The latest Netflix documentary You Are What You Eat features pairs of similar twins on different diets. For eight weeks, one in all the twins is on a vegan food regimen, the opposite on an omnivorous food regimen. The experiment is compelling because, due to genetic identity, the health of every twin was very similar before the study.
I won’t reveal the ending for many who have not seen it, but should you prefer the grey writings of scientists to the glitz and glamor of Netflix, you’ll be able to read the published article within the journal JAMA Network Open.
The documentary highlights the extraordinary contribution of twin research to advancing our understanding of the world. But it goes far beyond comparing different diets.
British politician Sir Francis Galton first documented the striking resemblance of twins in 1875, arguing that “nature” significantly influences our disposition and health. Since then, twins have been used extensively in research. So what makes twins so special and the way are researchers harnessing their power?
Twins as mutual comparisons
The Netflix documentary highlights one important thing about twins – they’re great for comparisons. Identical twins share just about all their genes and typically grow up in the identical household, which implies they experience the identical parenting, education, and so on.
The document is an example of, amongst others, randomized controlled trial, by which participants are randomly chosen to receive some intervention (e.g., a latest drug), and those that aren’t chosen function controls (in drug trials, they might receive a placebo). Randomized trials are often seen because the gold standard for assessing what works.
We don’t really need similar twins for such trials. In fact, relatively few trials use twins. However, twins can assist be sure that the treatment and control groups are as similar as possible. This is especially important when there are few participants. There were only 44 of them within the Netflix study. Without the twins, their results would have been more uncertain.
For ethical reasons or just practical reasons, we cannot at all times conduct randomized trials. This is where the twins can assist us. Let’s say we would like to know the effect education about earningsor effect smoking causes the event of lung cancer.
These and lots of other questions are answered by comparing differences in groups of similar twins (for instance, when one twin smokes and the opposite doesn’t).
By specializing in differences between twins, we eliminate genetic and shared family aspects and will be more certain about causality. Using twins doesn’t fully solve the issue of omitted aspects, however it helps reduce it.
Netflix
Twins and heritability
Galton’s fascination with twins stemmed from a desire to discover why we’re the way in which we’re. Are these our genes (nature) or perhaps our upbringing and private experiences (upbringing)? His early observations were informal, but eventually researchers developed sophisticated methods for untangling genes and environment.
The fundamental approach is essentially to test whether similar twins, who’re genetically the identical, are more similar than fraternal twins, who on average only have 50% of the gene variants that make us unique. If similar twins are more similar, it implies that genes matter.
For example, twin studies have shown that approx 40% individual differences in personality will be explained by genes, and in addition e.g 80-90% differences in height and weight at the top of childhood.
Limitations and misuse of twin studies
The drawback of twin studies is that twins are a chosen group and the outcomes cannot at all times be generalized to the broader population. Only o 1.4% of births in Australia are twins.
Twin heritability studies are also based on strong assumptions, just as a shared family environment has the identical importance for similar and dizygotic twins. This will be overcome by specializing in similar twins raised apartbut these studies are rare.
There has also been some misunderstanding and misuse of twin study results. Galton’s belief in the ability of nature led him to promotion eugenicsthe thought of selective breeding to achieve “genetic superiority” which had devastating consequences within the twentieth century.
But our genes aren’t our destiny. While a certain combination of genes may make you more likely to be an extrovert, who we grow up to be is a complex interplay between genes, upbringing, and private experiences. Even disorders with a genetic basis, similar to Alzheimer’s disease, are rarely certain, and we will take steps to reduce the chance.
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The way forward for twin research
Research on twins has been conducted for several a long time over 60 twin registers operating all around the world. In Australia the most important registry is Twin studies in Australiawhich have roughly 75,000 members.
With greater opportunities for data fusion, genome mapping, and advances in machine learning, what we will learn from twins will only increase in the longer term. We can expect twins to proceed to play a key role in deepening our understanding of the world for a few years to come.
