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  • This episode is sponsored by Morning Brew.

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  • [♪ INTRO]

  • Often, the bacteria in our  guts go pretty much unnoticed

  • unless, like, you get a stomach bug and feel sick.

  • But this week, a kind of  bacteria got extra attention,

  • and not for the reason you might think.

  • It's called Helicobacter  pylori, and scientists used it

  • to track how ancient humans spread  to the Americas from Siberia.

  • These bacteria have been around  for at least 100 thousand years.

  • And worldwide, it's estimated  that up to half the population

  • has had an H. pylori infection.

  • This microbe can cause a stomach  condition called chronic gastritis,

  • so it's something to pay attention to in medicine.

  • But it's also a convenient  bacteria for other research.

  • That's because its genetic sequence varies  slightly depending on where the bacteria lives

  • or rather, depending on where the  human they're infecting lives.

  • So, this microbe is a great tool  for tracking ancient civilizations.

  • In a study published in the journal PNAS,

  • researchers sequenced and then analyzed

  • H. pylori bacteria strains from samples  they'd collected from indigenous people

  • in Siberia and the Americas.

  • For the analysis part,

  • they used a technique called  Approximate Bayesian Computation

  • or just ABC for short.

  • It's a way of using statistics to determine  the likelihood that a hypothesis is true

  • based on new evidence.

  • So, in this case,

  • the researchers were testing scenarios

  • about where these bacteria might have come from,

  • and how they could have  spread throughout the world.

  • And by extension,

  • they were also testing ideas about  what that meant for human migration.

  • Since their methods were based on statistics,

  • the researchers can't definitively  say what happened in the past.

  • But their most likely hypothesis  was that H. pylori hitched a ride

  • from Siberia to North America with a small,

  • single group of humans some 12,000 years ago.

  • Then, that founder population eventually became

  • the indigenous people of the Americas,

  • whose descendants are around today.

  • As for how this group traveled

  • well, back then, sea levels were around  100 meters lower than they are now,

  • so they probably went over a land bridge  between Eurasia and North America.

  • But it's hard to know exactly why they moved,

  • because although the world  was in a glacial period,

  • Beringia, the vast supercontinent that  contained north-eastern Siberia, Alaska,

  • and the western parts of Canadawas relatively hospitable.

  • In fact, this study also found that other people

  • toughed out the weather and stayed in the area.

  • There did seem to be a third option, though:

  • By analyzing these bacteria,

  • the researchers proposed that  another group chose to hang out

  • in the warmer parts of Eurasia until the  glacial period ended about 300 years later.

  • Then, they joined up in Siberia

  • with those descended from the group  that had stuck around in the north.

  • Because the Eurasian populations  were separated geographically,

  • their gut bacteria ended up evolving differently.

  • And now, more than 10,000 years later,

  • that's helping us piece together human history.

  • In other evolution-related news,

  • scientists have discovered a new species  of hyrax in the forests of Africa,

  • and they did it by listening.

  • Hyraxes are mammals that kind of  look like tubby, scruffy guinea pigs,

  • with their rounded ears, lack  of tails, and stumpy toes.

  • And aside from their cuteness,

  • these creatures are known for  their distinctive vocalizations,

  • which sound like shrieking or barking.

  • This new species was presented  in a paper published Tuesday

  • in the Zoological Journal of the Linnean Society.

  • It all started when biologists on  a field trip noted that hyraxes

  • on one side of the Niger river sounded  different than those on the opposite side.

  • So, they took 418 recordings of hyrax  vocalizations from 42 locations across Africa,

  • then analyzed how long they were, their  pitch, and how often they repeated.

  • What the researchers heard was that

  • calls in the area between the Volta and  Niger rivers were more like rattling barks,

  • while those outside that area were  more like short, air-horn like shrieks.

  • After that, the researchers  went to museum collections,

  • and looked at close to 70 hyrax  skulls from animals found either

  • between or outside the rivers.

  • Turns out, hyraxes who lived  between the rivers had shorter,

  • broader skulls than those outside.

  • Also, museum specimens, photos,

  • and carcasses of the animals killed by hunters

  • revealed that the hyraxes  had different coat colors,

  • as well, with the between-river  animals sporting a lighter,

  • yellow-brown coat streaked with dark brown.

  • And their outside-the-river cousins  sporting a dark brown to almost black coat.

  • Finally, the researchers peered  at the hyraxes' genetics.

  • And, sure enough, the two groups had  some noteworthy genetic differences.

  • All those pieces together lead the researchers

  • to conclude these were two different species.

  • They called the new species D. interfluvialis  -- orbetween riversin Latin.

  • And hyraxes aren't the only  mammals who have different species

  • living between and outside these rivers.

  • In fact, rivers act as natural  barriers many animals can't cross.

  • Over time, populations on either side  become more and more different until,

  • eventually, they're so different that  they're considered separate species.

  • In other words, these  hyraxes are a classic example

  • of geographic isolation and speciation

  • all discovered thanks to some barks in the night.

  • Both studies just go to show  how evolution is constant

  • happening throughout history  and around us right now.

  • Whether the species are gut  bacteria or rock-dwelling mammals,

  • the environment can play a big part

  • in influencing genetics over  hundreds or thousands of years.

  • And these studies are just the appetizer  for all the great things that have happened

  • this week in science and in  other fields, like business!

  • And keeping track of all of  that can be overwhelming,

  • but today's sponsor, Morning Brew  can help you with some of that.

  • Morning Brew is a free daily  newsletter Monday through Sunday.

  • It helps you get up to speed on  business news in just 5 minutes!

  • So you can skip skimming through news websites

  • or just endlessly scrolling on Twitter.

  • Morning Brew gets all the need-to-know  information from business, finance,

  • and tech together in an accessible format,

  • and then sends it promptly every  morning right into your inbox!

  • Like on the morning of filming this episode,

  • they had some fascinating explainers

  • on Vermont's high vaccination  rate and Texas's power grid.

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  • [♪ OUTRO]

This episode is sponsored by Morning Brew.

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An Unexpected Tool to Track Ancient Civilizations...Bacteria

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    joey joey に公開 2021 年 06 月 28 日
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