David Attenborough examines some fascinating creatures. This episode looks at bizarre and sometimes deadly hybrids, like the pizzly bear and killer bee.
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The natural world is full of extraordinary animals
with amazing life histories.
Yet certain stories are more intriguing than others.
The mysteries of a butterfly's life cycle,
or the strange biology of the emperor penguin.
Some of these creatures were surrounded by
fantastic myths and misunderstandings.
Others have only recently revealed their secrets.
These are the creatures that stand out from the crowd,
the curiosities that I find particularly fascinating.
In this programme, we investigate the stories of two animals
that owe their existence to human interference.
Killer bees that were created accidentally
when a well-meaning breeding experiment went wrong.
And pizzly bears, the result of polar bears
and brown bears interbreeding.
How were these strange animals created,
and are they unnatural mutants, or valuable new hybrids?
This is a grizzly bear.
And that white one there is, of course, a polar bear.
But in between, there's a different kind of bear.
It's got the white coat of a polar bear, except that
around the eyes, it's rather brown, and its front legs are very brown.
It is, in fact, a hybrid,
the result of a mating between a polar bear and a grizzly bear,
and they're sometimes called a pizzly.
The first-ever pizzly bears were born in a German zoo in 1876,
after a polar bear and a grizzly - a type of brown bear -
were housed together.
Hybrid animals have frequently been born in captivity,
both intentionally and by accident.
Tigers and lions produce offspring called ligers,
and donkeys and zebra, babies known as zonkeys.
But usually, these hybrid creatures are sterile
and not well adapted for surviving in the wild.
Hybrid bears like this were considered to be
theoretical species, creatures that could never exist in the wild,
and the pizzlies of the Victorian era were largely forgotten.
Animals, of course, usually mate with their own kind.
If different species are to interbreed
and produce fertile young,
they have to be extremely closely related.
Grizzly bears and polar bears are certainly somewhat
similar in appearance.
But are they, in fact, closely related?
In the bear family, the black species came first,
and then came the brown bear, and finally, the white polar bear.
This was thought to have happened four to five million years ago,
but recent fossil evidence suggests that it may have
happened as recently as only half a million years ago.
So the polar bear is the relatively recent species of bear,
one that branched off late in the bear family tree.
Polar and brown bears are, in evolutionary terms, close cousins.
They share some characteristics,
but there are also many physical differences.
The most obvious is the colour of their fur.
Colour acts as camouflage, so that's not surprising,
since they live in very different habitats.
Grizzly bears have rounded heads and prominent shoulder humps
that have evolved for digging.
Polar bears, on the other hand, have more pointed heads,
but no shoulder humps.
Their feet are large and flat
so that they can act as paddles when swimming.
They also have hairy pads and short claws
which helps to prevent them slipping on ice.
The grizzly has more obvious footpads
and much larger, curved claws.
We know that polar and grizzly bears can mate successfully
because they've often done so in captivity.
But what sort of offspring do they produce?
For many years, zoos discouraged the breeding of pizzly bears.
But recently, there was a chance to study them in Germany.
In 2004, at Osnabruck Zoo, a brown bear called Susi
and a polar bear called Elvis,
who had shared an enclosure for 24 years, unexpectedly produced twins.
The small brown cubs are bigger now and have changed colour.
The male, named Taps, is brown,
and the female, Tips, has a lighter coat.
But otherwise, they have traits inherited from both parents.
Long necks and visible tails that are more typical of polar bears,
but also small shoulder humps
that are reminiscent of those of brown bears.
Their feet are intermediate in form.
And their size is between the two -
smaller than a polar bear, but larger than a brown bear.
In the wild, of course, it would be rare for the two species to meet,
for they inhabit very different kinds of country.
Brown bears are the most widely distributed of all bears.
They live in North America, in Alaska
and in Russia and Northern Europe.
They're omnivores - they'll eat not only flesh,
but nuts and grass and fruit.
And the biggest of all live in Alaska.
They can grow to a length of over three metres and weigh 600 kilos.
