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Comment by Dr. Krishna Kumari Challa on Friday

To determine whether Neanderthal X chromosomes contain alleles from humans, the team identified modern human DNA preserved in three Neanderthals—Altai, Chagyrskaya, and Vindija—and compared this dataset against one of diverse African genomes, a control group who had historically never encountered a Neanderthal.
What the researchers found was a striking imbalance. While modern humans lack Neanderthal X chromosomes, Neanderthals had a 62% excess of modern human DNA on their X chromosomes compared to their other chromosomes.
This mirrorlike reversal was their answer. If the two species were biologically incompatible, modern human DNA should have been missing from Neanderthal X chromosomes as well. But because the team found an abundance of human DNA in Neanderthal X chromosomes, they were able to rule out reproductive incompatibility or toxic gene interactions as the barrier.

The remaining explanation, the team argues, lies in sex-biased interbreeding.
Because females carry two X chromosomes and males carry only one, mating direction matters. If Neanderthal males partnered more often with modern human females, fewer Neanderthal X chromosomes would enter the human gene pool, and more human X chromosomes would enter Neanderthal populations.
Mathematical models confirmed that this bias could reproduce the observed genetic patterns. Other possibilities, such as sex-biased migration, could theoretically produce similar results—but only through complex, shifting scenarios that varied across time and geography.

Mating preferences provided the simplest explanation.
With the "who" and "how" of these ancient trysts established, the team is now turning their attention to the "why," investigating whether similar genetic comparisons—specifically the ratio of diversity between X chromosomes and autosomes—can reveal the gender dynamics of Neanderthal society, such as whether females stayed with their birth families while males migrated to new groups.

By mapping these ancient interactions, the researchers hope to further illuminate the complex social lives of human's closest evolutionary cousins.

Alexander Platt et al, Interbreeding between Neanderthals and modern humans was strongly sex biased, Science (2026). DOI: 10.1126/science.aea6774. www.science.org/doi/10.1126/science.aea6774

Part 2

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Comment by Dr. Krishna Kumari Challa on Friday

Neanderthal males, human females? How ancient attraction shaped the human genome

The human genome is a rich, complex record of migration, encounters, and inheritance written over thousands of millennia. Genomic research is revisiting a particularly intimate chapter, suggesting that ancient mating patterns between modern humans and Neanderthals shaped why Neanderthal DNA is largely missing from the human X chromosome.

Along our X chromosomes, we have these missing swaths of Neanderthal DNA scientists call 'Neanderthal deserts".

For years, researchers just assumed these deserts existed because certain Neanderthal genes were biologically 'toxic' to humans—as tends to be the case when species diverge—so they thought the genes may have caused health problems and were likely purged by natural selection.

Now,  this new research work has discovered a more social explanation.

In a paper published in Science, their analysis of Neanderthal and modern human genomes suggests that long-standing mating preferences—rather than genetic incompatibility—shaped which Neanderthal DNA sequences persisted in modern humans and which were gradually lost.

Their findings reveal the role social interactions in sculpting the human genome, challenging the idea that human evolution was driven solely by survival of the fittest.

Researchers found a pattern indicating a sex bias: gene flow occurred predominantly between Neanderthal males and anatomically modern human females.

Roughly 600,000 years ago, the ancestors of anatomically modern humans and their closest-related species, the Neanderthals, diverged, forming two distinct groups.

Our ancestors evolved in Africa, while the ancestors of Neanderthals evolved in and adapted to life in Eurasia. But that separation was far from permanent.

Over hundreds of millennia human populations migrated into Neanderthal territories and back again, and when these groups met, they mated, swapping segments of DNA.

Part 1

Comment by Dr. Krishna Kumari Challa on Friday

Single-celled organism becomes multicellular via three different pathways

Some single-celled organisms are known to transition to multicellularity during their lifetimes, usually either by cloning themselves or when many similar cells come together to form a larger multicellular organism. A new study published in Nature suggests that a combination of the two routes may be more common than previously thought—even in organisms distantly related to animals.

