beaches of the Atlantic coast  of America to lay their eggs.  

And every year, hundreds of thousands  of horseshoe crabs are rounded up and  

brought to the lab - not to be killed, but  for their blood to be carefully extracted.

These animals, often called living fossils, are  one of the 'oldest' creatures on the planet.  

They have remained nearly unchanged since they  first appeared on earth over 450 million years  

ago. This is due to some exceptionally effective  adaptations, and genes that code for remarkable  

molecules that have allowed the horseshoe  crab to survive, just as it is, for so long.

One of these ancient compounds is the reason  that hordes of these animals are dredged up  

from the ocean, jabbed with a hypodermic  needle, and their blue blood drained,  

processed, and sold. Their blood, made blue from  a copper-based oxygen-carrying molecule, is so  

valuable that it is the basis for a multi-million  dollar pharmaceutical industry. So valuable,  

that a single liter of it goes for around $16,000  - one of the most valuable liquids on earth.

Our reliance on these animals puts  immense pressure on a fragile ecosystem,  

and so far, scientists have struggled to  recreate this compound and its effects  

in the lab. What is it about this  primitive compound that we need  

so badly, and why can we only seem  to get it from this one creature?

The American horseshoe crab (on screen: Limulus  polyphemus) is an ancient, aquatic arthropod.  

They belong to their own class of animals, called  Merostomata, and are not actually crabs. They are  

more closely related to scorpions, with their  predecessors diverging from their arachnid  

cousins around 480 million years ago. Some  recent studies even suggest they are arachnids.  

The modern horseshoe crab as we know it has  technically only been around for 20 million years,  

but some of its early relatives, like Limulus  darwini, existed around 150 million years ago,  

and look nearly indistinguishable  from today's horseshoe crabs.  

The iconic body plan has been around even longer,  emerging around 450 million years ago. The  

changes within the horseshoe crab group have been  shockingly minor in the big picture of evolution.

Here's some perspective on just how long ago  horseshoe crabs came into existence. Pangea,  

the supercontinent of the past formed 335  million years ago and began to break apart  

about 175 million years ago. The non-avian  dinosaurs emerged 245 million years ago,  

and were wiped out 66 million years ago. The earth  descended into, and emerged from, 2 completely  

different ice ages since these crabs came about.  The world has changed so much since then. And all  

the while horseshoe crabs have been here, crawling  along the seafloor, standing the test of time.

Some of the reason natural  selection has preserved them,  

pretty much as they are, is their hardy body plan.

Their hard shell, called a carapace, is an  exoskeleton so strong that only sharks or turtles  

can penetrate it. And guiding them through the  ocean depths are 9 eyes - 2 compound eyes which  

act much like our own eyes, 5 secondary simple  eyes on top of their shell which can detect UV  

light, and 2 ventral eyes located on their  underside, perhaps to help with orientation.  

Along with their complex circulatory system, 5  pairs of gills, and 12 bristled legs, evolution  

created them to be creatures extremely well  adapted to their particular environmental niche.

But beyond the physical traits that we can  observe, much of their survival is due to  

something we can't see - their incredible, but  simple immune system. It's protected them as a  

species from bacterial infection for eons. It  works in an entirely different way from ours,  

and in the late 1960s, we began to  harness its power for ourselves.

In 1968, two researchers at the  Marine Biological Laboratory in  

Massachusetts observed that blood cells  from horseshoe crabs vigorously clot in  

the presence of bacterial endotoxin.  When they published their paper,  

they had no idea that what they found would  revolutionise drug safety testing forever.

Pretty much every creature in the  world is vulnerable to bacterial  

infection - and the horseshoe crab is  no exception. Once an infection begins,  

bacteria can reproduce quickly, and many give off  toxins which damage specific tissues in the body.

Botulism, for example, is an illness caused by a  neurotoxic protein produced by a bacteria called  

Clostridium botulinum. The toxin can affect  your nerves, paralyze you, and even kill you.  

