January 10, 2019 • 37 mins
As humans, we’re quite accustomed to our weird vertical spines and precarious two-legged gait. But habitual bipedalism is far from the norm. When did it first occur on planet Earth? Will the robotic future walk on two legs? And can we reasonably expect alien lifeforms to follow suit? Robert Lamb and Joe McCormick explore in this episode of Stuff to Blow Your Mind.
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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 I'm Joe McCormick.
And today we're talking about bipeds, bipedalism. Uh. And this
is a this is a topic that I was just
(00:25):
kind of rattling around my brain the other day because
for most of us, walking is just kind of every day, right,
you run a little bit, uh, maybe you hop a
little bit. It's of course involved multiple times and mammals.
You have macropods, kangaroo rats in my spring hair hopping,
my pangolins, and of course homing a apes um much
which includes ourselves and sometimes scientists, you know, make the
(00:47):
distinction between facultative and obligate bypeds, though this isn't a
standard distinction, suffice to say they're creatures such as the
human flightless birds, and to draw on a prehistoric example,
the t w rex, that have no real alternative to
bipedal movement. I mean, I can crab walk around, Yeah,
I wouldn't. If if you're crab walking, you're still bipedal
(01:09):
unless you can grow some crab legs. It depends which
version of the crab walk. Are you're talking, you're talking
about where you're I'm talking where you know, you lean
back and you go on all four your belly up
in the air. Because there's also the Zoidberg walk, where
you walk from side to side. That's a good one,
but that's not that that would just be bi Zoidberg
is a biped No no, no, no, I mean the
the Exorcist down the stairs. Well oh yes, yes, okay,
(01:30):
well that that would count, but I fully grant you
I probably wouldn't get around very quickly doing that all
the time. Other creatures, of course, are capable of bipedal locomotion,
but only employed under certain circumstances, like, for instance, a
lemur dancing you know, sort of prancing sideways across a
clearing between two trees, a giant ground sloth in in
(01:53):
in old and olden days, rising up to reach higher branches,
or or one of my favorites, a cat standing on
its hind lay eggs to better view pray or something
of interest. This is always a creepy, weird side if
you're lucky enough to witness it. Oh but it also
can be very cute when dogs stand on two legs
to to get up there closer to the treat that
they want. Oh, yeah, it's adorable. It's yeah. When dogs
(02:17):
do it, it's adorable. When cats do it, it is
it's a little unsettling, like they've suddenly become tiny people,
like they've been people all along, um or that's my
read on it. Now. When it comes to the hominans,
which again includes humans, the oldest evidence of bipedal movement
in a hominant species was probably six million years ago.
This would have been the selmthropists, and there's some dispute
(02:39):
over this, but any rate, we were mostly bipedal by
say four million years ago. We had a curved spine
by two point five million years ago, and it altered
our hip support by one point nine five million years ago,
and we were fully bipedal by the time of Fomo erectus,
with signature pelvis and thigh bones evident in the fossil record.
The legs lengthened over time, allowing for longer strides everything
(03:03):
that would enable the ministry of silly walks to do
its thing. Yeah. Now, some of what we know about
the posture and gate of our ancient ancestors and their
close relatives has to be inferred indirectly. I mean, you
can get a pretty good idea from like the shapes
of bones and stuff that that will tell you a lot.
There's other there's other evidence that's very direct. A great
piece of early direct evidence for bipedality is the fossil
(03:26):
formation known as the Late Totally Footprints. So, Robert, have
you have you seen what these look like? I think
I have everybody very cool in In nineteen seventy six
there was a team working with the paleontologist Mary Leaky,
and they discovered a collection of fossilized animal tracks in
late Totally Tanzania, which is south of the Old Duvai Gorge.
(03:47):
And the tracks were preserved in what had been a
soft bed of volcanic ash about three point six million
years ago or three point three point six three point
seven uh and it had hardened and been preserved for
us to discover in the twentieth century. And then so
after these tracks were initially discovered, in nineteen seventy eight,
Paul Able, a colleague of Leaky's, discovered that the formation
(04:10):
also contained a twenty seven meter or about eighty eight
foot long trail of ancient hominin footprints in addition to
the other animal footprints, probably made by Australian Epithecus afarensis,
the species to which Lucy belonged, And there were about
seventy hominin footprints at all in all in this formation.
And so the thing about these footprints is they're quite
(04:32):
clearly bipedal. You know, you're not seeing four legged movement,
and somebody was just walking on two feet through this
volcanic ash. The prints i've read are space close together,
meaning a short stride might mean short legs. And the
prints also show a big toe in line with the
foot rather than opposed to the foot, as you see
in arboreal apes. So like you know, your human big
(04:54):
toes go straight out, the arboreal apes have more kind
of a toe thumb, like a big toe thumb, uh,
that they used to climb trees and grab hold of stuff.
And also their footfalls apparently went heel toe, just like
ours tend to. So by about three point six million
years ago, we we've got direct evidence that our ancestors
and their close relatives were walking on two feet. Uh.
(05:16):
And I also can't help but mention I've read supposedly
there's this story of how the prints were discovered because
one of Leaky's colleagues, a paleo anthropologist named Andrew hill Uh,
stumbled across the fossil formation when he and another colleague
were running around throwing elephant poop at each other. Oh well,
you know you gotta keep it lighthearted on the dick, right, So, um,
(05:39):
like you said, we we know all of this based
on mostly fossil remains, and by that this, you know,
we're looking at the bones of our ancestors and observing
what the gradual shift to bipedalism did to us. And
it certainly certainly came at a cost. Yeah, now, to
be sure it was it was worth it, I guess.
I mean. It made it easier for us to pick
up fruits and pick up pick from a low line branches.
(06:00):
It gave us free hands for carrying food and also
very importantly carrying tools, carrying our young as well. It
allowed us to rise up and appear larger and more
fearsome to our enemies. Are many enemies of the wild.
This is something that I think we often don't think about.
But unless you're being instructed on how to react to
a bear in the win the wild, you know, they say,
(06:22):
make yourself as big as possible, and certainly there are
other animals that do just the same thing, but that's
one of the strengths of being able to at least
rise up on two feet. Yeah, now you can't know
this for sure, but I tend to think that bipedalism
is a sort of necessary precursor to advanced tool using intelligence.
(06:43):
I mean, you see some use of tools in quadrupedal apes,
but the fact that the fact that you're walking on
two feet gives you free hands, and having free hands,
it seems like suddenly you've got much more incentive to
be using them for all kinds of stuff. Well, it's
interesting when you think about the animals that do display
(07:03):
some form of tool use. I mean, certainly you have
the the apes, which are going to more or less
aligned with the human experience of tool use. But then
of course you have like the corvids uh and uh
and a few other birds that that also use tools. Now,
obviously they are engaging in bipedal ground movement. Their wings
are tucked away, but it's perhaps and it's a slightly
(07:26):
different situation with birds because those wings do have a purpose. Uh,
They've just specialized their their their beak functionality, and I've
learned how to use tools with that. The same is
truy of dolphins. You know they're using when they engage
in tool use, are using their snout um octopi slightly
different situation they have they have They have a wide
variety of limbs and are not necessarily gonna become bipedal
(07:49):
anytime soon. So anyway you shake it the back to
the human scenario, it helped us expand our range. It
It definitely played a part in our our ascension or dominance,
certainly our ability to invent things and expand, but we
also paid a price. We had to distribute all of
our weights on two limbs, resulting in all sorts of
painful experiences such as a lower back pain, slip discs,
(08:12):
arthritis in the lower body, fallen arches. Our spines are
ultimately just kind of weird. We evolved wider hips and
stronger knees to kind of cope with it to a
certain extent. But this is the reason that roughly of
adult humans will experience back pain in their lives. I
would say one of the biggest anatomical drawbacks is that
we can make finger guns at each other. I mean
(08:34):
that that is a true blow to the species you mean,
I mean the beneficial kind where like kids playing cowboys
and Indians or whatever on the playground, know the like
the like catch you later, bro Okay. So also it
also affected the way that we give birth and uh
and this is a I have to say, this is
a topic that we could easily have devoted an entire episode.
