mRNA is the Future of Medicine

Moderna's cancer vaccine reminds us of the vast potential of mRNA medicine:

An experimental mRNA vaccine allowed people with high-risk melanoma to live longer, cancer-free, the pharmaceutical companies Moderna and Merck announced Wednesday.

For decades, cancer vaccines have been one of the most tantalizing ideas in cancer treatment — offering the hope of harnessing a person’s own immune system to attack tumors. . . .

The mRNA technology that was instrumental in the rapid vaccine development in the Covid-19 pandemic added a new element of speed and flexibility to the quest for therapeutic cancer vaccines. Scientists can use the mRNA platform to create bespoke, individualized vaccines matched to the genetics of patients’ tumors.

Which makes the flaky, MAHA opposition to mRNA technology the absolute worst part of our contemporary politics. I have talked to people who are freaked out that this technology "changes your genetic code," which is completely wrong. It avoids messing with your genetic code by injecting pre-made mRNA molecules; your cellular DNA doesn't have to be involved. Summary here.

When a movement opposes the most exciting medical breakthrough in decades, you know that it is based mainly on ignorance and fear.

The Evidence

The Slowness of Niels Bohr

It is practically impossible to describe Niels Bohr to a person who has never worked with him. Probably his most characteristic property was the slowness of his thinking and comprehension. When, in the late twenties and early thirties, the author of this book was one of the “Bohr boys” working in his Institute in Copenhagen on a Carlsberg (the best beer in the world!) fellowship, he had many a chance to observe it. In the evening, when a handful of Bohr’s students were “working” in the Paa Blegdamsvejen Institute, discussing the latest problems of the quantum theory, or playing Ping-pong on the library table with coffee cups placed on it to make the game more difficult, Bohr would appear, complaining that he was very tired, and would like to “do something.” To “do something” inevitably meant to go to the movies, and the only movies Bohr liked were those called The Gun Fight at the Lazy Gee Ranch or The Lone Ranger and a Sioux Girl. But it was hard to go with Bohr to the movies. He could not follow the plot, and was constantly asking us, to the great annoyance of the. rest of the audience, questions like this: “Is that the sister of that cowboy who shot the Indian who tried to steal a herd of cattle belonging to her brother-in-law?” The same slowness of reaction was apparent at scientific meetings. Many a time, a visiting young physicist (most physicists visiting Copenhagen were young) would deliver a brilliant talk about his recent calculations on some intricate problem of the quantum theory. Everybody in the audience would understand the argument quite clearly, but Bohr wouldn’t. So everybody would start to explain to Bohr the simple point he had missed, and in the resulting turmoil everybody would stop understanding anything. Finally, after a considerable period of time, Bohr would begin to understand, and it would turn out that what he understood about the problem presented by the visitor was quite different from what the visitor meant, and was correct, while the visitor’s interpretation was wrong. 

– George Gamow

The Giant Filaments in the Galactic Core

MeerKAT radio map of the Milky Way's core. Notice the "vertical" filaments (perpendicular to the galactic plane), which are a couple of light years across and hundreds of light years long. What an image!

Another view.

The filaments seem to be made of synchrotron radiation, which is produced by particles moving at nearly the speed of light through a magnetic field. Nobody knows, though, what gave those particles their energy, since the don't seem to be streaming away from anything.

MeerKAT has also observed these filaments in other galaxies, and more recently other filaments have been discovered that are roughly parallel to the galatic plane ("horizontal").

More: Scientific American, LiveScience.

The Painters' Pigments of Pompeii

Among the things archaeologists have found in Pompeii are little bowls of painters' pigments.

These have been found in several houses, all of which seemed to be undergoing restoration or redecoration.

They have been studied for a long time, but early investigations were uncertain and contradictory. Now there is a new study from a bunch of Italian chemists who used both powerful microscopes and spectoscopy to study numerous samples.

The main finding is the complexity of some of these mixtures, and also their diversity, with different mixtures producing the same or similar colors. The authors also observe that besides the mixing that took place before the fresco was painted, pigments were also mixed by being applied in multiple overlapping laayers.