Toxins like this are called exotoxins. They  are released from live bacteria into the  

surrounding environment during an infection.  But, bacteria don't have to release these  

exotoxins in order to be dangerous. In  fact, they don't even have to be alive.

Once a bacteria is killed within the  body, they sometimes release endotoxins.  

Endotoxins are the lipid portions of  lipopolysaccharides (LPSs) that are  

part of the outer membrane of the cell wall of  some bacteria. The endotoxins are released when  

the bacteria die and the cell wall breaks apart.  This toxin is a pyrogen - a fever causing agent.  

If it gets into the bloodstream, it can  lead to septic shock, and can be deadly.

But, fighting off these types of  infections is what immune systems are for.  

Immune systems have developed  to protect all different kinds  

of organisms from foreign pathogens.  And during the course of evolution,  

two different kinds of general immune system  emerged within multicellular organisms.

Humans and many other vertebrates have adaptive  immune systems that protect us by strategically  

mounting a defense against invading bacteria.  It is activated by exposure to pathogens, and  

uses an immune memory to learn about the threat  and enhance the immune response accordingly.

But many invertebrates, including horseshoe  crabs, don't have this adaptive immunity. Instead,  

they have an innate immune system, which attacks  based on the identification of general threat.

The basis for a horseshoe crab's immune  response are cells called granular amoebocytes.  

When bacteria come into contact  with a horseshoe crab's blood,  

they trigger an enzyme cascade,  mediated by these amoebocytes,  

which causes the blood in the immediate area  of the infection to clot into a gel. The gel  

surrounds and isolates the infection from the rest  of the crab, and the pathogens are neutralized.

The clotting from granular  amoebocytes is a simple,  

but very effective way for the horseshoe  crab to defend itself from infection.  

And, as researchers began to realize in  the 1960s, it's a very effective way for  

us to detect the presence of toxins in places  where we really, really don't want them to be.

When creating injectable healthcare products  like vaccines, medical implants, and IVs, it is  

imperative that they are free of any invading  microbes. It's easy enough to sterilize the  

solutions or devices by blasting them with heat,  radiation, or gas that is deadly to bacteria.  

But killing bacteria isn't enough to make these  products safe. If certain bacteria was present  

before sterilization, the endotoxin will remain,  and can lead to severe consequences if injected.

Historically, pharmaceutical companies  got around this problem with huge colonies  

of rabbits - needed for what's  called the rabbit pyrogen test.  

To see if a product or drug is contaminated  with endotoxin, three (unlucky) rabbits would  

be injected with a small amount of the  drug or product in question and monitored  

for four hours. Rabbits have a similar pyrogen  tolerance to humans, so if any develop a fever,  

the batch would be considered to be contaminated  with bacterial endotoxin. This is an effective  

way of preventing endotoxins from accidentally  being injected into the public, but because it  

is an in-vivo test - meaning done inside a living  organism- it's very time-consuming and expensive.

So when researchers noticed the  clotting effect of the horseshoe  

crab's amoebocytes in the presence of  endotoxin, they realized it could be  

an in vitro way of spotting contamination  - a much cheaper, easier, and faster test.

This in vitro test is called the LAL test  - limulus amoebocyte lysate. Limulus being  

limulus polyphemus, the american horseshoe crab.  This test has become the worldwide standard for  

screening for bacterial contamination. It is  capable of detecting endotoxin at significantly  

lower levels than the rabbit pyrogen test.  Today, every drug certified by the FDA must  

be tested using LAL, as do surgical implants  such as pacemakers and prosthetic devices.

After the horseshoe crabs are  brought to the lab, the tissue  

around their heart is pierced with a needle  and up to 30 percent of their blood is drained.  

The amoebocytes in the blood are then  extracted from that for the LAL test.

