After Life: The Strange Science of Decay

Decay.

It happens to everything and everyone.

We try to keep it out of our everyday lives.

But decay is one of the most important forces in nature.

It underpins all life on Earth.

So what would we see, if we let it loose in our homes?

To find out, we've built a home of our own

inside this box.

We've filled it with everything you might find in a typical kitchen

and garden. And now we're going to let it all rot.

Well, here it is.

A team of engineers and scientists have spent eight months recreating

a kitchen and garden. On the inside is all the food you'd expect,

as if a family were just about to have a party.

Also on the inside are the bacteria and fungal spores that are going

to start the process of decay. I can't wait to see what happens next.

Over eight weeks, we're going to track every step

of the extraordinary process that breaks down and recycles our everyday things.

The house will be our lab, as we reveal the unexpected order behind

the chaos of decay, and will help us understand why

life itself depends on this process.

At times what we find might be disturbing and repellent...

This is probably going to be absolutely atrocious.

HE COUGHS

But there will also be moments of surprise.

The mould has just covered that entire box.

..as we uncover hidden beauty.

And I'll go beyond the box to see how decay affects our lives...

Ah! Can't do it!

..how we detect it...

Do you remember seeing the film The Blob?

..how we fight it.

It's definitely the best two-year-old sandwich I've ever had.

Something on this scale has never been attempted before,

so things might not go according to plan.

Ah! Now that's where all the flies went.

But whatever happens, it will be a fascinating journey

into the fate that awaits all living things.

To be broken down.

To be recycled. To be reborn.

It's a surprising thought,

life relies on death.

Living things, us included, can only be made

from the remains of dead things.

And that's the incredible cycle we hope to capture,

inside our After Life House.

As a biologist, I can't wait to see what new life will emerge from these

dead things by the time we're done.

This is day one. We have eight weeks to go.

This is my first chance to see inside the box.

And a party was obviously just about to happen.

Over here we've got cooked rice and chilli, there's cups of tea.

Over in the corner there's a raw fish,

that's going to get very smelly pretty fast.

Cheese and a fruit bowl here, masses of fruit flies on that, probably,

I mean, we don't know, it hasn't been tried before.

A vegetable box over here, again, it all looks fresh,

but that will, in a week or two, begin to rot down.

And look at this, a raw chicken.

Sausages, hamburgers, all this is

going to attract flies like nobody's business.

Out here in the garden you've got a whole pig on a spit.

That's going to become very smelly.

But it's not just food items out here in the garden.

We have a compost heap. We have a woodpile.

They'll rot down too.

It'll be interesting to see how, as all the things decay,

the wood and the plants and the pig, how they will interact.

Over there in the corner we have a dead rat as well.

In fact everything in here has been carefully arranged to help us

unravel the underlying patterns of decay.

We're going to keep an eye on how humid it is, and how hot it is.

It's already up to 66% RH which will make things go really quite fast.

I'm not sure if I'll be overcome by the heat, the stench or the flies.

Insects are my own speciality.

Together with moulds and bacteria, they are key agents of decay,

things that will break all this down.

To make sure they are all present in our house from the start,

we're introducing a selection of common species.

Look at that, straight underneath!

These guys, blow flies, are going to be the ones

to watch in the early stages.

And there they go.

Well, that's it. We're up and running

and it's time to leave all this to the agents of decay.

Now, for nearly two months,

we're going to track every stage in the process of decay.

And we're not the only ones following events.

The box and its contents are on display to the public within

Edinburgh zoo, to help explore our reactions to this

little understood process.

Oh my God, I've never seen anything like it

That's a real pig.

Ew, that's gross!

Oh, there's a mouse.

That's disgusting, eugh!

Look at that fish.

Can we go out now cos it's going to make us feel sick?

THEY LAUGH

I agree.

For the first 24 hours of our project,

visible signs of decay are subtle.

But the agents of decay are already battling it out to decompose

the food and get to the nutrients locked inside.

I want to investigate who's got the advantage in this opening stage

Well, it's the second day and it's really warm in here, it's 25 degrees.

That's like a warm summer day, so some things are drying out

the chilli con carne is already growing a layer of mould,

and that shows that there are fungal spores drifting around in the atmosphere

all the time and settling on food.

Over here, the sandwiches which originally filled the box,

up to the top, have sagged down to about half their height.

But what's really interesting me is what's happening over here.

The most obvious change so far has been on the surface of our chicken.

Our time lapse cameras show these blotches appearing on its skin,

over the course the past day.

To find out what's producing them,

I've asked Dr Clare Taylor, a microbiologist, to join me.

Well, Clare, that chicken is beginning to look a bit discoloured.

-It smells a bit as well.

-There's beginning to be a slight whiff. What have you got on this?

I tell you what I've got a UV light

so we can take a look more closely at the surface.

Now, ultraviolet I use for other things,

but I'm interested to see what happens here.

-Now you can't see it.

-No, can't see anything.

Take a look at that!

It's glowing! So all these areas are glowing sort of blue.

Exactly, so where you can see those glowing bits, that's bacteria.

-Any particular kind?

-That's likely to be pseudomonas.

Pseudomonas is a common type of food spoilage bacteria.

Our microscope shows a whole colony glowing under the UV light.

There could be as many as a billion individual bacterial cells

in this sample alone.

In sheer number terms,

bacteria are the most common agents of decay on the planet.

And, on dead animals, they're the first to attack.

Because they're already on the scene.

All creatures carry bacteria while they're alive.

These pseudomonas bacteria were on our chicken before it was killed,

feeding on its skin secretions.

Now it's dead, they've quickly switched to decomposing its flesh.

With ample food, and enough moisture,

they've multiplied rapidly.

As colonies of bacteria like this expand, something surprising happens.

The bacteria start to coordinate their actions.

Working together to benefit the colony.

The bacteria send signals to each other to direct what they do.

So the bacteria are talking to each other, telling each other where they need to go.

These E-coli bacteria have been genetically modified

to allow us to see this in action.

When the colony reaches a critical size all the bacteria start flashing in unison.

Bacteria are constantly exchanging chemicals that allow them

to sense their own numbers and those of rival colonies.

They can even detect when they have the numbers

to overwhelm a competitor.

