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Magic mushrooms evolved to scramble insect brains, send them on wild, scary trips

How psilocybin evolved has more to do with sending insects on terrifying trips than it does making Phish sound good.

Photo credit: Mister Starman on Unsplash
  • Fungi species that produce psilocybin—the main hallucinogenic ingredient in "magic" mushrooms—aren't closely related to one another.
  • Researchers have discovered that the way these fungi independently gained the ability to produce psilocybin is because of horizontal gene transfer.
  • Based on how uncommon horizontal gene transfer is in mushroom-producing fungi and the types of fungi that produce psilocybin, it seems likely that the hallucinogenic chemical is meant to scramble the brains of insects competing with fungi for food.

Throughout our history, human beings have demonstrated a powerful and committed love of tinkering with our brain chemistry. We drink the waste of sugar-eating bacteria, smoke the leaves of garden-variety weeds, and munch on mushrooms whose chemicals give us such a strange experience we have to call it magic. We've been doing this for thousands and thousands of years, too: Cave paintings of certain mushroom species suggested that our ancestors liked to turn on, tune in, and drop out as well.

But the very fact that magic mushrooms exist and that their main psychoactive ingredient—psilocybin—can provide such a powerful experience is odd. Nearly all of the qualities of the various species of life on Earth have some kind of functionality. Deer don't have antlers because they're pretty; they're there for mating displays. Cheetahs don't run fast because they're big fans of cardio exercise; its their strategy for catching prey. Magic mushrooms don't produce psilocybin because it makes human beings hallucinate; it's there for a reason.

What makes psilocybin so unusual?

The researchers believe that psilocybin production evolved to disorient insects that would otherwise compete with the fungi for food or consume the fungi themselves.

Photo by Егор Камелев on Unsplash

New research in the journal Evolution Letters has uncovered evidence for the functional purpose of psilocybin in fungi. It's there to screw with insects; specifically, those insects that wouldn't mind chowing down on a fungi's mushroom or on the food that fungi themselves like to eat—dung and wood.

Part of what's made it so difficult to pin down the purpose of psilocybin in mushrooms is that psilocybin-producing mushrooms are mostly not related to one another. It doesn't appear as though a common ancestor developed the ability to produce psilocybin and passed it down to its offspring. Instead, five distinct, distantly related families of fungi make psilocybin.

Psilocybin is a secondary metabolite, meaning it's an organic compound not involved in the growth, development, or reproduction of the fungi itself. Necessarily, its expensive to produce secondary metabolites, and psilocybin in particular is a complicated molecule to make. So, it's extremely weird that it's popped up in disparate species of fungi.

What put the magic in magic mushrooms?

Psilocybe cianescans, one of the psilocybin-producing fungi that the researchers studied.

Photo: Wikimedia Commons

It's unlikely that psilocybin production evolved in distinct mushroom species spontaneously, and since these species aren't related, it's pretty clear that vertical gene transfer—passing down genes from parent to child—is not responsible either. Instead, the researchers surmised that horizontal gene transfer must be the culprit.

Horizontal gene transfer doesn't take up much space in the general public's understanding of evolution. We typically think of evolution as gradual, random changes in the gene that accidentally improve the species' fitness in its environment, which are then passed down to offspring. But genetic material can also be passed between distinct but co-existing species.

While there are a few different mechanisms for horizontal gene transfer, larger critters probably receive genes from other species via transposons, genes that mostly do nothing besides jump around in the DNA and cause problems. Sometimes, transposons take another gene along with them, occasionally getting mixed up with viruses, insects, or other third parties who then deposit the gene into another species.

As an example, the transposon BovB makes up about a quarter of cows' genome, and it's also found in snakes, zebrafish, geckos, and other random species. Rather than there being a branch on the tree of life that traces a distinct line of critters with BovB, instead it looks more like a Jackson Pollock painting—random islands of animals with the BovB gene. Clearly, BovB didn't get to these disparate species by a common ancestor. Instead, it jumped around, hitching rides with third-parties like viruses and insects. Here's a video explainer.

Environment over ancestry

Horizontal gene transfer also appears to be how magic mushrooms got their magic. The interesting part about this is the outsized effect the fungi's environment plays on their evolution. Fungi compete with insects for dung and wood and also are frequently eaten by insects themselves. Producing psilocybin is a great way to scramble the brains of any insect that gets too familiar. Because psilocybin production is so useful to fungi that eat dung and wood, when genes for psilocybin production are randomly inserted in their genome, they thrive, outproducing non-psilocybin-producing fungi.

Psilocybin has recently gained recognition for its ability to treat depression, PTSD, and other mental disorders, which is wonderfully serendipitous for a chemical that started off as an insecticide. In fact, most of the chemicals humans use recreationally or medicinally were made by plants and fungi to ward off insects that would eat them or eat their food. Now, thanks to this research, we have another way to identify what kinds of plants and fungi might hold secret chemicals we can use to improve our lives.



