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In this weeks science news, new fossil has been found that might help us understand how jaw bones evolved into complex middle ears found in mammals, and a new treatment regimen for treating babies with HIV shows promise.

Hosted by: Hank Green

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Sources:
Mammal Ears
https://press.nature.com/cretaceous-fossil-reveals-a-new-pattern-in-mammalian-middle-ear-/17413100
https://www.nature.com/articles/s41586-019-1792-0
https://www.nature.com/articles/d41586-019-03605-1
http://www.geo.utexas.edu/faculty/rowe/Publications/pdf/023%20Rowe1996a.pdf
https://royalsocietypublishing.org/doi/full/10.1098/rspb.2016.2416
https://evolution.berkeley.edu/evolibrary/article/evograms_05
https://www.ncbi.nlm.nih.gov/pubmed/19674542
https://www.britannica.com/animal/reptile/Hearing


HIV
https://www.eurekalert.org/pub_releases/2019-11/aaft-eat112519.php
http://dx.doi.org/10.1126/scitranslmed.aax7350
https://aidsinfo.nih.gov/understanding-hiv-aids/fact-sheets/19/93/what-is-a-latent-hiv-reservoir-
https://stm.sciencemag.org/content/11/520/eaax7350

Image Credits:
https://www.eurekalert.org/multimedia/pub/218153.php
https://commons.wikimedia.org/wiki/File:Ptilodus_skull_BW.jpg
https://commons.wikimedia.org/wiki/File:Taeniolabis_NT_small.jpg
https://commons.wikimedia.org/wiki/File:Blausen_0330_EarAnatomy_MiddleEar.png
https://commons.wikimedia.org/wiki/File:Gray919.png
https://commons.wikimedia.org/wiki/File:Gray918.png
https://commons.wikimedia.org/wiki/File:Gray917.png
https://commons.wikimedia.org/wiki/File:Gray916.png
https://commons.wikimedia.org/wiki/File:Jaw_joint_-_mammal_n_non-mammal.png
[♪ 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 neat — it’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, mammals — including 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].