Over the millennia, animals have gone extinct on Earth for many different reasons. Sometimes it's because of a dramatic shift in the climate. Other times it was because of human intervention. 

Advances in science, specifically biotechnology, could enable scientists to bring some of these animals "back" from extinction, and there are a few already on the list. 

Generally, it helps if there is a species still alive today that is genetically similar to the extinct animal, like elephants for woolly mammoths or cows for aurochs. 

There are also certain criteria to consider, as bringing an animal back from the grave has a lot of biological and ecological implications.

Scientists must be able to show that the species is desirable, such as having an important ecological function or being beloved by humans. And they also must consider practical matters, such as whether we have access to tissue that could give us good quality DNA samples. Most importantly, though, the animals must also be able to be reintroduced into the wild in the first place, so sufficient habitats, food, and limited contact with humans are pretty important.

Unfortunately, dinosaurs score badly on all of these points, so there probably isn't ever going to be a real Jurassic Park. However, plenty of animals are still on the table.

Here are some of them from the list of candidate species for de-extinction from The Long Now Foundation, which was founded by biologist and writer Stewart Brand, plus some others added from our own research.

Jennifer Welsh contributed reporting on a previous version of this article.

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During their prime, Caspian tigers could be found in Turkey and through much of Central Asia, including Iran and Iraq, and in Northwestern China as well, but they went extinct in the 1960s. Some scientists want to bring them back by reintroducing the nearly-identical Siberian tiger to its old habitats, where they expect it to adapt.

The aurochs is an ancestor of domestic cattle that lived throughout Europe, Asia, and North Africa. Scientists want to bring them back through selective breeding of cattle species that carry some aurochs DNA. To this end, European science teams have been selectively breeding cattle since 2009.

The Carolina Parakeet was a small, green parrot with a bright yellow head and orange face that was native to the eastern United States. The last wild one died in 1904 in Florida, but the genes that made them still linger in close relatives in Mexico and the Caribbean.

As the human lifespan grows longer, the Earth becomes more crowded. Worst case scenario estimates that as many as 11 billion people could be alive by 2100. Here's what that reality could look like.

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A caterpillar recently discovered in Peru behaves unlike any other known caterpillar. 

The critter was spotted by Dr. Joe Hanson, the creator and host of the YouTube channel "It's OK to be Smart." Hanson, along with entomologist Aaron Pomerantz and guide Pedro Lima, were filming in the Peruvian Amazon when they came across the creature.

According to Hanson, this is the first known example of a caterpillar building itself a mobile shelter, which is why it has earned the name of the hermit caterpillar. 

While they were filming, the team noticed that leaf litter on the rainforest floor was moving. Upon closer inspection, they realized a big, fat caterpillar was inside, dragging along a home it had built out of leaves.

Caterpillars are masters of disguise, but this one was something special. When Hanson picked it up, it retreated inside its protective tube. If they hadn't seen it moving, they probably would have walked straight past.

The caterpillar had cut and glued itself a custom suit of camouflage leaf armor, which it drags behind itself like a caterpillar version of a hermit crab. The only difference is hermit crabs move into homes another animal has left behind whereas this caterpillar made its own from scratch.

Otters are one of the best animals on Earth. They're playful creatures that climb and slide down hills and wrestle with each other, they float on their backs and hold paws, and they use stones to bash open food like clams and mussels.

They're quite small creatures, but new research has shown this might not always have been the case.

There are 13 species of otter today of different sizes, and they live in various habitats; some in salt water and some in rivers. The largest of them all is the giant otter, which lives in South America and weighs up to 32 kg. 

However, researchers have uncovered fossils that show that the biggest ever otter was much larger than that. 

A new paper, published this week in the Journal of Systematic Palaeontology, explains how the scientists came to the conclusions about what this prehistoric otter looked like, which they called Siamogale melilutra, because of similarities both otters (lutra) and badgers (melis.) They examined limb bones and skull remains that were taken from carbon-rich rocks about a decade ago.

The skull was pretty crushed though, so the team used a CT scans to work out what the skull would have looked like, and a sophisticated computer program to digitally reconstruct it from 200 fragments.

They found that Siamogale melilutra's skull was 8 inches long. From this information they concluded the creature likely weighed around 50kg, which is about the size of a wolf, and roughly twice the size of today's giant otter. Carbon dating shows they lived around 6.2 million years ago in humid swamps which are now the Yunnan province in China.

