Game of Thrones star Hafthor “The Mountain”
Bjornsson recently broke the deadlift world record with a 501 kilogram lift… which is
absolutely, completely bonkers, but if he had the lifting power of a leafcutter ant,
he’d be able to lift a medium sized sedan completely over his head, and carry it home. Not bad. And if The Mountain had the same relative
strength as the taurus scarab dung beetle, he could pull a fully loaded Boeing 787 Dreamliner. Compared to us, ants and dung beetles and
nature’s other miniature weightlifters are special because they pull off their amazing
feats of strength without bones. And it turns out, for every species with an
internal skeleton like ours, Earth is home to around 20 species without one – and maybe
more. And that got me thinking, why did we end up
with our skeletons on the inside instead of the outside? [OPEN] Hey smart people, Joe here. It’s time to face the truth. You’re just meat, in a sack, tied to a bunch
of carefully organized rocks. That is basically what it means to be a vertebrate. And we owe everything we are and that we do
to our bones. Skeletons are rigid enough for this, and flexible
enough for this. It’s said that we’re built with 206 bones,
but 1 in 8 of us have an extra pair of ribs, some people can even have a pair less. And that doesn’t count sesamoids in tendons
in our hands, feet, and elsewhere. And speaking of feet, you have 52 bones in
your feet alone, twice as many as in your spine. Our hands and feet have more than half the
bones in our bodies. Consider that rocks in your fingers were moved
by muscles and nerves to help you click this video. The oxygen powering the brain that is watching
this is being fed by blood made in your bones. You are only even able to hear me talking
thanks to tiny bones in your ears. All of this from body parts that are about
70% mineral, made of an inorganic material called hydroxyapatite that is stiff when compressed,
combined with flexible protein called collagen to keep you from shattering. As a result the 20 or so pounds of bones in
the average body can withstand one ton of compression. And for most of us, they are the last thing
we’ll leave behind. Bones are pretty awesome. And also oss-ome. That’s the Latin root for “bone”… ANYWAY… Where did bones come from? That story goes back at least 1.5 billion
years. Which is a weird place to start because animals…
didn’t even exist yet. But at that moment, violently shifting tectonic
plates were washing tons of minerals into ancient oceans. The minerals that would one day become skeletons. Life stayed pretty squishy for a while. Early multicellular life depended on the water
in which it lived to support their skeleton-less bodies. But then, around 558 million years ago, through
a happy accident of evolution, life split in two, and two different skeleton stories
began. On one branch, strange creatures began to
develop the first hard protective parts, the precursors of exoskeletons. And this set off an arms race of armor. Newly shielded organisms might have gotten
eaten less, maybe they were better protected from the ocean, but partially hard creatures
survived more than their squishy friends, and like I always say, that’s what matters
in the game of natural selection. Early exoskeletons got fancier and we began
to see animals with crushing mouthparts, pinchers, and full suits of armor. It was during this period that we see the
earliest arthropods, the group that includes modern insects and crustaceans. But on that other branch, in squishy tadpole-like
creatures, something else was happening. Soft cartilage-like back rods began to form
in order to provide scaffolding for muscles and movement. And on the outside, some of these fishy creatures
evolved a cement-like armor. This was the precursor of bone, and soon,
this hard stuff formed the basis for new structures like jaws. Very big jaws. Later, this mineral armor was slowly internalized,
and those early backbones became mineralized, and together these became the key parts of
the vertebrate skeleton as we know it. Over the eons, nature has stumbled on many
different ways of desquishifying organisms. There’s the lignin and cellulose of plants,
calcium-rich shells of mollusks and coral reefs, and mineral bones like ours. But insects and crustaceans build exoskeletons
made from chains of modified sugars called chitin. Chitin is molecularly similar to the cellulose
we find in plants, but it’s harder and more stable. If you were to zoom into a lobster’s shell
on the microscopic scale you’d see chitin crystals arranged like stacks of plywood. These special nanostructure arrangements make
chitin exoskeletons incredibly tough for their weight. And that’s why insects are so strong pound
for pound… or gram for gram. So if exoskeletons are so strong, why don’t
we have them? Like most things in nature, there are tradeoffs. For starters, opting for an armored exterior
skeleton makes growing more difficult. Every time a lobster or a cockroach is ready
to size up, they have to molt, shedding their old skeleton and leaving them soft and vulnerable
for days or weeks while they wait for a new outer shell to harden. There’s also a weight problem. The strength of ants’ legs work at their
miniscule mass, but scale that ant up to our size and it would be crushed under its own
weight. And a few more leg days won’t cut it. Because as a creature gets bigger, its volume
and mass increase faster than the tubular strength of its hollow exoskeleton legs. On the other hand, or leg, our internal skeletons
provide bigger attachments for muscles than exoskeletons would, and our bones grow with
our muscles as we get bigger and stronger. But there’s also a tradeoff here. Bulkier vertebrates have to have more massive
bones. An elephant is about 13% bone by weight, not
super agile. A shrew is 4%, and while it’s quick, it’s
easy to squish. Humans are about 8.5%, a compromise between
strength and mobility, and if we had more bone to be stronger then we wouldn’t move
as well. Another problem is that a human-sized ant
would suffocate. Insects don’t really have blood. They have very limited circulatory systems
filled with a fluid called hemolymph, mostly full of metabolic stuff and immune cells. Insects breathe through tiny holes in their
exoskeletons that deliver oxygen to their tissues through a series of internal tubes. The distance oxygen can travel down the tubes
depends on its concentration in the air. During prehistoric times, two-foot dragonflies
did exist, because atmospheric oxygen levels were higher. And plus, having all your muscles attached
to your outside means that while you’re strong, you’re not that flexible. Yeah, let’s see you do this, super strong
grasshopper. So. Chitin exoskeleton: super strong, but only
if you’re small. A human-sized ant, very lethargic, very crumpled,
can’t do yoga. Remember that split that we talked about earlier? One branch led to bugs and exoskeletons, and
the other branch eventually led to you and me and every other vertebrate. And what’s crazy to think about it that
we are this way because of luck, or chance. Because when our ancestors began to build
hard bodies, the only ingredients they had to choose from were what nature provided. Those shifting tectonic plates a billion and
a half years ago? Well, when slabs of rock that make up earth’s
crust rub together, all the minerals they’re made of wash into the sea. And one of those minerals, calcium carbonate,
happens to be a very useful building material. Evolution is a lot like a chef stuck at home
during COVID quarantine, by which I mean, you’ve gotta use whatever ingredients you've
got around. Our very distant relatives were bathed in
calcium from those grinding tectonic plates, and so they used this to build the earliest
bone-like tissues. The evolution of bone wasn’t a grand aha!
moment in the story of evolution, it is just one of many such chance events, influenced
by the environment, that sent one arm of life on earth on a completely new course. And vertebrates aren’t the only ones who
ended up building bodies out of calcium. Invertebrates from mollusks to coral to starfish
all use calcium to build their bodies’ support structures. Exoskeleton-having animals like insects and
other arthropods just went another way, building chitin exoskeletons, thanks to the chance
events of evolution, and if we played the story of back again from the beginning, perhaps
our line would be built differently too. Which means, as we know now, we’d be very
small. But at least we’d have armor. And maybe some sweet pincers. And even some horns. But then… what would ants look like… Stay curious
Is that it’s ok to be smart?