JUANA SUMMERS, HOST:
Time now for our science news roundup from Short Wave, NPR's science podcast. I'm joined by Regina Barber and Jessica Yung. Hi, y'all.
REGINA BARBER, BYLINE: Hey.
JESSICA YUNG, BYLINE: Hi, Juana.
SUMMERS: So you all have brought us three science stories that caught your attention this week. Tell us what they are.
BARBER: Carnivorous California squirrels that hunt.
YUNG: A new study charting the biodiversity of ancient Earth.
BARBER: And new insights into humans longest standing relationship with dogs.
SUMMERS: OK, we got to start off with these squirrels. I thought squirrels ate nuts.
BARBER: Yeah, so a study that was just published in the Journal of Ethology shows a group of California ground squirrels hunting, killing and eating a vole, like a little mouse. And I talked with the lead researcher and a behavioral ecologist, Jennifer Smith. She's at the University of Wisconsin, Eau Claire.
JENNIFER SMITH: We have one squirrel approaching a vole, targeting that vole, biting it at the neck and taking it down, eventually crunching through the skull and then eating the meat from the bones.
SUMMERS: Wow, I am suddenly not hungry anymore. OK, this really sounds like serious predator behavior. Is this a new phenomenon?
YUNG: Well, Jennifer says that if you look through the literature, there are other accounts of this.
SMITH: There's been accumulating evidence of one or two events within a species of a red squirrel taking a sparrow. They tend to try to take chickens.
BARBER: There's also accounts of squirrels eating, like, road kill or insects. But what's new here is that they've documented the whole process from start to finish with video - the hunt, the kill and then the consumption. And they've shown that this isn't just, like, a one-off, but part of these squirrels' behavior.
SUMMERS: And where exactly do these fiercely predatory squirrels live?
YUNG: So this study is only looking at two populations of squirrels in a regional park in the Bay Area in California. They actually saw this during the 12th year of a long-term study.
SUMMERS: OK, so we're talking about just two sets of squirrels in the Bay, but did these researchers think it's common? Like, are all the squirrels out there that we see when we're going to work or going to the park or out on a run - are they just eating meat all the time, and, like, we just haven't noticed?
YUNG: So Jennifer says that squirrels are actually like raccoons, bears, coyotes. They're just really flexible animals. And this vole population had a huge increase this year, you know, five to six times higher than normal. So the squirrels just took advantage of that.
BARBER: Yeah. And Jennifer said the next big thing is to find out, like, how these squirrels learn this behavior. Are they teaching each other? Does this abundance of vole meat, like, lead to more squirrel babies? There's, like, so much to explore.
SUMMERS: All right. Speaking of animals undergoing change, let's talk about this new study of species on early Earth. What's going on there?
YUNG: OK. So first, just for context, if you look back at all the fossil evidence we have of life on Earth, we have an abundance of fossils starting around 540 million years ago. It's called the Cambrian Explosion, which is when suddenly there are fossils of ancient mollusks and stuff. But before that, things are really more of a mystery.
SUMMERS: Why is that?
BARBER: So there's a few reasons. One researcher said that the time period is just less studied. And also, it's generally harder for organisms from this time to become fossils because their bodies were so soft, and, like, they had no shells, no skeletons.
SHUHAI XIAO: They're not only soft, but also they are small. They are microscopic - so making it very difficult to, you know, accumulate enough data to have a meaningful analysis.
YUNG: OK, that is Shuhai Xiao, a geologist from Virginia Tech. He's tried to find and study new fossils from this period, and now he's trying to make sense of it all and draw lessons about how biodiversity has changed throughout Earth's history, including in that early period.
SUMMERS: Interesting. How's he doing that?
BARBER: So Shuhai and his team used the existing fossil record, even though it's small, as a sample of all the species at different times in history.
XIAO: Kind of like in an election, right? So the polls, they'll, you know, take a small sample of the voters and they get an idea, you know, what the voting result will look like.
BARBER: So from the small number of fossil samples, they can make some big-picture inferences about the history of life on Earth.
SUMMERS: OK, that makes sense. Tell us what they found.
YUNG: So their data published this month in the journal Science has finally provided quantitative confirmation of some hunches scientists have already had. For example, there's this period called the Boring Billion. This is a time span of 1 billion years starting around 1.8 billion years ago, in which paleontologists have guessed that there was probably very little diversity of life and pretty low turnover of species. And according to the paper's data, that's true.
BARBER: And they also found that, like, right after the Boring Billion, there were ice ages that were followed by super rapid species turnover and, like, a boom of diversity, which has made Shuhai wonder if ice ages reset evolution.
YUNG: And that's definitely one thing he wants to look into. And other researchers I talked to also told me that they just want more research and fossil data about the Boring Billion era in general because honestly, like, this kind of work on early life is just really important to understand not only how life started, but how life adapts to environmental changes, like thinking about climate change now and in the future.
SUMMERS: All right, let's go from one ancient era to another. Now we're going to talk about our ancient relationship with dogs. I have a very present-day relationship with my dog Bromo, who's kind of like my best friend.
BARBER: Aw.
YUNG: Totally. I mean, I think our relationship with dogs as humans is just very long-standing. Researchers think canids, which include wolves and dogs, were probably first domesticated in Eurasia between 19,000 to 12,000 years ago. And new archaeological evidence published in Science Advances gets a closer look at that relationship in Alaska in a window of time 12,000 years ago.
SUMMERS: OK, so just paint me a picture of what Earth was like in that time and how this relationship played out.
YUNG: Well, with the end of the last ice age, people had begun to cross the land bridge between Asia and North America. Researchers believe those people likely came with canid companions.
BARBER: And new evidence of canid bones from Alaska supports that theory. Their paper analyzes more than 100 specimens, but the most interesting bone was excavated in 2018 outside of Fairbanks. Their researchers found a single tibia, or lower leg bone, and DNA evidence suggests the bone belonged to some kind of ancient wolf or, like, protodog and dated the bone to 12,000 years ago.
SUMMERS: Interesting. What made that leg bone such a fascinating find?
YUNG: The clues inside the bone. The team sought permission to analyze the bones from the Healy Lake Village Council, which represents the indigenous people of the area. And when the scientists did a chemical analysis of the bones, they found substantial traces of salmon proteins, meaning these canids regularly ate fish.
SUMMERS: That's very Alaskan of them.
YUNG: (Laughter) Yeah.
SUMMERS: But, I mean, how do we know that these canids weren't just out there hunting salmon themselves?
BARBER: So salmon is not naturally available in big quantities in Fairbanks, which is why researchers think they were probably getting salmon from humans, like proof of domestication, at least for this one ancient wolf.
YUNG: An archaeologist, Angela Perri, who was not a part of the study, agrees with this conclusion - that this 12,000-year-old wolf with a salmon diet was either intentionally fed by humans or was heavily reliant on scraps, which suggests that this wolf lived in close constant contact with human communities.
SUMMERS: Sounds just like my dog when he sits under my kitchen table and begs for scraps.
(LAUGHTER)
SUMMERS: That is Jessica Yung and Regina Barber from NPR's science podcast, Short Wave. Subscribe for new discoveries, everyday mysteries and the science behind the headlines. Thanks, both of you, for coming on the show.
BARBER: Thank you.
YUNG: Thank you, Juana.
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