Did Spiders' Ancestors Come From The Ocean?

Whether you love spiders or can't be within 10 feet of them, you probably think of them crawling around on land. Historically, most researchers would probably say the same thing: Based on the fossil record, they've thought the earliest arachnid ancestors existed around 450 million years ago, living and diversifying exclusively on land. But a new study out this week in the journal Current Biology https://www.cell.com/current-biology/fulltext/S0960-9822(25)00822-X#:~:text=Mollisonia%20is%20an%20extinct%20arthropod,early%20Ordovician%20(480%20mya). suggests arachnid brains may have originated much earlier in the ocean. Want to hear more stories about the history of animals on Earth? Email us and let us know at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ atplus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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  You're listening to Short Wave from NPR.

• 0:17Regina Barber?

  Hey, Short Wavers. Regina Barber here.

• 0:19Speaker 03

  And Rachel Carlson. With our biweekly science news roundup, featuring the hosts of All Things Considered. And today, we have Mary Louise Kelly. Hi, Mary Louise.

• 0:28Speaker 04

  Hi, I'm so glad to be back. And I hear you've got some new research on why the ancestors of spiders may have originated in the oceans instead of land.

• 0:39Regina Barber?

  Yep, plus how you can see snapshots of a star's whole life in the Orion and Taurus constellations.

• 0:44Speaker 03

  And why the likelihood of having a male or female baby is much more complicated than a coin toss.

• 0:51Speaker 04

  I have so many questions. Can't wait.

• 0:54Regina Barber?

  I mean, I hope we answer them on this episode of Short Wave, the science podcast from NPR.

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• 2:25Regina Barber?

  So Mary Louise, where would you like to start?

• 2:27Speaker 04

  My skin is already crawling and hasn't stopped. Since you mentioned spiders, so let's start there. What do they have to do with the, you said, the ocean?

• 2:34Speaker 03

  Great question. So based on the fossil record, researchers thought that the earliest spiders and scorpions existed around 450 million years ago on land. But a new study in the journal Current Biology suggests arachnids may have actually originated much earlier in the ocean.

• 2:53Speaker 04

  Okay, so prehistoric ocean spiders. My skin is definitely crawling. I think we all are. What are scientists thinking? Why did they rethink this?

• 3:03Speaker 03

  Yeah, it's pretty cool, actually. They looked at the brain and nervous system of a fossil from a now extinct marine arthropod. It's called Molisonia symmetrica. And one of the study authors, Nicholas Strausfeld, told me that it lived during the Cambrian period. That's around 500 million years ago or so, when most life was still in the ocean. And this fossil is about a centimeter and a half long. They think that it probably had pincers by its mouth.

• 3:28Regina Barber?

  Yeah, on the outside, it doesn't look much like spiders, the ones we know today. But when they reexamined this fossil, they found that its brain and nervous system had a similar structure to arachnids, which made them think that this might push back the origin story for things like spiders and scorpions. Nicholas said that he thinks it's an early example of a modern spider brain with like organization that makes it easier to control movement, like walking around and weaving webs.

• 3:51Speaker 04

  And how is this new thinking landing with other scientists? Because it sounds like a big shift.

• 3:57Speaker 03

  It would be a big shift. So I got in touch with an evolutionary biologist who didn't work on the study. His name's Alejandro Isquero Lopez. And he told me in an email that Molisonia is a really exceptional fossil, and these findings are super cool. But looking at things like brains and the nervous system tissue of fossils like this is a really complex process. And it is possible that what seem like brains are other tissues. Plus, he says this finding would raise a whole host of other questions about arachnid evolution.

• 4:27Regina Barber?

  But if these findings are supported with like more research, that would make the Molsonia the earliest arachnid ancestor and confirm that spiders do really come from the sea.

• 4:37Speaker 04

  From sea spiders, maybe, to our next story, which has to do with the skies and the constellation Orion, which is one of two constellations I can actually find in the sky. Big Dipper Orion, so I'm so glad we're on one of these. Why are we talking about it?

• 4:51Speaker 03

  Scientists want to study it to understand life, or at least stellar life, because basically all stars are born in clusters of hundreds or thousands of stars. And an international team of astrophysicists studied open star clusters in Orion and its neighbor Taurus and determined that these clusters, or groups of stars, seem to grow old following some basic rules.

• 5:13Regina Barber?

  This study used computer modeling to simulate how thousands of stars in these clusters might evolve and change over 800 million years. And the simulations confirmed that these star groups in these constellations are indeed snapshots of like different phases of a star cluster's life. Here's Hossein Haki, one of the authors of this paper.