Back on our chicken, these tactics have allowed food spoilage bacteria to gain the upper hand.

But their actions are setting off a chain of events

that will attract a whole new set of decomposers.

As they break down the cells of the chicken to feast on the protein inside,

the bacteria are releasing strong smelling gases.

blow flies can pick up the smell of decomposing flesh within minutes of an animal's death.

So it's likely they've already laid eggs on the chicken and other meat throughout the box.

We'll find out if we start seeing maggots in the next few days.

These gases send a signal to us too.

It's our most important clue that food spoilage bacteria have been at work.

Right, let's see what folks make of these chicken drumsticks.

I want to see how sensitive we are to even the smallest signs of decay.

Hi, guys, would you care to have a smell of this?

-Erggh! I can smell it from here.

-Urgh!

THEY LAUGH

-It's horrible.

-Stop it.

-It's not nice.

So, if you found that in your house, what would you do?

I wouldn't eat it. I think I'd put it in the bin.

-I'd throw it away immediately.

-Throw it out.

It's disgusting.

We fight a daily battle to keep this kind of decay out of our kitchens.

Looking round the box already makes me think about what a challenge this really is.

Decay is a relentless opponent.

So, I'm interested in exploring what we've learnt about delaying its effects.

And in America, there's a team that's taking on

the ultimate food preservation challenge.

GUNSHOTS

Keep your head down or it's going to get shot off you!

GUNSHOTS

Now, this is not necessarily the first place I'd think of

when it comes to the latest advances in food science,

but the US army is right on the frontline in the war against decay.

Feeding an army in the field has always presented a challenge.

Soldiers need food that is quick to prepare,

light to carry and long lasting.

Traditionally, the US military uses vacuum packed food

called MREs, meals ready to eat.

Special packaging stops moisture and oxygen getting in

so bacteria can't grow. MREs have a shelf life of three years.

There's a problem though.

MREs are not exactly popular with the people who have to eat them.

Hands-down-worst MRE made is the veggie omelette.

It's like eating a... I don't know.

Wet, soggy cardboard is the best way I think you can describe it.

If I had to eat an MRE every day, that would basically suck.

GUNFIRE

So, when the army went looking for ways to spruce up the menu,

it wanted something more appealing.

Something that was quick and easy to eat.

And could deliver the huge amounts of energy that soldiers require.

The solution was a surprise.

A sandwich. But not just any sandwich.

A sandwich that remains fresh and tasty in the field for up to three years,

without refrigeration, freeze drying or the need to add water.

That is extreme preservation.

So how did they do it?

Food scientist Michelle Richardson was part of the team that developed the sandwich.

Her first challenge was to control the moisture you'd find in a typical sandwich.

HE LAUGHS

These sandwiches do not look very happy.

They really don't.

That's a ham and cheese wedge that's been in the car for three days.

If we open it up, we'll just have a look at this thing

cos if you had that in your backpack for three days...

That was just a normal shop-bought sandwich.

Urgh! It's soggy. It's really soggy. Look at that.

You wouldn't really want to eat that in the field?

You really wouldn't want to eat it for two reasons. It wouldn't taste good,

because the texture is not what you typically get. And also

because of that moisture excess you may have bacteria growing in it.

If you can control the moisture, you can slow down the process of decay.

Without water, bacteria cannot grow.

That's why drying is the classic way to stop food decaying.

But a sandwich without water would be inedible.

So Michelle has taken inspiration from another classic preservation technique.

Well, this right here is strawberry jam

-and as you can see in here, it's very firm.

-Yeah.

It's made from strawberries. Most fruits and vegetables contain

a lot of water, probably 95% water, but by adding different ingredients,

what that does is it holds the water in very tightly.

-Right, so it's locked away in there?

-Yes.

The sugar added to jam acts as what's called a humectant.

It traps the water from the fruit inside the jam.

That's why the jam is moist enough to spread,

but doesn't make the bread soggy.

Crucially for the battle against decay,

the water is also now locked away from bacteria.

The army's sandwiches deploy a whole range of ingredients

that have these water-retaining properties.

Honey, sugar and salt have all been enlisted.

Bacteria need water to thrive. Most also need oxygen too.

Michelle has found a way to cut off supplies of that as well.

Now, when I opened the pack I found this inside

-and I assume that's not edible.

-No, it's not.

What is this for?

This is an oxygen scavenger.

Basically what's contained in here are little iron shavings.

Oh, right. Iron filings.

If there is any oxygen or moisture still inside the packaging,

they'll react with the iron filings, and become trapped in a layer of rust.

This will prevent yeast and mould from growing as well as bacteria but

it will also prevent chemical reactions that require oxygen from taking place.

This is one seriously hi-tech sandwich!

Yeah, it is.

These simple but ingenious solutions have combined to make

a food that is highly resistant to decay.

But the ultimate test is whether anyone wants to eat it.

It's definitely the best two-year-old sandwich I've had. Better than a lot of new ones too.

I'm a big fan. I like the bread.

The bread just makes it, it's definitely great,

especially for two-years-old.

These sandwiches don't stay fresh for ever.

But they do show that, if you can reduce the moisture and oxygen that

bacteria thrive on, you can hold off decay for a very long time.

Back at the house, water and oxygen

certainly aren't in short supply, so bacteria are thriving.

And over the last eight days of decay we've started to see

the first maggots appearing in our pig.

I'd expect their numbers to rocket in a week or so.

Other insects have been busy around our dead rat.

These are sexton beetles.

In the wild they'll bury the carcasses of small mammals

to protect them from rival insects.

Their own larvae then break down the flesh.

But in our box, things are not quite going to plan.

Despite all the activity, our rat remains unburied.

So I'll try laying out a new rat and see if they prefer it.

But the most dramatic change has been in our kitchen.

It's been overrun by the next agent of decay, mould.

Moulds are masters of decay.

They're a form of fungi, the most versatile

and important decomposers on the planet.

Fungi can rot almost anything.

In our box, moulds are attacking our fruit and vegetables.

And they're also on our meat, battling with the bacteria for dominance.

It'll be fascinating to see how that one plays out.

The typical house will contain about 1,000 different species of mould.

They can start to grow the moment their spores land on a suitable food source.

I want to see which ones are at work in our box.