(08:56):
There's a lot of scholarship and debate on exactly how
the modern human birthing scenario pans out towards prehistoric examples,
but the move towards the bipedal form changed our skeletons.
This affected the pelvis. Most primates have a pretty straight
birth canal, but hominans soon boasted a narrow, distorted, kind
(09:17):
of fun house tube of a birth canal. The offspring
had to twist and turn in order to pass through.
This is true of our our ancestors. But our bodies
continued to evolve. We became taller, we grew larger brains.
That means meant bigger brained babies having to make it
through that twisting tunnel. Everything became tighter. Child birth became
(09:37):
a potentially more dangerous affair, because it also means giving
birth to a child an earlier stage of its development
in order to actually break it free from the confines
of our bipedally twisted bodies. Now, again, there's a lot
more to this. Scientists have gone back and forth on
the so called obstetric dilemma, but bipedal evolution certainly changed things.
(09:58):
All right, I think we should take a quick break.
We will be right back to discuss why bipedalism evolved
in humans. Thank alright, we're back. So this is a
big question because certainly we can point to all of
these like the pros and all the cons, but like,
what is the driving force right right now? What caused
our our ancient hominin ancestors to go on two legs? Primarily,
(10:22):
why did our ancestors become bipetle And this is an
ongoing debate. We know at some point we transitioned from
mostly four footed gate to a mostly two footed gate,
but why did it happen and what type of pressure
selected for this? So, first of all, when answering questions
like this, it's often hard to be certain, right, you know,
we only have the evidence we can find. Fossil evidence helps,
(10:44):
but it's hard to like run new experiments to test this.
We you know, we only have the fossil finds we
have and can only draw the conclusions we can draw
from them. And there have been all kinds of answers
over the years. So for a long time, consensus seem
to be that bipedalism was an adaptation to a change
in our primary habitat, as our ancestors moved down out
(11:08):
of the trees into a flat grassland, perhaps driven by
changing climate, like changing climate killed off forests and left
these you know, savannahs with tall grasses in their place,
or these creatures just moved down into the savannahs to
follow food sources or something. In this case, uh, these
hominins needed to stand up to see over the tall grass.
(11:30):
And this explanation is not still favored. This has fallen
out of favor among experts, and one reason is that
climate history analysis and physical fossil evidence indicate that we
were becoming bipedal at the same time that we were
still adapted to climbing and living in trees. And I
think there are multiple lines of evidence supporting this. It
(11:50):
appears that at some point our ancestors were both like
living in forests and climbing trees, but also having skeletons.
That's supported bipedal walking gate. Also, it's worth pointing out
that plenty of other animals that occupy areas with tall
grasses tall grasslands do just find staying on all fours right.
(12:11):
They don't need to stand up to see over the
grass in order to survive. Like grassland baboons today are
still quadrupedal. So that used to be what people thought,
but that is not no longer the main hypothesis. So
another theory that is popular with the public but not
with scientists in the relevant fields is the much much
(12:32):
beloved aquatic ape theory. Oh yes, we talked about this
um last year. Yeah, and our Aquatic Humanoids episode. We
concluded that there's not really any good evidence for this.
There's no direct fossil evidence for whatsoever. And the indirect
reasoning that causes people to think that there's evidence for
this is, uh, it's just not very good. But we
(12:52):
should mention it because this is bound to come up
whenever people address bipedality in its origins. I think it's
just because it's fun to imagine, maybe, and because it's
unconventional that makes it more interesting to people. Basically, it
says that the explanation for the main phenotypic variations between
us and our closest ape relatives is that our direct
ancestors briefly evolved to become water dwelling primates so sort
(13:17):
of like fishmen and uh, and then moved back to
dry land after that. And under this theory, bipedality evolves
because we need to keep our heads above water when
we're waiting around in search of shellfish for food. All Right,
it would be kind of like the idea that that
we became bipedal because we didn't want to get our
t shirts wet, you know, I mean, it's it's not
(13:41):
that bad, but yeah. So this was first proposed by
Alistair Hardy, and it was mainly developed by somebody named
Elaine Morgan. And in short, Morgan says, look, we're the
only mammal that consistently walks on two legs, but some
four legged animals can occasionally stand up on two legs
and wind. Do our closest stape relatives walk on two legs? Well?
(14:02):
She claims there's only one circumstance when they always walk
on two legs, and that's when they're waiting in water.
I see some pretty clear evidence running counter to this assertion,
just in publicly available video like primates. You look this up.
Primates sometimes stand up on two legs for all kinds
of reasons while carrying objects and moving around with them
(14:23):
during dominance displays to reach something like they don't. And
they also, on top of that, don't always stand up
when waiting in water. I found video of guerrillas waiting
around in water, and they tend to stay on all fours.
So if the classic explanation about seeing over the grass
is probably wrong and we don't put any stock in
the aquatic ape, what is the real explanation? Of course,
(14:45):
we still don't know, but there are a lot of
competing theories. Maybe there was a selection pressure on having
free hands, so maybe some of our ancestors began carrying
or throwing things, and for some reason this got started,
and then there was a great survival or reproduction advantage
for the ones that did this more and more of
(15:05):
the time. So being able this comes back to the
examples of being able to carry ones young, being able
to carry food that you've gathered, or being able to
carry a tool or a weapon, say a nice you
know jaw bone for smacking the other epe creatures around. Well,
I mean a big one I've seen suggested actually is throwing,
Like if if we evolved somehow a throwing hunting strategy
(15:26):
where you would throw objects, that this could have spurred
bipedality or some bridge to it. Another thing I was
reading about in a BBC article is that recent research
has suggested that perhaps partial bipedality helped these hominins adapt
to rocky, uneven terrain in geologically active areas. Essentially that
our ancestors were not only tree climbers, but rock climbers,
(15:50):
and this encouraged them to take on some traits that
bridge the gap to bipedalism. Another is, I guess sort
of the least the least interesting is an idea but
has seems to have a lot going for it, And
it's simply that a certain kind of bipedalism in tree
dwelling life became useful, as it is in many orangutans today.
(16:11):
Like you can look at orangutans living in the trees
that walk around on two feet, like they'll reach up
and grab branches with their arms over their heads while
walking around on other branches with two feet, it's just
a great way to anchor yourself between a lower and
upper branch. So there are a lot of competing theories.
I mean, I know there are other ones we didn't
even cover here, but this is this is an unsolved question.
(16:33):
We still don't know the answer now anyway to shake it.
We were not the first bipeds, not even close. I
already mentioned the t rex, you know that, that famous
the famous Cretaceous period, the carnivore Cretaceous spirit, of course,
banned hundred forty five million years ago to sixty six
million years ago. And this again, it's just an animal
(16:54):
that could scarcely be more of a biped you know,
those tiny little arms. And of course he or she
is just one of the many therapods that roamed the
prehistoric Earth, and in many cases not not not just
roamed it, but ran after their prey, running a key
advantage of their bipedal morphology. But even they, it seems
(17:17):
we're not the first. Um there's a two hundred and
ninety million year old fossil of a species that is
dubbed ood Obama's Kersaurus. This is a creature that was
very lizard like it seems, and it's a probable appearance,
had short fore limbs, relatively long tail and high and
also relatively long hind limbs. So these are kind of
(17:39):
the hallmarks of of a bipedal creature. But the other
curious thing about it is that it seems to have
been a herbivore rather than a meat eat or like
the theropods. Therefore it probably palin. I just think it
probably depended on bipedal running to flee from quadrupedal danger.
