Why don’t we know more about causation?

You’ve seen them – every week a new story about genes for this or that, or the environmental cause of some effect or other. Often the stories say opposite things; red wine is good for us in one article, bad in the next, depending on the study. Or it might be about coffee, eggs or vitamin supplements, and health advice to pregnant women is often contradictory. The gene for autism or dyslexia or asthma is found one week, but the finding can’t be replicated the next. Does hydraulic fracturing of rocks to mine natural gas and oil contaminate ground water? Are GMO foods good or bad for us? You’d think figuring out these things would be easy – genes do something, they make us what we are, while people who eat a given food get sick and those who don’t stay well, so what’s the problem?

The problem is complexity. Modern scientific methods are very good at finding cause when an effect is large or clear-cut – the fact that smoking causes lung cancer was easy to see once the question was asked, the genetic variant that causes cystic fibrosis was relatively straightforward to find because the effect of the mutation is so major. But determining causation gets thorny when a disease or effect is caused by multiple genes, or genes plus some environmental factor, or when there are many pathways to the same outcome - all of which are common scenarios. The fact that everyone is unique to start with makes it even thornier.

When an object casts a shadow, we know it's not the shadow causing the light or creating the object. Cause and effect are easy to determine. But sometimes causality can be a lot trickier to determine. Image credit: Dhilung Kirat

What must women avoid during pregnancy?

Pregnancy can be an anxious time full of contradictory advice: exercise is healthy, but don't overdo it. It's safe to use your mobile phone, but perhaps don't make too many calls. Don't drink too much caffeine, but the occasional cup of tea probably won't do any harm. No hot baths or hot tubs, although swimming is probably good for you. Eat a balanced diet… but no goat's cheese, shellfish, runny eggs, pâté or rare meat, and we're not completely sure about ham, tuna and salami.

Contradictory advice for pregnant women often sounds like "out of the frying pan, into the fire".
Image credit: waferboard

It can leave you feeling as though you might be better off locking yourself in a padded room for the duration with nothing but bread, water and pregnancy vitamins. This isn't helped by newspaper headlines such as the ones following the recent publication, by the Royal College of Obstetricians and Gynaecologists (RCOG), of a scientific impact paper on chemical exposures during pregnancy. The headlines ran the full gamut from “Pregnant women warned over household product chemicals” to the flat-out hysterical “Pregnant women told to avoid painting the nursery, buying new furniture or going near non-stick FRYING PANS as they may expose their unborn baby to dangerous chemicals”.

However, perhaps the most striking thing about the original paper is its title: “Chemical Exposures During Pregnancy: Dealing with Potential, but Unproven, Risks to Child Health”. In other words, they've compiled a long list of things that might be harmful, but which they're not really sure about. Do a little web searching for "things to avoid in pregnancy" and you will quickly find that many, many people have already written similar lists. However, this paper wasn't written by just anyone. It was written by the Royal College of Obstetricians and Gynaecologists, and unlike many commentators they did take the trouble to reference their comments thoroughly, reviewing the literature and assessing what evidence they found. The report examined a number of issues; let's look at them in a bit more detail.

Can we meet the water demand of future generations?

Water - we all need it, but is there enough?
Image credit: fox_kiyo

Approximately one in eight of the world's population don't have access to clean water^[1]. The situation is only expected to worsen with increasing water demand and diminishing sources. Population growth and higher water consumption per capita are to blame for greater consumption. The amount of water most of us use has grown mainly due to changes in diet, the increase in use of water intensive biofuel crops, and acceleration of energy demand which in turn requires water. Water is such an essential part of life it's thought to be one of the main reasons why the Earth is the only planet we've found to be inhabited so far (but we're still searching).

It's hard for anyone to try determining how bad our water shortage is or will be when basic things about water sources still remain a mystery. For example we are clueless about how much water is available and how the water supplies that are obtainable to us may reduce in the future.

Currently most of the water on our planet is not available to us, although it is still not known how much fresh water may be available to us. The water that is available is derived mainly from two origins - surface water such as lakes and river, or groundwater which is stored in underground reserves known as aquifers. On-going work involves exploring how large these reserves may be and how deep we may hope to extract water. For example recent surveys of Africa show there may be extensive groundwater reserves^[2], and the first attempt to map water reserves was made a year ago^[3]. In the future improved and more detailed maps are expected as scientists try to answer the basic question of how much water is left? Without this knowledge it is impossible to try and understand fully the extent of water scarcity.