Swedish Twin Research Finds 45% of Investing Behavior Is Genetic

"Until 2007, Sweden maintained a wealth tax that required citizens to disclose their financial holdings. That created one of the deepest household-level investing datasets ever assembled, allowing researchers to study actual portfolio behavior rather than relying on surveys or self-reported answers."

"Fraternal twins share roughly 50% of their DNA, while identical twins share nearly 100%. If identical twins consistently display more similar investing behaviors than fraternal twins, even after accounting for upbringing and environment, researchers attribute part of the difference to genetics."

"According to Parr, the researcher analyzed roughly 30,000 sets of twins, making the findings difficult to dismiss on statistical grounds. The study focused on several common investing mistakes that financial advisors spend years trying to help clients avoid."

"The uncomfortable implication is that roughly 45% of investing mistakes may feel like conscious choices but are, in part, genetic. Roughly 55% of behavioral variation still came from environmental factors, education, habits, and systems. That means investors can still improve outcomes, but some people may naturally struggle more with emotional discipline than others."

Sweden’s wealth tax required detailed disclosure of household financial holdings, creating unusually deep records of actual portfolio behavior. Researchers used a behavioral genetics approach comparing identical and fraternal twins, attributing greater similarity among identical twins to genetic factors. Analysis of roughly 30,000 twin pairs supported the conclusion that around 45% of savings and investing behavior may be genetic. The study examined common investing mistakes including excessive trading, performance chasing, home bias, and the disposition effect of refusing to sell losing investments. The results imply that some investing errors may feel like deliberate choices but partly reflect inherited tendencies. Environmental factors still account for about 55% of behavioral variation, leaving room for improvement through education, habits, and systems.

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