ROXANNE KHAMSI: This is Science Friday. I’m Roxanne Khamsi, in for Ira Flatow. Later this hour, we’ll talk to two autistic researchers adding their own lived experience and expertise to the study of autism, and we’ll dig into our history with parasites.

This week, air pollution regulators in California made a bold move to phase out sales of new gasoline-powered vehicles, with a complete ban on gas car sales by 2035. Joining me now to talk about this and other science stories of the week is Sophie Bushwick, technology editor at Scientific American, based in New York City. Sophie, welcome back to Science Friday. Thanks for being here.

SOPHIE BUSHWICK: Thank you. I’m excited to be here.

ROXANNE KHAMSI: So let’s talk first about this car decision. What exactly are these regulators in California banning?

SOPHIE BUSHWICK: So California regulators have said that by 2035, no gas-powered cars can be sold. So electric or hydrogen-powered vehicles will be all of the new vehicles sold. Used vehicles can still be there. And the other interesting thing is that they’re phasing them out. So by 2026, already 35% of new passenger vehicles have to produce zero emissions.

ROXANNE KHAMSI: Wow. So it’s not so much about going cold turkey.

SOPHIE BUSHWICK: Exactly. They’re easing into it. But it is still a significant change. And if other states follow them, this could affect a third of all automobile sales in the US.

ROXANNE KHAMSI: And so to make this change, is there going to be a need for new infrastructure, new charging stations? What’s needed to make this happen?

SOPHIE BUSHWICK: Absolutely. So one of the things that electric vehicles require are charging stations so they can go distances. And California is also making moves to put money towards establishing those. Another issue is that if you have a lot of electric cars charging off the grid, you’ll need to make sure that there’s enough electricity for them. So that will also have to be addressed by 2035.

ROXANNE KHAMSI: Hm. California’s super trendy. It’s on trend. What is the likelihood that other states will make the similar kind of move?

SOPHIE BUSHWICK: There’s about 16 states that tend to follow California’s lead when it comes to regulating auto emissions. And so those are pretty likely to follow suit. This could be an absolutely enormous impact on emissions. Transportation is the main source of greenhouse gas emissions in the United States, so not just cars, but the aviation industry as well. Still, cars are a big chunk of that. And if all these states do follow California’s lead here, this could be just as significant as the passage of the Inflation Reduction Act in terms of the future of greenhouse gas emissions and climate change in the US.

ROXANNE KHAMSI: Whoa. And since we’re talking about climate here, you have a related story this week about Americans’ opinions about climate change mitigation. There’s an unexpected twist here in what researchers found.

SOPHIE BUSHWICK: Yes, this is fascinating. So measures like California’s rule and like the IRA are actually pretty popular. A big majority of Americans think that climate change is a bad thing and support measures to mitigate climate change and to try to prevent some of the worst harms from it. And yet, even though we think these things ourselves, we underestimate hugely what our neighbors think of this.

Something like 80% to 90% of people surveyed in this new survey underestimated how much public support there is for climate change mitigation measures. And this is a really big deal because if you think that you’re the only one who is worried about climate change, you’re less likely to speak up and perhaps less likely to– if you are a member of Congress, you might be less likely to put forward measures to try to reduce the impact of climate change, when in reality, these measures are popular and people think that they’re necessary.

ROXANNE KHAMSI: I mean, this is a really fascinating insight into how we think others think about climate change. Do you think that this kind of false social reality shapes action on other issues as well?

SOPHIE BUSHWICK: Yes, I think that our willingness to, for example, act on climate change, but also to act on a bunch of other measures, that’s tempered by what we think other people will think. We don’t want to necessarily support a policy if we think it’s super unpopular with everyone else, even if we ourselves believe in it. So I think having an accurate idea of what our neighbors think could be pretty important. And it probably is up to the researchers who do these surveys and to the journalists who cover them to make sure people are aware of what their neighbors think and not just what they think their neighbors think.

ROXANNE KHAMSI: Yeah, this is definitely making me rethink how I think about what others think. So moving to a different topic, many people turn to sugar substitutes in a desire to cut calories or because they’re concerned about their blood sugar. Yet there’s new research saying that those substitutes might actually affect blood sugar. How does that all work?

SOPHIE BUSHWICK: So we tend to think of sugar substitutes as having zero calories and then just sort of moving through the body and not affecting us. But previous studies in rodents have found that these sugar substitutes do seem to affect blood sugar and the gut microbiome. And a new study in humans found that that is the case. So they got a cohort of people who don’t typically eat calorie-free sweeteners, and then they gave them four sugar substitutes or a filler, which is the non-active ingredient in the little packet of sugar substitute you might grab at a coffee shop.

And in this study, two of the sugar substitutes, saccharin and sucralose, were linked to spikes in glucose levels. And all four of them were linked to changes in the gut microbiome. So what they did is they had people either eat a specific sugar substitute or not for two weeks, and then they had them take actual glucose and measured how their blood responded to it. And people who had been taking saccharin or sucralose, their blood sugar levels spiked more in reaction to glucose than those who hadn’t been. And for all of them, when the researchers measured their gut microbiomes before and after, they did see changes.