And on the subject of dinosaurs and quadrupedal and bipedal arrangement,
(18:02):
I found a two thousand five article in Astrobiology magazine
that brings up a species that is dubbed Masso spondulous.
And this is a pro sorrow pod now Sara pods
as everyone remember that. You know, they're the giant Diplodocus
Brachiosaurus style kind of creatures, you know, big, enormous quadrupeds.
(18:24):
It just enormous, just ponderous creatures. The pro sauropods, unlike
their descendants, they could rise up on their hind legs
and go after food bi petally. So back in two
thousand five, University of Toronto at Mississaugua thiss ut M
biology professor Robert Rice. He looked at an embryo of
(18:46):
one of these massospondulous creatures and he found the thing
was that it looked like a four legged saara pod.
So he hypothesized that it would have grown into a
full bipedal form as it matured. Uh this is what
he told Astro Astrobiology magazine quote. Because the embryo of
massospondos looks like a tiny saua pod with massive limbs
(19:09):
in a quadrupedal gait. We proposed in our paper that
the sauropods gate probably evolved through a phenomenon called ptomorphosis,
the retention of embryonic and juvenile features in the adult.
So this is interesting cause we're talking about a creature
that potentially adapted bipedal, the bipedal gate, but then left
(19:30):
it behind. Uh paedomor morphosis. By the way, it's it's
something we see today in various amphibian speeches species. But
for for these saua pods and for the true sauropods,
it would mean that they were essentially man babies of
the prehistoric world, like they simply no longer had to
grow up like they were the biggest forest eating dumpsters
on the planet, and therefore they really didn't have to
(19:53):
augment their more or less larval form anymore. You know,
I have often wondered something when looking at bipedal therapod
dinosaurs like the t rex. Just look at that powerful
lower body and then the tiny little baby arms out front.
If this dinosaur fell down or even just you know,
(20:14):
went to have a little lie down in the meadow,
how did it get back up. I'm not saying it
would be impossible, it just seems very awkward. Of course,
we're by peedle and we can get up from the ground,
but we have long arms and strong upper bodies to
help us. Try lying down on the ground and then
getting up without using your arms at all. You can
(20:34):
probably do it, but it's not so easy, is it?
And the t rex probably has an even lower relative
center of mass than you. So what's going on? Like,
was it this much of a struggle for the t
rex every time it had to get up from the ground.
That's a great question. Well, I've been wondering this for
a while. I finally looked it up. There's actually a
really good explainer on this in Scientific American provided by
(20:57):
the paleontologist Gregory M. Ericson of Florida State University. And
so here's what Erickson says. First of all, there has
long been a dispute over exactly what the t rex
is tiny four limbs were four uh maybe you know.
One idea says, maybe they're just a vestigial, meaning they're
actually not good for much of anything at all, and
they only existed in diminished form because the rex hadn't
(21:19):
fully lost them yet. And then the next idea says, well,
maybe they're grasping arms used in copulation. And then the
next idea says, maybe there's some sort of meat hook
for feeding chunks of flesh into the mouth. Though this
hypothesis was beaten down when it became clear that the
arms of a t rex could not reach its mouth. Yeah,
this is one of those things that when we went
(21:40):
to the museum in Chicago, the Field Museum, that became obvious.
You can when you go up to the arm, Uh,
the fossil bones of the t rex's arm, they are
the size of my arm. But the t rex is
the size of like a two story house. And uh,
clearly this is a shrunken limb exactly. But another hypothesis
(22:01):
is that the baby arms were useful exactly for helping
the t rex get back up when it was lying
on the ground. So in the year nine seventy, the
British paleontologist Barney Newman speculated that maybe the arms could
help the t rex do a do a thing kind
of like a push up. It would be a push
up motion where the where it would help the rex
keep from sliding forward along the ground as it tried
(22:25):
to raise its body to a standing position. Just imagine
trying to rise without anything to brace you, like lie
flat on your stomach and then try to push yourself
up to standing using your legs alone. You might be
able to do it, but it's not easy. It's a
lot easier if you can use your arms right, and
it requires a fair amount of sort of coiling and
slithering around for for most people, I think, And it's
(22:47):
it's easier to imagine that kind of movement in our
bodies as opposed to the t rex. Yes, so Ericson says,
you know, now we know more about the biomechanics of
the t rex than we did back when these ideas
were hypothesized. So of course, and I'm one. As we mentioned,
the arms can't reach them out the mouth, so the
meat hook theory that's dead. One thing we have learned
is that t rex arms were often broken during life,
(23:10):
as opposed to in an injury that immediately caused death.
And this tells us some interesting things. First of all,
it tells us that the arms were probably kind of
bad at whatever the rexes were using them for. And
number two, they were not absolutely necessary for survival. The
fact that we could have like examples of them having
healed or not immediately killed the rex means that the
(23:33):
rex could break an arm and survive for at least
a month afterward. If an animal in the wild breaks
a survival essential limb, that I mean that animal is
generally pretty much done for, right, like a cheetah breaking
a leg, etcetera. It's it's, it's done. And this suggests
four limbs that were not survival essential. Also, though the
rex arms would have been strong by our standards, like
(23:54):
he says they could probably curl four hundred pounds, they
would not have had strong enough bone structure in the
wrists to lift what he calls large mechanical loads, and
that would include the rex's own body. So this means
Newman's push up hypothesis is probably wrong, right, that the
t rex did a push up in order to get
up from the ground. So how did they get up
(24:14):
once they were lying down? Well Ericson suggests looking to
birds who get up without the aid of four limbs,
and apparently what they do is they simply tuck their
legs directly underneath their center of gravity and then push
straight up. Actually, probably sort of the exact same thing
you would do if you tried to stand up from
the ground without using your arms. You try to gather
(24:35):
your legs under you and then push up right. Yeah, exactly.
But also therapod dinosaurs with tiny arms like the t
rex would have had the aid of their tails to
help gain additional leverage or bracing against the ground. So
the way I'm imagining this I could be wrong, but
it's the same way you would brace your hands against
the ground in front of you while extending your legs
(24:57):
to stand up. Imagine a t rex may being able
to brace its tail against the ground behind it while
pushing up with its legs, a sort of backwards standing.
You know, all of this, I think it goes It's
just another reminder that the t Rex one of the
most famous dinosaurs, if not the most famous dinosaur, that
was the specimen out there, and also one that we
(25:19):
we know a fair amount about there in a number
of the fossils that have been found, and yet there
are there's there's so much that we do not know
about the t Rex. There are things about it that
we will we will never know unless we get that
time machine to go back and start hunting them, or
if we somehow bring them back to life with a
Jurassic Park scenario. I propose a pre emptive ban on
(25:41):
dinosaur hunting before we have any time machines. We've got
to get the regulations in place. That's right, We've got
to think ahead of our technology. Alright. Well, on that note,
we're going to take a quick break and we'll be
right back. Thank alright, we're back, alright. So one of
the big questions I had to in all of this is, alright,
we we've looked at bipeds in prehistoric times, look at
(26:03):
the bipedal world around us, uh that the humans have built.
We're always trying to figure out what's going on or
what could be going on in other worlds, What other
kinds of life have evolved, are evolving, or will evolve
in the future. So, assuming the entire universe isn't dead
other than us, which you know, might be right. So, um,
(26:24):
what's the deal? Would we find legged creatures on other worlds?