Surprisingly, when the researchers looked at the shape of Siamogale melilutra's teeth, they concluded that they had evolved that way at least 3 separate times. So rather than all otters sharing a common ancestor, this prehistoric otter probably evolved along its own line, which is known as convergent evolution.

"The discovery of the otter helps solve some questions about otter relationships, but has opened the door to new questions," said Dr. Xiaoming Wang, Curator and Head of Vertebrate Palaeontology at the Natural History Museum of Los Angeles County and lead author of the paper, in a statement. "For instance, why was it so large, how did it crack open mollusks and shellfish for food, and how did it move in the water and on land?"

The team hope to fill in more pieces of the puzzle of the otter's prehistoric family tree with further research. 

SEE ALSO: A brand-new species called the hermit crab caterpillar makes its own armor out of leaves

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The remains of a mummified Copper Age man were discovered in a glacier in the Ötztal Alps in 1991 by two German hikers. Scientists named him Ötzi the Iceman because he was so well preserved in the ice, and he's revealed a lot about the similarities of people today and those who lived 5,300 years ago.

New research suggests that we may even have had one of the most popular favorite foods in common: bacon. 

Ötzi remains fascinating to researchers over 20 years later. His DNA was kept pretty stable in the ice, so scientists have been able to code his whole genome, and different things about his life are still being uncovered.

Teams have been able to determine that Ötzi died when he was 40 to 50 years old, and not only that, he was murdered. They've also worked out what he may have worn and what his voice may have sounded like. 

A new study, led mummy specialist from the European Academy of Bolzano Dr Albert Zink, has taken a closer look at Ötzi's stomach contents, which were first investigated in 2011. 

Back then, researchers determined that Ötzi's last meal consisted of goat meat and some grains, but on further inspection, Zink was able to uncover some more intriguing details. He analyzed the nanostructure of the meat fibers, which indicated that the meat had been dry-cured, rather than cooked or grilled, which would have weakened the fibers, reports the Local.

Ötzi was not found with a bow and arrow, so it is unlikely that he was out hunting when he died. Zink told the Local he probably brought the meat with him from home, like a packed lunch. Raw meat would probably have spoiled pretty quickly, so it makes sense that it would have been cured. 

The analysis also showed that Ötzi hadn't eaten any cheese or dairy products as his last meal.

"It seems probable that his last meal was very fatty, dried meat — perhaps a type of Stone Age Speck or bacon," Zink said.

As well as details about his diet, Ötzi's stomach contained the oldest known Helicobacter pylori bacterium, according to a study published last year in the journal Science. This pathogen has been linked to the development of ulcers and gastric cancer, meaning Ötzi's may have suffered from ulcers or stomach problems.

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After years of trial and error, scientists have finally done something incredible: They have successfully grown human stem cells in a pig embryo. Why would anyone do this?

Turns out, many scientists have been working on growing the organs of one animal inside of a different type of animal. For example, scientists recently reported the successfully growth of mouse pancreases inside of rats. 

The ultimate goal of this type of work is to grow human organs inside of other animals as a means to ending the organ shortage that is costing thousands of Americans — who need a transplant — their lives each year.

Now, using similar methods as the mouse-rat hybrid, scientists have produced the first human-pig hybrid embryo, which is more difficult than you might think. Getting cells from one species to survive in an entirely different species is extremely difficult and has eluded scientists for years. 

Even now, this breakthrough is preliminary. Only about one out of every 100,000 cells in the hybrid embryos was human. If the scientists had grown the embryos to maturity (which they did not), the organs would probably not have enough human cells in them for a human body to recognize. The result, would be the human body rejecting the organ and potentially killing the patient.

This is why more research is critical to pursue this research further, improving the techniques, and hopefully, one day, paving the way for the first human transplant with a human-pig hybrid organ. But that day is years, possibly decades, down the road.

The group of scientists published their work on Thursday, Jan. 26, in the prestigious science journal Cell.

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Dr. Bat Sheva Marcus, the sexual dysfunction specialist and clinical director of The Medical Center For Female Sexuality, explains that a "sex schedule" is good for your relationship, and most happy couples have one (perhaps without realizing it). 

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On Sunday the team at Shedd Aquarium in Chicago had a tough decision to make.

Granddad the lungfish, who had lived at the aquarium since 1933 and was the oldest captive fish in the world, was in a state of rapidly declining health. Eventually, the team decided it was time to say goodbye.