Choanoflagellates are single-celled flagellate eukaryotes considered to be the closest living relatives of animals. They are bacterium-eating aquatic organisms with a flagellum (a long, hair-like appendage that helps them swim) and a collar of microvilli, primarily used for absorption, secretion, and sensory functions.

Choanoflagellates possess the ability to form multicellular bodies. Like animals, they were thought to be purely clonal, but this has not been previously tested across different types. The choanoflagellate Salpingoeca rosetta, for example, only exhibits clonal multicellularity. However, other close relatives of animals have been shown to form aggregative groups.

Although animal multicellularity is purely clonal, other close relatives of animals exhibit diverse forms of multicellularity, including aggregation in filastereans and cellularization of multinucleated cells or cleavage-like serial cell divisions in ichthyosporeans.

The researchers set out to determine whether choanoflagellates can ever form aggregate groups. They were surprised by what they found. Not only did the choanoflagellates form clonal groups and aggregate groups separately, but they also formed mixed clonal-aggregative groups under certain conditions. They also found that the purely aggregative sheets were morphologically, behaviourally, and functionally equivalent to clonally grown sheets.

Furthermore, the team showed that the push to aggregative multicellularity was an active process.

They found that as salinity rises, multicellular sheets tend to dissociate, and cells turn into tough, unicellular cysts. When the pools are rehydrated, these cysts "wake up" and reform sheets using both division and aggregation methods.

The team also found that cell density had an interesting effect on whether the cells chose clonal or aggregative routes to multicellularity.

Núria Ros-Rocher et al, Clonal-aggregative multicellularity tuned by salinity in a choanoflagellate, Nature (2026). DOI: 10.1038/s41586-026-10137-y

Comment by Dr. Krishna Kumari Challa on Thursday

Women with severe burn injuries are more likely than men to develop blood poisoning

The skin forms a natural barrier that prevents bacteria entering the body. Severe burns stop this protective function from working properly, and germs can enter the blood more easily through the wounds. If the airways have suffered thermal or chemical injury through the inhalation of hot and toxic substances, they are also a gateway for infection.
Bacteria can multiply in the blood and spread throughout the body. In the worst case, this can cause blood poisoning—also known as sepsis—which can lead to multiple organ failure. This is a common cause of death in people with burn injuries. A new study has identified for the first time which patients are affected by such infections. The study was carried out before the disaster in Crans-Montana, but it can now help to better understand the physiological processes in critically ill burn patients.

The study focused on sex-specific differences. It analyzed data from 269 patients with severe burn injuries who were treated at the Center for Severe Burn Injuries at the University Hospital Zurich between 2017 and 2021. The insights, published in Burns, should help to prevent sepsis in patients with severe burn injuries or get it under control at an early stage.

Women with severe burn injuries are nearly twice as likely as men to develop bacteremia, which can progress to sepsis. This increased risk is not due to different bacterial species but may relate to altered immune or hormonal responses following burns. Understanding these mechanisms could improve prevention and management of sepsis in burn patients.
Women's immune systems often seem better able to cope with pathogens, and a number of studies have observed a stronger immune response.
In burn victims, however, it seems that this is not necessarily the case. The researchers are not yet able to answer the question of why the women with severe burn injuries in this cohort were much more likely to develop bacteremia.
One explanation that can be ruled out, however, is the presence of different pathogens, as predominantly the same bacteria were identified in the blood of male and female patients. These are species that colonize the skin and mucous membranes as part of the natural microbiome. They are usually harmless but can become dangerous if they enter the bloodstream in large quantities.
Sex hormones have an effect on human immune cells, which also fight infections. Female sex hormones such as estrogen are actually associated with a better response. But it is possible that burn injuries alter hormone metabolism, which then weakens the immune response, say the researchers.
While patients are usually given antibiotics early to fight the bacteria, the damaged barrier means that new infections keep occurring. Resistant bacteria can also quickly develop, for which very few effective antibiotics are available.