And if we did, would we find bipedal creatures? We
can certainly imagine extraterrestrial life that doesn't depend on legged locomotion,
but intelligent life, life capable of achieving technology along the
same lines as the human model. You know, we've we've
(26:44):
got into this a bit in the past, discussing the
notion of say a hypothetical aquatic species and what sort
of technology they might be able to develop. Uh. As
technico technology entails the mina manipulation of matter, one would
need some sort of limbs of manipulation. Now, terrestrial nature
provides us with other forms of manipulation beyond UH. You know,
(27:05):
our hands, in our arms, they are the arms and
tentacles of cephalopods. Uh, one could maybe turned to pseudopods
and UH and other organisms so they're not used for
tool use. But if we're just imagining some sort of
an organism manipulating things, I think pseudopods are on the table.
I just had a crazy idea, what about a magnetic organism,
like it's got like a skin surface that can manipulate
(27:27):
things by changing magnetic attraction or yeah, or it's picked up.
I mean there are animals in the natural world that
utilize magnetism to a certain extent, right, so maybe there's
something there. Um. But when we try and think of
tool users that engage in tool use, uh without engaging
in pipedal movement, well, you know, a few varieties of
(27:48):
of octopus come to mind. Uh. We can think of dolphins,
and we of course do see a lot of bipedole
use in apes and birds. But then we have these
animals that engage in tool use via the mouthparts or
in the case of elephants, with their trunks. You know
Ian M. Banks, the sci Fia writer, he actually explored
this idea, uh in his excellent novel Surface Detail. There
(28:11):
are these creatures called the the pav Pavoolians, and they
are they're like an elephant like quadrupedal species, but they
have a pair of trunks that they use for tool use.
In computer interface in the front, now, I was looking
around for for any writings on this subject, and I
ran across UH this paper Some engineering considerations on the
(28:33):
controversial issue of humanoids by Gean Carlo Guinta from the
Department of Mechanics and UH. This is UH from the
Polytechnico Deterreno and this was collected in Cellular Origin, Life
and Extreme Habitats and Astrobiology and UH. Guinta actually lays
out much of what I said concerning UH possible mobility methods,
(28:56):
UH and more in a very succinct way. He writes, quote,
mobility of a living being is strictly linked with how
it gets its food and energy. Autotrophic beings may not
need any sort of mobility, while heterotrophic ones and particularly predators,
usually need to move to obtain food. Large animals either
are supported on a solid surface, float in a fluid
(29:19):
under the effect of hydrostatic forces, or fly using aerodynamic forces.
Very small beings may use other supporting mechanisms like surface tension,
molecular interactions, etcetera. Since it is likely that an intelligent
being has a minimum size larger than allowing to to
use these mechanisms, they will not be considered. Other solutions
(29:39):
like magnetic levitation or jets are conceivable, but are quite
hypothetical and will not be considered and uh. He goes
on to point out that most animals on solid surface
surfaces do have legs, and the evolution on our planet
at least is characterized by a gradual reduction in the
number of legs. He continues quote in general, the large
(30:00):
is the animal and the lower is the gravity of
the planet. The easier it is to remain an equilibrium
on a small number of legs, in the sense that
the response of the nervous system to avoid falling down
maybe less quick. From this point of view, low gravity,
uh simplifies all operations related to motion. They go on
to point out that the speed is important, that speed
(30:21):
of course, is important for survival and uh and it's
an important factor in natural selection. And we can see
this reflected in our dinosaur examples, right, are prehistoric creature examples,
because something like the t rex is running quickly to
catch prey, as are its theropod um um uh kin.
And then that earlier example, the kind of weird lizard
(30:41):
herbivore that would have conceivably been running to escape from predator.
It seems another example where so much in evolution ends
up having to do with speed. Like you know, when
we talked about what called the ideas behind what caused
the Cambrian explosion, you know, this is another big open
question in UH, in paleon oology and in the history
of biology and evolution UH. And one of the ideas
(31:04):
there is that maybe suddenly the introduction of predation into
the food chain drove an explosion in body plan adaptation
because suddenly things needed to protect themselves and move quickly
in order to survive or in order to well sylvia,
in order to survive, to catch or evade predation. Indeed,
(31:26):
so again to continues and says that all of this
UH means there will be quote a strong incentive to
shift from walking a sequel of static equilibrium positions to running,
which includes positions in which static equilibrium is not guaranteed.
Large animals, possibly with a smaller number of legs may
have been an advantage, and bipeds are a very good
(31:47):
configuration for beings having an adequate controlled system. This is interesting.
So he's pointing out how one of the features of
running is that that, like you, you can be off
balance while you're running, because it's the same way like
a bicycle works. You know, a bicycle works because you're
by maintaining speed, you could do this thing that you
couldn't stay balanced to the lower speed. Yeah. And if
(32:08):
you're the t rex, ideally that that that herbivore is
going to break your fall and you're gonna do it
with mouth wide open. Right. So they also touch on
the fact that that tool use and manipulation amounts to
a shortcut and evolution uh quote objects that increase the
potentialities of its body working like prostheses. Uh Why why
(32:31):
slowly augment your body over the course of you know,
long stretches of time when you can do something like
this within a lifetime be a tool use. So they
conclude that such an alien, if if we're trying to
imagine an alien emerging in another world, that it would
need to have some sort of of locomotion and some
sort of manipulation organs quote the ladder being best derived
(32:53):
from locomotion organs like legs, the humanoid layout with two
arms and two legs seems to be optimal. This is
an interesting point. Yeah, I would I would have maybe said, okay, uh,
who knows how many legs an alien we encounter might have,
but if it's moving around on the land, I think
this is some pretty solid reasoning. There tends to be
(33:14):
evolution toward fewer numbers of legs over time for to
increase speed, and that this can free up other limbs
for tool use, which seems to be an important part
of tool using intelligence. Like you, you wouldn't need tool
using intelligence if you didn't have hands to use tools with, right, Yeah,
it's it's it's an interesting paper. I'm sure there's some
(33:36):
there's some astrobiologists and biologists that might evolutionary biologist that
may take issue with this, but but I think I
think the author makes an interesting argument here. And it
also as much as I love multi legged aliens in
my sci fi, it also gives me a little support
for visions of bipedal aliens being the dominant UH form
(33:59):
in so many different science fiction visions. Now, this also
makes me question what unexamined assumptions are we bringing on
void that could be clouding our vision Right here, we're
we're thinking, Okay, I'm just trying to universalize about like
the physics of planets and the principles of evolution and
not be you know, Earth chauvinist. But but I bet
(34:21):
there are ways that that we're somehow being Earth chauvinists
that we're not noticing. Yeah, and I we haven't even
talked about tales. I can easily imagine some sort of
an alien creature with a prehensile tail um or you know,
some other prehensile uh that if they're an animate that
they're able to use for tool use and manipulation. Well,
to bring it back to the t rex is, I
(34:41):
think we did mention this, but despite the fact that
we don't have tales, tales often form an extremely important
part of bipedal locomotion. The tails are there to counter
as a counterweight for the front of the body. If
you've only got two legs and you're like a t rex,
you're leading forward. You know, you saw these old pictures
where people used to illustrate t rex is with their
tail is dragging on the ground. That doesn't make any
(35:02):
sense that they of course had to have their tails
up in the air as a counterweight to the body
so they could move. Yeah. I am also reminded of kangaroos,
who have you know, engage in bipedal gates and their
tails is often utilized as a is a third limb.
So yeah, there's a whole bunch that we could do there.
I also have to say there's a whole episode we
(35:24):
should probably record on just bipedal robots and the attempt
to create functional bipedal robots, and perhaps getting into the
idea of why we want to do it as well,
because they've got to be like us, gotta be like us.
