In the last post, I reported on a three-day symposium where US state and federal judges were taught about science and scientific scepticism by a man with rather questionable values. The teaching is an excellent idea as even with a scientific background, it is easy to make assumptions about the accuracy of seemingly reliable ‘facts’. But the values of the teacher will influence the lesson. Any teacher will have a basic understanding of a topic, which may develop over time through further study and experience. So long as they are not just ‘cherry-picking’ data to support their ideas whilst dismissing anything which might counter them, the teacher should question long-held beliefs as new information emerges. But some people just cannot accept that their beliefs might be wrong; such people do not make good teachers.
One of the big problems in communicating science is how to simplify a complex message without rendering it inaccurate, if not plain wrong. To do so well takes time, another resource we seem to be running short of. The clear, cool waters of understanding may also be muddied when a guestimate becomes a widely-accepted ‘fact’. My particular favourite is the ratio of human to non-human cells in our bodies.
Question the questions
It used to be believed that only 1 in 10 of the cells of our bodies was of human origin, the rest being microbial. This figure came from an estimate made in 1972 by microbiologist Thomas Luckey; it was never meant or expected to be widely quoted decades later. Turns out that Luckey had roughly estimated the figure by scaling up the number of bacteria in a gram of faeces, to the whole length of the alimentary canal (mouth to anus) when most bacteria reside only in the colon. So while technologies such as DNA analysis might shed new light on a problem, simply taking the time to go back to original data can prove just as revelatory. Today, perceived wisdom dictates a roughly 1:1 ratio for microbial to human cells (with slightly more microbes but not ten times more).
This new information was published in Nature in January 2016 and the article included a graphic depicting the relative proportions of different cell types based on number and mass. I feel I should have known this already, but I was surprised to learn that over 80 per cent of the human cells that make up our bodies are red blood cells, also known as erythrocytes. These small cells contain no nucleus or organelles; they are simply packed with haemoglobin, the molecule which transports oxygen and carbon dioxide to and from our tissues. As far as genes and replication go, some cell biologists might say that red blood cells are not true cells at all.
Which got me thinking: why would anyone care about the ratio of human to non-human cells within our bodies if not for matters pertaining to ‘self’? And surely genetic material is key here? If we consider how many DNA-filled human cells, carrying our genes, are replicating in our bodies compared to how many DNA-filled non-human cells are replicating in our bodies, it comes out as just under 7 per cent human, even lower than Luckey’s 10 per cent estimate. It is not just the answers to questions which should be queried, but sometimes the questions themselves.
Correlation is not causation
Another potential trap on the road to truth is confusing correlation with causation and a good example of this featured in BBC Radio 4’s Inside Science earlier this year (21:18 min). In evolutionary theory, genes mutate over time and give new functions to their owners. If these new functions are beneficial, the mutated gene will likely be passed on to future generations. Fruit flies feed on rotting fruit and, until recently, it was understood that their ability to tolerate a high-alcohol environment was due to the presence of an enzyme which breaks down ethanol. Today, genetic engineering allows us to reconstruct ancient gene varieties and test them in live animals. Despite the modern fruit fly having this mutated alcohol metabolism gene, there was no difference between the ethanol tolerance of the modern fruit fly and one carrying the ancient, non-mutated version of the gene. So while a plausible link had been made, in this case the gene mutation was not responsible for the ethanol tolerance of fruit flies.
Furthermore, the gene mutation idea was not a strong claim made in the paper where it first appeared. Nonetheless, this nugget of information made it from the world of peer-reviewed and seldom-read papers into the academic textbooks, where students the world over would innocently assume its truthfulness. There was no intention to mislead in either of these cases, just mistake by assumption.
In the next post, I’ll look at some examples of devious miscommunications. In the mean time, question everything, have a happy Hogmanay and all the best for 2018!