, a wildlife biologist and filmmaker who contributed to "Tiger Island." Previously, it was thought that tiger moms raise their cubs for up to two years without any help from the male tiger.

But this may not be the norm.

"It just shows that we really know nothing about them," O'Neill told Live Science. "And they're so much more complex than people realize."

That's just one of the scenes in Tiger Island that challenges our understanding of the tigers' solitary nature. In another scene, a female tiger cares for another tigress's cubs.

"We have these very rigid ideas of how these animals live," O'Neill told Live Science. But the natural world is "diverse and ever-changing," and tigers are no exception, he said.

The footage of the female caring for another tiger's cubs could offer clues about how mother tigers protect their young. Male tigers, like male lions, sometimes kill cubs ‪—‬ a behavior known as infanticide ‪—‬ particularly when a new male takes over a territory. Allowing another female tiger to care for cubs might help more cubs survive to adulthood, O'Neill suggested. Previous observations of female tigers have shown females helping to co-parent each other's cubs, but it's a rare event.

To capture these scenes, the crew used drones with powerful optical-zoom lenses and quiet propellers to observe the tigers in places that were difficult to access without disturbing the big cats. Traditional camera traps often capture animals along trails, leaving much of their private lives unseen. O'Neill noted that the drone propellers were quieter than the local bees where the filming took place, thus giving the crew candid views of the tigers as they went about their lives.

Solitary animals in urban jungles

Though tigers (Panthera tigris) are solitary animals, they often live close to or share habitat with human communities. That means tigers sometimes attack people and kill livestock, O'Neill said. "It would be absolutely naive and wrong to suggest that they [attacks on people] don't happen," O'Neill said. As a result, conservation efforts must account for the circumstances in which people and big cats encounter one another, rather than treating human communities as separate from wildlife, he said.

The same issue affects other big cats. O'Neill, a researcher with the wild-cat conservation organization Panthera, has spent years studying jaguars, pumas and snow leopards. He said the popular image of these animals living in remote wilderness can obscure how closely they overlap with human lives.

For O'Neill, conservation requires more than studying the animals' behaviors or protecting their habitats. It also means helping people who bear the cost of living alongside these apex predators.

"Helping those people is how you help tiger conservation," he said.

In the U.S. "Tiger Island" Part Two airs on Wednesday, Oct. 28 at 12:30 am on the PBS channel.

Think you know about lions and tigers? Test your smarts with our big cat quiz!

'> Rare tiger behaviors captured on camera show 'we really know nothing about them'

Based on the small number of genomes from Gravettian people that were previously sequenced, experts believed that groups in Western Europe were largely separate from groups in Eastern Europe. But in a study published Oct. 23 in the journal Science Advances, researchers sequenced the genomes of three people who lived in what are now Spain, France and Italy during the Gravettian period. They discovered that one person had mixed genetic ancestry that revealed East-West exchange at least 30,000 years ago.

"Our results show that eastern and western European populations were not as genetically isolated as previously assumed," study first author Pere Gelabert, an evolutionary anthropologist at the University of Vienna, said in a statement.

The new information about mixed ancestry comes from a woman who died around 30,000 years ago and whose bones were found in Isturitz Cave in southwestern France. Originally used by Neanderthals, Isturitz Cave was occupied off and on from about 80,000 to 10,000 years ago. Cups made out of human skulls dated to roughly 15,000 to 12,000 years ago have also been found in Isturitz Cave.

Researchers found that the DNA from the Gravettian woman in Isturitz Cave was most similar to the previously known Western European genomes, but with an intriguing connection to Eastern and Central European groups.

This discovery of gene flow from the East is uncommon for the Late Stone Age, also known as the Upper Paleolithic, the researchers wrote in the study. It "could be explained by movements of people from Eastern Europe during the Gravettian period, which eventually contributed to this ancestry in Isturitz." Specifically, the researchers dated this "pulse" of gene flow to about 31,500 to 32,500 years ago.

The DNA evidence supports the archaeological theory that Isturitz Cave was an important cultural and biological hub for tens of thousands of years during the Late Stone Age, as the cave was located at a critical passage between continental Europe and the Iberian Peninsula, the researchers wrote.