We got to create a mechanical man. So we'll will
inevitably come back to that topic in a future episode,
but for now, there you have it. Bipedalism something we do,
(35:47):
something other organisms do, something organisms have been doing on
this planet for a very long time, and conceivably there
could be other bipeds out there in the universe doing
their thing as well. Now, if you want to check
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(36:09):
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(36:30):
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(36:52):
blow the Mind at how stuff works dot com for
more on this and thousands of other topics. Does it
how stuff works dot com? I think the differ
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 I'm Joe McCormick.
And today we're talking about bipeds, bipedalism. Uh. And this
is a this is a topic that I was just
(00:25):
kind of rattling around my brain the other day because
for most of us, walking is just kind of every day, right,
you run a little bit, uh, maybe you hop a
little bit. It's of course involved multiple times and mammals.
You have macropods, kangaroo rats in my spring hair hopping,
my pangolins, and of course homing a apes um much
which includes ourselves and sometimes scientists, you know, make the
(00:47):
distinction between facultative and obligate bypeds, though this isn't a
standard distinction, suffice to say they're creatures such as the
human flightless birds, and to draw on a prehistoric example,
the t w rex, that have no real alternative to
bipedal movement. I mean, I can crab walk around, Yeah,
I wouldn't. If if you're crab walking, you're still bipedal
(01:09):
unless you can grow some crab legs. It depends which
version of the crab walk. Are you're talking, you're talking
about where you're I'm talking where you know, you lean
back and you go on all four your belly up
in the air. Because there's also the Zoidberg walk, where
you walk from side to side. That's a good one,
but that's not that that would just be bi Zoidberg
is a biped No no, no, no, I mean the
the Exorcist down the stairs. Well oh yes, yes, okay,
(01:30):
well that that would count, but I fully grant you
I probably wouldn't get around very quickly doing that all
the time. Other creatures, of course, are capable of bipedal locomotion,
but only employed under certain circumstances, like, for instance, a
lemur dancing you know, sort of prancing sideways across a
clearing between two trees, a giant ground sloth in in
(01:53):
in old and olden days, rising up to reach higher branches,
or or one of my favorites, a cat standing on
its hind lay eggs to better view pray or something
of interest. This is always a creepy, weird side if
you're lucky enough to witness it. Oh but it also
can be very cute when dogs stand on two legs
to to get up there closer to the treat that
they want. Oh, yeah, it's adorable. It's yeah. When dogs
(02:17):
do it, it's adorable. When cats do it, it is
it's a little unsettling, like they've suddenly become tiny people,
like they've been people all along, um or that's my
read on it. Now. When it comes to the hominans,
which again includes humans, the oldest evidence of bipedal movement
in a hominant species was probably six million years ago.
This would have been the selmthropists, and there's some dispute
(02:39):
over this, but any rate, we were mostly bipedal by
say four million years ago. We had a curved spine
by two point five million years ago, and it altered
our hip support by one point nine five million years ago,
and we were fully bipedal by the time of Fomo erectus,
with signature pelvis and thigh bones evident in the fossil record.
The legs lengthened over time, allowing for longer strides everything
(03:03):
that would enable the ministry of silly walks to do
its thing. Yeah. Now, some of what we know about
the posture and gate of our ancient ancestors and their
close relatives has to be inferred indirectly. I mean, you
can get a pretty good idea from like the shapes
of bones and stuff that that will tell you a lot.
There's other there's other evidence that's very direct. A great
piece of early direct evidence for bipedality is the fossil
(03:26):
formation known as the Late Totally Footprints. So, Robert, have
you have you seen what these look like? I think
I have everybody very cool in In nineteen seventy six
there was a team working with the paleontologist Mary Leaky,
and they discovered a collection of fossilized animal tracks in
late Totally Tanzania, which is south of the Old Duvai Gorge.
(03:47):
And the tracks were preserved in what had been a
soft bed of volcanic ash about three point six million
years ago or three point three point six three point
seven uh and it had hardened and been preserved for
us to discover in the twentieth century. And then so
after these tracks were initially discovered, in nineteen seventy eight,
Paul Able, a colleague of Leaky's, discovered that the formation
(04:10):
also contained a twenty seven meter or about eighty eight
foot long trail of ancient hominin footprints in addition to
the other animal footprints, probably made by Australian Epithecus afarensis,
the species to which Lucy belonged, And there were about
seventy hominin footprints at all in all in this formation.
And so the thing about these footprints is they're quite
(04:32):
clearly bipedal. You know, you're not seeing four legged movement,
and somebody was just walking on two feet through this
volcanic ash. The prints i've read are space close together,
meaning a short stride might mean short legs. And the
prints also show a big toe in line with the
foot rather than opposed to the foot, as you see
in arboreal apes. So like you know, your human big
(04:54):
toes go straight out, the arboreal apes have more kind
of a toe thumb, like a big toe thumb, uh,
that they used to climb trees and grab hold of stuff.
And also their footfalls apparently went heel toe, just like
ours tend to. So by about three point six million
years ago, we we've got direct evidence that our ancestors
and their close relatives were walking on two feet. Uh.
(05:16):
And I also can't help but mention I've read supposedly
there's this story of how the prints were discovered because
one of Leaky's colleagues, a paleo anthropologist named Andrew hill Uh,
stumbled across the fossil formation when he and another colleague
were running around throwing elephant poop at each other. Oh well,
you know you gotta keep it lighthearted on the dick, right, So, um,
(05:39):
like you said, we we know all of this based
on mostly fossil remains, and by that this, you know,
we're looking at the bones of our ancestors and observing
what the gradual shift to bipedalism did to us. And
it certainly certainly came at a cost. Yeah, now, to
be sure it was it was worth it, I guess.
I mean. It made it easier for us to pick
up fruits and pick up pick from a low line branches.
(06:00):
It gave us free hands for carrying food and also
very importantly carrying tools, carrying our young as well. It
allowed us to rise up and appear larger and more
fearsome to our enemies. Are many enemies of the wild.
This is something that I think we often don't think about.
But unless you're being instructed on how to react to
a bear in the win the wild, you know, they say,
(06:22):
make yourself as big as possible, and certainly there are
other animals that do just the same thing, but that's
one of the strengths of being able to at least
rise up on two feet. Yeah, now you can't know
this for sure, but I tend to think that bipedalism
is a sort of necessary precursor to advanced tool using intelligence.
(06:43):
I mean, you see some use of tools in quadrupedal apes,
but the fact that the fact that you're walking on
two feet gives you free hands, and having free hands,
it seems like suddenly you've got much more incentive to
be using them for all kinds of stuff. Well, it's
interesting when you think about the animals that do display
(07:03):
some form of tool use. I mean, certainly you have
the the apes, which are going to more or less
aligned with the human experience of tool use. But then
of course you have like the corvids uh and uh
and a few other birds that that also use tools. Now,
obviously they are engaging in bipedal ground movement. Their wings
are tucked away, but it's perhaps and it's a slightly
(07:26):
different situation with birds because those wings do have a purpose. Uh,
They've just specialized their their their beak functionality, and I've
learned how to use tools with that. The same is
truy of dolphins. You know they're using when they engage
in tool use, are using their snout um octopi slightly
different situation they have they have They have a wide
variety of limbs and are not necessarily gonna become bipedal
(07:49):
anytime soon. So anyway you shake it the back to
the human scenario, it helped us expand our range. It
It definitely played a part in our our ascension or dominance,
certainly our ability to invent things and expand, but we
also paid a price. We had to distribute all of
our weights on two limbs, resulting in all sorts of
painful experiences such as a lower back pain, slip discs,
(08:12):
arthritis in the lower body, fallen arches. Our spines are
ultimately just kind of weird. We evolved wider hips and
stronger knees to kind of cope with it to a
certain extent. But this is the reason that roughly of
adult humans will experience back pain in their lives. I
would say one of the biggest anatomical drawbacks is that
we can make finger guns at each other. I mean
(08:34):
that that is a true blow to the species you mean,
I mean the beneficial kind where like kids playing cowboys
and Indians or whatever on the playground, know the like
the like catch you later, bro Okay. So also it
also affected the way that we give birth and uh
and this is a I have to say, this is
a topic that we could easily have devoted an entire episode.
