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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 Canada,  was 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  -- or “between rivers” in 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,

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