IRA FLATOW: This is “Science Friday.” I’m Ira Flatow. We know baleen whales are the largest animals in history, but why? Hmm, that’s a good question, but no good answer yet. But a new theory from researchers at the Smithsonian suggest it could be because of global cooling. About three million years ago, baleen whales suddenly got bigger, and more specifically, the larger individuals thrived while their smaller brethren were phased out by natural selection. The reason why could have to do with encroaching glaciers. And here to explain all of this, as well as other short subjects in science, is Nick Stockton, science reporter for “Wired.” Welcome.

NICK STOCKTON: Hi, Ira. How are you?

IRA FLATOW: Hi. Thank you, Nick. How are you? Let’s get right to this. It’s nice to be able to blame something on global cooling for once. What was going on three million years ago that caused these large whales to thrive?

NICK STOCKTON: Well, the earth started to cool. And it was a really long cooling process, took several million years to do so, but part of that was the top of the earth and the bottom of the earth started developing ice caps. And in particular, the North Pole ice cap, these ice caps would encroach down in the winter and then melt back in the summer. And every time they melted, they would start draining all these nutrients into the seas.

And part of this big cooling climate change was the shift in wind patterns. And one of the things these wind patterns did was cause this coastal upwelling of the oceans against the continents, which caused the nutrients to accumulate, algae bloomed, and then krill would pop up. And krill is, of course, baleen whales’ favorite food. And so this made this huge food source. But because the seasonal nature of these blooms, they would happen at odd ends of the world very, very far apart. So it started to be more advantageous to have a larger body size to go collect these krill blooms.

IRA FLATOW: So they’d just outswim the little guys.

NICK STOCKTON: Yeah, exactly.

IRA FLATOW: How do we know this about this?

NICK STOCKTON: So as you mentioned, this is Smithsonian scientists. The Smithsonian Institute has a huge collection of whale skulls. And the researchers behind this study came up with a new method of measuring body size based on the whale skulls. And so they had this gigantic collection of skulls dating back to as far as 30 million years ago.

And they started to see a pattern across all these different species of whales where larger ones started cropping up around 3 million to a couple 100,000 years ago. And the mean bigger body size ended up being around this period when the earth was cooling. And so they discarded a few hypotheses and finally came up with this one that had to do with the food source.

IRA FLATOW: So can we extrapolate anything about this now that we’re not cooling anymore, and now that the current– we’re a warming planet?

NICK STOCKTON: Well, it might be a little optimistic to think that this might lead to smaller whales. One of the ideas that scientists think now is that if the planet continues to warm, it’s happening in such a fast scale that the whales might not have time to adapt to it. And it’s also potentially irreversible, where we’re not going to get the glaciers back again. And so we’re not going to have these accumulations of nutrients against the coastlines like the ones that were potentially selected for these large body sizes.

IRA FLATOW: Yeah. Because we had the glaciers to begin with, which is where all the nutrients flowed off. We don’t have the glaciers anymore. We don’t have the flow of that food, right?

NICK STOCKTON: Right, right.

IRA FLATOW: Wow. Let’s move on because another topic that’s really interesting this week is that scientists have come up with a model of a new type of planet. And here it looks like a bit of a certain butterscotch candy, the Werther’s candy.

NICK STOCKTON: Right. Yeah. My grandparents had these all the time. And when I saw this paper, it was the first thing it reminded me of. It looks like a gigantic Werther’s candy, like a big donut shape with a really solid thin membrane in the middle. And this study came from a pair of scientists, one at UC Davis and the other at Harvard University– who were modeling how planets formed by taking these cosmic rocks and mathematically modeling how they collided with one another. And as they kept the model going and they saw these rocks get bigger and bigger all the way at the planet size, they eventually saw this shape take form of this large, vaporized rock shape. And it’s huge. You know, these rocks get to be earth-sized. And so this torus of molten rock is gigantic, the volume of many planets.

IRA FLATOW: OK. So much for theory. You come up with a model. Have we actually seen one of these giant Werther rock candies out there?

NICK STOCKTON: No, we haven’t. But to be fair, we haven’t seen a lot of planets. We know they’re out there because we see their characteristic wiggle when they pass by their suns based on the data that we get from the space telescopes. But we haven’t actually seen any of these planets close up, like we can only guess what they look like and what their shapes are to some degree. So there are 1,000 planets been discovered recently– or exoplanets been discovered recently. So some of these could have been the [INAUDIBLE]. And potentially, it’s something to look for now when we have the new telescopes come up, like the James Webb telescope.

IRA FLATOW: Well, now we’ll get into the debate all over again whether it’s a planet or a dwarf planet, once we find one.

NICK STOCKTON: We all love that debate.

IRA FLATOW: Let’s finally talk about– there’s a new genetic mapping that shows the Zika virus could have been infecting people in Brazil a lot earlier than scientists originally thought.

NICK STOCKTON: Right. So the first case of Zika in Brazil got reported in 2015, but a new genetic map made by some of the people who were behind the genetic mapping of the Ebola crisis in 2014 shows that the earliest case could have been at least two years earlier. And so what they did was they used some of the same portable sequencing machines they used during the Ebola crisis. But they found that Zika is a little more sneaky than Ebola, and it’s hard to get genetic material from these blood samples. So this really kind of a superstar computational biologist named Pardis Sabeti, at Harvard’s Broad Institute, came up with a method of copying and making these multiple duplications of the genetic material found in these blood samples, and was able to make these maps of where the disease went and how it spread.

IRA FLATOW: So does it tell us anything about how it might spread in the future? Or is this just looking backwards on its spread before?

NICK STOCKTON: Potentially it shows how the virus evolves as it spreads from person to person. And it shows where it likes to go. And one of the things that they have found is they’re able to kind of track how it changes. And one of these has to do with the mosquito that transmits the virus. And in the US, the places where Zika was able to establish are places where the mosquito was able to live year round and also have large international airports, of course. So this is useful for people who are working on vaccines because they can figure out how the virus evolved [INAUDIBLE], and also public health officials who want to develop better responses to contain the virus and other viruses when they break out.

IRA FLATOW: We’re hoping that helps them. Thank you, Nick. Nick Stockton, science reporter for “Wired.” Thanks for joining us today.

NICK STOCKTON: Awesome. Thank you, Ira. Have a nice weekend.

IRA FLATOW: You too.

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