(08:56):
There's a lot of scholarship and debate on exactly how
the modern human birthing scenario pans out towards prehistoric examples,
but the move towards the bipedal form changed our skeletons.
This affected the pelvis. Most primates have a pretty straight
birth canal, but hominans soon boasted a narrow, distorted, kind
(09:17):
of fun house tube of a birth canal. The offspring
had to twist and turn in order to pass through.
This is true of our our ancestors. But our bodies
continued to evolve. We became taller, we grew larger brains.
That means meant bigger brained babies having to make it
through that twisting tunnel. Everything became tighter. Child birth became
(09:37):
a potentially more dangerous affair, because it also means giving
birth to a child an earlier stage of its development
in order to actually break it free from the confines
of our bipedally twisted bodies. Now, again, there's a lot
more to this. Scientists have gone back and forth on
the so called obstetric dilemma, but bipedal evolution certainly changed things.
(09:58):
All right, I think we should take a quick break.
We will be right back to discuss why bipedalism evolved
in humans. Thank alright, we're back. So this is a
big question because certainly we can point to all of
these like the pros and all the cons, but like,
what is the driving force right right now? What caused
our our ancient hominin ancestors to go on two legs? Primarily,
(10:22):
why did our ancestors become bipetle And this is an
ongoing debate. We know at some point we transitioned from
mostly four footed gate to a mostly two footed gate,
but why did it happen and what type of pressure
selected for this? So, first of all, when answering questions
like this, it's often hard to be certain, right, you know,
we only have the evidence we can find. Fossil evidence helps,
(10:44):
but it's hard to like run new experiments to test this.
We you know, we only have the fossil finds we
have and can only draw the conclusions we can draw
from them. And there have been all kinds of answers
over the years. So for a long time, consensus seem
to be that bipedalism was an adaptation to a change
in our primary habitat, as our ancestors moved down out
(11:08):
of the trees into a flat grassland, perhaps driven by
changing climate, like changing climate killed off forests and left
these you know, savannahs with tall grasses in their place,
or these creatures just moved down into the savannahs to
follow food sources or something. In this case, uh, these
hominins needed to stand up to see over the tall grass.
(11:30):
And this explanation is not still favored. This has fallen
out of favor among experts, and one reason is that
climate history analysis and physical fossil evidence indicate that we
were becoming bipedal at the same time that we were
still adapted to climbing and living in trees. And I
think there are multiple lines of evidence supporting this. It
(11:50):
appears that at some point our ancestors were both like
living in forests and climbing trees, but also having skeletons.
That's supported bipedal walking gate. Also, it's worth pointing out
that plenty of other animals that occupy areas with tall
grasses tall grasslands do just find staying on all fours right.
(12:11):
They don't need to stand up to see over the
grass in order to survive. Like grassland baboons today are
still quadrupedal. So that used to be what people thought,
but that is not no longer the main hypothesis. So
another theory that is popular with the public but not
with scientists in the relevant fields is the much much
(12:32):
beloved aquatic ape theory. Oh yes, we talked about this
um last year. Yeah, and our Aquatic Humanoids episode. We
concluded that there's not really any good evidence for this.
There's no direct fossil evidence for whatsoever. And the indirect
reasoning that causes people to think that there's evidence for
this is, uh, it's just not very good. But we
(12:52):
should mention it because this is bound to come up
whenever people address bipedality in its origins. I think it's
just because it's fun to imagine, maybe, and because it's
unconventional that makes it more interesting to people. Basically, it
says that the explanation for the main phenotypic variations between
us and our closest ape relatives is that our direct
ancestors briefly evolved to become water dwelling primates so sort
(13:17):
of like fishmen and uh, and then moved back to
dry land after that. And under this theory, bipedality evolves
because we need to keep our heads above water when
we're waiting around in search of shellfish for food. All Right,
it would be kind of like the idea that that
we became bipedal because we didn't want to get our
t shirts wet, you know, I mean, it's it's not
(13:41):
that bad, but yeah. So this was first proposed by
Alistair Hardy, and it was mainly developed by somebody named
Elaine Morgan. And in short, Morgan says, look, we're the
only mammal that consistently walks on two legs, but some
four legged animals can occasionally stand up on two legs
and wind. Do our closest stape relatives walk on two legs? Well?
(14:02):
She claims there's only one circumstance when they always walk
on two legs, and that's when they're waiting in water.
I see some pretty clear evidence running counter to this assertion,
just in publicly available video like primates. You look this up.
Primates sometimes stand up on two legs for all kinds
of reasons while carrying objects and moving around with them
(14:23):
during dominance displays to reach something like they don't. And
they also, on top of that, don't always stand up
when waiting in water. I found video of guerrillas waiting
around in water, and they tend to stay on all fours.
So if the classic explanation about seeing over the grass
is probably wrong and we don't put any stock in
the aquatic ape, what is the real explanation? Of course,
(14:45):
we still don't know, but there are a lot of
competing theories. Maybe there was a selection pressure on having
free hands, so maybe some of our ancestors began carrying
or throwing things, and for some reason this got started,
and then there was a great survival or reproduction advantage
for the ones that did this more and more of
(15:05):
the time. So being able this comes back to the
examples of being able to carry ones young, being able
to carry food that you've gathered, or being able to
carry a tool or a weapon, say a nice you
know jaw bone for smacking the other epe creatures around. Well,
I mean a big one I've seen suggested actually is throwing,
Like if if we evolved somehow a throwing hunting strategy
(15:26):
where you would throw objects, that this could have spurred
bipedality or some bridge to it. Another thing I was
reading about in a BBC article is that recent research
has suggested that perhaps partial bipedality helped these hominins adapt
to rocky, uneven terrain in geologically active areas. Essentially that
our ancestors were not only tree climbers, but rock climbers,
(15:50):
and this encouraged them to take on some traits that
bridge the gap to bipedalism. Another is, I guess sort
of the least the least interesting is an idea but
has seems to have a lot going for it, And
it's simply that a certain kind of bipedalism in tree
dwelling life became useful, as it is in many orangutans today.
(16:11):
Like you can look at orangutans living in the trees
that walk around on two feet, like they'll reach up
and grab branches with their arms over their heads while
walking around on other branches with two feet, it's just
a great way to anchor yourself between a lower and
upper branch. So there are a lot of competing theories.
I mean, I know there are other ones we didn't
even cover here, but this is this is an unsolved question.
(16:33):
We still don't know the answer now anyway to shake it.
We were not the first bipeds, not even close. I
already mentioned the t rex, you know that, that famous
the famous Cretaceous period, the carnivore Cretaceous spirit, of course,
banned hundred forty five million years ago to sixty six
million years ago. And this again, it's just an animal
(16:54):
that could scarcely be more of a biped you know,
those tiny little arms. And of course he or she
is just one of the many therapods that roamed the
prehistoric Earth, and in many cases not not not just
roamed it, but ran after their prey, running a key
advantage of their bipedal morphology. But even they, it seems
(17:17):
we're not the first. Um there's a two hundred and
ninety million year old fossil of a species that is
dubbed ood Obama's Kersaurus. This is a creature that was
very lizard like it seems, and it's a probable appearance,
had short fore limbs, relatively long tail and high and
also relatively long hind limbs. So these are kind of
(17:39):
the hallmarks of of a bipedal creature. But the other
curious thing about it is that it seems to have
been a herbivore rather than a meat eat or like
the theropods. Therefore it probably palin. I just think it
probably depended on bipedal running to flee from quadrupedal danger.
