The Memory of Slime

So you're telling me slime molds can solve mazes and recreate trade routes? Yes, indeed we are. In this episode, Julie and Robert explore the "intelligence" of slime molds and why they force us to re-think the evolution of intelligence.

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow your Mind from how Stuff
Works dot com. Hey you welcome to Stuff to Blow
your Mind. My name is Robert Lamb and my name
is Julie Douglas, and we are rounding up the Trilogy
of Slime. Here we have. We started off with an
episode tital Trilogy of Slime, where we talking about the
natures of the nature of slime and organisms and all

(00:26):
the important roles that it serves. Then we did a
little Valentine special about the sex life of slugs, which
is also very slimy but also a little stabby. And
then finally we are discussing the slime mold, which is uh,
taking it in a in a different direction, but a
really really deceptively mind blowing direction, because when you just

(00:47):
talk about the word mold itself is kind of boring.
Mold is something that grows somewhere that you don't think about,
you know, It's like it's it's that's the stuff that
grows in the tub, it grows in the corner, grows
under the house maybe and unless you think about it
the better. Yeah. Um, but slime mold is actually something
that is helping is to redefine intelligence and we'll talk

(01:09):
a bit more about that in a moment. Um. But
when we talk about slime mold and we say mold,
we actually are not talking about any sort of fungus here, right,
We're talking about mainly when we talk about slime old
is something called phi serum polycephalum, and that that name
actually means many headed slime mold. Slime is not a

(01:31):
slime mold is not a plant or an animal. It's
not a fungus, though it sometimes resembles one structurally. Yeah,
it's a single, single celled creature, brainless, brainless, No, no
brain and that's important here, no nervous system to speak of.
And yet it's intelligence. It's what fascinates us. Yeah, I
mean it ultimately makes us really think hard and deep

(01:53):
about what intelligence is and what it can be, especially
when we're trying to think about what what life could
be like elsewhere in the in the universe. Um. And
when you say in the universe, you should consider that, Uh,
these guys go back in evolutionary history history about a
billion years. And according to Dr Baldolph, who is a
Swedish biologist studying the DNA of slime mold species, she

(02:16):
says that they might be tightly linked to the development
of soil on land, which is very cool to think
about when you think about slime mold. Yeah, it's kind
of triggy to to to really look at our history
of fly mold because it's not something that really lends
itself well to the fossil record. Yeah, exactly. We do
know that there are nine hundred known species of slime mold,
but they're really only about two that are studied in earnest.

(02:38):
Slime mold's live in moist terrestrial habitats like decaying wood
or fresh captung nice and once the mold has found food,
such as a piece of decaying vegetation or a micro organism,
it grows over it and it secretes digestive enzymes. So
something like polycephalum then construct an elaborate network of interconnections

(02:59):
between foods sources which allow it to shuttle nutrients around
and get the full form of the organism fully fed. Um.
Slime molds then devour many parts of bacteria, and then
this releases those nutrients for other organisms to grow on.
So it's a huge part of the ecosystem. So what
does it look like, Um, it does not really so

(03:19):
much look like slime per se like, it doesn't look
like Nickelodeon bucket of slime falling on someone's head. And
it has more of a yellowy consistency to it. It It
doesn't particularly look viscous. Yeah, a lot of people have
lined it to dog vomit. Um. That's a that's the
usual thing that people spot. UM. But it actually comes

(03:40):
in nearly every color of the rainbow except green because
it lacks chlorophyll um. Some resemble honeycomb lattice structures, others
kind of look like BlackBerry configurations. UM. And then of
course there's the dog vomit, which is the classic thing. UM.
Some remain microscopic to the eye, but others grow large,
and you can form boldest masses as long as ten

(04:02):
to thirteen feet long. So in the second we're gonna
we're gonna get into the idea of what happens when
you put slimold in a maze. But but imagine you
have a slime mold working its way down a corridor
and what happens when it encounters another slime mold coming
down the corridor from the opposite direction. You probably want
to do they do they fight each other? Do they

(04:24):
is there a war of slime mold that takes place here? Well,
if food is scarce is what's interesting is they do
essentially team up into it like a single communicating mass. Yeah,
it's really cool. Um. This is from a New York
Times article, Can answers to evolution be found in slime mold? Yeah?
The organisms do respond to starvation by rushing together by

(04:44):
the thousands into a single blob. And the blob stretches
out into a slug shaped mass about one millimeter long,
which is about one inch, and then it begins to
crawl along like a worm toward light. Wow, like like
a caravan of line. Really yep yep. And then once
it reaches the surface surface of the soil, the slug,

(05:05):
this the slug configuration undergoes another transformation. Some of the
cells turn into a stiff stock, while the others crawl
to the top inform a sticky ball of spores and
they stick to the foot of an animal and travel
to a hospitable place. So inside the slug. And this
again is according to the article, about one percent of
the miba's turn into police. This is really cool. They

(05:28):
crawl through the slug in search of infectious bacteria and
then they vanquish it. Really, they find this pathogen and
they devour it. And then these sentinels drop away from
this slug configuration of slime mold, taking the pathogen with it,
and then they die of the infection, while the slug
itself remains healthy, the colony of it remains healthy. So um,

(05:51):
this is so amazing to me. This is all going
on at this microscopic level. This these acts of altruism. Really. Yeah,
all right, we're gonna take a quick break and when
we come back, we will enter the maze with the
slime mold and discuss exactly how it finds its way out.

