The Natural History Museum has one of the world's greatest collections, capturing the earth's huge biodiversity. Ahead of a major new BBC TV series – Museum of Life – six members of their world-class team of 300 scientists each pick a treasure

The statistics defy comprehension. The mammal collection on its own contains 860,000 items, ranging from the skeleton of a blue whale to a dormouse. Yet this array of old bones and fur represents a mere slice of the contents of the Natural History Museum.

Over the three acres of storage space that forms a labyrinth around the museum in South Kensington, London, there are rooms that contain the remains of 58 million animals, drawers of five million pressed plants, and cupboards filled with nine million fossils. For good measure, this magnificent terracotta edifice – designed by Alfred Waterhouse and opened in 1881 – also provides a home for 300,000 rocks and minerals as well as 2,000 meteorites. This, quite simply, is one of the planet's most important natural history collections, a repository of the biological and geological wonders that have appeared on earth over its 4.6 billion-year history.

Yet only a tiny minority of these marvels is ever seen by the public. The rest are kept behind the scenes at the museum, although these artefacts are still of tremendous importance to researchers, as a new BBC2 TV series, Museum of Life, intends to show. Six documentaries examine some of the star specimens among the museum's scientific treasures and will demonstrate how they are being used as tools to understand, and improve, the planet's threatened ecology. Thus we will learn of the importance of giant tortoise excrement to the regeneration of the ebony forests of Mauritius and come to understand the usefulness of making moulds of dinosaur skeletons.

As Richard Fortey, one of the museum's most important palaeontologists, explains: "The golden rule of museum life is simple. Don't throw anything away. You never know – a technique or technology could come into existence and reveal a new scientific use for it."

As to the identity of the greatest treasures to be found within the walls of this scientific Hogwarts, there is, inevitably, disagreement. So the Observer asked some of the museum's personnel to name their favourites and explain why they have selected them.

Of course, opinions change over time and future generations will no doubt take a very different view – a point demonstrated by the museum's own walls. Waterhouse stipulated there should be carved images of living species on the west wing's walls while the east would only have those of extinct creatures. These included the coelacanth, then thought to be extinct, but which was discovered, very much alive, in 1934. As a result the coelacanth now finds itself commemorated on the wrong wall.

Museum of Life starts on Thursday

The diplodocus



'Dippy', the diplodicus at the museum. Photograph: Natural History Museum

Mike Dixon, director of the Natural History Museum

"It is hard to believe that the great skeleton of Dippy, our fossil diplodocus, has not always dominated the museum's entrance hall. The two look as if they had been made for each other: a vast cathedral-like space filled by that wonderful 26m-long skeleton of a long-extinct dinosaur. It is a sight that never fails to hypnotise youngsters when they first set foot in the museum.

"Yet we were without Dippy for the first 24 years of our existence. Indeed, it might never have ended up here at all had not King Edward VII asked for a copy of the newly discovered dinosaur when he visited the Carnegie Museum in America. Over the next 18 months, casts of the fossilised bones were made from five different diplodocus skeletons and shipped to Britain in 36 crates. Dippy was assembled and formally introduced to the public on 12 May, 1905, in the reptile gallery before ending up in the great hall in 1979.

"He has also changed over the years. For a long time we reckoned the diplodocus must have lumbered about in swamps because its body would have been too heavy to move about on dry land and would have needed water or mud for support. However, our ideas about sauropod dinosaurs have changed and we now believe they were much more dynamic and active than we had thought. So we have raised Dippy's head and also his tail, which would have acted as a counterbalance. Essentially, though, he is the same old Dippy that has entranced visitors to the museum for more than 100 years."

The Nakhla meteorite



The Nakhla Meteorite crashed to Earth in 1911. Photograph: Natural History Museum

Caroline Smith, curator of meteorites

"There are about 38,000 meteorites in museum and private collections in the world but this one is special because it's one of only a handful that are known to have come from another planet: Mars. About 12m years ago an asteroid or comet crashed on to Mars. The resulting blast blew pieces of rock into space and into orbit round the Sun. Then, in 1911, the Earth passed through that orbit and swept up some of those pieces of rock and these fell over the Nakhla area of Egypt. There was a fireball, a detonation and then a shower of stones. Locals claimed a dog was killed – which would have made the animal the only known victim of an interplanetary attack. However, the story is pretty suspect.

"The piece, which is a star specimen in our vault gallery, has a beautiful shiny black exterior. This is known as a fusion crust and was created by the intense heat of the meteorite's fiery passage through the atmosphere. Its interior is mostly a mixture of iron and magnesium silicates called pyroxene and olivine. Some scientists say they can see signs of fossil bacteria-like entities in the meteorite but I am not convinced. On the other hand, it is now clear some of that the minerals that make up the meteorite could only have been created in the presence of water. This shows that Mars – at least in the distant past – must have been a wet, fairly hospitable place."

Archaeopteryx



Archaeopteryx is half-way between a bird and a small dinosaur. Photograph: Natural History Museum

Angela Milner, research associate in the palaeontology department

"Archaeopteryx has unique, iconic importance for a very simple reason: it is a perfect example of evolution in action. It looks half-way between a bird and a small meat-eating dinosaur which, of course, is exactly what it is.

