It’s challenging to understand how something as simple and small as a gene can affect something as complicated as human behavior — the effects can take a long time to manifest. With this in mind, UC Berkeley psychologist Robert Levenson embarked on a 20 year study.

Levenson began looking at a gene that’s involved in the regulation of serotonin in the brain: 5-HTTLPR (aka the serotonin transporter gene).

Serotonin is one of the major neurotransmitters (i.e. chemicals) in the brain. It’s not a coincidence that a lot of the drugs that are used to treat depression and anxiety act on the serotonin system in the brain. This is clearly an important chemical for determining the nature of our emotional lives.