According to the aquarium's website, Granddad was not just the oldest living resident there, but also the oldest fish in any public zoo or aquarium in the world, being in his mid-90s. In his final days, Granddad stopped eating and showed signs of organ failure, so the team decided the most humane thing to do was euthanize him.

President and CEO of the aquarium Dr Bridget Coughlin said in a statement: "It is incredible to know that more than 104 million guests had the opportunity to see Granddad in our care and learn about his unique species over eight decades," and that Granddad "sparked curiosity, excitement and wonder among guests of all ages."

Granddad apparently led an easy-going life, just as lungfish tend to do in the wild in their native Australia. They like to live in deep pools with free-slowing waters, but they get their name from possessing a primitive lung as well as gills, which means they can survive in stagnant water. However, they can't survive by breathing air alone.

In the wild, lungfish can live over 100 years. In Australia, they are a protected species. The fish have been around for nearly 400 million years, and fossils have shown they haven't changed much in over 100 million years.

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Genetic data collected from roughly 770,000 tubes of spit are helping researchers get a better idea of the migration patterns that took place once immigrants moved to North America. 

Published Tuesday in Nature Communications, the study used Ancestry's DNA test along with information users provided about their family trees to find more than 60 different genetic communities that sprang up in the US from the 1800s to the 1900s.

Before this point, we had a good idea of what pre-colonial migration patterns looked like from a genetic perspective, but once European settlers got into the mix, things got a bit more complicated.

But this report changes things. "Because we have so much more genetic data than ever before, and we have all these supporting family trees showing where they came from, we are able to not only able to come up with the structure of North America, we are able to annotate that structure with the people they’re descended from," Cathy Ball, chief scientific officer at Ancestry, told Business Insider.

Ancestry conducted the research alongside a history professor from Harvard. This helped the team corroborate historical observations in a way they hadn't been able to before with genetics. 

"It's an unprecedented use of the two datasets," Jake Byrnes, one of the study's authors and a manager of population genetics at AncestryDNA, told Business Insider.

One of the most notable findings was that the genetic communities were the same from Maine to Louisiana. Historically, that shift happened when the Acadians, descendants of French colonists, moved to Louisiana — another French colony — following the French and Indian War. 

Here are two maps of those groups, plotted out in clusters. (These show what the groups looked like around the 1850s to 1900s, not what they'd look like today.)

Something that surprised the researchers is the amount of structure there was at that time — with pretty clear clusters of Scandinavians up in the Midwest sticking together even after immigrating to the US.

Ancestry plans to integrate the results of the study into its test results, Ball said. That's expected to launch sometime this spring. 

SEE ALSO: I shipped my spit to AncestryDNA to see how much I could learn from my genes — and found out my family history is more complex than I thought

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More than 700 mammals and birds currently threatened with extinction already appear to have been adversely affected by climate change, according to a major review of scientific studies.

Primates and marsupials are believed to have the most individual species suffering as a result of global warming, according to a paper in the journal Nature Climate Change.

Only two groups of mammals, rodents and insect-eaters, are thought to have benefited. This is partly because they have fast breeding rates, tend not to be specialists suited to a particular habitat, and often live in burrows which provide insulation against changes in the weather.

The figures are much higher than previously thought, making up 47 per cent of land mammals and 23 per cent of the birds on the International Union for Conservation of Nature's Red List of species threatened with extinction.

According to the list itself, just seven per cent of the mammals and four per cent of the birds are described as being threatened by "climate change and severe weather".

The researchers developed a model to compare the animals' weight and other characteristics with changes in the climate, such as the temperature.

"Using this model, we estimated that 47 per cent of terrestrial [non-flying] threatened mammals (out of 873 species) and 23.4 per cent of threatened birds (out of 1,272 species) may have already been negatively impacted by climate change in at least part of their distribution," the article in Nature Climate Change said.

"Our results suggest that populations of large numbers of threatened species are likely to be already affected by climate change, and that conservation managers, planners and policy makers must take this into account in efforts to safeguard the future of biodiversity."

Primates and marsupials are more at risk than other animals partly because they have lived mostly in tropical parts of the world which have had a stable climate for thousands of years.

"Many of these [animals] have evolved to live within restricted environmental tolerances and are likely to be most affected by rapid changes and extreme events," the paper added.

"In addition, primates and elephants are characterised by very slow reproductive rates that reduce their ability to adapt to rapid changes in environmental conditions."