It is reminder of the astonishing riches of Pompeii, which holds more knowledge of the past than ten thousand ordinary archaeological sites.

Organic Molecules in the Plumes from Enceladus

On October 28, 2015, NASA steered their Cassini spacecraft past the south pole of Saturn's moon Enceladus. The idea was to use Cassini's dust analyzer to sample the plumes of water that regularly erupt from the south polar region (above) and see if anything could be learned about Enceladus' buried ocean. NASA cautioned at the time that Cassini's equipment was not designed for this task, so it might not work very well, plus the spacecraft's speed at closest approach would be about 17.7 kilometers/second (39,000 mph), not exactly ideal for sampling. They also warned that it might take "some time" for results to be made available.

They weren't kidding about the long wait. The first serious study of this study was finally published yesterday in Nature astronomy. 

The results are interesting but not mind-blowing. Besides the small organic molecules everyone expected (methane, ethane), there were some larger finds: benzene or aryl rings, and what appeared to be compounds that also included Oxygen or Nitrogen; they especially think they may have found Benzyl methyl ether.

The discovery of these molecules, if that is indeed what Cassini found (again, the instrument was not designed for this), shows that the ocean contains organic molecules and has some interesting chemistry. But none of this points toward living organisms.

Again, though, this sample was collected in space by a spacecraft moving very fast and analyzed by an instrument not designed to look for larger organic molecules. So these findings in no way rule out life. But they don't make me believe.

RIP Jane Goodall

Jane Goodall and David Graybeard

When Jane Goodall went to Gombe to observe chimpanzees, in 1960, the world knew almost nothing about them. Everything we know about their social structure, mating habits, diets, and so on springs from her studies. Hers was the first such intensive, intentional study of wild primates I know of, but its success led to dozens of others. She was courageous, meticulous, clear-headed, and caring, and she publicly changed her mind about important claims she had made when new data convinced her that she had been wrong. To my mind, she was the perfect scientist.

Sometimes I marvel at how recent so much of my knowledge of the world actually is. What we knew about the operations of a cell when I was born could have been written on a single sheet of paper. We got our first look at the outer planets when I was in high school; we found the first extra-solar planet in 1992. My universe is vastly large than those of my ancestors.

So I honor Jane Goodall and all the other pioneering researchers who opened the world to us, giving us new tools for thinking about the universe and our place in it.

More Researcher Trouble at Harvard

Sad to say, the evidence the Trump administration is using to blame autism on Tylenol comes from a Harvard dean. The Crimson:

Harvard School of Public Health Dean Andrea A. Baccarelli received at least $150,000 to testify against Tylenol’s manufacturer in 2023 — two years before he published research used by the Trump administration to link the drug to autism, a connection experts say is tenuous at best.

Baccarelli served as an expert witness on behalf of parents and guardians of children suing Johnson & Johnson, the manufacturer of Tylenol at the time. U.S. District Court Judge Denise L. Cote dismissed the case last year due to a lack of scientific evidence, throwing out Baccarelli’s testimony in the process.

“He cherry-picked and misrepresented study results and refused to acknowledge the role of genetics in the etiology” of autism spectrum disorder or ADHD, Cote wrote in her decision, which the plaintiffs have since appealed.

Something about autism seems to make a lot of people crazy. 

Autism is really weird, and I get why a strange condition that destroys young minds in a largely random way freaks people out. But we absolutely do not know what causes it or even what it is, so at present all claims about causes are just sound and fury.

On Medical Research Gone Wrong

At the NY Times, Ari Schulman on Jay Bhattacharya, the new head of the NIH. Bhattacharya got the job because he was a strident critic of Covid lockdowns, but he is a real scientist with an agenda:

Take Alzheimer’s research. Nearly every scientific research reformer will cite the fact that the N.I.H. funded vast amounts of research based on a single theory of the disease that largely turned out to be wrong.

Dr. Bhattacharya argues that this happened because science is structured around authority. “You have, in field after field after field, a kind of set of dogmatic ideas held by the people who are at the top of the field. And if you don’t share those ideas, you have no chance of advancing within those fields,” he told me.