All three newly sequenced Gravettian genomes revealed close biological connections to Western European groups, as well as genetic traits suggesting they had dark skin, dark hair and dark eyes. What's more, all of them had parents who weren't closely related to each other, suggesting that those populations may have actively avoided inbreeding.

"Overall, our results suggest that population structure and gene flow in western Europe during the Gravettian were more complex and dynamic than previously assumed," the researchers wrote.

See how much you know about early humans with our human evolution quiz!

'> 30,000-year-old bone found in French cave reveals vast genetic connections between people of Eastern and Western Europe during the Stone Age

When caught in infancy or early childhood, over 90% of HBV infections become chronic. About 15% to 25% of people with chronic HBV go on to develop liver scarring (cirrhosis), a form of liver cancer called hepatocellular carcinoma, or another chronic liver disease. So, an uptick in chronic HBV infections would translate to an uptick in these harmful liver conditions.

Increases in infection

"Not every pregnant person is tested for hepatitis B," said study co-author Dr. Amir Mohareb, an infectious-diseases physician-investigator at Massachusetts General Hospital and Harvard Medical School. For those who are tested, there's a chance their results are inaccurate or that they're not provided the right care after testing positive. "Something can be missed at any step in the care process, so the vaccine dose at birth provides protection," he said.

Mohareb and his colleagues built a simulation model using published data, including the current prevalence of HBV and the screening rate among pregnant people. The team also factored in the HBV test's sensitivity, the share of children who are fully vaccinated by age 2, and the risk of developing chronic HBV infection in different age groups. They made estimates of how often children are exposed to the virus through contact with infected household or community members.

HBV is "very, very transmissible," Mohareb said. It can spread from mother to child at birth or through exposure to tiny amounts of bodily fluids, like blood from a scratch, after birth. So, even if a baby does not get HBV from their mother, if they are unvaccinated, they can still get from another family member or from other children.

With this data, the researchers tested what would happen if vaccination were postponed to 2 months of age for babies whose mothers tested negative. Among babies born in 2026, 19% more would have chronic HBV infections by age 20, compared with universal birth-dose vaccination, they found.

In this scenario, the babies would still start the HBV vaccine series, albeit two months later than usual. However, the CDC's proposed recommendation offers more wiggle room; it says that parents should consult with their children's doctors to "decide when or if their child will begin the hepatitis B vaccine series" at all.

The researchers ran a stimulation to compare these two scenarios: one where kids get their first shot two months late and one intended to capture this looser "shared clinical decision-making" scenario.

"Other vaccines whose recommendations employ similar language had uptake as low as 25%," Mohareb noted. This aspect of their modeling has some uncertainty, he emphasized, since it's unknown exactly how the public will respond to such loosening of the guidance.

The researchers assumed that about 87% of kids would complete the vaccine series by age 2 under the deferred strategy, while only 50% would under the shared decision-making strategy. That 50% coverage, in turn, would increase chronic HBV infections acquired by age 20 by 83%, and about 50% and 70% of those born under that guidance would be susceptible to HBV infection at age 20.

That's about 1.8 million people in this age group per year, compared with fewer than 250,000 under universal birth-dose vaccination. "This represents a population that is at risk for acquiring HBV via sex, drug use etc — behaviors more prevalent among young adults," Terrault said.

A "missed opportunity to protect against infection"

To test the robustness of the findings, Mohareb's team varied the most uncertain inputs across wide ranges and ran the model 1,000 times. In every simulation, the birth-dose strategy led to fewer chronic infections than either alternative.

These conclusions seem "robust" because "they are the same conclusions no matter how we change the numbers of the model," Mohereb noted. Though of course "the specific magnitude of change depends on how many people defer vaccination," he said.

The new study does not specifically show how many additional cases of liver disease or cancer would result from the uptick in HBV infections. But Terrault said that the risks of liver failure, cirrhosis and liver cancer "would be anticipated to increase due to the missed opportunity to protect against infection."

Mohareb stressed that he is in no way opposed to the principle of shared decision-making between doctors and patients. "They should always make the decision together," he said. "But we rely on our public health agencies not to tell us that we should be making decisions with the patient, but rather to tell us what policy would make us healthier as a country."