Together with polar bears,
they are the biggest carnivores on this planet.
The other parent of the pizzly, the polar bear, lives high in the Arctic
and is slightly bigger than the brown bear in both size and weight.
It lives on snow and ice and hunts seals.
We know from Osnabruck Zoo that when polar bears and grizzlies mate,
they can produce pizzly cubs.
But what are the chances of these very different bears
meeting in the wild?
This is the grizzly bear's home range in North America.
Polar bears live higher up in the Arctic.
So the two species are neighbours, but ones with very different
lifestyles and feeding habits that restrict their ranges.
But their habitats are changing as the climate is warming.
Ice is melting and more land is being exposed.
And that is beginning to have an effect on the behaviour
of the two species in the wild.
In 2003, a researcher working on a remote island between Churchill
and the North Pole discovered strange bear footprints in the snow
together with brown hairs.
The hair came from a grizzly. This was extraordinary.
The grizzly must have strayed hundreds of miles from its home
and travelled deep into polar bear territory.
So it was clear that the chances of these cousins meeting
and mating in the wild was becoming a real possibility.
But would their offspring survive?
Research on captive pizzly bears suggested that they could.
The hair of brown bear, polar bear
and pizzly bear are quite different -
not only in colour, but in structure.
Here are cross-sections of a hair from each of them.
The brown bear has a central canal
which is filled with a honeycomb structure.
The polar bear, that central canal is almost empty, making that hair
good for insulation - just what you need in a cold climate.
And the pizzly bear is a sort of compromise between the two.
The central canal has just a little infilling, so you might
say that it is not bad for cold temperatures and not bad for warm.
Possessing a mix of characteristics of both parent bears
could actually help these hybrids to survive in a rapidly changing world.
Their hunting skills have also become more variable.
Not only that, so has their hunting behaviour.
Tips and Taps sometimes fish like brown bears,
but at other times behave like polar bears.
Stomping, for instance.
Polar bears push down on ice to break it
during their search for seals.
The Osnabruck pizzlies perform a similar action.
Hurling is also one of their favourite pastimes.
Polar bears fling their prey about in order to kill it.
This mixture of physical and behavioural characteristics
suggest that pizzlies may be well-equipped to
survive in the wild if conditions in the Arctic continue to change.
And, in 2006, this notion became reality.
An odd-looking bear was shot during a polar bear hunt
in northern Canada.
It was small, hunched and had dark smudges around its eyes and muzzle.
DNA testing showed that its mother was a polar bear
and its father, a grizzly, that had travelled further north
and was hundreds of miles beyond its normal range.
This was the first proof of a hybrid pizzly bear in the wild.
So pizzly bears aren't just the result of captive breeding.
Several have been reliably identified in the wild,
though none has yet been caught alive.
But as the climate warms, so brown bears are moving north
and polar bears coming south,
and their close genetic relationship means that not only can
they interbreed, but the offspring are likely to be fertile.
So, what will happen in the future?
Will this mixing of bear DNA increase?
Will pizzly bears become so common
that they might seriously dilute the polar bear species?
The ranges of these bears are now increasingly overlapping
and they're roaming deeper into each other's former ranges.
It's now not uncommon to see polar and grizzly bears feasting together
when there's plenty of meat around, as there is after a whale hunt.
So are we seeing a new development
in the evolutionary history of bears?
Hybridised brown and polar bears may not be such a new phenomenon.
DNA analysis of both bears indicates that they have previously mixed
their genes thousands of years ago, but now we're witnessing it again.
In April 2010, biologists in the Northwest Territories
of Canada shot a dangerous polar bear.
It was strange in appearance,
and DNA analysis showed something very significant -
this was a second-generation pizzly bear,
the result of a female pizzly mating with a polar bear.
This proves that these hybrids are not sterile
and could potentially form wild populations.
As global warming continues to diminish the Arctic sea ice habitat,
climate scientists believe that the polar bear will struggle
to survive as a species.
But at least some of the polar bear traits will be
preserved in these strange-looking hybrids.
