

 

Yassine Souilmi at the University of Adelaide, Australia, says the team’s approach was able to identify regions of the genome that weren’t known to be under selection before, in addition to previously identified regions. “Their new method takes full advantage of the large amount of ancient DNA available now,” Souilmi says.

 

The results are the tip of the iceberg, says Colbran. As more genomes are sequenced – especially more non-European ones – we’ll find much more evidence of recent evolution.

 

Le papier

[Mégille]

Vous avez vu passer l'étude selon laquelle ce sont surtout des hommes néanderthaliens qui se sont reproduit avec des femmes sapiens ? J'ai l'impression qu'on en comprend les implications de travers. Ce que je vois tourner sur le sujet l'explique en terme de préférence sexuelle mutuelle, sous entendu individuelle, ce que je trouve surprenant. Il y a assez peu de chance que tout ce monde ait vécu dans une même société, avec un dating game individuellement concurrentiel. On n'estime pas que nos chromosomes Y de pasteurs des steppes aient remplacé les précédents par le charme sensuel de l'accent indo-européen. Si le constat portait sur des rapports entre populations sapiens, on aurait plutôt expliqué ça par un rapport de violence ou de pouvoir d'un groupe sur l'autre : soit que l'un attaque souvent l'autre et capture ses femmes, soit que l'autre "offre" ses femmes au premier pour l'apaiser, ou pour reconnaître une soumission. C'est intéressant parce qu'on en était venu à voir sapiens comme une sorte d'envahisseur remplaçant néanderthal entre autre par une sorte de violence. Mais ce serait en fait néanderthal qui aurait maintenu une position de dominance, soit en terme de violence, soit par une forme de vassalité (soit, plus vraisemblablement je crois, quelque chose entre les deux), malgré sont effacement progressif par la pression démographique. 

Enfin, ceci en supposant que les mécanismes de don de femmes à la Levi-Strauss/Héritier ne concerne pas que le sapiens historique et actuel (ou au moins, concerne aussi le sapiens dans d'anciennes relations au non-sapiens), ce qui est évidemment très spéculatif. Si on imagine, comme au XIXème, un matriarcat paléolithique, le rapport inter-espèce s'inverse.

 

Autre chose, sans rapport, vous avez vu passer ça ? https://eon.systems/updates/embodied-brain-emulation
Un nouveau saut dans la science fiction.

[Lameador]

On 10/31/2025 at 12:47 AM, Hugh said:

Il y a une pétition pour:

 

 

https://superintelligence-statement.org/

 

Bien, beaucoup de non-conservateurs qui veulent du conservatisme?

 

L'URL https://superintelligence-statement.cn  ne fonctione pas

[Rincevent]

il y a 51 minutes, Mégille a dit :

Vous avez vu passer l'étude selon laquelle ce sont surtout des hommes néanderthaliens qui se sont reproduit avec des femmes sapiens ? J'ai l'impression qu'on en comprend les implications de travers. Ce que je vois tourner sur le sujet l'explique en terme de préférence sexuelle mutuelle, sous entendu individuelle, ce que je trouve surprenant. Il y a assez peu de chance que tout ce monde ait vécu dans une même société, avec un dating game individuellement concurrentiel. On n'estime pas que nos chromosomes Y de pasteurs des steppes aient remplacé les précédents par le charme sensuel de l'accent indo-européen. Si le constat portait sur des rapports entre populations sapiens, on aurait plutôt expliqué ça par un rapport de violence ou de pouvoir d'un groupe sur l'autre : soit que l'un attaque souvent l'autre et capture ses femmes, soit que l'autre "offre" ses femmes au premier pour l'apaiser, ou pour reconnaître une soumission. C'est intéressant parce qu'on en était venu à voir sapiens comme une sorte d'envahisseur remplaçant néanderthal entre autre par une sorte de violence. Mais ce serait en fait néanderthal qui aurait maintenu une position de dominance, soit en terme de violence, soit par une forme de vassalité (soit, plus vraisemblablement je crois, quelque chose entre les deux), malgré sont effacement progressif par la pression démographique. 

Je l'ai vu passer, j'en tire des conclusions similaires (et encore un peu plus de mépris envers les chercheurs incapables de pondre des scenarii expliquant les faits sans être outrancièrement idéologiques).