Well, in the kitchen there is mould absolutely everywhere.

The vegetables in the tray are covered in fungus.

There's at least three sorts of fungus I can see.

The hamburgers, sausages, even the hamburgers that are wrapped up are now covered in mould.

That's looking quite... woah! That might blow at any time.

The soft fruit in particular have been attacked.

The peaches have gone and there's mould everywhere.

The melon's just incredible, it's really been hammered.

It's just covered, all over there.

I'm a little bit nervous about taking this lid off.

This is going to be... Urgh!

Urgh! That's an incredible smell.

It's almost sweet.

It's an incredible sort of yeasty, smell.

The mould has just covered the entire box.

That's actually quite beautiful in a bizarre way.

It's like just furry growths everywhere.

That's amazing! That's only a week.

In close up, the unexpected beauty of mould is even clearer.

These networks of filaments we see on the surface of our bread

are the mould's fruiting body.

At the ends of the filaments are spore heads, each packed with individual spores,

all waiting to be released to grow into new colonies.

There are 500 spores in every cubic metre of air in the average home.

So there's plenty of competition for the chance to attack our bread.

I've asked Dr Patrick Hickey, our fungi expert to investigate

which moulds have managed to gain control.

Now, Patrick, it's only week one and we've got incredible fungal growth

all over the kitchen. Particularly on the bread.

Well, the bread is a perfect food source for the fungi.

The spores probably landed on the bread when it was being prepared and

they've grown quickly into the bread and they're taking up the nutrients.

What we're actually seeing is two moulds meeting.

In the background, we've got a dark green-grey mould

that's penicilium. These bright dots in the front

are the sporilating structures of aspergillus competing.

So they're kind of trying to out compete each other for the bread,

for the food resource.

Each mould is trying to seize territory by out-growing its competitors.

But they are also using powerful chemical weapons to try to

kill off other moulds and rival decomposers, like bacteria.

In the case of penicillium, the toxin it produces to win

the battle for decay, has turned out to be highly beneficial to us.

We call it penicillin.

But not all moulds are good for us.

Now, I have to admit, I sometimes cut the mould off bits of bread

and toast it. Is that really harmful?

Well, what you're scraping off is really the tip of the iceberg.

The fungus grows deep into the bread and it also depends on what kind of

mould is growing into the bread. You have various different moulds,

some of which are harmless. Others like aspergillus produce deadly mycotoxins,

these are toxic chemicals, which can rot your liver,

they can give you cancer.

So, what you're saying is, I shouldn't really do that.

It's dangerous I should just throw it in the bin.

Absolutely, the fungus penetrates quite deep into the bread you're

not going to get rid of the toxins in the mould just by scraping it off.

Most of us might prefer not to have to cope with mouldy bread

in the first place. Moulds and other types of fungi are things that ruin our food, and may cause us harm.

But fungi are vital to life on this planet.

They're amongst the Earth's oldest life forms.

On land, they pre-date plants by at least 300 million years.

And they rise to almost any challenge.

There is a fungus growing inside the brain of this ant.

It's producing chemicals that control the ant's behaviour,

forcing it to climb to the top of a plant.

Then the killer fungus bursts out of the ant's head,

allowing its spores to spread.

Fungi have found ways to work on a microscopic level too.

This one is lying in wait for tiny roundworms.

At the right moment, it strangles them in a vice-like grip,

then feeds on their flesh.

But it's fungi's unrivalled ability to decay organic matter that

makes them so important to us.

A world where fungi couldn't decay things

would be a very different place.

To see just how different, we have to go back in Earth's history.

To a period when a new form of organic matter emerged.

One that challenged fungi's powers of decay.

The fate of life on Earth, hung in the balance.

Rewind 300 million years to the Carboniferous Period.

A time when plants, struggling to compete for sunlight,

had evolved into trees.

That new organic material was wood.

It gave plants the strength to grow taller.

But this evolutionary leap left fungi behind.

They weren't able to decompose wood.

The delicate mechanism of decay had been upset.

Without decay the trees grew, died and lay where they fell.

The effect on the planet's climate was spectacular.

Professor Lynne Boddy is an expert in the history of fungi.

Trees absorb carbon dioxide from the air.

They absorb nutrients from the soil.

And then the carbon is locked up within the trees,

so when they fall and die, the carbon is still locked up inside them.

-So huge changes simply because trees can't decay?

-Absolutely.

With fungi unable to break down wood, over time, more and more

carbon was removed from the air and locked up in dead trees.

The Earth's atmosphere began to change.

Oxygen levels shot up from 20% to 30%,

as carbon dioxide levels dropped.

This allowed insects to grow to gigantic proportions.

Spiders were as wide as a human head.

Dragonflies were ten times larger than they are today.

If the atmosphere had stayed like this, life on our planet would have looked very different.

The stumbling block for fungi was a molecule in trees called lignin.

It's what makes wood tough.

It took 50 million years for fungi to evolve a way to overcome it.

And Lynne is able to show me the modern descendents of

the fungi that solved the problem.

If you pick up that log we could have a better look.

No, the one underneath. That one, there.

The first thing I see about it, it's not heavy at all.

-It's light as a feather.

-It hardly weighs anything.

Yes, it's been rotted and you can see that it's really white.

Why is it white?

It's white because the fungi have broken down the lignin in the wood.

-Which was brown.

-Yes.

It's pretty easy to see what effect the fungi have had on the wood,

but can we actually see the fungi themselves?

We can't actually see them rotting the wood,

not with our naked eye because they're microscopic.

To show me the fungi in action, Lynne has grown this sample in soil.

-That's pretty.

-What we've got here is a little bit of beech wood

that's got the fungus growing in it, and then you put the wood

on top of this soil, and the fungus has grown out of the wood,

looking for other pieces of wood that they can colonise and get food from.

The fungus sends out a network of tiny threads called hyphae.

They've aggregated together so we can actually see them with the naked eye.

-And they're heading off to find other bits to eat?

-That's right.

The hyphae release powerful enzymes into the wood.

They are able to break down the lignin into nutrients

the fungi can then absorb.

This releases carbon from the wood, back into the air.

It was the evolution of these enzymes that allowed fungi to rebalance the Earth's atmosphere.