So, pizzly bears are not bizarre, Frankenstein-like creatures.
They're valuable new hybrids that may become increasingly common
as the Arctic landscape changes.
Our next story concerns a more sinister hybrid,
the killer bee,
that was created when a well-meaning experiment to breed
a superior honeybee went disastrously wrong.
In the 1960s and '70s,
bees hit the headlines.
Huge swarms were attacking people
and livestock for no apparent reason.
The bees launching these attacks were, in fact, honeybees -
the sort from which we've been collecting honey for centuries.
In the Western world, monks traditionally kept bees
for honey and for the wax that they used to make candles.
Bee colonies were originally kept in closed wicker skeps
and later, in more accessible hives
that allowed keepers to tend the bees
and get the honey without harming the nest.
For centuries, bees have had an association with human beings
and passive, easy-to-handle bees have been selectively bred,
so the European honeybee became a tolerant, well-tempered bee.
So, why would a species of bee that has lived amiably alongside
people for so long suddenly change its nature?
The temperament of a bee colony is determined
by that of the queen bee -
the one seen here marked with a blue spot.
She lays all the eggs in the hive
so her genes are passed on to
all the female workers and the male drones.
An aggressive queen will produce very ferocious workers,
while a passive queen produces calmer ones.
European honeybees are generally very passive.
African bees, however, are very different.
They are extremely aggressive.
Historically, they were seldom kept domestically because they were
so common that it was easier to collect honey from the wild.
But doing that inevitably disturbs the bees,
and as a result,
the wild species is now inclined to be very aggressive.
When other creatures, including human beings,
get too close to their colonies,
the bees are likely to attack...
..and in large numbers.
Nonetheless, they're very hard-working
and manage to produce substantial quantities of honey in dry
habitats where good quality flowers are often hard to find.
In the 1950s, honey production in Brazil was failing
and it was thought that African bees might be able to help.
European bees had previously been introduced to Brazil,
but they didn't succeed in making much honey in their new environment.
So a Brazilian scientist, Dr Warwick Kerr,
who was a specialist in bee genetics, was consulted.
The Brazilian Ministry of Agriculture asked Kerr
if he could obtain some
African queens to experiment with
in order to breed a bee that
combined the passive nature of the European bee with the higher
productivity of the African bee.
The bees there had originated from stock imported to
North America by British colonists.
Although these bees were productive in the North, the more tropical
climates of Central and South America didn't suit them so well.
Here, they were not so productive.
To make just one drop of honey,
a bee has to visit up to 1,500 flowers.
It's made from liquid nectar that the worker bees collect using
a long proboscis.
European honeybees normally live in temperate climates where
an abundance of flowering plants provide a lot of nectar.
So they're able to produce honey quite easily.
But conditions were not like that in Brazil, and the imported
European bees struggled to make honey in any quantity.
The habits of the African bee
seemed more suited to the South American climate.
They thrive in hot, dry conditions and make plenty of honey.
But they have to work very hard to do so,
starting their day several hours earlier
than their European cousins...
..and foraging for longer.
Honeybees are very choosy feeders.
They will carefully select those flowers that have the strongest
nectar, the sweetest nectar,
and I can demonstrate that by this.
Here is a little bee
in a bee holder.
Let me first try her
with a dilute solution of sugar.
Now let me try her
with a stronger solution,
a sweeter solution.
And out comes her proboscis.
You won't let go!
Western European bees can afford to be choosy because there's flowers
with rich nectar available
for such a long period of time.
African bees have no such luxury.
They have to feed at times when there are very few flowers
open anyway and those that are, are not very rich in nectar.
So they are much more industrious.
Now, let's release you,
so you can go back
and collect some more nectar.
Kerr planned to take the industrious,
less fussy African bee and combine it with the passive European bee
to produce one that would work hard, but not be aggressive.
He persuaded particularly successful African beekeepers from Tanzania
and South Africa to let him have some of their most gentle
and passive queens - 133 in all.
Unfortunately, on his journey back to Brazil,
a customs agent sprayed his bees
with insecticide and they all died.
