Failed your resolutions already? Maybe blame your genes

If your friends are asking about your New Year's resolutions and they've already fallen by the wayside, today we bring you an easy out: according to current research, your chances of resisting temptation are affected by your genes. 

Dozens of studies have explored how much of a role genes may play in explaining why some people have excellent self-control while others really struggle to overcome impulses and temptations. But this past body of work has produced a wide range of results, making it difficult to draw any firm conclusions, note the authors of a new paper in Neuroscience and Behavioural Reviews. 

Now, Y. E. Willems at the Free University of Amsterdam and colleagues report the results of a major meta-analysis of 31 papers in this field, all on groups of identical twins, fraternal twins, or both. The 31 papers included more than 30,000 individual twins in total, and were published between 1997 and 2019. The vast majority were done in the US, with two also coming from China, and single studies from Germany, Italy, Japan, and the Netherlands.  

The meta-analysis led the researchers to conclude that about 60% of the variability in levels of self-control between any two people is down to their genes — though exactly which genes is yet to be ascertained. The new analysis also found that though some earlier studies have suggested that females may have more self-control than males, there were no gender or age differences in the extent to which genes versus environment influence self-control. 

Comparing data on identical twins, who share almost 100% of their DNA, with data on fraternal twins, who share around 50% of their DNA, led the team to another conclusion: there is "little to no evidence" that shared environmental effects account for the environmental contribution to levels of self-control. In other words, unique environmental effects — such as a twin's own perceptions of their parents' behaviours, rather than their behaviours per se — seem to be the key non-genetic influences on self-control. However, the team notes, more studies are needed to understand exactly which environmental effects lead to individual differences in self-control in children who grow up in the same family. 

There are some limitations to this research, in particular the heavy reliance on data from the US, which could mean that the results aren't generalisable to other populations. Also, the 31 papers used no fewer than 20 different measures of self-control (a research problem highlighted in a recent paper). Earlier work has found that different measures can tap into slightly different aspects of self-control, but given the small number of studies in this meta-analysis that used the same measure, the team couldn't explore whether certain aspects of self-control (the ability to ignore distractions, for example) are more tightly linked to genes than others. For some researchers, another limitation is an assumption intrinsic to the classical twin study design — that the environment of identical twins is no more similar than the environment of fraternal twins. This assumption has been challenged by some studies, but supported by others.

The finding that genes have a "robust" impact on individual differences in self-control is important, though. Numerous studies have found that people with high self-control are happier, healthier and wealthier than people with low self-control, who are likely to do worse in school, relationships and jobs. These new results suggest that some people will, because of their genes, be predisposed to finding it harder to resist impulses and temptations while in the same environment — the same family, school, or workplace — as others who are genetically predisposed to excelling at self-control. "These findings imply that the environment — peers, parents, teachers — should take into account such innate differences in people's self-control capacities," the team argues. 

So, if a friend or relative is checking in on a failed resolution and you're looking to break the news gently, perhaps link them this article.

Read the study in full: https://doi.org/10.1016/j.neubiorev.2019.02.012