And on the subject of dinosaurs and quadrupedal and bipedal arrangement,
(18:02):
I found a two thousand five article in Astrobiology magazine
that brings up a species that is dubbed Masso spondulous.
And this is a pro sorrow pod now Sara pods
as everyone remember that. You know, they're the giant Diplodocus
Brachiosaurus style kind of creatures, you know, big, enormous quadrupeds.
(18:24):
It just enormous, just ponderous creatures. The pro sauropods, unlike
their descendants, they could rise up on their hind legs
and go after food bi petally. So back in two
thousand five, University of Toronto at Mississaugua thiss ut M
biology professor Robert Rice. He looked at an embryo of
(18:46):
one of these massospondulous creatures and he found the thing
was that it looked like a four legged saara pod.
So he hypothesized that it would have grown into a
full bipedal form as it matured. Uh this is what
he told Astro Astrobiology magazine quote. Because the embryo of
massospondos looks like a tiny saua pod with massive limbs
(19:09):
in a quadrupedal gait. We proposed in our paper that
the sauropods gate probably evolved through a phenomenon called ptomorphosis,
the retention of embryonic and juvenile features in the adult.
So this is interesting cause we're talking about a creature
that potentially adapted bipedal, the bipedal gate, but then left
(19:30):
it behind. Uh paedomor morphosis. By the way, it's it's
something we see today in various amphibian speeches species. But
for for these saua pods and for the true sauropods,
it would mean that they were essentially man babies of
the prehistoric world, like they simply no longer had to
grow up like they were the biggest forest eating dumpsters
on the planet, and therefore they really didn't have to
(19:53):
augment their more or less larval form anymore. You know,
I have often wondered something when looking at bipedal therapod
dinosaurs like the t rex. Just look at that powerful
lower body and then the tiny little baby arms out front.
If this dinosaur fell down or even just you know,
(20:14):
went to have a little lie down in the meadow,
how did it get back up. I'm not saying it
would be impossible, it just seems very awkward. Of course,
we're by peedle and we can get up from the ground,
but we have long arms and strong upper bodies to
help us. Try lying down on the ground and then
getting up without using your arms at all. You can
(20:34):
probably do it, but it's not so easy, is it?
And the t rex probably has an even lower relative
center of mass than you. So what's going on? Like,
was it this much of a struggle for the t
rex every time it had to get up from the ground.
That's a great question. Well, I've been wondering this for
a while. I finally looked it up. There's actually a
really good explainer on this in Scientific American provided by
(20:57):
the paleontologist Gregory M. Ericson of Florida State University. And
so here's what Erickson says. First of all, there has
long been a dispute over exactly what the t rex
is tiny four limbs were four uh maybe you know.
One idea says, maybe they're just a vestigial, meaning they're
actually not good for much of anything at all, and
they only existed in diminished form because the rex hadn't
(21:19):
fully lost them yet. And then the next idea says, well,
maybe they're grasping arms used in copulation. And then the
next idea says, maybe there's some sort of meat hook
for feeding chunks of flesh into the mouth. Though this
hypothesis was beaten down when it became clear that the
arms of a t rex could not reach its mouth. Yeah,
this is one of those things that when we went
(21:40):
to the museum in Chicago, the Field Museum, that became obvious.
You can when you go up to the arm, Uh,
the fossil bones of the t rex's arm, they are
the size of my arm. But the t rex is
the size of like a two story house. And uh,
clearly this is a shrunken limb exactly. But another hypothesis
(22:01):
is that the baby arms were useful exactly for helping
the t rex get back up when it was lying
on the ground. So in the year nine seventy, the
British paleontologist Barney Newman speculated that maybe the arms could
help the t rex do a do a thing kind
of like a push up. It would be a push
up motion where the where it would help the rex
keep from sliding forward along the ground as it tried
(22:25):
to raise its body to a standing position. Just imagine
trying to rise without anything to brace you, like lie
flat on your stomach and then try to push yourself
up to standing using your legs alone. You might be
able to do it, but it's not easy. It's a
lot easier if you can use your arms right, and
it requires a fair amount of sort of coiling and
slithering around for for most people, I think, And it's
(22:47):
it's easier to imagine that kind of movement in our
bodies as opposed to the t rex. Yes, so Ericson says,
you know, now we know more about the biomechanics of
the t rex than we did back when these ideas
were hypothesized. So of course, and I'm one. As we mentioned,
the arms can't reach them out the mouth, so the
meat hook theory that's dead. One thing we have learned
is that t rex arms were often broken during life,
(23:10):
as opposed to in an injury that immediately caused death.
And this tells us some interesting things. First of all,
it tells us that the arms were probably kind of
bad at whatever the rexes were using them for. And
number two, they were not absolutely necessary for survival. The
fact that we could have like examples of them having
healed or not immediately killed the rex means that the
(23:33):
rex could break an arm and survive for at least
a month afterward. If an animal in the wild breaks
a survival essential limb, that I mean that animal is
generally pretty much done for, right, like a cheetah breaking
a leg, etcetera. It's it's, it's done. And this suggests
four limbs that were not survival essential. Also, though the
rex arms would have been strong by our standards, like
(23:54):
he says they could probably curl four hundred pounds, they
would not have had strong enough bone structure in the
wrists to lift what he calls large mechanical loads, and
that would include the rex's own body. So this means
Newman's push up hypothesis is probably wrong, right, that the
t rex did a push up in order to get
up from the ground. So how did they get up
(24:14):
once they were lying down? Well Ericson suggests looking to
birds who get up without the aid of four limbs,
and apparently what they do is they simply tuck their
legs directly underneath their center of gravity and then push
straight up. Actually, probably sort of the exact same thing
you would do if you tried to stand up from
the ground without using your arms. You try to gather
(24:35):
your legs under you and then push up right. Yeah, exactly.
But also therapod dinosaurs with tiny arms like the t
rex would have had the aid of their tails to
help gain additional leverage or bracing against the ground. So
the way I'm imagining this I could be wrong, but
it's the same way you would brace your hands against
the ground in front of you while extending your legs
(24:57):
to stand up. Imagine a t rex may being able
to brace its tail against the ground behind it while
pushing up with its legs, a sort of backwards standing.
You know, all of this, I think it goes It's
just another reminder that the t Rex one of the
most famous dinosaurs, if not the most famous dinosaur, that
was the specimen out there, and also one that we
(25:19):
we know a fair amount about there in a number
of the fossils that have been found, and yet there
are there's there's so much that we do not know
about the t Rex. There are things about it that
we will we will never know unless we get that
time machine to go back and start hunting them, or
if we somehow bring them back to life with a
Jurassic Park scenario. I propose a pre emptive ban on
(25:41):
dinosaur hunting before we have any time machines. We've got
to get the regulations in place. That's right, We've got
to think ahead of our technology. Alright. Well, on that note,
we're going to take a quick break and we'll be
right back. Thank alright, we're back, alright. So one of
the big questions I had to in all of this is, alright,
we we've looked at bipeds in prehistoric times, look at
(26:03):
the bipedal world around us, uh that the humans have built.
We're always trying to figure out what's going on or
what could be going on in other worlds, What other
kinds of life have evolved, are evolving, or will evolve
in the future. So, assuming the entire universe isn't dead
other than us, which you know, might be right. So, um,
(26:24):
what's the deal? Would we find legged creatures on other worlds?