He told Congress that he believes there are promising ways to prevent Alzheimer’s that haven’t received support because they don’t align with the “dominant narrative,” as he called it. “This is why I’m so interested in replication,” he told me, referring to the need for researchers to repeat each other’s findings, because it “turns over the determination of what’s true to nature rather than authority.”

Which is interesting, and perhaps explains why MAGA types like Bhattacharya. But it is, I think, far from sufficient to understand the problems with our scientific establishment. Schulman agrees:

It’s a plausible diagnosis and a good prescription. Science can’t answer questions if it’s conformist. But there’s another way to think about the problem.

Dr. Susan M. Fitzpatrick, a former biochemist, has pointed not to ideology but the mechanics of research. Large-scale medical studies rely on standardized methods, one of which is testing theories on mice. But mice don’t get Alzheimer’s, only humans do. So studying them might be useless. Yet, she wrote, this approach “dominates federal funding and academic science” on Alzheimer’s research because it easily produces the publications and citations that careers depend on.

From this angle, the N.I.H. looks like a big factory that churns out research papers. Dr. Bhattacharya is like a new manager trying to figure out why sales are down and proposing more diversity in the product line.

For the sharpest reformers, like Dr. Cook-Deegan and Dr. Fitzpatrick, the issue isn’t which group of scientists’ ideas win out. It’s that when countless jobs and storied institutions depend on the mills to keep churning, it stops mattering what comes out on the other end. The question is not whether the factory’s settings are wrong but whether it should be a paper factory in the first place.

Here is the fundamental point that science reformers keep screaming about: the system can't be reformed until we have some other way, besides publication counts, of  judging researchers and research. Since nobody has any idea what that might be, real reform seems unlikely.

There seem to be whole fields of research that exist mainly because scientists can publish about them and thus keep their jobs. But what else are scientists supposed to do? They, like everybody else, want to keep their jobs. Many of them would probably rather do weird, cutting-edge stuff that will most likely fail; others would rather switch to a completely different area of science, but our system makes that extremely difficult.

In his conclusion, Schulman comes back to the weirdness of Bhattacharya talking scientific reform in a department headed by RFK, in an adminstration headed by Trump. True, those are big hurdles, but until we have a workable model for reforming science it almost doesn't matter who the president is.

The Four Pests

Beginning in 1955, the Chinese government began calling for the extermination of the "four pests": rats, flies, mosquitoes, and sparrows. People have long claimed that the "smash sparrows campaign" in particular was a disaster, because sparrows controlled insect pests. Wikipedia: 

The eliminate sparrows campaign resulted in severe ecological imbalance, and was one of the causes of the Great Chinese Famine.

According to the government, 2 billion sparrows were killed in 1958, and 1 billion in 1959. 

First hand account: 

It was fun to 'Wipe out the Four Pests'. The whole school went to kill sparrows. We made ladders to knock down their nests, and beat gongs in the evenings, when they were coming home to roost.

It seems to have worked, with very few sparrows reported in China by 1961. On the other hand, sparrows didn't just eat grain, and by 1960 ornithologists began sounding the alarm about multiplying insect pests.

But as I said, that is old news, and most of the articles I have found about it don't radiate objectivity. Lots of "look what happens when people mess with nature" sort of stuff. But now a new paper from Chinese researchers supports this claim and offers some serious estimates of the harm:

How do large disruptions to ecosystems affect human well-being? This paper tests the long-standing hypothesis that China's 1958 Four Pests Campaign, which exterminated sparrows despite scientists’ warnings about their pest-control role, exacerbated the Great Famine—the largest in human history. Combining newly digitized data on historical agricultural productivity in China with habitat suitability modeling methods in ecology, we find that, after sparrow eradication, a one-standard-deviation increase in sparrow suitability led to 5.3% larger rice and 8.7% larger wheat declines. State food procurement exacerbated these losses, resulting in a 9.6% higher mortality in high-suitability counties—implying nearly two million excess deaths. 

I suggest a new list of the four pests: tyrants, the lackeys of tyrants, ignorant ideologues, and people who venerate "action" over understanding. 

