How would you feel if you accidentally killed the world's oldest tree? In 1964 graduate student Donald Rusk Currey was studying the tree rings of bristlecone pines in the mountains of Nevada. The small, gnarled, slow-growing trees can be over 2000 years old, and by counting and measuring their annual rings climatologists can see the effect of weather and climate change over centuries. Normally this is done by drilling out a core sample, which doesn't harm the tree. Currey, however, was having trouble: he'd already broken two borers trying to sample a tree nicknamed Prometheus. He asked for permission to cut it down and count its rings, and the authorities, who didn't consider Prometheus to be an especially notable tree, agreed.

You can imagine Currey's shock when he got the trunk's cross-section back to the lab and realised that Prometheus was actually at least 4844 years old, and possibly over 5000. That would have made it the oldest single tree in the world at that time. (A 5062-year-old bristlecone pine was discovered, and still lives, in 2012 in California.)

The danger of inadvertently destroying what you're meant to be studying is every biologist's worst nightmare.

Recently, museum biologists have been debating whether collecting museum specimens, especially of endangered species, might have this very effect. In the 19th century there was a brisk trade in rare birds, and the attitude seems to have been "get 'em before they go extinct": the last two great auks were strangled to death in 1844 and stuffed for museums. But this sort of collecting only happened after species had already been brought to the brink of extinction by hunting, introduced predators, or habitat destruction: hundreds of thousands of great auks had already been killed for fish bait or to stuff feather pillows. The depredations of museum collectors are nothing in comparison.

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Museums today collect far fewer specimens than they used to, but their historic collections are turning out to be increasingly important.

DNA recovered from museum skins can reveal an animal's family relationships, and one day, might even allow us to bring species back from the dead.

The effect of the insecticide DDT on the environment was only revealed when the shells of bird eggs, collected by museums over many decades, turned out to be getting gradually thinner over time.

New technology is helping museum collections reveal their secrets in ways that the original collectors could never have imagined, and we should anticipate that the next 100 years will bring a whole suite of new tools.

When people see the number of specimens - stuffed, mounted, in alcohol - in even a medium-sized museum like Whanganui, they sometimes ask why we need them, and need so many. Wouldn't a photograph and a DNA sample suffice? But compared with the number of animals that die naturally every day, or are killed for recreation, or just to eat, a museum's collection is tiny. Collecting is an essential part of the research we need for species conservation, part of a museum's mission and its legacy to the future.

Dr Mike Dickison is Curator of Natural History at the Whanganui Regional Museum