If those fungi weren't here today then decay would come to a grinding

halt and we would be in a similar position to what we were

in the Carboniferous period.

By evolving the ability to unlock the carbon in dead wood,

fungi saved the world.

We still rely on this delicate balance between all living things,

and the agents that can decompose them.

At the After Life house another eight days have gone by.

Just after my last visit we captured something extraordinary.

The new rat that I left out in the garden has been

buried by the sexton beetles, as I hoped it would be.

Despite their size, it took the two of them less than 12 hours to

get the whole carcass underground, and away from rival decomposers.

The female will lay her eggs in the rat

so her young will have food to eat when they hatch.

In about a month's time, we'll dig up the rat

and see what the beetle larvae have done.

Elsewhere in the box,

bacteria and mould are still battling it out on the meat.

The bacteria inside this sealed pack of burgers are hard at work,

producing this build up of gas.

I'm not looking forward to smelling that.

Where meat was left exposed to the air, like these sausages,

mould has been able to move in,

suggesting that the bacteria have been overwhelmed.

But just over two weeks in to our project,

and an army of even more voracious decomposers is taking control.

The maggot population has exploded.

Our pig is literally seething with them.

Maggots are some of decay's most effective operators.

The question is, how long will it take them

to munch their way through the contents of our house?

I haven't even got into the box and already I can see escaping maggots.

So, even though we try really carefully to keep

all the insects on the inside, some have escaped.

They can squeeze through the tiniest gap

The time-lapse cameras have shown a real fever pitch,

especially on the chicken and the fish.

I just want to show you the fish though. It's completely eaten out.

If I just... look at that, look at the inside of that.

Pwahh.

It's just a writhing mass of maggots

and the smell of ammonia is overpowering.

They've eaten everything.

All that remains is the dry skin on the outside and the bones.

These are the most efficient recyclers on the planet.

I think they are just amazing insects.

It's 15 days since I released about 100 blow flies into the box.

As soon as they mate, female flies look for a place to lay eggs.

Up to 300 at a time.

The gases given off in the very early stages of decomposition,

will have attracted them to the dead meat and fish.

They're the ideal food source for the maggots,

when they start to emerge, around 24 hours later.

Now they've hatched, these maggots have only one aim.

To eat. Non-stop.

Now, I've got the thermal image camera here

and this is actually quite a useful item.

It can show heat that's produced by organisms.

The fly larvae, when they feed en masse, do generate quite a bit of heat.

Now, I'm just shining it on the chicken drumsticks,

which are cold, they're not hot at all.

The chicken's not very hot. But wooo! Look at that!

The burgers are glowing like a beacon.

Now, that means that there are lots of fly larvae in there and they

are generating masses of heat, which actually makes them grow faster.

Our time lapse camera shows how maggots feed as a pack,

so they can share not just heat, but digestive enzymes too.

They carefully coordinate their movements.

As the meat in one burger runs out, the maggots move together, almost

as a single unit, over to the fresh supplies of the second burger.

Maggots are a perfectly adapted mechanism for turning

dead meat into flies.

At the head end, you've got these amazing hooks,

which are basically a pair of sharp, curved hooks

with which the maggot rasps its way through food.

As you move further down, you see it doesn't have legs.

There isn't any obvious head, thorax and abdomen.

It has got these bands of raised bumps,

they're like spikes for a grub.

They're bands of raised welts,

which help the maggot move through its food so it's essentially

in a pile of slop.

These welts enable it to undulate through the food.

Otherwise, it's very hard to move.

At the other end, let's go down to the back end.

These structures here are the breathing holes of the fly.

These are the spiracles through which it gets its air.

They're on the rear end. It has a pair of them, quite big.

So it's able to insert its head into wet food and still feed

while its rear end is in the air.

All in all, it is just about the perfect eating machine.

To me, maggots are the clearest example we've seen

so far of the fundamental principle behind decay.

Recycling the nutrients from dead animals,

and turning it into new life.

But, of course, for many of us they represent everything

that's disgusting about decay.

I'm intrigued as to what these strong feelings of revulsion are, so I've devised a little test.

I'm going to put a £5 note inside a plastic bag

and I'm going to hide it inside a tub, inside which I'm going to put

loads of maggots. We're going to end up with a pretty simple test,

which is essentially this,

a large box full of writhing maggots and a £5 note.

Now, I reckon only one person in ten will be able to

overcome their deep seated revulsion for maggots

and put their hand in to retrieve the fiver. Well, we'll find out.

Who would like to put their hand in a bucket of maggots for a fiver?

Oh, you would, would you?

It looks like my bin at home. THEY LAUGH

-I can't do it!

-Five pound note.

No, I can't do it.

-Maggots.

-Ew! SHE LAUGHS NERVOUSLY

-Oh.

-It's a little gross, they're writhing on my fingers.

Oh, no! Oh! Oh! No, no.

-No, I can't do it.

-Five pound note.

SHE SCREAMS

-You're nearly there.

-I've got it! Ah!

You nearly got it. Yes!

THEY APPLAUD

This feeling of disgust is an emotion that evolved over thousands of years.

It's not just maggots. All signs of decay revolt us.

It's a great mechanism for stopping us

from eating food that might make us sick.

But it's also why we so rarely look at decay,

we're hardwired to be repulsed by it.

In the next few weeks, I hope our After Life house will start

to show why this disgusting process is so important.

Why decomposition is vital to life.

And there's one part of our box where we're attempting to demonstrate that, in a unique way.

These dead mustard plants are the starting point of an experiment

that will help me trace how new life emerges from old.

I've made liquid compost from the mustard

and fed it to these seedlings.

We plan to track individual nitrogen atoms from the dead mustard leaves,

to see if they are re-used in the new plants.

No-one has ever followed the cycle of life in this way before.

In a couple of weeks time we can come back and, with any luck,

we'll be able to track this vital part of the cycle from death and decay to new life.

It's the 23rd day in the After Life house.

The first waves of decay have now passed.

Vegetables and soft fruit have been consumed by mould.

In some places there's not much left for them to feed on.

They'll need to find new supplies.

Anything with a hard skin, like this orange,

remains apparently unaffected.