One reason why climate change is causing a problem for animals is changes in the distribution of plants.

"In areas with reduced precipitation and/or temperature seasonality, it is likely that plant species may have narrower climatic tolerances, and therefore that these areas may have already experienced vegetation changes with consequential loss of habitat for animals living there," the paper said.

"A more specialised diet was also associated with greater probability of negative responses in mammals.

"Our findings are in agreement with previous studies on the predictors of general extinction risk, in which species with narrower diet breadths were associated with lower ability to exploit resources and adapt to new environmental conditions and selective pressures."

Birds living in the world's cold mountain regions appear to be particularly at risk.

"Populations of species living at high altitudes and in colder places have fewer opportunities to move towards cooler areas or upslope to avoid increasing temperatures, and hence may have increased extinction risk," the paper said.

Another problem is that higher temperatures are inducing birds to lay eggs earlier.

"For animals living in these environments the effects of temperature changes may have been exacerbated, potentially leading to disruption in synchronisation between the timing of chick-feeding and peak food availability," the paper said.

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Hold your hand in front of you, palm up and fingers splayed.

Now bend your fingers at their first joint past the knuckles. Your hand should look a bit like a spider on its back, curling up its legs — that's your proximal interphalangeal joints (PIJs) bending.

Let your hand splay out again. This time, curl just your pointer finger and let it uncurl. Now do your ring finger.

What do you think is going on here? If you had to guess, where would you say the muscle involved is?

Having never taken a medical anatomy course, I'd always assumed it was located entirely in the finger itself, just like the main muscles for flexing your elbow live in your upper arm.

Turns out, this intuition is wrong. The main muscle for flexing your PIJs actually runs all the way up your arm. Called the flexor digitorum superficialis, it bends your fingers by contracting and bending them back toward itself.

This video (of unknown origin) which we saw Tweeted by the account How Things Work, illustrates the effect using a cadaver limb:

I can't stop staring at it.

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A team of scientists from Harvard has said it might soon be able to create a hybrid elephant and woolly mammoth by combining the two animals' DNA using the gene-editing technology Crispr.

At the American Association for the Advancement of Science annual meeting in Boston this week, the team introduced its idea for "an elephant with a number of mammoth traits," which it believes could become a reality in the next two years.

Scientists have wanted to bring back woolly mammoths for a long time. The reason they went extinct in the first place is a subject of much debate— nobody really knows whether humans were to blame. Either way, they're a firm favorite for de-extinction, and researchers now believe mammoths could be roaming around in just a few years.

This "mammophant" would have features of a mammoth such as long, shaggy hair and adaptations to the cold like subcutaneous fat and specially adapted blood.

The project started in 2015, and since then the team has been able to add more and more edits into elephant DNA.

"We're working on ways to evaluate the impact of all these edits and basically trying to establish embryogenesis in the lab," the leader of the research team, professor George Church, said, according to The Guardian.

While reintroducing mammoths is a passion project for some, and there's an argument it could help preserve the endangered Asian elephant in a hybrid form, others aren't so sure.

Mark Carnall, the Life Collections manager at the Oxford University Museum of Natural History, tweeted his concerns:

Many, including Carnall, think the ethical and ecological implications of bringing back major species have not been fully thought through. For example, mammoths were social animals like elephants, but there's no way of knowing how a herd of elephants would welcome a mammophant.

There's also the possibility they could destroy native species and disrupt the ecosystem in ways that haven't been considered. The reasons behind bringing them back are shaky too, considering mammoths haven't been around for 4,500 years after being killed off by climate change or hunting. Questions surround whether such an animal will be an asset to the environment or whether it is being reintroduced just a means of clearing our conscience.

But this hasn't deterred the Harvard team, who hope to eventually grow the hybrid embryo within an artificial womb, and think that technology to do so will be ready within 10 years. The de-extinction of these animals is more possible than ever before thanks to sophisticated gene editing techniques like Crispr. It's also made easier by the fact mammoth DNA has been unusually well preserved because specimens have been frozen in Siberian ice for thousands of years.

SEE ALSO: Some of the scientists aiming to 'bring back' the woolly mammoth originally wanted to do it using 40,000-year-old cells

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Sometime not necessarily too far from now, the first humans whose DNA has been intentionally edited by scientists could very likely be born.

The technologies that make that theoretically possible have existed for some time now and in the past few years, new discoveries have made genetic editing tools far simpler, cheaper, and more accurate — though they still aren't precise enough to use safely on human embryos that will be carried to term.

