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© Adriana Loureiro Fernandez for The New York Times

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A team of researchers examined 23 teeth from at least 20 individuals from South Africa‘s Rising Star Cave system and found no evidence of the male-specific Amelogenin-Y protein.

A recent study, published in Cell, marks the first ancient protein analysis of Homo naledi and raises the possibility that the Dinaledi Chamber may contain predominantly, or possibly exclusively, female individuals. If confirmed, Homo naledi would become the first known non-human species to practice sex-specific burial.

A Decade-Old Puzzle

Since its discovery in 2013, Homo naledi has puzzled paleoanthropologists. This extinct human relative lived between 335,000 and 241,000 years ago and combined ape-like anatomy with distinct human features. So far, Homo naledi remains have only been found in the Rising Star Cave system in South Africa.

For over a decade, scientists noted that the adult fossils from the Dinaledi Chamber were nearly identical, lacking the skeletal variation usually seen between males and females. The reason for this similarity remained unclear.

Proteins Where DNA Fails

To investigate further, a team from the University of York, the University of Copenhagen, and additional institutions analyzed the remains at the molecular level. They used a minimally destructive acid-etching method to extract protein fragments, or peptides, from the enamel of the 23 teeth.

“Unlike those found in other remains like bone fragments, proteins in tooth enamel are preserved because dental enamel—the hardest tissue in the human body—shields proteins from environmental contamination even for millions of years. This makes them ideal carriers of genetic information from deep time. Our study helps explain the long-standing mystery of why Homo naledi lacked significant variation; it’s probably because they could have all belonged to one sex,” said Palesa Madupe, who conducted the research during her postdoctoral fellowship at the University of Copenhagen.

A Missing Male Marker

The researchers specifically searched for Amelogenin-Y, a protein produced only by the male Y chromosome, but detected none of it in the sampled teeth. To make sure the results were not due to modern contamination, a specialized chemistry team at the University of York independently confirmed that the amino acids were genuinely ancient. The findings remained consistent.

“The lack of male markers within the group is truly fascinating. It is incredibly exciting to gain a window not only into the biology of our ancestors, but also into how they lived. These findings offer rare insights into a culture that has, until now, been difficult to access directly. Advances in ancient protein analysis are opening the door to a far richer and more nuanced understanding of ancient hominins,” said Dr. Marc Dickinson from the university’s Department of Chemistry.

Ritual or Genetic Fluke?

The findings allow for two possible explanations. One is cultural: if the chamber were reserved for females, it could indicate that Homo naledi practiced sex-specific, symbolic mortuary behavior, a trait previously thought to be unique to modern humans.

The second explanation is biological. The researchers note that a small, isolated Homo naledi population could have lost or mutated the Amelogenin-Y gene, leaving males without the protein marker typically used to identify male remains.

Either explanation could reshape what scientists know about Homo naledi. If researchers confirm the site as an all-female burial chamber, it would suggest that symbolic behavior emerged earlier in the human lineage than previously believed. On the other hand, a genetic change across the population would show how isolation can shape a species’ biology in ways that fossils alone cannot reveal. This study shows how ancient protein analysis from teeth can open new windows into human evolution.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.

In a groundbreaking study published in Translational Psychiatry, researchers have unveiled a novel cross-species approach to unraveling the neural circuitry underlying irritability—a pervasive emotional state with significant clinical implications. The investigation, led by WL Tseng, Z Li, and E Leibenluft, harnesses the concept of frustrative non-reward (FNR) as a potent experimental probe, enabling unprecedented insight into the brain mechanisms that drive irritability across humans and animal models.

Irritability, often characterized by heightened sensitivity to frustration and negative affect, is a hallmark symptom in various psychiatric disorders, including mood and anxiety conditions. However, the challenge in dissecting its neurobiological roots has historically stemmed from the lack of translational tools that can bridge findings from animal models to human pathology. By focusing on frustrative non-reward—the experience of being denied an expected reward—this study provides a quantifiable and comparable construct to systematically explore irritability’s brain basis.

Central to the research is the deployment of paradigms that elicit FNR responses in both humans and animals, enabling scientists to examine conserved neural circuits modulated by this emotional challenge. Functional neuroimaging data reveal that regions such as the anterior cingulate cortex, ventral striatum, and amygdala exhibit altered activity during frustrative episodes. These findings suggest a neurobiological signature of irritability that transcends species boundaries, emphasizing the role of reward processing and emotional regulation networks.