Maggot activity too has begun to die down,

leaving behind a sort of meat slurry in our burger packet,

where a few late developers eke out a meal from the remains.

Most of the maggots have started to pupate,

the next stage before they turn into adults.

So we should soon see an explosion in our fly numbers.

And our chicken has gone through an alarming metamorphosis.

Bacteria continue to rot away at it, releasing gases as they feed.

This week the carcass bloated to even more grotesque proportions

before deflating as the gases escaped.

One month into the project and our house really isn't somewhere

you'd want to visit, unless you had to.

Every time I go into the box there's one thing that hits me.

That is, the all-pervading, hideous stink of decay.

Imagine sticking your nose deep into a rubbish bin.

That's the smell I'm talking about.

But if you can get beyond your revulsion,

the smell of decay gives real clues to its underlying mechanisms.

And the different ways plants and animals are broken down.

I want to share some of these smells with our audience.

I've got two tubs.

One's got far gone vegetables and this one meat that's far gone.

I want to find out which our visitors find most disgusting.

This is decaying vegetables. Have a smell of that. See what you think.

-It smells like vegetables, still.

-Have a good sniff.

-THEY LAUGH

-It's not that bad, is it?

That's not terrible.

I think it's only fair to warn you, this is not nice.

Have a smell of that.

That smells like a pig barn!

THEY LAUGH

As expected, the meat gets the same response every time.

That's pretty grim, isn't it?

His eyes are watering!

Ew!

Rotting meat is far more dangerous to us than rotting vegetables.

So we're programmed to find it more offensive.

But what are we actually smelling?

Plant cells are largely made up of starches and sugars.

So when fruit and veg decay, they ferment,

turning the sugars into alcohol, and releasing

volatile compounds which have a sweet odour.

But fish and meat are going to produce really smelly gases

like hydrogen sulphide, sulphur dioxide and ammonia

so I'm just going to extract

some of the gases from the inside of this decaying chicken,

suck it up into this syringe

and blow it over a gas analyser and see what happens.

LOUD BEEPING

Look at that! The hydrogen sulphide shot up to 10%.

That really is smelly.

Oh, God.

HE COUGHS

Unlike plant cells, animal cells are made up largely of proteins.

The foul smelling gases are produced

when these proteins are broken down into amino acids.

To understand more about that process, and why the smell

it generates is such an important part of decay, I am going to

experience rotting flesh on a scale that even the box can't provide.

At a secret location in north-west England

a grotesque but important experiment is taking place.

65 pig carcasses are being left to rot.

They're part of an investigation into exactly how

flesh decomposes, under different conditions.

And the smell of death is everywhere.

Well, I haven't been here very long and there's a real whiff of dead animal.

Sometimes the wind changes direction and it catches your nose.

I'm used to dealing with smells and excrement and stuff but I'm

wondering if I'm up to this. There's a lot of dead animals around here.

The pigs are stand-ins for human remains.

The aim of the experiment is to help police forensic teams

establish an accurate time of death, based on the state of decomposition.

Dr Tal Simmons is the research director for the project.

And she's going to help me understand how

the different stages of decay account for what we smell.

-Good morning, Tal.

-Good morning, George.

-I won't shake hands.

-Possibly not.

-What's happening here?

Let's move the cage and we'll be able to see a bit better.

Well, we've got a pig we put out four days ago.

He's just begun to really show some of the early stages of decomposition.

The first thing that's obvious to me, it's swollen up there.

He's beginning to bloat

and he'll bloat more in the next couple of days and that's due to the cellular breakdown, inside the body.

All those cells are starting to collapse, the cell membrane is going.

It's exuding all the fluids inside the cell.

A lot of those contain digestive enzymes.

He's starting to eat himself from the inside.

The moment blood stops flowing in an animal,

this process of cell death begins.

As each cell membrane splits, enzymes inside are released

and begin to break down other cells.

Bacteria then start to feed on these protein rich contents,

releasing the gases that are bloating the pig.

All of these gases produced inside are coming up the digestive tract.

So that smell is actually coming out and that's what attracts the flies?

-We can't smell it but flies can.

-It's not obvious at all.

-No.

But, as I know from the rotting meat and fish in the box,

it doesn't take long for the smell to become something we can detect.

HE COUGHS

Oh, that's a lot worse.

Let's pull this off.

Oh, dear!

He's much more advanced, as you can see.

HE COUGHS

We're now smelling a cocktail of highly volatile gases and

liquids produced, not just by the break down of the animal proteins,

but by the agents of decay themselves.

The body is largely composed of water, so as the cells break down

and the cell walls go, you get the liquid coming from that,

you get the liquid that was part of the organs, and you get the liquid

that the maggots are excreting as part of their digestive process too.

If you look at it really closely, it's actually rather interesting.

It's a fascinating process.

-I wouldn't say it's attractive.

-I wouldn't go that far either!

Many of the molecules in this cocktail of decomposition fluids

have a particular property, they are highly electrically charged.

It's a bit like when you rub a balloon on a woollen jumper.

The molecules of the balloon pick up a charge, which means they stick to

other materials they come into contact with.

Which is why the smell of decay can literally stick to our clothes.

And it also explains why decay can leave a trace

that lingers far longer than you might think.

Top off.

Tal's colleague Peter Cross is measuring what effect

the decomposing pigs are having on the surrounding earth.

Just draw the water up. It's even frothing.

-It's foaming.

-Yeah.

Well, it's clearly not fresh.

Argh!

That's pretty bad!

This is soil water taken from the site of a buried pig carcass.

This machine is passing an electrical current through the soil water

and then measuring how well that soil water conducts electricity.

The contaminated water is 30 times more conductive than

soil water taken from ten metres away.

This is the trace that decay leaves behind.

We think that because of all the electrolytes

that are leaching into the soil water from the decomposing pig,

that they are changing the electrical properties of the soil water.

How long will that remain?

I'd expect conductivity to continue increasing for up to two years.

So that really is a fingerprint of death, isn't it?

Absolutely, yes.

And it's a fingerprint that allows scientists to detect

signs of decay, not just over years, but over centuries.

OK, Chris, do you want to grab the remote probes?

Dr Jamie Pringle is a forensic geophysicist.

Today he's using the conductive qualities of decomposition fluids

to identify unmarked graves in this churchyard.