ROXANNE KHAMSI: Well, definitely it’s finding that sweet spot, you could say.

SOPHIE BUSHWICK: [GROANS]

ROXANNE KHAMSI: [CHUCKLES] But this next one we’re going to talk about is a little creepy. People that look like you might actually share chunks of your DNA with you even if you’re not related at all. And that’s the thing that surprised me the most.

SOPHIE BUSHWICK: I think this is fascinating. So it started with an artist, actually, a photographer, Francois Brunelle, doing a photography project where he took pairs of people who were unrelated but looked alike and photographed them together. And what researchers have now done is they looked at 32 pairs from this photography project, and they tested their DNA. And what they found is in half of the pairs, there were genetic similarities in the DNA of these two people who thought they were completely unrelated.

ROXANNE KHAMSI: And are there any practical applications here with this new finding?

SOPHIE BUSHWICK: Well, it could be interesting to see how this affects, for instance, likelihood of developing a disease. So if you and your doppelganger have similar DNA, maybe you’re both susceptible to cancer. So this could be used for that.

But just as interesting as the fact that some of these doppelgangers had similar DNA was the fact that some of these doppelgangers didn’t. So for about half the pairs, there weren’t significant similarities in DNA even though they looked so much alike. And it suggests that there’s only so many different combinations of features that you can put on a face before you start churning out faces that look different. So I think that’s fascinating, that someone who you’re not that genetically close to could still look just like you.

ROXANNE KHAMSI: Yeah. Yeah, and it makes me want to find my doppelganger and maybe do some genetic analysis to see if we’re related.

SOPHIE BUSHWICK: Absolutely. I’m going to be staring at all the dark-haired women I see. Oh, are you– you look like me.

ROXANNE KHAMSI: So now that we’re approaching the end of summer, you also have a story about theories on how we can better engineer sandcastles. Can you say something about that?

SOPHIE BUSHWICK: So this is a very important engineering project for anyone who’s planning to head to the beach before the end of summer. Yes, and the key to engineering the perfect sandcastle has to do with a couple things. One of them is the ratio of water to sand. So in laboratory conditions, you would want to have one parts water to eight parts dry sand.

But you don’t necessarily– you’re not in the lab when you’re out on the shore. You know, you’re dealing with yelling kids and birds and trying to find the spot in between everyone else’s beach umbrellas. So geotechnical engineers would recommend maybe you want to go down to about where the tide line is at low tide, and you want to take sand from that area. That’s going to be your sweet spot of sand to water.

And then the other really important thing is you got to pack that sand as tight as possible. So you can do the classic, traditional method of smooshing sand down into a pail or into a mold and then flipping it upside down and using that to make blocks. But what this engineer actually recommends is creating a mound of compacted sand and then carving out your castle from it the way a sculptor carves a statue from a block of marble.

And if you’re really serious about this, you might want to actually go beyond the beach. Apparently, having sand grains that are a little rougher and spikier and less regular actually lets them stick together better and gives you a better castle. So professional sandcastle builders will actually import sand from rivers so it’s closer to the mountains. And apparently those grains are a little spikier and they stick together better, and they let you make a more cohesive castle.

ROXANNE KHAMSI: Wow, it sounds like these castle engineers will build something that’s going to last longer than the hour or two when I make them.

SOPHIE BUSHWICK: Oh, yeah. My sand castles collapse almost immediately. I think that I would love to learn from this longevity.

ROXANNE KHAMSI: Finally, we might like to see familiar faces, but it turns out dogs do, too. Can you tell us more about this new study?

SOPHIE BUSHWICK: This is delightful. A researcher noticed that his dog’s eyes seemed to be filled with tears when she interacted with her puppies. And then he also noticed that the dog seemed to be tearing up when she saw him. So what he did was he studied a couple different things. First of all was, do dog’s eyes fill with tears? And what makes that happen?

And he found that oxytocin, which is associated with social bonding, levels of oxytocin can cause a dog’s eyes to well up. And the other thing is that, yes, when a dog’s owner comes in the door, its eyes do fill with tears in a way that it wouldn’t respond to, say, going to a doggie daycare. It might act excited, but its eyes don’t water in the same way.

So this suggests that dogs are reacting socially to the presence of this familiar human. And their reaction then intensifies our reaction to them. When humans looked at pictures of dogs where either their eyes were filled with tears or they weren’t, we were more likely to want to cuddle and play with the teary-eyed ones. So you could see this creating a feedback loop that helps dogs and owners bond.

ROXANNE KHAMSI: And they’re happy tears, just to be clear.

SOPHIE BUSHWICK: I mean, I hope so. [LAUGHS] Yes, they seem to be mediated by this bonding hormone.

ROXANNE KHAMSI: We’ll tell ourselves that. Well, thanks so much, Sophie.

SOPHIE BUSHWICK: Thanks for having me.

ROXANNE KHAMSI: Sophie Bushwick is technology editor for Scientific American.

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