(06:14):
All right, we're back. So the maze. We we did
a whole episode on mazes, and we discussed what they
are and what they symbolize for us humans. Essentially, you're
talking about uh binding, confusing pathway corridors that end in
dead ends while other corridors take you ever closer to freedom.
So we often use these in science experiments. Put a

(06:37):
mouse inside of a maze. See what happens when it
gets stressed out? See if it can find its way out?
What happens when you put a slime mold into a
maze is really fascinating because now, for one thing, you
do have to sort of um. You have to create
a situation where the slime old quote unquote wants out,
the slime mold wants to find its way to food.
So that becomes the the idea here um for a

(06:59):
dead end. To be a true dead end, it needs
to not have something that the slime old can eat
at the end of it, whereas they dad end with
food at the end of it is essentially kind of
an exit. So they found that if you put a
Researchers have found it that if you put a slime
mold inside of this maze, it will start off by
mapping its environment out. It will send out these uh,

(07:19):
these tendrils, and they will follow every course in the
maze to its end. And if they find a true
dead end where everything just ends and there's no food there,
then it will retract, but it will leave a trail
of slime that kind of works as an external memory
of where it has been, and that is a that
is a hallway that it need not go down again

(07:40):
because there's no food down there, and then it will
concentrate its efforts on the pathways that do lead to food. Yeah,
it's really cool. As you say, it's like this externalized
spatial memory and um. And again no brain. Creature does
not have a brain, and it is not intelligent in
the larger sense of the word. But it is is

(08:00):
using a certain amount of matt making intelligence. It's using
that chemical scent to figure out where it's been and
then not expend the effort on searches that won't pay off. Right,
So it's saying, I've been down that hallway, there's no
no reason I need to redouble my efforts on this.
Another cool thing is that the five serum slime mold

(08:20):
sends these tendrils of protoplasum out search for food. And
it's but but it's not just hey, wholesale everybody find food.
What they do is they say, okay, this one over
here to the left has found some food. These guys
over here on the right have not. All right, everybody
reconfigure and now let's bolsh for our efforts to that
food to the left. So they reorganize themselves to then

(08:43):
sort of go in and effectively cover that food spectrum
that they did find, which is amazing. So not only
are they making sure that they're not going into areas
they've already been, but when they do find food, they're
able to to sort of say, all right, troops, here
we go, We're now going to some trade on this.
All right. All of this is really amazing when you

(09:04):
look at it in the context of engineering problems that
we humans try to solve every single day. Yeah, particularly
um it's it's interesting when you take the slime mold
and you put it over a major city, and then
you distribute the food in a way that resembles uh,
major population points, major points of interest, places that you

(09:24):
need to say, a public transportation system to reach. So
if it were a map of Atlanta, for instance, you
would have like central Atlanta, Midtown, you'd have the Bucket
area where we are, and and various other important places.
Um well, several of those in both places are probably
not gonna reach by public transportation down here as far
as the train goes. But that's a whole another story.

(09:46):
But you put the slime mold in there and you
let it figure out the best ways to get to
its food sources, and researchers have found that the paths
that the slime mold creates are comparable to the major
public transportation system in those cities. You know, we've seen
this again and again. It's not just Okay, there's just
one set of researchers doing this. But I think the
standout in this is the Tokyo railway system. Um, it's

(10:10):
a two excuse me. In two thousand and ten, mathematical
biologists toshi Yuki naga Aki and his colleagues observed how
this networking behavior could translate into efficient city planning. So
they drew a map of Japan. They put oat flakes
on the map to represent cities, and then they let
the five serum loose on the area that represented Tokyo, Okay.

(10:32):
So key to this is that they're obviously going to
be obstacles in city planning, like waterways that you can't
you have to make sure that you didn't try to
transverse long standing buildings and areas that you're just not
going to bulldoze to build your right. So what they
did is they took bright lights in these areas and
which slim olds will avoid they do not like, and

(10:52):
so those represented those areas that they knew that you
couldn't do any sort of public transportation around. And then
what bloomed in front of the researcher with the FI
serum network that produced interconnections just that were strikingly similar
to the layout of the Tokyo railway system and um
in the ways that they differed from the actual Tokyo

(11:12):
railway system. It turns out that their methods of reaching
uh net networked UM places was much more effective that
than what was already in place. So what we're saying
here is that slime molds are solving engineering problems. I mean,
this is amazing. This is stuff that we spend a

(11:34):
lot of time on. This is these are computer programs,
are modeling that's going on, and you just let a
sly old loose and they can help. It'll equal or
exceed human production on those of those same trade routes
are same public transportation routes. Because another one that I
ran across what was they were actually able to get
up of the serum to um to reproduce the silk

(11:57):
road in various other global trading routes. Put it on
a map of the Earth and you'll see, oh, it's well,
there's a silk road right there. It's thinking along the
same lines as uh as as as humans did when
they were trying figure out how to get from a
point A to point B in the most effective manner possible, right,
And when they took that globe to they configured it
so that again there were certain places that that mold

(12:17):
couldn't try to transfer because of the configuration of the
continents and the continents of that time. And so they
tried to reproduce that and that is amazing that the
silk road came up. That popped up. Another example I
think it's really cool is this is by Andrew Adamatzki,
and he's a researcher at the University of West England.