On a molecular level, the study points toward dysregulation in neurotransmitter systems implicated in reward anticipation and frustration tolerance, including dopaminergic and serotonergic pathways. These alterations may underlie the exaggerated irritability seen in clinical populations, offering targets for therapeutic intervention. Furthermore, the team’s use of advanced computational modeling to integrate behavioral, neuroimaging, and neurochemical data sets a new standard for mechanistic research in affective neuroscience.

Importantly, this cross-species strategy enhances the validity of animal models used in preclinical research on irritability, fostering improved translational potential. It opens avenues for testing pharmacological agents aimed at modulating FNR responses, thereby attenuating irritability symptoms with higher specificity. The quantitative nature of FNR as an experimental probe may also facilitate the development of biomarker-driven diagnostic tools in psychiatry.

The research underscores the significance of irritability not merely as a symptomatic complaint but as a fundamental affective process with distinct neurobiological underpinnings. By delineating the brain circuitry common to humans and animals during frustrative non-reward, the study propels the field toward more effective interventions for irritability-related psychopathologies.

As psychiatric research increasingly embraces an integrative cross-species framework, studies like this highlight the potential for converging evidence to unravel complex emotional states. The elucidation of neural mechanisms underlying irritability promises to revolutionize both our understanding and treatment of disorders marked by heightened frustration sensitivity.

This pioneering work marks a crucial step forward in affective neuroscience, establishing frustrative non-reward as a versatile and robust probe to decode irritability. Future investigations building on these findings are poised to translate laboratory insights into therapeutic breakthroughs that improve mental health outcomes worldwide.

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Subject of Research: Neural mechanisms of irritability using frustrative non-reward as a cross-species probe

Article Title: Frustrative non-reward: A cross-species probe to study brain mechanisms of irritability

Article References:
Tseng, WL., Li, Z. & Leibenluft, E. Frustrative non-reward: A cross-species probe to study brain mechanisms of irritability. Transl Psychiatry (2026). https://doi.org/10.1038/s41398-026-04257-2

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41398-026-04257-2

The extreme heat smothering Europe has upended Climate Week in London.

© Pool photo by Yui Mok

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© Lenny Ignelzi/Associated Press

Deep within the labyrinthine caves of northeastern Mexico dwells a remarkable species of fish, the blind Mexican cavefish (Astyanax mexicanus), whose evolutionary journey over hundreds of thousands of years has led it to adapt to a life shrouded in perpetual darkness. This fish has lost its eyes and pigmentation, hallmark traits of cave-dwelling organisms, while simultaneously acquiring a suite of physiological and behavioral adaptations tailored to survive in nutrient-scarce subterranean environments. Its dual existence as both a sighted surface fish and numerous independently evolved cave forms presents a unique biological system for examining how extreme environments drive evolutionary changes in brain structure, sensory processing, and behavior.

Researchers from Florida Atlantic University, collaborating with experts from institutions across the United States, have leveraged cutting-edge genetic and imaging technologies to decipher the neural underpinnings that distinguish cavefish from their surface relatives. By employing genetically engineered lines of this species that express fluorescent markers in their neurons, the scientists conducted real-time, whole-brain imaging at cellular resolution, unveiling intricate patterns of neural activity in response to sensory stimuli. This approach allowed direct comparison of neural circuitry when fish were exposed to alternating light and dark conditions, providing profound insights into how evolution recalibrates brain function to orchestrate behavior appropriate for radically different environments.

The study, recently published in Science Advances, reveals an astonishing reversal in sensorimotor behavior between the two ecotypes. Whereas surface fish exhibit increased locomotor activity upon sudden darkness—presumably an adaptive mechanism to enhance exploration for light sources—the cavefish respond inversely, with heightened activity triggered by light exposure. This counterintuitive response is theorized to serve as an adaptive avoidance strategy, steering cavefish away from illuminated cave entrances where predation risk and environmental fluctuations are higher. Such behavioral rewiring exemplifies how neural circuits can be evolutionarily repurposed rather than completely reinvented.