Still, that reality is close enough that the scientists who work closely with these tools have said that guidelines for this research are urgently needed. And on February 14, the National Academy of Sciences and the National Academy of Medicine issued a report that outlines the circumstances under which research into editing human embryos could be permitted.

"Although heritable germline genome editing trials must be approached with caution ... caution does not mean prohibition," the National Academy committee said in a statement.

That's a big statement. Right now, the US Food and Drug Administration (FDA) prohibits any research that would include germline genome editing; a number of other countries also prohibit similar research.

These groups are hesitant because "heritable germline genome editing" is a world-changing sort of thing. It means that researchers would go into the unique genetic blueprint for a person before they are born and make changes and substitutions, snipping out code for traits they don't want and potentially replacing them with something else. Then, all of these changes would be passed on if that person had children, meaning that we'd have introduced manually edited genes into the wild. 

The National Academies panel convened to assess this is concluding that under certain circumstances, that may be okay.

Still, even if the panel thinks that research and trials into human genome editing should go forward, the cases for which they think this should be permitted are very limited, for now at least.

The sorts of changes we might see

After evaluating the issue for a year, the National Academies panel concluded that clinical trials involving inheritable changes to the genome could be allowed, so long as they treat or prevent genetic diseases that we have no other way of dealing with.

This could make a huge difference for the cases where it's basically a certainty that parents will pass a devastating disease on to a child. Specific diseases that might fit this category include the blood disorder beta thalassemia, cystic fibrosis, and sickle-cell anemia. But those cases are very rare.

Perhaps more interestingly, the researchers leave open the possibility of using genetic editing to remove or replace mutations that make people susceptible to other diseases. They mention mutations of BRCA1 and BRCA2, which can increase risks for breast and ovarian cancers. Edits like that could help remove mutations that make people more likely to get many forms of cancer, Alzheimer's disease, and other conditions. This could have a far-rippling effect on human health in the long run.

If we get to the point that it's possible to safely and completely remove these sorts of dangerous mutations, the conclusion the panel arrived at may allow for edits that prevent disease in this way. They don't think this would be the same as making "enhancements," which they say should not be allowed at this time, though they call for public discussion of those possibilities.

Still, there are obstacles to overcome before this happens. For now it's hard to apply a genetic editing tool (like CRISPR) to an early embryo and have it make all the changes to a genome that you want (and no unwanted extra changes). When you let that editing tool loose it seeks out the segments of DNA you are targeting to eliminate or replace, but it may miss some of those segments or accidentally cut something else. These tools are becoming more and more accurate, but they aren't good enough that scientists would feel comfortable implanting an edited embryo yet.

Even once those tools are perfected, the panel is saying a go-ahead with trials seems permissible. It is not recommending that this technology should immediately go into wide use. Plus, the FDA would have to allow these sorts of procedures for this to happen in the US and it's unclear if that will happen anytime in the near future. 

The basic implication of this is clear though. We know that these tools are improving and we're using them more and more. In some places, like Sweden, the UK, and China, researchers have already started editing (or have received permission to edit) embryos — some viable, some not, but none that they plan to implant yet. All of this will further improve the accuracy of these tools, to the point it may at some point be possible to make all the changes to a genome that we want with no unwanted side effects.

Once that's done, the first "designed" babies could — or will — be born. If all goes well and these guidelines are followed, they'll be healthier and free of a disease that could or would have been devastating.

The question that many have is whether we'll see edits that happen for other purposes, to make babies smarter or stronger, not just healthier. The research the committee wants to allow wouldn't permit those sorts of changes. But it would prove that they are indeed possible.

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NOW WATCH: NASA can't explain these giant 8,000-year-old formations in Kazakhstan

Strange microbes have been found inside the massive, subterranean crystals of Mexico's Naica Mine, and researchers suspect they've been living there for up to 50,000 years.

The ancient creatures appear to have been dormant for thousands of years, surviving in tiny pockets of liquid within the crystal structures. Now, scientists have managed to extract them — and wake them up.

"These organisms are so extraordinary," astrobiologist Penelope Boston, director of the NASA Astrobiology Institute, said on Friday at the annual meeting of the American Association for the Advancement of Science (AAAS) in Boston.

The Cave of Crystals in Mexico's Naica Mine might look incredibly beautiful, but it's one of the most inhospitable places on Earth, with temperatures ranging from 45 to 65°C (113 to 149°F), and humidity levels hitting more than 99 percent.