(12:37):
He wanted to figure out what would happen in the
nuclear disaster. In other words, if a reactor melted down,
what would be the best course of action for citizens
to flee from it. So he took those ice eilier
modes that um that are used for highway like patterns,
and they grew a slime mold network of highways for Canada.

(12:59):
And then they placed a crystal of salt which repels
slime molds on the map where the Bruce nuclear power
plants located in Canada. And then what they found is
that the slime mold abandoned its tendrils near the salt
and then grew a new highway pattern that efficiently re
routed food across Canada and also showed different paths that
you could leave obviously this area. So it sheds some

(13:22):
sort of light on what can happen in disaster situations. Yeah,
that's it's just amazing to think about slime mold is
that is, being capable of doing this um and again
it ultimately makes us rethink what intelligence is, um is
as we we look at possible models for extraterrestrial life. Yeah.

(13:42):
Adam Rogers, he's a senior editor at Wired. He has
a really interesting riff on this, so if you want
to see his video, check that out on Wired dot com.
I believe the column is observation Deck Intelligent slime Molds
and the applications here with slime molds, I mean, aside
from possible shooting scenarios that were in addition to UH

(14:03):
their biophysicist in Germany and Singapore who think that the
mathematical models that they were agam based on sly mold
behavior might lead to new ways to starve tumors of
blood and essentially to a fight cancer, Yeah, which is
because what they found is that again there's this mathematical
similarity in the ways that a tumor tries to gain

(14:25):
nutrients from the body and the way that slim mold grows.
So taking those those two um examples, they can actually
try to figure out ways that they could try to
starve that tumor. As you say, yeah, I mean it
all comes down I think to the idea you think about, Okay,
what is what is mathematics? What is our what is
our spatial understanding? What is what is the the ability

(14:46):
to create a map on a piece of paper as
a as an intelligent human like, it all comes down
to our ability to navigate the physical world. Um, it's
just kind of a an ability that has grown, uh
for more robust with the passage of time, with our
evolution and then with our the building of our culture.
But at it's at the very like base level, something

(15:09):
even without a brain, has to be able to do
this to some level. And the and the slime mold
does a fantastic job. So if you ever find yourself
lost wandering about, think about, yeah, I think about the
serum polysphal um, and take take heart in saying that
this uh, this organism that goes back a billion years

(15:33):
can find a way and so too can you. All Right, well,
there's slime Mold for you, and that finishes out our
three episodes on slime. If you missed it any of
the other two, do check them out. There's a lot
of cool data in there, and it really really made
me rethink what slime is. And really, as I mentioned before,
a long time fan of slime loved slimy monsters, slimy

(15:53):
things even as I hated slugs, and uh, and there's
just so much more there, uh, not only understanding how
slime works, but but slugs as well. I mean, they're
I think, to slug like monsters that have appeared in
various uh forms of fiction and even once where they
do a pretty good job of making the creature monstrous, like,

(16:13):
they really don't dive into all of the just weird
and fascinating biology of a slug. So just putting that
out there, are there any potential filmmakers and fiction weavers
in the audience, Well, let's call the robot over and
do one quick listener mail this when it comes to
us from Catherine and she has a book recommendation for us,
She says, Robert and Julie, your most recent podcast made

(16:34):
me think of one of my favorite books by my
favorite author. For a great book about pretending to be
someone you're not, I recommend Mother Night by Kurt Vonnegut.
The main character is an American playwright who has spent
most of his life in Germany. As an adult, during
World War Two, he was recruited by the US government
to help transmit messages to the Allies. He does this
via code inserted into his Nazi propaganda radio show. He

(16:55):
is so good at pretending to be a Nazi that
he has respected as a leader within the Nazi Party.
He also managed to get on the list of wanted
war criminals. The problem is that he entered this knowing
that the U s would never recognize his work, nor
would they come to his defense. So really, the only
people invested in keeping him alive or the nazis a
group he does not truly want to be a part of.
There's a movie made of the book starring Nicknolty. Read

(17:18):
the book. Thanks as always for the entertainment and education.
I hate the term entertainment. Yeah, I don't think we
really use entertainment either. But let's got a bit of
a musty ring to it. Yeah, but we hit the idea.
But we're we're glad that we're providing some interesting tidbits
for you guys. That's an awesome book recommendation, something I
definitely want to follow up on. Yeah, I've I've only

(17:39):
read a couple of Vonnegut stories of read Slaughterhouse Five
and The Sirens of Titan. Good stuff, especially Slaughterhouse Five,
one of my all time favorites. So hey, if you
want to reach out to us, you want to share
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(18:01):
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(18:21):
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