Nicole J.M. Schweizer et al, Impact of sex on the development of bacteremia in critically ill burn patients: A retrospective cohort study, Burns (2026). DOI: 10.1016/j.burns.2025.107845

Comment by Dr. Krishna Kumari Challa on Thursday

Why corals bleach: Neutrons show algae photosynthesis breaking down

Rising sea temperatures are causing coral reefs around the world to bleach. For the first time, a research team has investigated the biological processes behind coral bleaching directly in living corals. With the help of neutrons, they were able to visualize structural changes during the bleaching process.
Rising sea temperatures disrupt photosynthesis in coral-associated algae by altering the structure of their thylakoid membranes. Using small-angle neutron scattering, researchers directly observed these structural changes in living corals, linking membrane stress to the breakdown of symbiosis and subsequent coral bleaching. Persistent bleaching can lead to coral death.

Robert W. Corkery et al, In hospite and ex hospite architecture of photosynthetic thylakoid membranes in Symbiodinium spp. using small-angle neutron scattering, Journal of Applied Crystallography (2025). DOI: 10.1107/s1600576725007332

Comment by Dr. Krishna Kumari Challa on Thursday

How a one‑eyed creature gave rise to our modern eyes

There is a tiny cyclops among your oldest ancestors, and humans share these remarkable ancestral roots with all other vertebrates. Researchers have found that all vertebrates evolved from a distant ancestor that had a single eye located at the top of its head. The study, published in Current Biology, also reveals that the remnants of this so-called median eye have today become the pineal gland in our brains.

This cyclops-like creature, which is our very distant relative, existed almost 600 million years ago. It was a small, worm-like organism that had adopted a sedentary lifestyle and fed by filtering plankton from seawater. Previously, this creature had some form of paired eyes, like most other animals.

We don't know whether the paired eyes in our branch of the evolutionary tree were just light-sensitive cells or simple image-forming eyes. We only know that the organism later lost them.
The increasingly calm lifestyle meant that the worm-like creature no longer needed paired eyes, and therefore that function was lost over the course of evolution. However, the animal kept a group of light-sensitive cells in the middle of its head. These cells developed into a small, primitive median eye that could keep track of night and day, and sense what was up and down.
Over the following millions of years, our distant ancestor once again began to live an active, swimming life, increasing the need for paired eyes. From parts of the small median eye, new image-forming eyes in pairs developed, the researchers conclude in the study.
Now we finally understand why the eyes of vertebrates differ so radically from the eyes of all other animal groups, such as insects and squid. The film of our eyes—the retina—developed from the brain, whereas the eyes of insects and squid originate in the skin on the sides of the head.
In other words, vertebrate eyes constitute a more modern model that evolved thanks to this peculiar detour via a cyclops' sedentary life. The conclusion that our modern eyes evolved through this specific evolutionary path, and not via some other ancient animal, is based on the researchers' extensive analysis of light-sensitive cells in all animal groups, as well as the physiology and placement of these cells in the body.
All vertebrates evolved from an ancestor with a single median eye atop its head, which later became the pineal gland in the brain. This median eye, originally used for light detection, was retained after the loss of paired eyes and eventually gave rise to the paired, image-forming eyes of modern vertebrates. The retina’s brain origin distinguishes vertebrate eyes from those of other animals.

George Kafetzis et al, Evolution of the vertebrate retina by repurposing of a composite ancestral median eye, Current Biology (2026). DOI: 10.1016/j.cub.2025.12.028

Comment by Dr. Krishna Kumari Challa on Thursday

Women show greater tau buildup and faster cognitive decline than men in Alzheimer's

Tau proteins act like the brain's maintenance crew, helping maintain the structure and proper function of brain cells. In neurodegenerative diseases such as Alzheimer's, the tau proteins can form tangles that disrupt normal cell function. A recent study published in JAMA Neurology found that women show significantly higher levels of tau protein accumulation and experience faster cognitive decline than men.

A multinational team of researchers analyzed data from 1,200 participants across five major studies—one clinical trial and four observational studies—to better understand how Alzheimer's disease progresses differently in men and women. Their focus was on a trigger protein called amyloid-beta that leads to tau abnormalities.