And if we did, would we find bipedal creatures? We
can certainly imagine extraterrestrial life that doesn't depend on legged locomotion,
but intelligent life, life capable of achieving technology along the
same lines as the human model. You know, we've we've
(26:44):
got into this a bit in the past, discussing the
notion of say a hypothetical aquatic species and what sort
of technology they might be able to develop. Uh. As
technico technology entails the mina manipulation of matter, one would
need some sort of limbs of manipulation. Now, terrestrial nature
provides us with other forms of manipulation beyond UH. You know,
(27:05):
our hands, in our arms, they are the arms and
tentacles of cephalopods. Uh, one could maybe turned to pseudopods
and UH and other organisms so they're not used for
tool use. But if we're just imagining some sort of
an organism manipulating things, I think pseudopods are on the table.
I just had a crazy idea, what about a magnetic organism,
like it's got like a skin surface that can manipulate
(27:27):
things by changing magnetic attraction or yeah, or it's picked up.
I mean there are animals in the natural world that
utilize magnetism to a certain extent, right, so maybe there's
something there. Um. But when we try and think of
tool users that engage in tool use, uh without engaging
in pipedal movement, well, you know, a few varieties of
(27:48):
of octopus come to mind. Uh. We can think of dolphins,
and we of course do see a lot of bipedole
use in apes and birds. But then we have these
animals that engage in tool use via the mouthparts or
in the case of elephants, with their trunks. You know
Ian M. Banks, the sci Fia writer, he actually explored
this idea, uh in his excellent novel Surface Detail. There
(28:11):
are these creatures called the the pav Pavoolians, and they
are they're like an elephant like quadrupedal species, but they
have a pair of trunks that they use for tool use.
In computer interface in the front, now, I was looking
around for for any writings on this subject, and I
ran across UH this paper Some engineering considerations on the
(28:33):
controversial issue of humanoids by Gean Carlo Guinta from the
Department of Mechanics and UH. This is UH from the
Polytechnico Deterreno and this was collected in Cellular Origin, Life
and Extreme Habitats and Astrobiology and UH. Guinta actually lays
out much of what I said concerning UH possible mobility methods,
(28:56):
UH and more in a very succinct way. He writes, quote,
mobility of a living being is strictly linked with how
it gets its food and energy. Autotrophic beings may not
need any sort of mobility, while heterotrophic ones and particularly predators,
usually need to move to obtain food. Large animals either
are supported on a solid surface, float in a fluid
(29:19):
under the effect of hydrostatic forces, or fly using aerodynamic forces.
Very small beings may use other supporting mechanisms like surface tension,
molecular interactions, etcetera. Since it is likely that an intelligent
being has a minimum size larger than allowing to to
use these mechanisms, they will not be considered. Other solutions
(29:39):
like magnetic levitation or jets are conceivable, but are quite
hypothetical and will not be considered and uh. He goes
on to point out that most animals on solid surface
surfaces do have legs, and the evolution on our planet
at least is characterized by a gradual reduction in the
number of legs. He continues quote in general, the large
(30:00):
is the animal and the lower is the gravity of
the planet. The easier it is to remain an equilibrium
on a small number of legs, in the sense that
the response of the nervous system to avoid falling down
maybe less quick. From this point of view, low gravity,
uh simplifies all operations related to motion. They go on
to point out that the speed is important, that speed
(30:21):
of course, is important for survival and uh and it's
an important factor in natural selection. And we can see
this reflected in our dinosaur examples, right, are prehistoric creature examples,
because something like the t rex is running quickly to
catch prey, as are its theropod um um uh kin.
And then that earlier example, the kind of weird lizard
(30:41):
herbivore that would have conceivably been running to escape from predator.
It seems another example where so much in evolution ends
up having to do with speed. Like you know, when
we talked about what called the ideas behind what caused
the Cambrian explosion, you know, this is another big open
question in UH, in paleon oology and in the history
of biology and evolution UH. And one of the ideas
(31:04):
there is that maybe suddenly the introduction of predation into
the food chain drove an explosion in body plan adaptation
because suddenly things needed to protect themselves and move quickly
in order to survive or in order to well sylvia,
in order to survive, to catch or evade predation. Indeed,
(31:26):
so again to continues and says that all of this
UH means there will be quote a strong incentive to
shift from walking a sequel of static equilibrium positions to running,
which includes positions in which static equilibrium is not guaranteed.
Large animals, possibly with a smaller number of legs may
have been an advantage, and bipeds are a very good
(31:47):
configuration for beings having an adequate controlled system. This is interesting.
So he's pointing out how one of the features of
running is that that, like you, you can be off
balance while you're running, because it's the same way like
a bicycle works. You know, a bicycle works because you're
by maintaining speed, you could do this thing that you
couldn't stay balanced to the lower speed. Yeah. And if
(32:08):
you're the t rex, ideally that that that herbivore is
going to break your fall and you're gonna do it
with mouth wide open. Right. So they also touch on
the fact that that tool use and manipulation amounts to
a shortcut and evolution uh quote objects that increase the
potentialities of its body working like prostheses. Uh Why why
(32:31):
slowly augment your body over the course of you know,
long stretches of time when you can do something like
this within a lifetime be a tool use. So they
conclude that such an alien, if if we're trying to
imagine an alien emerging in another world, that it would
need to have some sort of of locomotion and some
sort of manipulation organs quote the ladder being best derived
(32:53):
from locomotion organs like legs, the humanoid layout with two
arms and two legs seems to be optimal. This is
an interesting point. Yeah, I would I would have maybe said, okay, uh,
who knows how many legs an alien we encounter might have,
but if it's moving around on the land, I think
this is some pretty solid reasoning. There tends to be
(33:14):
evolution toward fewer numbers of legs over time for to
increase speed, and that this can free up other limbs
for tool use, which seems to be an important part
of tool using intelligence. Like you, you wouldn't need tool
using intelligence if you didn't have hands to use tools with, right, Yeah,
it's it's it's an interesting paper. I'm sure there's some
(33:36):
there's some astrobiologists and biologists that might evolutionary biologist that
may take issue with this, but but I think I
think the author makes an interesting argument here. And it
also as much as I love multi legged aliens in
my sci fi, it also gives me a little support
for visions of bipedal aliens being the dominant UH form
(33:59):
in so many different science fiction visions. Now, this also
makes me question what unexamined assumptions are we bringing on
void that could be clouding our vision Right here, we're
we're thinking, Okay, I'm just trying to universalize about like
the physics of planets and the principles of evolution and
not be you know, Earth chauvinist. But but I bet
(34:21):
there are ways that that we're somehow being Earth chauvinists
that we're not noticing. Yeah, and I we haven't even
talked about tales. I can easily imagine some sort of
an alien creature with a prehensile tail um or you know,
some other prehensile uh that if they're an animate that
they're able to use for tool use and manipulation. Well,
to bring it back to the t rex is, I
(34:41):
think we did mention this, but despite the fact that
we don't have tales, tales often form an extremely important
part of bipedal locomotion. The tails are there to counter
as a counterweight for the front of the body. If
you've only got two legs and you're like a t rex,
you're leading forward. You know, you saw these old pictures
where people used to illustrate t rex is with their
tail is dragging on the ground. That doesn't make any
(35:02):
sense that they of course had to have their tails
up in the air as a counterweight to the body
so they could move. Yeah. I am also reminded of kangaroos,
who have you know, engage in bipedal gates and their
tails is often utilized as a is a third limb.
So yeah, there's a whole bunch that we could do there.
I also have to say there's a whole episode we
(35:24):
should probably record on just bipedal robots and the attempt
to create functional bipedal robots, and perhaps getting into the
idea of why we want to do it as well,
because they've got to be like us, gotta be like us.
We got to create a mechanical man. So we'll will
inevitably come back to that topic in a future episode,
but for now, there you have it. Bipedalism something we do,
(35:47):
something other organisms do, something organisms have been doing on
this planet for a very long time, and conceivably there
could be other bipeds out there in the universe doing
their thing as well. Now, if you want to check
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