The Fermilab g-2 Results Fail to Budge the Standard Model

A generation ago an experiment featuring muons found a possible problem with the Standard Model of particle physics. Muons have a quantity called "g" that a naive view of the theory says ought to be 2. Measurement showed that it is not 2. The difference between the measured value and that naive value is called "g minus 2," written g-2. This issue is called the Muon Magnetic Anomaly.

Since that time we have had, on the one hand, a series of experiments that has reduced the value of g-2, and, on the other, calculations which show that in a real-world scenario g should not be 2, since the value would be impacted by other factors. Much of the difference between experiment and theory has therefore disappeared.

But not all of it. So there was a lot of attention focused on a big experiment at Fermilab designed to measure g-2 with very high precision and accuracy. The results are now in and they confirm that the discrepancy is real.

However, the experimenters do not think this undermines the Standard Model. They think the issue is with those calculations, which are very difficult and complex, and in particular with one of the values that goes into them. 

So for now the Standard Model still holds, and the hope that some new experiment will point a way beyond it fades again.

Fermilab announcement, good 5-minute video from Sabine Hossenfelder.

Chemicals in Food

As you have probably heard, RFK Jr. wants to ban a range of chemical food additives, starting with petroleum-based dyes. Ok, whatever, we can live without bright orange Cheetohs. But I was very disturbed by this Julia Belluz piece in the NY Times. Here is the red flag:

Research on chemicals that have been vetted by the F.D.A. tends to be extremely narrow in focus, looking mostly for cancer, genetic mutations or organ damage in animal or laboratory studies. This means the ingredients in our coffee creamer, cereal, ketchup and frozen pizza aren’t tested for more subtle effects on long-term health, or whether they may increase the risk of the other common chronic diseases, such as obesity, cardiovascular disease and Type 2 diabetes. What’s more, most safety studies examine single chemicals in isolation, not how the hundreds or thousands of chemicals we consume might interact with one another or affect our long-term health.

How, even in principle, would you study how hundreds or thousands of chemicals consumed in various combinations might impact our health? I submit that this is completely impossible. But don't take my word for it, go read John Ioannidis's magnificent article (summary here) on dietary research:

Individuals consume thousands of chemicals in millions of possible daily combinations. For instance, there are more than 250 000 different foods and even more potentially edible items, with 300 000 edible plants alone. Seemingly similar foods vary in exact chemical signatures (eg, more than 500 different polyphenols). Much of the literature silently assumes disease risk is modulated by the most abundant substances; for example, carbohydrates or fats. However, relatively uncommon chemicals within food, circumstantial contaminants, serendipitous toxicants, or components that appear only under specific conditions or food preparation methods (eg, red meat cooking) may be influential. Risk-conferring nutritional combinations may vary by an individual’s genetic background, metabolic profile, age, or environmental exposures. Disentangling the potential influence on health outcomes of a single dietary component from these other variables is challenging, if not impossible.

The mistake that both Belluz and Kennedy make is assuming that if our food is making us sick, the problem must be some nefarious modern chemical. But why assume that? We live much longer than our ancestors, which means that 1) we are exposed to potential natural hazards for decades longer, so whatever dangers those compounds present will show up much more often in our world, and 2) whatever dangers modern food presents, it doesn't keep us from leading long, healthy lives.

So far as I can see, the biggest dangers in the modern diet are fat and sugar, which are both perfectly natural. The reasons we eat too much are complicated, and the advertising and product optimization of big food companies probably play a role. But mainly we do it because we like it. Giving up things that make you feed good is just hard, especially if you feel that your life doesn't offer enough other pleasures. The notion that this can be fixed by tinkering with chemical food additives strikes me as absurd.

The RFK Regime is Censoring Researchers Who Agree with Their Agenda

Kevin Hall:

After 21 years at my dream job, I’m very sad to announce my early retirement from the National Institutes of Health. My life’s work has been to scientifically study how our food environment affects what we eat, and how what we eat affects our physiology. Lately, I’ve focused on unravelling the reasons why diets high in ultra-processed food are linked to epidemic proportions of chronic diseases such as diabetes and obesity. Our research leads the world on this topic.

