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  • [♪ INTRO]

  • Last week in the journal Nature, researchers announced

  • that they've found a new fossil that might help us understand

  • one of the most unique features of mammals: our ears.

  • Also, the little guy is, like, really cute... so there' that.

  • Called Jeholbaatar kielanae, this animal was found

  • by paleontologists in Northeast China.

  • It lived in the Cretaceous period, about 120 million years ago,

  • and it likely ate things like bugs and plants.

  • It was pretty small, not much bigger than a mouse.

  • Though technically it wasn't a rodent.

  • It's what's known as a multituberculate,

  • a different mammal group that was pretty successful

  • until they died out about 34 million years ago.

  • So that's neatit's always fun to find new fossil species.

  • But this fossil was also special because

  • its ear bones had been preserved.

  • Besides signature adaptations like producing milk

  • or having fur, mammalsincluding humans

  • are also have unique, complex middle ear bones.

  • These three little bones, called the malleus, incus, and stapes,

  • help transfer sound from the eardrum to the cochlea.

  • Reptiles, in contrast, typically only have one bone

  • in their ears, the stapes.

  • Thanks to our unique set-up, mammals have superb hearing,

  • able to detect much higher frequencies than other land animals.

  • But these bones are also a bit of an evolutionary mystery.

  • We know two of them, the malleus and incus,

  • evolved from bones in our jaws.

  • But eventually, they moved to our ears,

  • and we don't fully understand why.

  • Just because they're helping us hear better now

  • doesn't mean that was the original evolutionary pressure

  • that got them moving.

  • And fossil evidence suggests this actually happened

  • more than once, independently each time.

  • Researchers have proposed a few ideas

  • for why middle ears evolved.

  • Perhaps they really did improve hearing right from the get-go.

  • Or maybe the moving bones were a side effect

  • of larger brains reshaping the skull.

  • But the evolution of Jeholbaatar's ears

  • may actually have had more to do with its diet.

  • Because Jeholbaatar is so old, scientists were

  • able to spot one bone seemingly caught in transition

  • from being part of the jaw to being part of the ear.

  • Analyzing the shape and placement of the bones,

  • the scientists came to the conclusion that the shift

  • wasn't a result of the brain changing the shape of the skull

  • or other ideas.

  • Instead, by moving up towards the ears,

  • the bone was essentially getting out of the way of its chewing.

  • This let Jeholbataar move its jaws in a unique,

  • forwards-and-backwards motion.

  • This improved grinding power, and made it easier

  • for the animal to hear over the sound of its own noshing.

  • This doesn't necessarily explain how

  • our own middle ears developed.

  • Jeholbaatar's group is a cousin to our mammal group,

  • not an ancestor, and we don't chew the same way they did.

  • But it does represent an interesting new hypothesis

  • for how jaw bones can become ears.

  • And it might help explain why multituberculates

  • were so successful for so long.

  • In more modern news, scientists publishing in the journal

  • Science Translational Medicine have found that starting

  • HIV treatment within hours of birth may help HIV-positive newborns.

  • HIV can be passed from an infected parent

  • to their unborn child, and it can be fatal or cause serious,

  • irreversible damage to the baby's immune system.

  • The World Health Organization recommends

  • that doctors start treatments that can control the infection

  • within just weeks of birth.

  • This new study suggests starting treatment even earlier,

  • within hours rather than weeks, might be even better.

  • The researchers, working in Botswana, started treating

  • a group of ten HIV-positive newborns with antiviral drugs

  • just hours after they'd been born.

  • They then tracked the children over the course of two years,

  • taking periodic blood samples and comparing them

  • to another group of ten babies who received

  • the currently accepted treatment regimen.

  • The blood samples allowed the scientists to examine

  • traces of the virus within the DNA of the children's immune cells.

  • They were able to watch how the infection

  • evolved and changed, as well as how their bodies

  • were responding to the infection.

  • They found that starting the antiretrovirals earlier

  • resulted in better immune system responses and signs of

  • a reduction in something called the viral reservoir.

  • Typically, when the virus infects a cell, it hijacks

  • the cell's machinery and starts producing new copies of itself.

  • However, some cells go into a resting state instead,

  • where they don't produce new copies of the virus.

  • Those resting cells are effectively hidden

  • from medicines targeting the virus.

  • These cells can lay dormant for years before turning back on.

  • This hidden cache of the virus makes up the viral reservoir.

  • By peeking at the traces of viral DNA in immune cells,

  • the scientists could essentially gauge the size of the reservoir.

  • They found that shortly before the babies turned two,

  • the ones that got the earlier treatment had very low levels

  • when compared to the infants that received the standard regime.

  • The scientists think follow-up studies might find

  • even more beneficial effects later on in life.

  • Now, you might think it seems obvious

  • that more medicine earlier is better.

  • But when people's lives are on the line,

  • scientists have to show that treatments are effective.

  • This study seems to do that.

  • There are still some barriers, though.

  • The study was pretty small.

  • Starting HIV treatment earlier on a large scale

  • could represent a huge logistical challenge

  • and require innovations in diagnosis and infrastructure.

  • Remember, we're talking about catching it within hours,

  • sometimes in places with very limited resources.

  • But these results show that this change could have real,

  • dramatic benefits for some of the world's most vulnerable populations.

  • And if nothing else, the scientific insights from this study,

  • about precisely how the newborn immune system

  • responds to the virus, could help optimize or tailor future treatments.

  • Thanks for watching this episode of SciShow News,

  • which was brought to you with the help of our amazing

  • President of Space, Matthew Brant!

  • You too could become President of Space

  • by joining our awesome community of supporters

  • over on patreon.com/scishow.

  • AND before you go, we want to show you these neat

  • lunar calendars now available over on DFTBA.com!

  • They'll help you keep track of the phases of the moon

  • for all of 2020, so you can stay astronomically informed.

  • You can grab one now.

  • [♪ OUTRO]

[♪ INTRO]

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這隻古哺乳動物的耳朵是為咀嚼而生的 (This Ancient Mammal's Ears Were Built for Chewing)

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    林宜悉 發佈於 2021 年 01 月 14 日
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