Some are estimated to be 200-years-old.

Jamie's kit sends an electrical current into the ground to measure conductivity.

It can detect electrically charged molecules

left behind by the bodies buried centuries ago.

BEEPING

Oh, that's interesting, lads. Looks like it's going down there.

I've just downloaded the data from the machine

and the results show there's one, two, three, four, five areas

of blue, which means it's high conductivity results,

which suggests to me that's where the graves are going to be located

and where the decompositional fluids have been retained in the soil.

This technology opens up new possibilities in forensic science.

Not only can it be used for unmarked graves, it can be used for

other things as well, such as looking for buried murder victims.

For crime fighters, the powerful lingering effect of decay,

turns out to be one of its most useful qualities.

We're more than halfway through our investigation of what happens

when decay is allowed to run its course in a typical home.

We set out to see how quickly its contents would be broken down

and transformed into new life.

One month in, we have our most striking result yet.

The clue is in our rapidly increasing fly numbers.

These flies are the first generation to be born and bred in the box.

Two weeks ago, they were the maggots that were so active in all the meat.

Once a maggot has fed enough, it pupates.

Within about seven days, the adult blow fly emerges.

It inflates a soft spongy sack on the top of its head to help push itself out.

Then blood pumps into the wings, spreading them out

ready for take off.

There isn't anything better than flies to illustrate

the transformative power of decay.

The fly larvae have eaten this pig. I want to show you

just how little is left behind.

If I get this torn back without cutting my finger, it's quite tough.

The outer surface of the skin is now quite dry. Look at that.

Oh! The smell of ammonia is quite overpowering.

If I peel it back...

What we've got here is basically dried skin

and a few bits of fat All the meat has gone.

The fly larvae have eaten this pig out completely

All that's left are some ribs and fat.

All that meat that was once pig is now flying around this room.

Who says pigs can't fly?

Seven days later and the number of blow flies is becoming a problem inside the house.

Well, it's a week since I was here before

and, as I predicted, the numbers of flies have absolutely sky rocketed,

they've gone through the roof.

I'm going to wear an all-in-one suit for a bit of protection this week.

I reckon there could be as many as 10,000 flies inside.

Because our box is sealed, they can't escape to find

new sources of food and places to lay their eggs.

I'm worried that their sheer numbers may disrupt the natural course of decay elsewhere in the box.

There are now simply too many flies here, it's becoming quite unpleasant.

It's causing a problem because of the fly speck, that's the excrement,

which they leave on the surfaces, inside the glass.

So, it's time I tried to reduce them a bit...

manually.

The trouble is, they're flying quite low and sitting on surfaces.

It's hard to get them.

Half the flies are drunk because

the fruit bowl has become alcoholic

and the flies are flying under the influence at the moment.

It's probably why there are so many on the floor.

You can hear them.

A constant buzz.

This is pretty unpleasant.

Oh! Look at this!

It's no wonder that flies are so hard to capture.

Their compound eyes give them 360 degree vision.

So they can respond to movement in less than 30 milliseconds.

Me and my net can only do so much.

It will be hunger that kills off these flies in the remaining weeks,

as food supplies in the box run out.

Their role in our project is coming to an end.

We should start to see other insects moving in to carry on

the process of breaking down what's left of the meat.

In the meantime, the flies need for food is affecting one of our other agents of decay.

Six weeks in, mould is still ravaging the sandwich box.

It's even grown out from under the lid.

And it's attracted the attention of our starving flies.

Now, this to me, is one of the most amazing things I've ever seen.

Patrick Hickey has returned to investigate what's been happening to the moulds in our house.

How many actual species of fungus are here?

At least 20 or 30, maybe more.

20 or 30 species of fungus! I can't wait to have a sort of...

It's the perfect environment. Some of them are fairly dangerous.

One of the moulds here, aspergillus flavus, a greeny-yellow one,

can produce a nasty toxin. So, you want to be careful.

Look at this, it's a solid mat.

There are the layers of sandwich.

It's completely through. There aren't any flies, of course.

It was sealed in the box so the flies couldn't get in.

Big contrast to the fruit bowl, which was left open.

A couple of weeks ago it was covered in thick layers of fungus and

the flies have stripped it bare.

They've eaten the fungus and spores and recycled the fungi.

Fruit has become mould. Mould has become flies. Flies fly off.

And, if they were outside, they'd be eaten by something.

Outside in the garden,

other forms of fungi rely on insects to help them do their job.

This is the fruiting body of a stinkhorn fungus.

The rest of the fungus is below the soil,

feeding on wood and plant matter in the soil.

These stalks emerge when the fungus is ready to fruit,

growing up to 15cms in less than 24 hours.

When they break through the top layer of soil,

they release an intense smell that flies find irresistible,

the smell of dead and decaying meat.

The flies strip the jelly-like flesh from the mushroom,

and help spread its spores.

Even after 30 years of studying biology,

I'm still amazed by the complex behaviour of these simple organisms.

But stinkhorns aren't the strangest things feeding on the decaying wood in our garden.

Hidden away in our woodpile is something even more intriguing.

This is a slime mould.

It's the largest single-celled organism on Earth.

It can grow to more than three square metres.

Scientists have recently discovered that these primitive life forms

have some rather sophisticated talents.

At Oxford University, Dr Mark Fricker is one of a team of

botanists and computer scientists studying a species of slime mould

called Physarum Polycephalum.

For years slime moulds have fascinated scientists

with their remarkable ability to solve simple mazes.

Put food at the end of a maze

and the slime mould will find the quickest route through.

But scientists started to wonder

if the mould could do more than just perform clever tricks.

You can set them lots of little tasks, and

you can allow them to forage and connect up little

-food sources to see what sort of network they would make.

-OK.

And a geometric shape, so a square or something more complicated,

is interesting, but we wanted to see whether they would

be able to solve a slightly more complex problem.

Mark is recreating an experiment

he worked on with colleagues at Tokyo University.

He takes a blob of slime mould and then surrounds it with

a pattern of oat flakes, an irresistible treat to slime mould.

What happens next is recorded by a time-lapse camera.

The slime mould locates the oat flakes by growing out in all directions.

But within hours the slime mould shrinks back,

leaving an intricate web of tubes that connect the oat flakes.