Given recent bipartisan goals to prevent diet-related chronic diseases, and new agency leadership professing to prioritize scientific investigation of ultra-processed foods, I had hoped to expand our research program with ambitious plans to more rapidly and efficiently determine how our food is likely making Americans chronically sick.

Unfortunately, recent events have made me question whether NIH continues to be a place where I can freely conduct unbiased science. Specifically, I experienced censorship in the reporting of our research because of agency concerns that it did not appear to fully support preconceived narratives of my agency’s leadership about ultra-processed food addiction.

I was hoping this was an aberration. So, weeks ago I wrote to my agency’s leadership expressing my concerns and requested time to discuss these issues, but I never received a response. Without any reassurance there wouldn’t be continued censorship or meddling in our research, I felt compelled to accept early retirement to preserve health insurance for my family. (Resigning later in protest of any future meddling or censorship would result in losing that benefit.) Due to very tight deadlines to make this decision, I don’t yet have plans for my future career.

Dire Wolves?

Colossal Biosciences, which spent years trying and failing to bring back the woolly mammoth, now claims to have brought back the dire wolf. (NY Times, Time, company post on Twitter/X with wolf pup howls)

Sort of. What they did was find some dire wolf DNA, identify 22 places on the genome where they differed from modern gray wolves, alter those locations to be like their dire wolves, insert that DNA in a gray wolf egg cell and have it carried to term by a wolf.

The offspring are different from modern wolves, bigger and with paler, thicker fur. So they are something different from modern wolves. But I am not willing to call them dire wolves.

Still, this is pretty cool, the biggest step yet in the de-extinction program. But note that dire wolves were so closely related to gray wolves that they seem to have interbred with them in the past. Nothing about this success says we might be close to bringing back animals without such a close living relative.

Letting the Data Speak for Itself

From Khoa Vu on Twitter/X.

Soviet Cybernetics

From Tyler Cowen's interview with Stephen Kotkin:

COWEN: Why were the Soviets so obsessed with cybernetics and AI, say, in the 1960s? Is it that they understood where things were going? Or it just was a big stupid mistake?

KOTKIN: You can never rule out big stupid mistakes if we’re honest, certainly about our own lives and analogizing from them. The Soviets were interested in cybernetics because it was about more efficient ways of gathering and using information — the planned economy at core, which was a fantasy, never a reality.

In practice, the planned economy was central control over some scarce commodities, resources, products so that you could prioritize. And you could therefore supply those privileged factories in your supply chains with the scarce resources to produce predominantly military-industrial products, but not exclusively, and the rest of the stuff come what may. That was black market, including black market factory of factory.

Cybernetics was a solution whereby you could make planning work better. You could optimize the information you were getting from the localities, and then you could optimize the way that you organize things. It was a fantasy in a different light, and it’s the same one that the Chinese Communist Party has today, which is to say if your authoritarian politics and your productive economy don’t mesh very well, turn to technology, turn to technological solutions to get beyond the fact that you refuse to do the structural reforms on the institutional side to ensure that the productivity, the dynamism continues.

It’s this eternal fantasy that science and tech will enable you not to have to give up central control, power, Communist Party monopoly. From the scientific point of view, it was fascinating because that’s who they were. They were exceptional world-class mathematicians, world-class physicists, world-class computer scientists, and so for them, it was the same thing it would be for scientists anywhere.

The whole interview is very interesting, especially on life in Magnitogorsk. 

Science and Politics in the US

Not that anyone should read too much meaning into Donald Trump's slapdash appointment process, but I agree with M. Anthony Mills (NY Times) that one theme is a rejection of science:

The leader of the Republican Party and our country’s next president has tapped a pro-choice scion of the country’s most famous Democratic dynasty to lead the Department of Health and Human Services. In keeping with the bewildering dynamics of today’s negative partisanship, conservative groups such as the Heritage Foundation have cheered the selection of Robert F. Kennedy Jr., while liberals have near categorically denounced him.

Mr. Kennedy’s transformation from left-wing vaccine skeptic to potential Republican cabinet member overseeing America’s vast health apparatus represents a profound shift not only in the character of the American right but also in the politics of science more generally. The emergent MAGA science policy agenda, driven by skepticism and anti-elitism, blends familiar conservative and libertarian ideas with a suspicion of expert power once more associated with the left. The result is a uniquely American brand of populism that has the potential to fundamentally reshape national politics.