Upon exposure to endotoxins, the  amebocytes undergo a rapid enzyme cascade  

that causes the cells to stick  together and form a thick clot.  

This clot can form in around 90  seconds, giving a nearly instant result.

We've never found anything that is as  sensitive in detecting endotoxin than  

the horseshoe crab's amoebocytes. If there  are dangerous bacterial endotoxins—even  

at a concentration of one part per trillion  - a clot will form and can be detected.

This is great news for us. Pretty much every  single person who has ever had an injection  

of any sort has been protected because of this  compound from this strange, ancient creature. The  

only problem is that for this test to be readily  available, pharmaceutical companies need a large  

supply of the blood of live crabs - which, as  you'd guess, is not such great news for the crabs.

In theory, the process of extracting blood  from the horseshoe crabs does not kill them.  

It's sort of like blood donation, albeit a  nonconsensual one. And once their blood is taken,  

the crabs are released in a new location so they  do not accidentally get caught a second time,  

ensuring they have a chance to recover.  Their blood volume rebounds in about a  

week - and the LAL industry states that there  are no long term ill effects for the crabs.

They measured mortality rates of less than 3%.  But conservationists tell a different story.  

Between 10 and 30 percent of the bled animals,  according to varying estimates, actually die.  

And 30% of the animals per year dying equates  to losses in the hundreds of thousands.

And this isn't just bad for the horseshoe crab,  but for the entire ecosystem in which they live.  

Many other species of animals rely on  the horseshoe crabs' eggs for food,  

like shorebirds and turtles.

So the obvious question is - why haven't  scientists made a synthetic alternative to LAL?

Since the 1970s they have certainly  been trying - and luckily for the  

crabs they have started to have some success.

In 1995, scientists from the National  University of Singapore were finally able to  

identify and isolate the gene responsible for the  endotoxin-sensitive protein called Factor C – the  

most important component in the LAL test – and  produce it in yeast. Several years after that,  

they were able to create a rapid endotoxin  test based on this recombinant protein.

But despite these advances, these synthetic  tests are still not widely available.  

They have been adopted extremely slowly  due to regulatory and safety concerns.  

Europe did not recognize the synthetic protein  as an alternate endotoxin detection until 2015,  

and the FDA in the US did not approve the first  drug that used an endotoxin test based on the  

synthetic protein until 2018. And earlier this  year, the American Pharmacopeia, which sets the  

scientific standards for drugs and other products  in the U.S., declined to place the synthetic  

protein on equal footing with crab lysate,  claiming that its safety is still unproven.

For now, we still need the horseshoe  crab and their baby blue blood.  

But as more and more studies come out that  demonstrate the safety of the synthetic  

version of the endotoxin test, the horseshoe  crabs can breathe a bit of a sigh of relief.  

While they still face threats from  overfishing for bait and habitat destruction,  

the adoption of this technology will  relieve at least one major pressure.

Our medical need for horseshoe crabs is what has  started to push these animals towards extinction  

in recent decades, but this is not the first time  they have faced such a profound threat. Since the  

first days of the horseshoe crab's ancestor,  they have faced - and survived - all FIVE  

mass extinctions. These extinction events  are defined as the loss of least 75 percent  

of species, happening in the geological blink  of an eye. Volcanoes erupting, oceans warming,  

ice sheets forming, or oceans acidifying  - the great die-offs result from a perfect  

storm of multiple calamities. The horseshoe  crab and its ancestors were one of the few  

creatures to survive - but if so many things  die, how does life rebound to flourish again?

This is the question that researchers at the  University of Oslo are trying to understand,  

and is the focus of the documentary “Breakthrough:  Recovering From Extinction” on CuriosityStream.  

They are pioneering an investigation  about what survived, and what emerged  

after the largest mass extinction on  our planet, 252 million years ago..

This is one of many paleontology documentaries  on CuriosityStream, which are all really good.  

And now, CuriosityStream has partnered  with us to offer an incredible deal.  

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