Hulu's original movie "Palm Springs" is the comedy we needed this summer

Andy Samberg and Cristin Milioti get stuck in an infinite wedding time loop.

Gear
  • Two wedding guests discover they're trapped in an infinite time loop, waking up in Palm Springs over and over and over.
  • As the reality of their situation sets in, Nyles and Sarah decide to enjoy the repetitive awakenings.
  • The film is perfectly timed for a world sheltering at home during a pandemic.
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Two MIT students just solved Richard Feynman’s famed physics puzzle

Richard Feynman once asked a silly question. Two MIT students just answered it.

Surprising Science

Here's a fun experiment to try. Go to your pantry and see if you have a box of spaghetti. If you do, take out a noodle. Grab both ends of it and bend it until it breaks in half. How many pieces did it break into? If you got two large pieces and at least one small piece you're not alone.

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Our ‘little brain’ turns out to be pretty big

The multifaceted cerebellum is large — it's just tightly folded.

Image source: Sereno, et al
Mind & Brain
  • A powerful MRI combined with modeling software results in a totally new view of the human cerebellum.
  • The so-called 'little brain' is nearly 80% the size of the cerebral cortex when it's unfolded.
  • This part of the brain is associated with a lot of things, and a new virtual map is suitably chaotic and complex.

Just under our brain's cortex and close to our brain stem sits the cerebellum, also known as the "little brain." It's an organ many animals have, and we're still learning what it does in humans. It's long been thought to be involved in sensory input and motor control, but recent studies suggests it also plays a role in a lot of other things, including emotion, thought, and pain. After all, about half of the brain's neurons reside there. But it's so small. Except it's not, according to a new study from San Diego State University (SDSU) published in PNAS (Proceedings of the National Academy of Sciences).

A neural crêpe

A new imaging study led by psychology professor and cognitive neuroscientist Martin Sereno of the SDSU MRI Imaging Center reveals that the cerebellum is actually an intricately folded organ that has a surface area equal in size to 78 percent of the cerebral cortex. Sereno, a pioneer in MRI brain imaging, collaborated with other experts from the U.K., Canada, and the Netherlands.

So what does it look like? Unfolded, the cerebellum is reminiscent of a crêpe, according to Sereno, about four inches wide and three feet long.

The team didn't physically unfold a cerebellum in their research. Instead, they worked with brain scans from a 9.4 Tesla MRI machine, and virtually unfolded and mapped the organ. Custom software was developed for the project, based on the open-source FreeSurfer app developed by Sereno and others. Their model allowed the scientists to unpack the virtual cerebellum down to each individual fold, or "folia."

Study's cross-sections of a folded cerebellum

Image source: Sereno, et al.

A complicated map

Sereno tells SDSU NewsCenter that "Until now we only had crude models of what it looked like. We now have a complete map or surface representation of the cerebellum, much like cities, counties, and states."

That map is a bit surprising, too, in that regions associated with different functions are scattered across the organ in peculiar ways, unlike the cortex where it's all pretty orderly. "You get a little chunk of the lip, next to a chunk of the shoulder or face, like jumbled puzzle pieces," says Sereno. This may have to do with the fact that when the cerebellum is folded, its elements line up differently than they do when the organ is unfolded.

It seems the folded structure of the cerebellum is a configuration that facilitates access to information coming from places all over the body. Sereno says, "Now that we have the first high resolution base map of the human cerebellum, there are many possibilities for researchers to start filling in what is certain to be a complex quilt of inputs, from many different parts of the cerebral cortex in more detail than ever before."

This makes sense if the cerebellum is involved in highly complex, advanced cognitive functions, such as handling language or performing abstract reasoning as scientists suspect. "When you think of the cognition required to write a scientific paper or explain a concept," says Sereno, "you have to pull in information from many different sources. And that's just how the cerebellum is set up."

Bigger and bigger

The study also suggests that the large size of their virtual human cerebellum is likely to be related to the sheer number of tasks with which the organ is involved in the complex human brain. The macaque cerebellum that the team analyzed, for example, amounts to just 30 percent the size of the animal's cortex.

"The fact that [the cerebellum] has such a large surface area speaks to the evolution of distinctively human behaviors and cognition," says Sereno. "It has expanded so much that the folding patterns are very complex."

As the study says, "Rather than coordinating sensory signals to execute expert physical movements, parts of the cerebellum may have been extended in humans to help coordinate fictive 'conceptual movements,' such as rapidly mentally rearranging a movement plan — or, in the fullness of time, perhaps even a mathematical equation."

Sereno concludes, "The 'little brain' is quite the jack of all trades. Mapping the cerebellum will be an interesting new frontier for the next decade."

Economists show how welfare programs can turn a "profit"

What happens if we consider welfare programs as investments?

A homeless man faces Wall Street

Spencer Platt/Getty Images
Politics & Current Affairs
  • A recently published study suggests that some welfare programs more than pay for themselves.
  • It is one of the first major reviews of welfare programs to measure so many by a single metric.
  • The findings will likely inform future welfare reform and encourage debate on how to grade success.
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