Back in 1970 Republicans were much more pro-science than Democrats, and the hippie, whole earth, split wood not atoms, make love not bombs thing was launched mainly from the left. Now things have largely switched, and that strikes me as quite important.

Why did this happen? 

Fights over teaching evolution in the schools.

Fights over climate change. You will never understand America until you grasp the intense devotion of many men to their gasoline-powered machines, and more broadly to the old manly economy of mining, logging, and making things in fire-filled factories.

Environmentalism more generally; some of you probably would not believe me if I explained to you the arcana of wetlands law, bat preservation, and other regulations that genuinely hamstring building in this country. 

Covid-19. As all my readers know, I do not forgive the tergivisations of government pandemic policy – e.g., saying that masking is ineffective, then requiring it, or saying that closing schools was not needed and then closing them – or the attitude of leftists toward all of this, e.g. demanding that churches close but insisting that racial injustice is so important that mass protests had to go ahead. 

One could sum all of this up in a more general point, The alliance of science with bureaucrats who tell people what they can and cannot do.

Others:

Health and diet advice more broadly. This one is complex because in many ways medicine has gotten a lot better over the past 25 years, thanks largely to drugs created by Big Pharma and getting doctors to take actual science more seriously. On the other hand that process involved rejecting a lot of what was established medicine 25 years ago, like heart bypass surgery; the weary cry of many science skeptics these days is "they keep changing their minds about everything."

The end of physics. As I regularly post here, I have been convinced by a group of skeptical scientists that sub-atomic physics is at a complete dead end, and astrophysics also seems radically stuck; spending on these things keeps going up and the number of papers published keeps rising, but fundamental progress seems to have halted. Plus there's the phantasm of fusion power, still 15-25 years away. Don't get me started on string theory. None of this inspires confidence in science.

The instututionalization of science. Lots of cutting-edge science used to be done by smart people in tiny labs. Now science is funded at vast expense by huge government agencies and mega-corporations. The scientists themselves are constantly complaining about the process involved in competing for, administering, and accounting for grants, and you don't have to be anti-science to suspect the agendas of the people involved. It strikes me as possible that absolutely nobody understands either the overall nature of this process or its impact on the world, and certainly the average voter has no clue. So if your biggest complaint about the modern world is excess bureaucracy, you're probably going to be suspicious of modern science.

Speaking only for myself here, I understand the frustrations of many people with our science establishment. I would do a lot of wholesale reform if I could, starting by slashing the budgets of sub-atomic physics and manned space flight. I would also radically reform my own field and drastically reduce the number of archaeological sites dubbed "significant."

But we need science. It is the root of everything good about the modern world, and the only possibly solution to many of our problems. We can't survive without it. 

So the turn of a whole political party against the foundation of our world is a bit concerning. Part of me thinks that science is so fundamental that we can't really do much to get rid of it or even change it, but certainly there could be cases where we cast it aside and a lot of people end up dying as a result.

The Scientist's Nightmare

I dreamed that I submitted a workplan for an upcoming project and received the comment that we should be employing Advanced Super Techniques (AST). Then there was a call about the project in which I was again urged to use Advanced Super Techniques. I pretended to know what this meant and made what I hoped were some appropriate remarks about what we might learn using AST, meanwhile frantically googling to find out what it meant; but my screen filled up with a solid block of random letters and symbols.

Then I somehow heard about an expert in AST and went to consult him. His lab was in an old brick factory building. When I entered the building I discovered that the lower floors had been made into artists' spaces, studios with a shop in the center. Everyone looked at me strangely. The geometry of the building was an Escherian impossibility and I was completely lost, but I pretended to know where I was going and fumbled my way around, getting increasingly hostile looks. I eventually made my way up a mad staircase to the Fourth Floor, where I pushed open a door and entered a forest of trees growing in complete darkness. Feeling like I was finally getting somewhere I pulled out my phone, turned on the flashlight, and entered the forest, where I saw strange instrumets and old smartphones hanging from wires around the trees. Then I woke.

