August 4, 2009, 9:30 pm
Last week, I visited the Oxford University Museum of Natural History. Stepping inside is, in some ways, like entering a time warp. The vaulted, iron-and-glass ceilings are reminiscent of a 19th century railway station; the ornate carvings and ironwork decorations conjure a time of Imperial splendor and grand ambition. Statues of Galileo, Newton, Darwin, and other men of science, stand on pedestals around the ground floor. Many of the skeletons and skins on display were collected by the explorers and administrators of Empire. And if you get bored with the dodos and dinosaurs, you can visit the Pitt Rivers Museum — the entrance is behind the skeleton of the giraffe — a fascinating repository of human objects and artifacts that includes totem poles and shrunken heads.
But the place nods to modernity, too. In a corner by the lavatories, a model of DNA rotates silently; a screen connected to a camera in the museum’s tower shows young swifts in their nest, a link between the cases of dead animals inside the building and the living ones outside.
The Oxford Museum ranks in the annals of evolutionary history because, just after it opened in 1860, it was the scene of a debate that immediately became legendary. Several people spoke, but today only two are remembered: Samuel Wilberforce, Bishop of Oxford, and Thomas Henry Huxley, a friend and colleague of Darwin’s. (Huxley became known as “Darwin’s bulldog,” and went on to become an important force in the public understanding of science, writing and lecturing for a general audience, usually on matters evolutionary.)
A few months earlier, Darwin had published “On the Origin of Species,” in which he presented extensive evidence for evolution by natural selection and argued that all living beings are descended from a common ancestor.
In it, he said little about humans and evolution, but the implications were lost on no one. Before a huge audience, Huxley and Wilberforce argued over whether human beings have evolved — whether we are, in fact, a species of ape.
The climax came — so the story goes — when the Bishop asked Huxley whether it was through his grandmother or his grandfather that he was descended from a monkey? Huxley is said to have replied that he would not be ashamed to have a monkey as an ancestor, but he would be “ashamed to be connected with a man who used great gifts to obscure the truth.” A woman fainted.
But I’m afraid I wasn’t really thinking about Huxley and Wilberforce. As I gazed around the museum, my thoughts were with that DNA molecule. For it is that molecule that links us all together, from Goliath beetle and pygmy shrew to iguanadon and kangaroo. And it is that molecule that has made museums strangely — wonderfully — relevant to biology in the 21st century.
At the time of the Huxley-Wilberforce debate, natural history museums were not places to study evolution, they were catalogs of nature. Large and impressive catalogs, but catalogs all the same. And of course, they are still hugely important stores of information about biodiversity, both now and in the remote past. But they have also become something much more.
It’s all those dusty specimens. The ability to extract DNA from dead creatures means that the skins and skeletons of animals that were alive 50, 100, 200 years ago can provide an invaluable source of knowledge about recent genetic changes.
This isn’t to say there aren’t difficulties. Dealing with old samples remains tricky, and the quality of preserved DNA is variable. However, unlike many other sources of old DNA, such as bodies frozen in permafrost, museum collections often (though not always!) have notes about where and when an organism died, as well as having several animals of the same species taken in successive years. In other words, museums sometimes have dead populations, rather than one or two individuals.
The collections also span an interesting and important period in global history: the past century, during which we humans have affected other beings on the planet as never before. Human population growth, the invention of antibiotics and pesticides, the clearing of forests, hunting and fishing — all these and more have had an impact on the genetics of countless species. By using museum specimens to look back in time, we can potentially assess that impact in detail.
Consider, for example, Hector’s dolphin, a species that lives in the coastal waters off New Zealand, and that, these days, often gets tangled up in fishing nets. The dolphins are rare: there are thought to be fewer than 4000 individuals at large. They also have rather low genetic diversity — a factor that, combined with small populations, is thought to be a risk factor for extinction. But perhaps there isn’t really a problem: perhaps their genetic diversity has always been low?
It hasn’t. Specimens of the dolphin have been collected since the 1870s. A comparison of DNA from the museum material with that from dolphins out and about today shows that genetic diversity has eroded substantially over the past 130 odd years. If we’re not careful, Hector’s dolphin may not be with us much longer.
Or take the American black duck. During the 19th century, black ducks were the most common duck to the east of the Appalachians. That changed in the 1940s, when mallards started to arrive in large numbers; by 1969, mallards had become more common than black ducks. Moreover, genetic analysis of modern specimens shows that the two species are close — so close that they might as well be considered one.
Again, it wasn’t always thus. DNA analysis of museum specimens collected before 1940 show that black ducks and mallards used to differ much more markedly. So what has caused the change? Hanky panky. Yes, members of the two species have been interbreeding. There are even hints that the female black ducks prefer to mate with male mallards.
I could go on.
But I’ll stop with one last thought. The techniques for extracting DNA, and sequencing it, are getting better and better: you can do much more with much less material than you could, even ten years ago. In fact, the techniques are changing at warp speed. In five years time, we will have tools to cheaply sequence the entire genomes of these specimens; we will be able to expand our understanding of evolutionary patterns in ways we can presently only dream of.
And, as I reflect on this, it begins to seem that the time warp I stepped into on entering the museum is one zooming forwards, not back.
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Notes:
Anyone interested in visiting the Oxford Museum from the comfort of their living room can take a virtual tour here. For further information about the collections or the architecture (including a complete who’s-who of the statues), see the museum’s index page.
There is some uncertainty about exactly what was said during the Huxley-Wilberforce debate; I have taken my account from pages 3-7 of Irvine, W. 1956. “Apes, Angels and Victorians.” Weidenfeld and Nicolson, and pages 118-125 of Brown, J. 2002. “Charles Darwin: The Power of Place.” Pimlico.
For an overview of the possibilities and pitfalls of extracting DNA from museum specimens, as well as a review of studies that have applied the technique, see Wandeler, P., Hoeck, P. E. A., and Keller, L. F. 2007. “Back to the future: museum specimens in population genetics.” Trends in Ecology and Evolution 22: 634-642. For the analysis of modern and museum samples of Hector’s dolphin, see Pichler, F. B. and Baker, C. S. 2000. “Loss of genetic diversity in the endemic Hector’s dolphin due to fisheries-related mortality.” Proceedings of the Royal Society of London B 267: 97-102.
For black ducks merging with mallards, see Mank, J. E., Carlson, J. E., and Brittingham, M. C. 2004. “A century of hybridization: decreasing genetic distance between American black ducks and mallards.” Conservation Genetics 5: 395-403. For (slim) evidence that female black ducks prefer male mallards, see Brodsky, L. M., Ankey, C. D., Dennis, D. G. 1988. “The influence of male dominance on social interactions in black ducks and mallards.” Animal Behaviour 36: 1371-1378.
Many thanks to Dan Haydon for insights, comments, and suggestions.
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