• 5:32Speaker 05

  It's like seeing photos of the same person as a baby, teenager, and elder.

• 5:39Speaker 04

  Baby, teenager, and elder. So fascinating to think of stars in that way. Tell me more.

• 5:44Regina Barber?

  So they looked at three clusters of different ages. So the baby cluster that they're talking about is the Orion Nebula. It looks fuzzy because the stars are still like forming in the gas and dust. It's part of the sword that hangs from Orion's belt, if you remember like the three stars in the belt.

• 5:59Speaker 04

  Yep.

• 5:59Speaker 03

  And then the teenage star cluster is the Pleiades in Taurus. It's more spread out than the Orion Nebula stars. So, Mary Louise, looking at these three together, you can see how these types of clusters evolve, from bunched up fuzzy balls to big, spread out groups of stars.

• 6:15Speaker 04

  Although I'm wondering why they've only just been able to figure this out? Like, why scientists couldn't do this before this, these latest simulations?

• 6:24Regina Barber?

  So this hypothesis that these were snapshots of star cluster evolution, that already kind of existed. But to have it correspond with simulations just happened because the computing power just wasn't there yet. Until now, star cluster simulations were... Very simple. The stars had minimal interaction with the dust and gas they formed from. But in this study, they are able to like add that dynamic in and more accurately model like the relationship between stars over a long period of time. The findings were published in the journal Monthly Notices of the Royal Astronomical Society.

• 6:54Speaker 04

  All right, from maybe baby stars to human babies, our final topic. And you were telling me about the odds of having a male or female child, which I always thought would be like 50/50, coin toss.

• 7:06Regina Barber?

  Right. I mean, I also thought that. But in big families with more than like three children, that may not be the case, according to reporting from our colleague Scott Newman.

• 7:15Speaker 04

  Say more. What's going on?

• 7:16Regina Barber?

  Well, Harvard researcher Siwen Wong and her colleagues noticed something interesting among their own families and friends, which is that families with many children often have a string of male babies or like a string of female babies.

• 7:27Speaker 06

  To the extent that we're wondering this happens so frequent, whether it's simply by chance or is there any underlying biology explaining these sex clustering within families?

• 7:38Speaker 03

  So to study this more, they turned to data that already existed. It's something called the Nurses' Health Study. It tracked over 100,000 pregnancies from 1956 to 2015. And examining the birth records of more than 58,000 women, Siwen's team found a pattern. In families with at least three children of the same sex, the next baby's sex tended to follow a weighted coin toss.

• 8:02Speaker 04

  I love studies like this, by the way, that that start with a researcher just being like, huh, there's this thing in my family. Is this true everywhere? Let's investigate. But it sounds like you're telling me, Rachel, each family may have a distinct tendency towards males or toward females?

• 8:18Speaker 03

  Exactly. So in families with three male children, the probability of having another male child was 61%. And in families with three female children, the probability of having another female child was 58%.

• 8:31Speaker 04

  61 and 58%. That's not 50/50 or any we're close to it. Do they know why?

• 8:36Regina Barber?

  Well, one of the first things that stood out in the data were the mother's age at first birth. Women who started their families at the age of 28 had a slightly higher chance of having families with all females or all males.

• 8:46Speaker 03

  We also know that maternal age during the reproductive years is associated with several physiological changes, including shorter menstrual cycles and a lower vaginal pH. So the age of the mom might influence the biological sex of the child. And in speaking with NPR, Siwan noted that parents' ages are often similar to one another. And since the study focused on maternal data and didn't include paternal age or genetic information, the potential influence of fathers on these outcomes remains an open question for the researchers.

• 9:17Speaker 04

  Okey dokey. Cue up the next study on the daddies.

• 9:20Speaker 03

  Yeah, absolutely. Mary Louise, it is always such a pleasure having you on.

• 9:25Regina Barber?

  Agreed. You should always come back.

• 9:27Speaker 04

  I will indeed. Invitation accepted. Thank you.

• 9:30Speaker 03

  Thank you.

• 9:36Regina Barber?

  You can hear more of Mary Louise Kelly on Consider This, NPR's afternoon podcast about what the news means for you.

• 9:43Speaker 03

  This episode was produced by me, Rachel Carlson, and Jordan Marie Smith. It was edited by Rebecca Ramirez, Christopher Intagliata, and William Trup.

• 9:53Regina Barber?

  Tyler Jones checked the facts. Tiffany Vera Castro and Robert Rodriguez were the audio engineers. I'm Regina Barber.

• 9:59Speaker 03

  And I'm Rachel Carlson. Thanks so much for listening to Short Wave, the science podcast from NPR.

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