Not only are temperatures hellishly high, but the environment is also oppressively acidic, and confined to pitch-black darkness some 300 metres (1,000 feet) below the surface.

In lieu of any sunlight, microbes inside the cave can't photosynthesise — instead, they perform chemosynthesis using minerals like iron and sulphur in the giant gypsum crystals, some of which stretch 11 metres (36 feet) long, and have been dated to half a million years old.

Researchers have previously found life living inside the walls of the cavern and nearby the crystals — a 2013 expedition to Naica reported the discovery of creatures thriving in the hot, saline springs of the complex cave system.

But when Boston and her team extracted liquid from the tiny gaps inside the crystals and sent them off to be analysed, they realised that not only was there life inside, but it was unlike anything they'd seen in the scientific record.

They suspect the creatures had been living inside their crystal castles for somewhere between 10,000 and 50,000 years, and while their bodies had mostly shut down, they were still very much alive.

"Other people have made longer-term claims for the antiquity of organisms that were still alive, but in this case these organisms are all very extraordinary — they are not very closely related to anything in the known genetic databases,"Boston told Jonathan Amos at BBC News.

What's perhaps most extraordinary about the find is that the researchers were able to 'revive' some of the microbes, and grow cultures from them in the lab.

"Much to my surprise we got things to grow,"Boston told Sarah Knapton at The Telegraph."It was laborious. We lost some of them — that's just the game. They've got needs we can't fulfil."

At this point, we should be clear that the discovery has yet to be published in a peer-reviewed journal, so until other scientists have had a chance to examine the methodology and findings, we can't consider the discovery be definitive just yet.

The team will also need to convince the scientific community that the findings aren't the result of contamination — these microbes are invisible to the naked eye, which means it's possible that they attached themselves to the drilling equipment and made it look like they came from inside the crystals.

"I think that the presence of microbes trapped within fluid inclusions in Naica crystals is in principle possible," Purificación López-García from the French National Centre for Scientific Research, who was part of the 2013 study that found life in the cave springs, told National Geographic.

"[But] contamination during drilling with microorganisms attached to the surface of these crystals or living in tiny fractures constitutes a very serious risk,"she says. I am very skeptical about the veracity of this finding until I see the evidence."

That said, microbiologist Brent Christner from the University of Florida in Gainesville, who was also not involved in the research, thinks the claim isn't as far-fetched as López-García is making it out to be, based on what previous studies have managed with similarly ancient microbes.

"[R]eviving microbes from samples of 10,000 to 50,000 years is not that outlandish based on previous reports of microbial resuscitations in geological materials hundreds of thousands to millions of years old,"he told National Geographic.

For their part, Boston and her team say they took every precaution to make sure their gear was sterilised, and cite the fact that the creatures they found inside the crystals were similar, but not identical to those living elsewhere in the cave as evidence to support their claims.

"We have also done genetic work and cultured the cave organisms that are alive now and exposed, and we see that some of those microbes are similar but not identical to those in the fluid inclusions,"she said.

Only time will tell if the results will bear out once they're published for all to see, but if they are confirmed, it's just further proof of the incredible hardiness of life on Earth, and points to what's possible out there in the extreme conditions of space.

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Octopuses are some of the most alien-looking creatures on the planet. With eight arms, over 1,000 suckers, and three hearts, they are unlike any other animal you could ever hope to meet.

What's more, they're smart — really smart. About 95% of the animals on Earth are invertebrates and guess who's the smartest of them all: the octopus!

To better acquaint you with this creature of the sea, we've compiled 10 of the most mind-blowing facts that we learned while reading Katherine Harmon Courage book, "Octopus!" Check them out, be amazed, and tell a friend!

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During the approximately 40 weeks of pregnancy, a woman's body undergoes some significant changes.

As the fetus grows, it occupies more and more space inside the mother. This is the cause of the obvious pregnancy bump, but just expanding outward isn't enough — her internal organs are also put under a significant amount of pressure, which can cause some discomfort.

That movement can also be pretty dramatic to look at. In the GIF below, which we spotted when it was recently tweeted out by the UK publication Scienmag, you can see those nine months of change sped up to just a few seconds.

The GIF is from an ongoing exhibit at Chicago's Museum of Science + Industry which shows the "impact of a pregnancy on a mother's body as she adjusts physically and mentally to the changes inside her."