The data indicated that when amyloid levels were high in both women and men, women had significantly higher levels of p-tau217 than men, suggesting that the tau protein clumps together more quickly in a woman's brain, making them more susceptible to the very early stages of the disease process. On the other hand, when the p-tau217 levels are lower, women seem to do better at cognitive tests than men.

Gillian T. Coughlan et al, Sex Differences in P-Tau217, Tau Aggregation, and Cognitive Decline, JAMA Neurology (2026). DOI: 10.1001/jamaneurol.2025.5670

Comment by Dr. Krishna Kumari Challa on Thursday

Dry eye often precedes autoimmune disease diagnosis, new study finds

Frequent dry eyes may signal more than simple irritation and could be an early warning sign of an autoimmune disease. This symptom has long been associated with Sjögren's Disease, a chronic autoimmune condition in which the immune system mistakenly attacks the tear ducts and salivary glands, causing inflammation that leads to dry eyes and dry mouth. Now, a study of 67,264 patients in Taiwan with autoimmune diseases found that dry eye disease (DED) preceded the autoimmune diagnosis by about three years.

Predictably, in Sjögren's Disease, the prevalence of diagnosis following the occurrence of DED exceeded 80%. Across nine other autoimmune conditions, rates consistently exceeded 20%, with rheumatoid arthritis ranking second highest at 39.3%, while Crohn's disease recorded the lowest rate at 23.0%.

DED provides a vital window of opportunity for doctors to perform earlier clinical evaluations for underlying autoimmune issues and plan effective treatment plans to deal with the symptoms. The findings are published in JAMA Network Open.

Greater awareness of DED as a potential early warning sign could encourage more people to seek evaluation, leading to earlier detection of underlying autoimmune disease when present, and if not, proceed with a general DED treatment plan.

Nan-Ni Chen et al, Epidemiology of Dry Eye in Patients With Autoimmune Disease, JAMA Network Open (2026). DOI: 10.1001/jamanetworkopen.2025.60275

Comment by Dr. Krishna Kumari Challa on Thursday

Urine tests confirm alcohol consumption in wild African chimpanzees

 If you want to measure the alcohol intake of chimps in a Ugandan rain forest, where a breath-analyzer is impractical, collecting urine for analysis is your only choice.

In 2025, researchers documented that the fruits chimps eat in the wild contain enough alcohol from fermentation to provide around 14 grams per day—the equivalent of two standard drinks. But the proof is in the urine.

So they collected the urine of Chimps to test. 

Their new results, published in the journal Biology Letters, show that the urine of most chimps sampled contains a metabolic by -product of alcohol, ethyl glucuronide, that proves they ingest significant quantities of ethanol in their diet—likely from those fermenting fruits.

Of the 20 urine samples from 19 different chimps (the Western chimpanzee, Pan troglodytes), 17 tested positive on commercial strips sensitive to 300 nanograms per milliliter (ng/ml) or more ethanol. Eleven samples were tested with strips sensitive to 500 ng/ml or more; 10 were positive (making a total of four out of 20 below the 500 ng/ml cutoff).

In humans, 500 ng/ml is a level expected after light drinking—one to two standard drinks—within the previous 24 hours. Similar levels would be expected in a chimpanzee that had spent the morning scarfing down slightly fermented fruit.

This confirms that the drunken monkey hypothesis—that there's enough alcohol in the environment for animals to experience alcohol in a way analogous to humans.

Urinary concentrations of a direct ethanol metabolite indicate substantial ingestion of fermenting fruit by chimpanzees, Biology Letters (2026). DOI: 10.1098/rsbl.2025.0740

Comment by Dr. Krishna Kumari Challa on Wednesday

Why our immune system remembers vaccinations for decades
Long-lived immunological memory after vaccination is maintained by memory T cells that enter an energy-saving, low-metabolic state early after activation. This metabolic restraint enables them to persist for decades and rapidly respond to future infections. The principle applies broadly, including to COVID-19 vaccination, and may inform improved vaccine design.

Sina Frischholz et al, Metabolic quiescence of naive-like memory T cells precedes and maintains antigen-specific T cell memory, Nature Immunology (2026). DOI: 10.1038/s41590-026-02421-w

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