It's these tubes that transfer nutrients around the slime mould.

Incredibly, everything you can see is part of one single cell.

It needs to build a network that is quite efficient, to transport all those resources.

At the same time, that network mustn't cost too much.

It mustn't take up too many of its own resources.

And then the other problem it has is, it's going to be subject to damage.

If there was only ever one connection,

there's a risk it would break.

The slime mould takes no chances.

It grows back-up routes to make sure that its food supply isn't cut off.

But there's something even more extraordinary about what the slime mould has done.

Mark hasn't just laid out the flakes in a random pattern.

The large blob in the middle is Tokyo

and each of the food sources are positioned as cities nearby Tokyo.

-So, it's a re-creation of the area around Tokyo?

-Indeed.

This is actually what it's based on, the rail network around Tokyo.

We can superimpose that over. Ok, so we align it...

That's identical! It's absolutely identical!

You see a lot of these connections. It's formed the same sort of links, it's got a few extra ones in as well,

-it's a slightly more resilient network than the ones the engineers designed...

-Hold on!

You're telling me, wait a minute,

that this slime mould has built a better network...

A remarkably similar network.

-..than the humans built.

-Yes.

The Tokyo rail system is one of the most efficient

and well organised in the world.

It took lots of skilled engineers using lots of brain power to plan.

Yet, somehow, slime mould has achieved the same goal,

how to efficiently link together multiple locations.

Slime mould has also been put to work in other parts of world.

Here it tackles some of Britain's major motorways.

This is its take on the best routes around Spain.

And here are some interesting alternatives to Americas Route 66.

What is the slime mould actually displaying here?

It's a sort of smart behaviour. It hasn't got a brain,

it hasn't got a nervous system, but it still seems to be able to solve

these sorts of complex problems with very simple rules.

It's something the computer scientists we work with are getting very interested in,

whether or not you can take inspiration from this system and apply it to other sorts of problems.

How does one of the most simple life-forms on Earth,

a single-celled amoeba that spends most of its time on woodland waste,

match its wits against transport engineers and computer scientists?

The clue seems to lie in its extraordinary biology.

Professor Bruce Ing is a self confessed slime mould obsessive.

He's going to help me track down some slime mould

in one of its native habitats.

Slime moulds aren't rare things?

-Oh, no. They're very common, indeed. They're everywhere.

-But overlooked?

Overlooked because they are shy, not easy to find,

-unless you know where to look.

-Shy slime moulds!

-Do you remember the film The Blob?

-Yes.

A giant mass of jelly, eating caravans?

-It was a slime mould?

-It was.

But not one we'll find here.

Not as big as that, I hope.

Bruce's 54 years in the field prove vital as we hunt the elusive slime mould.

After half an hour, he finds what we are looking for.

-It's not quite the sheet I was hoping for.

-No, indeed not.

But it's still the real McCoy.

This small patch of orange is creeping slime mould.

Up close, you can see how it's constantly pulsating.

When one part of it finds something it likes to eat,

it pulses more rapidly.

Scientists believe that it's this pulsating that helps transmit

information across the entire cell,

allowing the slime mould to move towards its food source.

These pulsations control where and how they grow across the forest floor,

or even around the oat flakes of the Tokyo rail map.

What's so special about slime mould is that it can use

this information to make multiple decisions, simultaneously.

Pretty ingenious stuff for a single-celled organism.

Slime moulds are what's known as self organising systems.

It's not a unique phenomenon in nature.

Flocks of birds work in a similar way.

With no leader, no overall control,

the flock nevertheless acts as a single unit.

But slime mould can do something that flocks of birds could never do.

Meet the Phi-Bot, the world's first slime mould controlled robot.

The Phi-Bot is the brain child of Dr Soichiro Tsuda

and Dr Klaus Peter Zauner from Southampton University.

Their robot takes its orders from a tiny blob of slime mould.

I sort of don't believe you, I want to...

HE LAUGHS

..I want to see it working. Prove it!

THEY LAUGH Soichiro, flip the switch.

It just seems almost unbelievable.

It's not instant, is it? It's not instant... Oh!

Wow! That's fantastic!

The slime mould sits on an electronic chip, inside the robot.

As it transmits information around its single-cell by pulsing,

the robot detects these pulses and translates them

into much larger movements across the surface of the table.

How did you get the idea for having a live organism inside a robot?

One inspiration source obviously from the Daleks, from Doctor Who?

-This is inspired by a Dalek?

-Yes.

-Well, it's the same thing, isn't it?

-Yeah exactly.

You've got a live organism in the machine, which controls it.

The Phi-Bot is pioneering a new approach to computing.

Today's computers use a single central processing unit to do their thinking.

But the slime mould has no need to ask a brain what to do,

all parts of the cell just work together, for the good of the whole.

The simple organism inside, processes information in a completely

radically different way from our conventional computing technology.

We want to learn more about how it can do that information processing.

So slime mould could hold the secret to a revolution in computing.

Or even the creation of artificial intelligence.

Not bad for something you can find in your wood pile.

There's only a week left to go in our project to study decay in a typical house and garden.

The pace of change in the box is beginning to slow down.

But, even now, decay is following an ordered sequence.

What one decomposer leaves behind is food for others.

Well, it's day 44 and the one thing that's immediately obvious,

it doesn't smell nearly as bad in here. It's actually quite pleasant.

The other thing that's obvious is there are very few flies now,

the majority of the flies that hatched out have died.

There aren't as many dead ones lying about as I'd expected, but

it looks like a few flies might have got themselves stuck in this

bottle of wine, as they searched for something to drink.

This is solid. Uh!

Look at this. Oh my God!

Urgh! That is incredible.

HE LAUGHS

I can't get them all out.

I've never seen so many flies in one bottle, in my life.

I can barely get them out.

That sort of explains why I wasn't seeing as many flies

flying around, as I expected.

It's because most of them were in here.

Look at it. It's just incredible. It's thick.

That's thick with flies.

Conditions in the box are very dry.

All that remains of the meat are hardened chunks of sinew and skin.

Even if the flies had survived there's nothing left for another generation of maggots to feed on.

But this is the perfect fodder for beetles.