If you go to the museum's website, you can actually play with an interactive slider that shows what's happening throughout pregnancy. During weeks 29 through 32, for example, they note that organs are being squeezed.

In the YouTube video below, you can see a slower version of the interactive, beginning near the start of pregnancy and going through birth.

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A pair of bacterial genes may enable genetic engineering strategies for curbing populations of virus-transmitting mosquitoes.

Bacteria that make the insects effectively sterile have been used to reduce mosquito populations. Now, two research teams have identified genes in those bacteria that may be responsible for the sterility, the groups report online February 27 in Nature and Nature Microbiology.

"I think it's a great advance," says Scott O'Neill, a biologist with the Institute of Vector-Borne Disease at Monash University in Melbourne, Australia. People have been trying for years to understand how the bacteria manipulate insects, he says.

Wolbachia bacteria "sterilize" male mosquitoes through a mechanism called cytoplasmic incompatibility, which affects sperm and eggs. When an infected male breeds with an uninfected female, his modified sperm kill the eggs after fertilization. When he mates with a likewise infected female, however, her eggs remove the sperm modification and develop normally.

Researchers from Vanderbilt University in Nashville pinpointed a pair of genes, called cifA and cifB, connected to the sterility mechanism of Wolbachia. The genes are located not in the DNA of the bacterium itself, but in a virus embedded in its chromosome.

When the researchers took two genes from the Wolbachia strain found in fruit flies and inserted the pair into uninfected male Drosophila melanogaster, the flies could no longer reproduce with healthy females, says Seth Bordenstein, a coauthor of the study published in Nature. But modified uninfected male flies could successfully reproduce with Wolbachia-infected females, perfectly mimicking how the sterility mechanism functions naturally.

The ability of infected females to "rescue" the modified sperm reminded researchers at the Yale School of Medicine of an antidote's reaction to a toxin.

They theorized that the gene pair consisted of a toxin gene, cidB, and an antidote gene, cidA. The researchers inserted the toxin gene into yeast, activated it, and saw that the yeast was killed. But when both genes were present and active, the yeast survived, says Mark Hochstrasser, a coauthor of the study in Nature Microbiology.

Hochstrasser's team also created transgenic flies, but used the strain of Wolbachia that infects common Culex pipiens mosquitoes.

Inserting the two genes into males could be used to control populations of Aedes aegypti mosquitoes, which can carry diseases such as Zika and dengue.

The sterility effect from Wolbachia doesn't always kill 100 percent of the eggs, says Bordenstein. Adding additional pairs of the genes to the bacteria could make the sterilization more potent, creating a "super Wolbachia."

You could also avoid infecting the mosquitoes altogether, says Bordenstein. By inserting the two genes into uninfected males and releasing them into populations of wild mosquitoes, you could "essentially crash the population," he says.

Hochstrasser notes that the second method is safer in case Wolbachia have any long-term negative effects.

O'Neill, who directs a research program called Eliminate Dengue that releases Wolbachia-infected mosquitoes, cautions against mosquito population control through genetic engineering because of public concerns about the technology. "We think it's better that we focus on a natural alternative," he says.

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The evolution of penguins is a bit of a puzzle for scientists. Did their ancestors fly or were they always confined to land and sea?

More importantly, were they always the size they are now?

Scientists from New Zealand and Senckenberg finally have some answers, thanks to their recent discovery of a fossil belonging to a giant, 150-centimeter long penguin. The fossil dates pack to the Paleocene era approximately 61 million years ago, making it one of the oldest penguin fossils in the world.

According to a new study which the scientists published in the journal The Science of Nature, these newly discovered bones differ significantly from other discoveries of the same age, which means early penguins were probably much more diverse than scientists previously thought. And their evolution likely began much earlier than previous research has suggested — maybe even as early as the dinosaur age, the scientists conclude.

Where this fits in with what we knew about penguins

Some genetic analysis has shown that the Spheniscidae family, which present penguins belong to, evolved from flightless birds that lived 40-100 million years ago. Other scientists believe their earliest ancestors may have been birds that lived during the Cretaceous period 60-65 million years ago and were able to fly. 

"What sets this fossil apart are the obvious differences compared to the previously known penguin remains from this period of geological history," said Dr Gerald Mayr, an ornithologist at Senckenberg Research Institute in Frankfurt and lead author of the study, in a statement. "The leg bones we examined show that during its lifetime, the newly described penguin was significantly larger than its already described relatives."

