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Hank describes to us some news stories that illustrate how science is continually changing the things we think we "know" - from the status of various animals species, to the way our senses work and even where the Moon came from - scientists ask questions and make discoveries that change the world, and our understanding of it, every day.

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Hello this is Hank Green for SciShow news.

I had someone ask me about Pluto this morning on Tumblr and why it isn't a planet anymore and whether I think that's, like, fair.

Well, Tumblr person, science isn't about being fair, it's about understanding the universe better, and frankly, every time something we used to know changes, that's science at work, and we should celebrate. That's what science is all about, and there were a number of examples of that this very week.

 Data Points (0:38)

Let's warm up with some animal news.

I love me some charismatic fauna, and in the past week we've learned something new about two creatures with charisma to spare.

First, biologists in Cuba said they've re-rediscovered an animal that's so rare it's thought to have gone extinct more than once. It also carries the distinction of being one of the very few venomous mammals on earth. 

The Cuban Solenodon is a nocturnal carnivorous mammal found only in a tiny corner of eastern Cuba. It was thought to have gone extinct by 1890 and again in 1970, but by 1975 three of them were captured by scientists and only two had been seen alive since them.

Until this spring, when a team of Cuban and Japanese biologists managed to capture and study seven more. So, for now at least, they're still in the running, existence-wise.
The Solenodon's must unusual feature is its venomous saliva which it injects into its prey, usually small reptiles and insects, through hollow teeth.

Only five other species of mammal, mostly rare kinds of shrews, are known to have poisonous spit like this. And they, along with male platypuses, which have venomous spurs of their hind legs, are the world's only known venomous mammals.

But this hasn't protected the Solenodon from its greatest threat: invasive species. The Solenodon's tropical habitat has been overrun by feral cats and black rats over the past century, and doesn't help matters that they pretty much suck at self-defense.

Biologists say that when threatened, Solenodons just curl up into a ball, tuck their tails, and prepare for the worst. Not a super great strategy for avoiding extinction.

Now compare those little guys, to lions. Lions, which have been the subject of every nature documentary since David Attenborough was in diapers. You'd think by now we'd have learned everything there is to learn about them, but lo! 

British scientists have discovered that a very small and very distinct population of African lions are genetically distinct from all the others and they're all living in the same zoo.

The twenty lions at the Addis Ababa Zoo in Ethiopia are descendants of seven lions that were captured in 1948 by then Emperor Haile Selassie.

They're distinctive because the males sport large, dark, bushy manes that extended all the way down their bellies. These lions once thrived in parts of Ethiopia, but they seem to have disappeared in the wild completely, in part, because of trophy hunting.

Genetic testing done by biologists from the University of York shows that these lions have mitochondrial DNA unlike that found in any wild population.

So they're still considered the same species, Panthera leo, but as a unique population they warrant separate conservation status and may become the subject of a new breeding program to increase their numbers and even return some of them to the wild.

Last week, I told you about the winners of the Nobel Prize in Physics and Physiology or Medicine, and once again, congratulations on that guys, but since then, the recipients of the 2012 Nobel Prize in Chemistry have been named, and theirs is a truly huge contribution to science.

How huge? Well, discoveries made by Robert Lefkowitz and Brian Kobilka explain the mechanisms behind nearly all of human sensory function. Like precisely how we see, how we experience fear, and how I can tell that someone in the office is making popcorn. 

It's long been known that our cells interact with the outside world by way of receptors, structures on the outside of our cells that respond to stimuli, like hormones or even light. How our cells responses to those stimuli were carried out was a mystery until these two identified and understood specialized proteins called G-Proteins.

Lefkowitz became the first to identify an active receptor in 1970, when he located the one on our cells that responds to adrenaline. But still, unable to understand how the receptor created a change inside the cell, he recruited the help of Kobilka, a student who came up with a creative approach.

Instead of trying to observe the receptor in action, he decided to find the gene that coded for it, which would give us a blueprint for exactly how it's made.

In the 1980s, these two began searching the entire human genome for that one special gene. Now bear in mind that this is more than a decade before the genome was actually fully sequenced, and yet they found it.

After analyzing the gene, Lefkowitz and Kobilka discovered that the receptor for adrenaline has the exact same structure as light receptors in the back of our retinas, seven long, fatty molecules that straddle the membranes of our cells.

So, they theorized, most of our sensory receptors, now known as G-Protein receptors, were basically the same everywhere. And once they understood the structure of the receptors, Lefkowitz and Kobilka were able to figure out how they worked.

When a hormone or other stimulus activates the part of the seven piece receptor on the surface of the cell, it changes the shape of the part that's inside the cell, allowing it to connect to those G-Proteins.

The proteins then break up into little messenger chemicals that go around telling the cell, "Look! There's a cute kitten!" or, "You're in danger!" or, "There is bacon in this room!"

So, the next time you experience a sensation of any kind, remember that you have Lefkowitz and Kobilka to thank for understanding how.

 Bits (5:25)

Finally, some more new knowledge that's erasing some things that we previously thought that we knew.

First, where did the moon come from?

Now there's a question that's pretty much hanging over your head every day. Eh?

For decades, scientists have theorized that the moon was formed when a small planet slammed into Earth very early in its history.

But the problem is, the chemistry of Earth and the chemistry of the moon is surprisingly similar. If the moon was created by the impact of another planet, the theory goes, the moon would resemble that planet, not Earth.

But this week, scientists from Harvard University and Southwest Research Institute report in the journal Science that they figured out how such a collision could have resulted in Earth and the moon having such similar compositions.

Simulating the impact with computer models, they found that the conditions were probably a lot different than scientists had assumed. For starters, the interloper that smashed into us was much more massive than was thought. Probably about the same mass as early Earth, and more importantly, baby Earth was spinning twice as fast as it is now. 

In this scenario, a giant impact would create a huge spinning cloud of mixed up material that would eventually accrete to form the Earth and moon with similar chemistry as we know them today.

Now, another question that we would all like answered: why can't we bring back the dinosaurs? You know you want to, but the problem is that fossilized dinosaur tissue has never yielded viable DNA, so, despite the best wishes of Michael Crichton, Stephen Spielberg, and 5 year olds everywhere, cloning T-Rex is impossible.

Last week, in the proceedings of the Royal Society Bee, Australian paleontologists explain why. They studied the DNA from 158 different bones, all of different ages, of an extinct bird called the Moa. By comparing the relative rates of decay in the samples, the scientists were able to measure the half-life of DNA at 521 years. 

Meaning that half of the existing bonds in a DNA sample decay in that time, and then half of what's left decomposes over the next 521 years, and so on.

From this, they extrapolated that even under the best conditions, DNA could remain intact for no more than 6.8 million years. So dinosaurs, which except for birds, disappeared about 65 million years ago, are a done deal, I'm afraid. Mammoths, on the other hand, still fair game. 

Thanks for watching this episode of SciShow News, if you have any questions or suggestions or ideas for us you can leave them on Facebook or Twitter or of course down in the comments below. And if you wanna keep getting smarter with us here at SciShow you can go to and subscribe.