Central to this behavioral dichotomy is the alteration of activity within the posterior tuberculum, a brain region long implicated in sensorimotor integration and motivational states. The researchers identified not only region-specific shifts in activity patterns but also characterized a previously undescribed neuronal cell type that appears to play a pivotal role in mediating light-evoked responses. Intriguingly, neurons that in surface fish were activated by darkness exhibited robust activation in cavefish under light stimulus, underscoring the concept of evolutionary neural circuit reutilization. This finding challenges conventional assumptions that new behaviors necessitate de novo neural architectures and instead supports a model where existing circuits are modified to generate novel functional outputs.

Further mechanistic insights emerged from the investigation of dopaminergic signaling pathways. Dopamine, a neurotransmitter extensively involved in motor control, reward processing, and sensory modulation across vertebrates, was found to be centrally implicated in mediating these light-driven behavioral shifts. The study demonstrates that evolutionary tuning of dopamine circuits underlies the behavioral adaptation in cavefish, representing a conserved neurochemical axis modified through natural selection. This work sheds light on the plasticity and evolutionary potential of neuromodulatory systems in shaping species-specific behaviors.

These findings have significant implications beyond the realm of evolutionary biology. Since dopaminergic circuits are highly conserved from fish to mammals, understanding how these systems adapt to environmental pressures provides a window into fundamental brain functions relevant to health and disease. For example, alterations in dopamine signaling underlie numerous neurodevelopmental and neurodegenerative disorders in humans, including Parkinson’s disease, schizophrenia, autism spectrum disorders, and attention deficit hyperactivity disorder (ADHD). By elucidating natural mechanisms of dopamine circuit modification, this research may inform therapeutic strategies targeting related pathologies characterized by dysregulated sensory processing and motor responses.

The genetically controlled inheritance of photokinetic behavior further underscores the robustness of these adaptations. Crossbreeding experiments between surface fish and cavefish yielded hybrid offspring exhibiting a spectrum of activity responses to light and dark, confirming that these sensorimotor traits are encoded within the genome. Dissecting the genetic loci and developmental pathways responsible for remodeling neural circuits remains a crucial next step. Such investigations promise to unravel molecular drivers of behavioral evolution and highlight how genetic variation translates into neural and behavioral diversity.

The blind Mexican cavefish stands as an exemplary model system to probe how sensory systems are sculpted by evolutionary forces and how brains dynamically reconfigure to interpret environmental signals. By disentangling the neural rewiring that facilitates survival in total darkness, researchers gain a clearer picture of how sensory inputs are transformed into adaptive motor outputs. This contributes to a broader understanding of brain evolution applicable across vertebrates and illustrates nature’s ingenuity in leveraging existing neural frameworks to solve complex ecological challenges.

Through advanced imaging and behavioral quantification, the Florida Atlantic University team has carved new ground in charting the neural circuit modifications that underpin a dramatic shift from dark-evoked to light-evoked photokinesis. This work provides a compelling paradigm illustrating that evolution does not invariably mandate the invention of novel structures but can preferentially repurpose and recalibrate pre-existing neural substrates to generate behavioral novelty.

The evolutionary narrative of the blind Mexican cavefish enriches our comprehension of neuroecology—the study of how nervous systems evolve in response to environmental variables. It reveals that sensory deprivation, far from being a mere loss, can instigate intricate neural and behavioral innovations that confer selective advantages. Such insights deepen our appreciation for the complexity and flexibility inherent in neural systems when confronted with extreme ecological niches.

Finally, this research exemplifies the power of integrative methodologies combining genetics, neurobiology, and behavioral science to unravel the enigma of brain evolution. It paves the way for future interdisciplinary studies to identify specific genes orchestrating neural circuit plasticity, decode developmental mechanisms driving neuronal subtype specification, and ultimately connect genotype to phenotype in a context of evolutionary adaptation.

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Subject of Research: Animals

Article Title: Evolution of a central dopamine circuit underlies adaptation of a light-evoked sensorimotor response in the blind cavefish

News Publication Date: 22-May-2026

Web References:
DOI: 10.1126/sciadv.adv3770

Image Credits: Florida Atlantic University

Keywords: Evolutionary biology, Brain, Neurons, Sensory neurons, Photoreceptors, Neurological disorders, Neurodegenerative diseases, Parkinson’s disease, Schizophrenia, Fish, Brain activity maps, Behavioral ecology, Ecological adaptation, Neural pathways, Dopamine pathways

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