Childhood HBV infections in the U.S. dropped from more than 25,000 cases a year in 1985 to fewer than 100 reported cases in 2024. This steep decline is credited to HBV screening during pregnancy, antibody treatment for babies born to HBV-positive mothers and universal birth-dose vaccination.

"Certainly without following a universal dose vaccination recommendation there would be a lot more hep B infections early in life," Dr. Brian McMahon, a hepatologist and the director of the Liver Disease and Hepatitis Program at the Alaska Native Medical Center, told Live Science in an email.

This article is for informational purposes only and is not meant to offer medical advice.

'> Hepatitis B could surge, infecting millions more in childhood, under proposed CDC guidance Alexander Ioannidis, a computational geneticist at Stanford University, told Live Science. "Each genome encodes an enormous number of ancestors. So with even a few individuals, we can get information about an enormous number of people from each island."

Specifically, the scientists compared the length of chromosomal segments shared among people from different islands. The longer these shared segments are between two people, the more recently they shared a common ancestor.

Even though Hawaii and Easter Island are far-flung, the researchers discovered that the Indigenous people of Hawaii and Rapa Nui are the most genetically related to one another. The team reported its findings Oct. 8 in the journal Science.

"This was really shocking at first — these islands are so distant from one another," Ioannidis said.

The scientists found that Hawaii and Easter Island were likely both settled by members of a single "ultravoyager" culture from the Mangareva islands, about 3,440 miles (5,530 km) southeast of Hawaii and 1,600 miles (2,600 km) west of Easter Island. (In 2020, the researchers found that members of this ultravoyaging group had mixed with Indigenous people in what is now Colombia, although it's unclear if this partnering occurred on an island or on the continent.)

"Once you know there was this extremely capable long-distance ultravoyaging culture capable of reaching one of these islands, having it reach the other makes more sense," Ioannidis said.

The area near Mangareva, including the Austral Islands, the Society Islands, the Marquesas Islands, and the Tuamotu Archipelago, "spans an area the size of Europe," Ioannidis said. "Sailing in-between these islands would have required skilled navigation. So it makes sense that developing such long-distance navigation skills would have ultimately helped people settle far-off Easter Island and Hawaii."

All in all, these genetic findings suggest the ancestors of Native Hawaiians and Easter Islanders shared some time together as a common group after splitting away from the population of ancient Mangareva. Some members of this group then went on to settle Hawaii, and others from this Mangareva group voyaged to Easter Island.

This new genetic data linking Hawaii, Easter Island and Mangareva "agrees very well with what we see archaeologically," Patrick Kirch, an archaeologist at the University of Hawai'i at Manoa who did not take part in this research, told Live Science. "It gives scientists a lot of confidence when independent lines of evidence from different disciplines give similar results."

Founder effect

The researchers also investigated the effects of genetic bottlenecks that resulted when these islands were settled by small numbers of people — phenomena known as "founder effects."

"If you have a rare genetic trait that happens to occur in this small number of individuals, if this small population grows rapidly, this trait can go on to show up in a high percentage of the resulting population," Ioannidis said. "So if a rare genetic variant once only affected a few people, it can start affecting a decent number of individuals."

The scientists found that Native Polynesian populations examined in the study often experienced a compounding set of founder effects over time. This is because islands settled by a few people then went on to send out small groups to settle other islands, and so on.

Previous research has looked at the founder effects in groups of European descent, such as the Amish, Finns and Ashkenazi Jews, resulting in standard screenings for certain genetic conditions in these groups.

The new study revealed that an even stronger founder effect has been overlooked among Native Hawaiians, with founder effects more than 10 times larger than in those European groups.

"The founder effect doesn't just reflect genetic diversity, but also cultural and linguistic diversity," Kirch said. "It probably helps explain why the cultures of eastern Polynesia all share a lot in common — they all trace to one central group."

These findings not only shed light on Polynesians' past, but also their current health. The researchers found that three genetic variants that are exceedingly rare among the global population — linked with dislocated lenses in the eyes, progressive vision loss, and kidney failure — are carried by 2 to 3% of the eastern Polynesians they studied.

"There should be a lot more resources going into learning more about gene variants of potential clinical significance among this population of Native Hawaiians, which is twice as large as the U.S. Amish population," Ioannidis said. "There are really opportunities for precision health here."

'> Native Hawaiians and Easter Islanders came from same 'ultravoyager' group