[Sloonz]

1 hour ago, Lameador said:

L'URL https://superintelligence-statement.cn  ne fonctione pas

https://carnegieendowment.org/research/2025/06/how-some-of-chinas-top-ai-thinkers-built-their-own-ai-safety-institute

 

Et sur le statement en question

 

 

(mais oui, c’est vrai que c’est une énorme crainte, le parti communiste chinois est spécialement connu pour son ultralibéralisme et sa frilosité à réguler la tech)

[Adrian]

Scientists revive activity in frozen mouse brains for the first time

 

Citation

‘Cryosleep’ remains the preserve of science fiction, but researchers are getting closer to restoring brain function after deep freezing.
 

A familiar trope in science fiction is the cryopreserved time traveller, their body deep-frozen in suspended animation, then thawed and reawakened in another decade or century with all of their mental and physical capabilities intact.

Researchers attempting the cryogenic freezing and thawing of brain tissue from humans and other animals — mostly young vertebrates — have already shown that neuronal tissue can survive freezing on a cellular level and, after thawing, function to some extent. But it has not been possible to fully restore the processes necessary for proper brain functioning — neuronal firing, cell metabolism and brain plasticity^1,2.

A team in Germany has now demonstrated a method for cryopreserving and thawing mouse brains that leaves some of this functionality intact. The study, published on 3 March in Proceedings of the National Academy of Sciences³, details the authors’ use of a method called vitrification, which preserves tissue in a glass-like state, along with a thawing process that preserves living tissue.

“If brain function is an emergent property of its physical structure, how can we recover it from complete shutdown?” asks Alexander German, a neurologist at the University of Erlangen–Nuremberg in Germany and lead author of the study. The findings, he says, hint at the potential to one day protect the brain during disease or in the wake of severe injury, set up organ banks, and even achieve whole-body cryopreservation of mammals.

Mrityunjay Kothari, who studies mechanical engineering at the University of New Hampshire in Durham, agrees that the study advances the state of the art in cryopreservation of brain tissue. “This kind of progress is what gradually turns science fiction into scientific possibility,” he says. However, he adds that applications such as the long-term banking of large organs or mammals remain far beyond the capabilities of the study.

Preserved for the future

The main reason the brain struggles to fully recover from freezing is because of damage caused by the formation of ice crystals. These displace or puncture the tissue’s delicate nanostructure, disrupting key cellular processes. “Beyond ice, we must account for several considerations, including osmotic stress and toxicity due to cryoprotectants,” says German.

German and his colleagues turned to an ice-free method of cryopreservation called vitrification in an effort to preserve brain function. Vitrification cools liquids fast enough to trap molecules in a disorganized, glass-like state before they have a chance to form ice crystals. “We wanted to see if function could restart after the complete cessation of molecular mobility in the vitreous state,” says German.

They first tested their method on 350-micrometre-thick slices of mouse brains which included the hippocampus — a core brain hub for memory and spatial navigation. Brain slices were pre-treated in a solution containing cryopreservation chemicals before being rapidly cooled using liquid nitrogen at −196 ºC. They were then kept in a freezer at −150 ºC in a glass-like state for between ten minutes and seven days.

After thawing the brain slices in warm solutions, the team analysed the tissue to see whether it had retained any functional activity. Microscopy showed that neuronal and synaptic membranes were intact, and tests for mitochondrial activity revealed no metabolic damage. Electrical recordings of neurons showed that, despite moderate deviations compared with control cells, the neurons’ responses to electrical stimuli were near normal.

Hippocampal neuronal pathways still showed the synaptic strengthening or ‘long-term potentiation’ that underlies learning and memory. However, because such slices naturally degrade, observations were limited to a few hours.
 

The team scaled up the method to the whole mouse brain, keeping it in a vitreous state at –140 ºC for up to eight days. However, the protocol needed repeated tweaking to minimize brain shrinkage and toxicity from cryoprotectants.

When the brains were thawed, brain slices were prepared and recordings from the hippocampus confirmed that neuronal pathways — including hippocampal pathways involved in memory — had survived and could still undergo long-term potentiation. However, because the recordings were made using slices of brain tissue, the researchers were not able to measure whether the animals’ memories had survived cryopreservation.

Still science fiction

German and his team are expanding their method from mice to human brain tissue. “We already have preliminary data showing viability in human cortical tissue,” he says. The team is also exploring how the vitrification method might be used for whole-organ cryopreservation, particularly for the heart.

However, Kothari points out that the success rate was low on the whole-brain protocol and that the results might not translate directly to larger human organs, which present other challenges. “Some of these challenges are related to heat-transfer constraints and higher thermo-mechanical stresses that may cause cracking,” Kothari says.

German adds that “better vitrification solutions and cooling and rewarming technologies will be necessary before these principles can be applied to large human organs”.