Avocados, Giant Ground Sloths, and the Machine of Popular Science

You may have heard that avocados evolved to be eaten by giant ground sloths. After all, most nutrient-rich fruits exist to get seeds deposited in a pile of poop, and what animal could be swallowing and pooping out the huge seeds of avocados? The idea that this might have been giant ground sloths goes back to a biologist named Dan Jansen in a paper published in 1982, but Jansen only offered it as a suggestion in a study mainly about other things, and he did not defend or analyze it. Then a popular science author named Connie Barlow found that obscure paper and put the notion in a book called The Ghosts of Evolution: Nonsensical Fruit, Missing Partners, and Other Ecological Anachronisms (2002).  From there it spread across the the whole landscape of popular science: Atlas Obscura, Smithsonian, etc.

But is it true? According to this this video from people who call themselves Sci Sho (transcript here), it is not. These people claim that 1) we have a lot of data about what ground sloths ate, from analysis of their bones and vast quantities of fossilized poop – some giant ground sloths slept in caves, and they pooped on the megafaunal scale – and it mostly points to leaves and grass, not fruit; and 2) avocados seeds used to be much smaller, 1-2 centimeters instead of the 5-6 centimeters of modern varieties, and that the seeds grew large thanks to domestication by humans. But they cite no sources and don't really radiate reliability.

So I started searching to see what I could find out. One thing I learned very quickly was that the ideas in that video are spreading, so you can get a lot of results if you search for the Myth of Ground Sloths and Avocados. 

But once something gets dubbed a "Myth" in this kind of discourse, you should start to suspect that it might have some kind of truth in it. So we must look deeper.

Somebody on Reddit who calls himself 7LeagueBoots says this:

Just regarding the avocado/giant sloth connection, there is a lot of misinformation embedded in that. There are a lot of different kinds of wild avocados, some with very large seeds, some with seeds about the size of an olive. They're reproducing just fine in the wild right now without any giant sloths running about. The fruit portion of these wild avocados is eaten by a wide range of animals, including bears in South America, birds all across their range, squirrels, and many more. The fact that these wild avocados, including those with large seeds, still persist places a very large question to the oft cited presumption that the were depended on giant sloths that have been extinct for around 11,000 years at this point. The research papers I've read on this subject say that it's a possibility that the trees were dependent on the giant sloths, but they all fail to address the elephant in the room. I worked in Ecuador for a while tracking Andean Spectacled Bears and one of their favorite foods was these wild avocados.

So he basically agrees with Sci Sho, although he says wild avocados have a diversity of seed sizes. But one of the responses to that post, from somebody called Bromelia_and_Bismuth, still comes down hard for ground sloths.

So I decided to look into avocado domestication. This very techincal paper on the avocado genome says that modern avocados are hybrids of three distinct wild "races" that were domesticated separately, and have been selectively bred so they bring out the desirable characteristics of each wild ancestor. And this:

The avocado is heterodichogamous, with 2 flowering types: A and B. Type A trees are female (receptive to pollen) in the morning of the first day and shed pollen as males in the afternoon of the following day. In contrast, type B trees are female in the afternoon of the first day and male in the morning of the next day.

This is presumably to limit self-fertilization, but, wow. Genderfluid trees.

Anyway.

This 2009 article on domestication says, "The large size of the avocado fruit appears to have developed before humans arrived in Mesoamerica, and then changed little in size or shape under human influence." Which seems to be a direct refutation of the claims made by Sci Sho. And on the subject of the three landraces, a term of art new to me, "Fruit size does not help differentiate between domestic and wild avocados due to the variation in fruit size caused by environmental factors and individual tree traits." This is important because the oldest archaeological evidence of avocado consumption by humans comes from mountain caves, so the small size of the seeds in that environment may tell us nothing about the size of ancient avocados in the tropical lowlands.

The data on ground sloth diet has a similar problem, because the surviving coprolites are found in mountainous areas with caves, and they only tell us what ground sloths ate in that environment. We don't have any data on what ground sloths ate in the tropical lowlands where most  avocado trees grew. Tropical forests are just a terrible environment for the preservation of anything.