This dried meat gives off a far less pungent odour, but the smell

it does produce gives them a signal that starts the next stage in decay.

Decay happens in a series in waves, this fish is dry and hard,

there are beetle larvae who will eat it. So there's no waste.

That's what I'm hunting for now, I'm hunting for the larvae

of a larder beetle and there's one right there.

Larder beetle larvae are present in around half of all homes.

They only colonise a carcass once it's become dried and desiccated.

Their powerful jaws allow them to eat through flesh, hair and skin.

And they can strip an animal down to the bone.

This stage in decay moves slowly though.

Larder beetle larvae take months to pupate into these adults.

The job of recycling what remains in the box could take generations of them, years to complete.

But another beetle in our box does allow us

to see how effective these insects can be.

36 days ago, two sexton beetles took less than 12 hours

to bury our dead rat.

What I'm aching to do now is a spot of archaeology.

Because what has happened is, the sextons beetles have taken

the rat down and they will have formed it into a ball,

on which their larvae have fed and hopefully 36 days should be

enough time. I should find a crypt in which the rat sits,

surrounded by its own fur, which they smear on the outside.

And there should just be bones left.

This, for me, is about as exciting as it gets.

I'm going to use a hoover to gently take away the soil.

What is amazing about these insects is,

they're one of the very few insects who look after their young.

They take care of their young. Once they've dragged the prey down,

and hidden it underground, they'll lay the eggs around the crypt,

and then the larvae will move in and feed.

And they'll help them to feed as well.

We're beginning to see a shape here.

This is very exciting. Turn that off.

Wonder if I can free it.

That is just fantastic.

There look at that, that's all that remains of the rat.

You can see the top part of the skull and the teeth.

The rest of it has completely disappeared,

there's nothing left of that rat.

We're now at week eight. We're nearing the end of our project.

But there is one final stage of decay I want to investigate.

And it's probably the most important.

We've watched as the nutrients, locked up in plant

and animal remains, have been re-used by other organisms.

In the process, complex things like chickens, rats and fruit,

have become simpler ones, insects, fungi, bacteria.

But the true power of decay is its ability to reduce complex things

right back to the most basic building blocks of life.

And all through the project,

that's been quietly happening in a corner of the box.

This is one of best places to see decay in action. We set this up

eight weeks ago and it was piled to the top with plant material.

It's now completely decayed down, we've been adding to it.

What I really want to do, is have a look inside and see what's going on.

Now, decay has been happening and the further you go down,

the more advanced it is. There's a snail on the trowel handle.

As all gardeners know, compost heaps turn dead plants

into a form of nutrients that new plants can use.

On the surface, animals like snails, slugs and worms begin the process

by eating the remains of plants, helping to break them into pieces.

The waste they excrete, and anything else left behind,

is eaten by smaller creatures like these mites.

Too tiny to be seen with the naked eye.

And this process continues down through the compost.

Ever smaller organisms,

reducing the plant waste to ever smaller components.

Until tiny fungi and bacteria are able to break down the very cells of the plant.

A teaspoon of soil contains four billion micro-organisms.

They finally release the nitrogen

and other building blocks of organic life, back into the soil.

What we end up with,

is an incredibly very fine soil,

the result of the breakdown processes of countless organisms.

Having begun with a big pile of green material, you may think that is an end point, but it's not,

it's just the beginning.

From here, life can begin to rebuild.

To me, this is the most amazing moment in the story of decay.

When we began eight weeks ago,

we wanted to demonstrate its significance in a unique way.

This is probably one of the most important experiments we've set up in the box.

These may look like ordinary plants but they're going to show us

a part of the story that's absolutely crucial. These are the marigolds and radish seedlings

I planted back at the beginning of the project.

They've flourished into mature plants.

I've been feeding them with a special liquid compost

made from plants grown using chemically labelled nitrogen atoms.

If everything has gone according to plan,

we should be able to track how individual atoms of nitrogen

are transferred from the mustard plant to our seedlings.

From death to life.

We sent samples of our plants to Professor Malcolm Clench.

It's time to find out if our experiment has worked.

The first one is from the marigold.

What can you see at the moment is a photograph of the marigold leaf.

He's able to pinpoint exactly where the labelled nitrogen has ended up.

As I start to play the video clip, we'll come up with

an overlay that shows the nitrogen in high abundance.

-That's really clear.

-Yes, very clear.

Each one of these dots shows where we found traces of the labelled

nitrogen from the mustard plant in our marigold leaf.

White areas show where it's concentrated.

How can we be 100% sure that labelled nitrogen has come from our experiment and nowhere else?

The form of nitrogen we're using is only 0.3% naturally abundant.

We can see areas of high intensity and they can only have come from

the mustard that was grown with the labelled nitrogen in.

-So, that is the definitive proof of the cycle of life?

-Indeed.

I think you're going to be pleased with the radish results.

We can see first off a very nice radish.

One that you prepared earlier.

Wow look at that!

That is absolutely cast iron proof,

that we have transferred material, an element in this case,

from one plant, dead and decayed, fed to something else and it takes it up.

Yes, it's incontrovertible.

This is what I hoped we'd see when we began our project.

It's the fundamental principle of decay,

revealed in front of our eyes.

For me, this is as good as it gets.

Two months of decay have transformed the After Life box.

Little is left of the fresh food we began with.

And what remains will continue its inexorable journey back to the basic building blocks of life.

But, as our plant experiment so dramatically demonstrated,

what we have witnessed in the box is a process of renewal.

That we are all part of.

It's a real snap-shot of everyone's life.

To see things changing, as they do, is a fantastic experiment.

We'd be in a horrible mess if we didn't have decay.

When you see what nature can do to get rid of all the dead things in the world...

We need that decay to happen in order for life to go on, I guess.

-Oh, my God!

-Look at that.

We tend to think of life as a linear process, with a beginning and end.

Things go from life to death.

I hope the box has shown this process in a new light.

Life is an ever repeating cycle.

One that's not just happening here, but everywhere on the planet.

The plants and animals of Earth's ecosystems rely on this continuing cycle.

Even the atoms that make us up are recycled.

They come from the food we eat, the air we breathe,

they're in our flesh, blood and bones.

They've been used millions of times before,

and they'll be used millions of times again.

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