Upset and frustrated, Kerr then chose a second batch,
but this time he didn't screen out the most aggressive bees.
47 of these queens survived, but they were far too fierce to
give to the local Brazilian beekeepers, so Kerr decided
to breed them with some gentler drones to reduce their ferocity.
Dr Kerr set up 35 colonies
in an isolated area of eucalyptus forest
near Sao Paulo.
And to prevent the queens from escaping,
he used a device called a queen excluder.
It fits on top of the brood box, here.
The bars are sufficiently wide apart
to allow worker bees to pass through,
but not so wide that the queen can.
And Dr Kerr fitted, to be absolutely sure, two of them to each hive.
AND employed a caretaker to watch over them
AND built a wall around the entire group of colonies.
But you can't cater for human error.
And in his absence, a local beekeeper came
and noticed that the worker bees as they passed through here
were losing some of the pollen that they had collected,
so he removed the queen excluders
and by the time Dr Kerr came back...
..26 of the queens had escaped into the wild
and were already swarming.
Swarming is the way bees naturally increase their population,
by dividing the colony.
A hive usually has a single queen.
If she is old or the hive becomes crowded,
she starts to lay eggs that hatch into new daughter queens.
If a queen leaves the nest, many workers will follow her.
They gather around her in a swarm
and eventually fly off together to found a new colony.
This is exactly what Kerr's queen bees did as soon as they escaped.
African bees swarm more frequently than their European cousins
and divide to form multiple colonies.
Kerr's escaped queens and the Africanised worker bees inherited
this tendency to swarm and they spread quickly across South America.
It was assumed that the abundant native European bees would
weaken the escaped African bees' more aggressive nature,
but this didn't happen.
The African genes were strong and their behaviour dominated.
By 1965, most Brazilian hives had been devastated
and the aggressive Africanised bees swept their way through
South America and headed up into North America.
They started to attack people with little provocation
and with sometimes fatal results.
Africanised bees became sensationalised
and the story of the "killer bee" was born.
Horror movies pictured them as crazed killers with lethal stings.
But this was far from the truth.
In any case, it wasn't the African bees' sting that was fatal...
..it was their behaviour.
European bees send out just a few defenders to sting an enemy.
African bees however, react differently.
Up to 90% of a colony will launch an attack.
Their venom is not actually more potent than that of European bees,
but they sting in such number -
sometimes in thousands - that they can kill an enemy.
Kerr's hybrid bees were fearless and had inherited this attack behaviour.
African bees will chase African elephants
and sting the soft tissue around their ears and faces.
They will particularly target baby elephants that are smaller
and softer skinned.
Not surprisingly, elephants have developed a strong
dislike of bees and make a great effort to avoid them.
They recognise the sound of angry bees
and have a specific call to warn each other if one is attacked.
They even warn distant members of the herd by sending out
The escape of such aggressive bees into the wild was
devastating for Kerr's career.
Africanised bees spread as far as the lower parts of North America,
but here, their takeover halted.
The more temperate climate didn't suit them.
Kerr's intentions had been good,
and he later dedicated his research to try to correct the problem.
Eventually, Kerr did help to create a productive,
more passive bee, as had originally been his plan.
And South America is now one of the world's largest exporters of honey.
The creation of a so-called killer bee by Dr Kerr's experiments
was indeed a grave mistake.
But in recent years, a more gentle form of African bee has been bred.
And it's also possible that the ferocity of the African bee
has now been turned to our advantage.
Elephants are said to be terrified of bees and in recent years,
farmers in Africa have started playing the sounds of swarming bees
over their fields and the elephants have kept away.
So as well as pollinating plants, bees can actually protect them.
So both the Africanised honeybee
and the pizzly bear are here to stay,
but these unusual hybrids owe their success in one way or another
Hybrids can be bizarre and they can be deadly. We look at two hybrid animals that owe their existence to human interference - the pizzly bear (a cross between a polar bear and grizzly), which has come into being because of global warming, and the killer bee, brought into existence because of the transfer of African bees to South America.