Nepenthes and scientific truth

By Miguel Franco

We all love David Attenborough’s programmes. An investigation by Philip Jones (http://www.prkjonesphotography.com/#! ), a masters student at Oxford University who graduated in 2011, found that natural history programmes in general, and David Attenborough’s in particular, have played a crucial role in students opting for degrees in ecology and biodiversity conservation.  The subject of yesterday’s news (http://www.bbc.co.uk/nature/20273855) was about what David Attenborough has learned from a life devoted to natural history documentaries. I do not need to emphasize his amazing contribution. What I wish to refer to is a flawed, currently peddled view on the nature of scientific truth with which the news concludes.

The news highlighted the case of a tree-shrew found dead inside a specimen of the pitcher plant Nepenthes rajah in Borneo in the 1990’s, with the inference that the plant ate small mammals as part of its diet. David Attenborough recounted this story in the series The Secret Life of Plants, but fifteen years later the story turned out to be not only wrong, but incredibly more interesting and beautiful. The development of the pitcher itself is another beauty: http://www.bbc.co.uk/programmes/p00lxsvx. You can witness an experimental test of the idea that small mammals can drown in a pitcher plant here http://www.dailymail.co.uk/sciencetech/article-2124440/The-Mousetrap-Flesh-eating-plant-grows-5-metres-high-dines-rodents.html. There are several flaws in the way this story is portrayed, and I am sure you can spot these flaws yourselves. What worries me is the reporter’s non-sequitur conclusion in this piece of otherwise well presented, engaging news: “What we know now could be considered ridiculous, old-fashioned or basic in another 60 years…”

This panders to the idea that scientific truth is transitory. It is not the case that shrew-eating Nepenthes was true and now it isn’t.  Try applying this to Magellan, or Plymothian Drake (alright, “Tavistockian”, if you insist), returning to Europe after circumnavigating the Globe, with the period’s BBC-equivalent declaring: “the Earth may look round today, but in 60 years this may be considered ridiculous…” Scientific truth—all truth, in fact—is not transitory. The media and groups identified with flawed ideologies relish in portraying science as “just another possible explanation”, i.e., on a par with unfalsifiable hypotheses.

The hypothesis, for it was nothing beyond this, that species of the genus Nepenthes could eat small mammals was never an established truth. Finding evidence that it is most likely wrong still does not prove it one way or the other, but provides significant evidence in one direction. More convincing evidence would be provided if one could quantify the lifetime diet of a large number of Nepenthes plants. Furthermore, one would also need to quantify the specific effects that different prey species would have on fitness, or at least on significant aspects of fitness, such as the provision of essential nutrients in quantities that would make a difference to survival and reproduction. Collecting this evidence is not a trivial enterprise.

The error in having assumed one thing based on one piece of dubious evidence in no way diminishes the importance of David Attenborough’s achievements. A mistake is easily done and, after all, this one is expertly corrected by David Attenborough himself. I thought it necessary, however, to point out the fallacy of using this example of honest approach to the truth as evidence that scientific truth is transitory. We can be pretty certain we will never know everything there is to know. Yet, although our understanding of natural phenomena varies with the complexity of the phenomena themselves and with the intellectual tools that we have developed to understand them (e.g., maths) there are truths whose understanding is such that they are utterly beyond doubt. Science strives to get to this point in everything there is to know.