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TO EXPAND KNOWLEDGE, WE MUST FIRST ADMIT IGNORANCE
by Olivia Judson

Far more is known about short-lived bacteria than ancient pines - and that reflects one of science's most enduring problems.

In 1879 Dr William James Beal, a professor of botany and forestry at a small college in the United States, began an experiment. He filled 20 bottles with a mix of sand and seeds - each bottle containing 50 seeds from each of 21 species of plant. Then he buried the bottles in a row, their necks pointing down so that water could not get in. His idea was that the bottles should be dug up at fixed intervals, and the seeds planted to see how many of them would sprout.

Beal died in 1924. But his experiment is still going on: it has now been running for more than 120 years. The next bottle is due to be disinterred in 2020 - and if all goes according to plan, the experiment will finish in 2100.

This makes it important, for a couple of reasons. First, it addresses (albeit on a small scale) a question that we don't know the answer to: how long can seeds of different plants remain viable? The answer matters because we are busy building facilities to store seeds for long periods. For instance, the massive Svalbard Global Seed Vault, built inside a mountain on the Norwegian island of Spitsbergen, opened its doors last year. Yet there may be little point to such a project if seeds, in general, last only a few years.
Second, Beal's experiment is an example of something rare. Most experiments run for months, or perhaps a year or two. Experiments that run for decades, let alone centuries, are few and far between. And it's easy to see why. Scientific interests and questions change: most experiments from 50 or 100 years ago now seem absurdly outdated.
Indeed, in biology the advances in technology have been so fast that we can now answer questions that a decade ago it would not have made sense to ask, because we did not have the tools to approach them. And even if that were not so, most science is paid for on a short-term basis - three to five years, rather than 10 or 20. This makes long-running experiments difficult to plan or to create.

The beauty of Beal's experiment is that it doesn't cost anything to speak of, and the technology is simple. But it faces an unusual problem: it depends on the enthusiasm of scientists not even born yet for its completion.

Which illustrates a more general point. There are certain sorts of data - long-term data being just one example - that are extremely hard to collect. It's no coincidence that we know much more about the bacterium Escherichia coli (which can go through more than six generations a day) and fruit flies (which, kept at room temperature, go through one generation every 10 days) than we do about giant tortoises (which can't start reproducing until they are 20 years old or so, and often live for more than a century) or Great Basin bristlecone pines - a species of tree where individuals can live to be more than 4,000 years old.

In other words, if you imagine scientific knowledge as having a frontier with ignorance, then parts of that frontier are advancing rapidly - ignorance is yielding (though usually this is a process of revealing more questions to ask, more that we don't know). But other parts of the frontier are essentially static. Sometimes, the stasis will be due to mundane obstacles such as lack of money or insufficient tools. Sometimes, though, it will be due to more subtle problems - such as the fact that certain kinds of experiments, while simple and elegant in principle, are extremely hard to do.

An important class of "experiments possible but not done" consists of experiments where we are so sure we know what will happen that we don't bother to check that we are right. And yet, when we do, the answers are often surprising.

Here are two examples. The first comes from another set of 19th-century experiments with seeds, this time carried out by Charles Darwin. In the 1830s and 40s, it was widely believed that seeds could not survive in salt water. But no one had done the experiments. Darwin did. (He was moved to do so because he was trying to imagine ways that animals and plants could reach remote islands and begin evolving there.) He found that, contrary to what everyone had assumed, the seeds of many plants could sprout after long periods of immersion in brine.

The second example is more recent and more practical. For decades, doctors "knew" that ulcers were caused by stress. So they were incredulous when, in the early 1980s, two Australian doctors - Robin Warren and Barry Marshall - announced that ulcers were actually caused by the activities of the bacterium Helicobacter pylori. But they were right - and the discovery won them a Nobel prize in 2005.

Of all the limits on expanding our knowledge, unexamined, misplaced assumptions are the most insidious. Often, we don't even know that we have them: they are essentially invisible. Discovering them and investigating them takes curiosity, imagination, and the willingness to risk looking ridiculous. And that, perhaps, is one of the hardest tasks in science.