So far as I can tell, this remains an open question. Avocado fruit are nutrient rich, so just about any herbivore could have eaten them. The fact that wild avocados of recent times survive without ground sloths seems to show that the dependence was not absolute, but it does not rule out ground sloths as key transmission vectors or co-evolution between them. After all there is no real "wild" place left in Central America, and all the forests have been shaped to one degree or another by humans; just as acai palms are a wild species that in practice mainly grows around old human settlements, wild, large-seeded avocados may in practice grow mainly where humans have encouraged them.

There is neither fact nor myth here, just an ongoing struggle to understand.

Which brings me to my real point, the perilous state of popular science writing. To get attention, the science press is constantly proclaiming that things are true when they are at best iffy, revolutionary when they may be decades old, "myths" when they still might be true. Sometimes much of the fault resides with the scientists themselves, who exaggerate their findings. But in this case the scientists are blameless. All Dan Jansen did was wonder what used to eat tropical fruit and suggest that somebody should investigate the possibility of ground sloths, which was a great idea. It might be true. But we don't know, and I hurl foul oaths and imprecations at anyone who says otherwise, and no I don't care what you have to do to get clicks. Tell the truth as best you can or shut up.

The World Grows

Part I: The Earth

The oldest known world map, Babylonian, 6th century BC. The text says this is a copy of a much older map, possibly 9th century BC. Babylon is at the center, surrounded by nine kingdoms, then the "Bitter River."

Reconstruction of the world map of Anaximander (c. 610-546 BC), based on much later texts.

Nineteenth-century reconstruction of the world map of Eratosthenes (c. 276-194 BC), showing the geographic knowledge of the Hellenistic Greeks.

World map drawn at Constantinople c. 1300 AD, based on the work of Ptolemy, c. 150 AD.

Reconstruction Al-Idrisi's Tabula Rogeriana, drawn for Roger of Sicily in 1154 AD. North is at the bottom.

Da Ming Hunyi Tu, the Amalgamated Map of the Ming Empire, c. 1400 AD. China makes up half of this world.

The Fra Mauro Map, c. 1456.

Cantino Planisphere, 1502: The two halves of the globe are united.

Hendrik Hondius, Nova Totius Terrarum Orbis Geographica ac Hydrographica Tabula, 1630

Our planet from space.

Part II: the Cosmos

Egyptian, from The Book of the Dead of Nestanebetisheru, c. 950 BC.

Cosmos of the ancient Hebrews, from here.

Page from the Codex Fejervary-Mayer illustrating a key principle of Maya cosmology, often called the Quincunx, that is, the Five: the Maya world was made up of four cardinal directions and a central point around which everything revolves. The altar in a temple represented that central point. Each direction had its own suite of deities, and there was also a god for each level of heaven and each level of the underworld; counts varied for how many levels there were but went as high as 13.

The geocentric cosmos of Aristotle and Ptolemy, as drawn in 1524.

The heliocentric cosmos, from Copernicus' De revolutionibus orbium coelestium.

In 1755, Immanuel Kant theorized that the visible stars were all in a cluster he dubbed an "island universe," and that the clouds known as nebulae were other island universes a vast distance away. In 1785 astronomer William Herschel drew this map of our island universe, the Milky Way.

By the late 1800s telescopes had grown powerful enough to resolve details in nearby galaxies; this is an 1899 photograph of the Andromeda Galaxy. But many astronomers remained unconvinced that these were really other galaxies as large as our own. In 1917, Heber Doust Curtis observed what he took to be a nova within the Great Andromeda Nebula. Searching through old photographs, he found 11 more novae. He calculated that these novae were about 10 magnitudes fainter than those within the Milky Way. As a result, he was able to come up with a distance estimate of 150,000 parsecs to Andromeda. In the 1920s Edwin Hubble used stars known as Cepheid Variables to refine this estimate to be about 275,000 parsecs, or 900,000 light years.

The Hubble Deep Field, to my mind the most important photograph ever taken. Based on Hubble data, astronomers calculated that there were 500 billion galaxies in the observable universe; that number has since been revised upward to around 2 trillion.