In other words, penguins reached a giant size quite early in their evolution. This size increase appears to have started soon after they became flightless, according to the paper, with giant species existing for at least 30 million years, from the mid-Paleocene to the late Oligocene period.

The penguin is almost as big as the largest-known penguin fossil which belonged to Anthropornis nordenskjoeldi. Nordenskjoeldi is thought to have lived in Antarctica about 45-33 million years ago, and reached enormous heights of 180 centimeters. For comparison, Emperor penguins are the tallest current living species of penguin, and they grow up to 122 centimeters.

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Somewhere in Martin Matzuk’s collection of two billion chemicals, he hopes, is one that might safely make a man temporarily sterile—the elusive “male pill.”

Right now, male contraception means a condom or a vasectomy. But Matzuk, who is director of the Center for Drug Discovery at Baylor College of Medicine, is among a handful of scientists who are renewing the search for a better option—an easy-to-take pill that’s safe, fast-acting, and reversible.

Big drug companies long ago dropped out of the search for a male contraceptive able to chemically intercept millions of sperm before they reach a woman’s egg. But Matzuk’s lab shares in $600,000 worth of awards that the Bill and Melinda Gates Foundation gave out last year to “test the feasibility” of “disruptive and high-risk approaches” to male birth control.

That sum is pocket change next to the $147.9 million the same foundation spent in 2015 on family planning efforts aimed at women—efforts that it says reduce poverty.

That sum is pocket change next to the $147.9 million the same foundation spent in 2015 on family planning efforts aimed at women—efforts that it says reduce poverty.

Scientists like Matzuk also think excessive population growth is a cause of scarcity and environmental degradation. “We just can’t sustain the population at the rate we’re going,” he says. A male pill could reduce the number of unintended pregnancies, which by one account make up 40 percent of all pregnancies worldwide.

“Right now the chemical burden for contraception relies solely on the female. That’s an unfair balance in the equation,” says Charles Easley, an assistant professor at the University of Georgia, who is also involved in the Gates-backed hunt for a male pill. “I think there’s not much activity in this field because we have an effective solution on the female side.”

To restart the search for a pill, Matzuk is beginning with lists of genes active in the testes and then creating mice that lack those genes. To do that, he’s working with researchers in Japan to use the gene-editing technology called CRISPR to snip out the genes one by one. Matzuk has so far made more than 75 of these “knockout” mice and says CRISPR makes the work much faster than it would be otherwise.

These mice are allowed to mate, and if their female partners don't get pregnant after three to six months, it means the gene might be a target for a contraceptive. Of 2,300 genes that are particularly active in the testes of mice, Matzuk has zeroed in on 30. His next step, he says, will be a novel screening approach to test whether any of about two billion chemicals can disable these genes in a test tube. Promising chemicals could then be fed to male mice to see if they cause infertility.

Female birth control pills use hormones to inhibit a woman’s ovaries from releasing eggs. But hormones have side effects like weight gain, mood changes, and headaches. A trial of one male contraceptive hormone was stopped early in 2011 after one participant committed suicide and others reported depression. And there’s another reason testing potential contraceptive drugs in male volunteers is tricky: some drug candidates have made animals permanently sterile.

There’s another reason testing potential contraceptive drugs in male volunteers is tricky: some drug candidates have made animals permanently sterile.

“The technical challenge is, how do we prevent sperm being made without permanently sterilizing an individual?” says Easley.

As a better way to test drugs, Easley is investigating yet another high-tech approach. He’s turning skin cells into stem cells that look and act like the sperm-making factory cells in the testes. Testing drugs on such human cells might provide more accurate leads than tests on mice, he thinks.

Any male pill would also have to start working quickly—maybe a lot sooner than the female pill, which takes a week. “As you can imagine, having a male contraceptive where you have to wait for it to work isn’t practical,” says Paul Andrews, director of operations at the National Phenotypic Screening Centre at the University of Dundee in the U.K.

Andrews and his team, also backed by Gates, use cameras to track how fast sperm swim and to capture what’s called the “acrosome reaction,” when sperm shed a cap-like structure before penetrating an egg. A drug able to immobilize sperm, or block that reaction, could be a starting point for an effective contraceptive, he says.

Scientists admit they’re facing a biological challenge. A man makes millions of sperm every day, while women’s ovaries usually release one mature egg each month. “You can’t really afford to have something that is 90 percent effective,” Andrews says. “It has to be 100 percent effective.”

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