"It was found inside a piece of limestone in southern Germany and brought in 1862 to the museum, where Thomas Huxley recognised it is a transitional fossil that links modern birds with dinosaurs. Thus it became a key piece of evidence in the debate about natural selection. Our specimen is 147m years old and is the earliest known fossil of an animal that we can definitely call a bird. In other words, its lineage had only relatively recently evolved from dinosaur predecessors. It is wonderfully preserved despite the age, however. You can see its feathers in perfect detail.

"Archaeopteryx would have been about the size of a magpie and would have had a long tail like a magpie's. However, in its case this tail was made out of bone. Since then, birds have evolved tails that are made out of feathers. Intriguingly, we actually have two versions of this particular archaeopteryx. It was preserved in a slab of lithographic limestone which was split apart to reveal the bird inside.

"Both sides reveal detailed impressions of the bird. A copy of one is displayed in the earth gallery and another in the bird gallery."

The Broken Hill Skull



The Broken Hill Skull was discovered in Zambia (then Rhodesia) in 1921. Photograph: Natural History Museum

Chris Stringer, research leader of human origins at the museum

"This is a beautifully preserved skull of an early human being who we think lived about 300,000 years ago. It is also a fossil of special historical importance. In the 19th century, Charles Darwin had predicted science would show that the origins of humanity lay in Africa. But for the next 50 years the only fossils dug up were in Europe and Asia. The Broken Hill Skull – which was found in a mine in Zambia (then Rhodesia) in 1921 - changed that perspective and helped show our birthplace is, indeed, an African one. It has personal importance as well. When I saw a replica of the skull in the museum when I was a youngster, I was captivated, and decided, there and then, to study evolution.

"The skull of Broken Hill Man – we believe it is male from its size – was coated in ore when it was dug up. However, the huge brow-ridges over its eyes marked it out as special and it was sent to the museum.Today we now believe it belongs to a species called Homo heidelbergensis: big-brained, powerfully built hunter-gatherers who may also have been our direct ancestors.

"The skull – a replica is displayed in our human evolution gallery - also reveals clear evidence of illness among ancient people. It has a hole at the back which was probably caused by a small tumour or brain abscess which burst through the skull wall. However, to judge from the subsequent bone growth around the hole, this appears to have partly healed.

"In fact, it is more likely his teeth killed Broken Hill Man. These, and his upper jawbone, were riddled with abscesses that would have caused him immense pain and may even have led to the spread of a fatal infection."

The arapaima fish



The arapaima breathes oxygen from the water, and the air. Photograph: Michiganscienceart.com

Oliver Crimmen, lead curator in the fish group in the zoology department

"When I was young I was fascinated by the aquarium at London zoo and, in particular, by the tank that contained marine creatures from the Amazon. There was one fish, called the arapaima, which I thought was especially exciting. It was huge, around two metres, and looked truly spectacular.

"Then one day I found the tank had been closed and was being cleaned out. I never found out what happened to the arapaima – until I went to work for the Natural History Museum. There I came across a specimen preserved in alcohol. It was only when I checked the label that I discovered it had come from the zoo. It was, in fact, the very fish that had drawn me to the aquarium a decade earlier and begun my fascination with marine biology. The arapaima seems to have haunted my life.

"In fact, it is a really intriguing fish – not just because of its unusual size. For example, the adult arapaima looks after its young by keeping a shoal of them in its mouth to protect them. The fish is also rare in that it breathes oxygen from the water - and from the air.

"Unfortunately, the arapaima is easily harpooned because of its size and because it swims near the surface. As a result, it is suffering a serious loss of numbers in the wild. On the other hand, it is also being bred today in fish farms. I doubt if I could eat one though."

Darwin's pigeon



Darwin's Pigeon helped the scientist develop his theory of evolution. Photograph: Natural History Museum

Jo Cooper, curator of anatomical collections in the museum's bird group

"Charles Darwin collected many bird specimens on his voyage on the Beagle. However, his research had only just begun when he returned to Britain in 1836. Still seeking evidence years later, he began studying domestic animals – and the pigeon turns out to be a surprising favourite. Darwin brought together many different breeds of the bird – which helped to demonstrate the general point that a wide variety of animals can be created from a single originating type. Between 1855 and 1858, Darwin devoted a large part of his time to pigeon breeding – just as fellow scientists, such as Charles Lyell and Joseph Hooker, were pressing him to publish his ideas about evolution. Just write something - 'pigeons, if you please' - but make sure you get your theory into print, Lyell urged.

"Then, in 1858, Darwin got a letter from Alfred Russel Wallace outlining his own version of natural selection, and he dropped everything to write On The Origin of Species. Crucially, this includes many observations about domestic animals – including the pigeon. Later Darwin left his pigeon specimens to the museum and these have turned out to be some of the best preserved items in all his collections. My favourite is a skeleton that has been carefully labelled, in Darwin's own handwriting, and dates back to 1856, just when his ideas about natural selection were crystallising. It is not on permanent display but it is usually included in most, behind-the-scenes tours of the museum."