The interplay of genetics & environment in shaping who we are

“I used to be way over on the nurture side, but I’ve swung way of the nature side,  …  And it’s because of Mona and having kids. My daughter is 14 months old, and it’s already clear what her personality is. ”  Steve Jobs

There ain’t a better way to start today’s scientific digest than talking about Steve Jobs. He is known for being one of the most inspirational characters of our times through his inventions and vision. His story is also one of many that reflects the role of genetics and environment in shaping who we are.

Steve Jobs was the first child of a couple of two graduate students from Wisconsin university. The biological parents gave him up for adoption due to family pressure. He grew up in a modest adobtive family without higher education, he was unable to go to college and yet managed to become an icon of the twentieth century. The biological parents had another child together, a daughter named Mona Simpson. Mona grew up with her mother and became one of the most known novelists in America.

Steve Jobs tracked down his biological parents and met his sister in early 90s and became best friends.

From a scientific perspective, this story can tell us a lot about the influence that DNA (Steve & Mona have shared DNA) can have versus the environment effect (both Steve & Mona grew up in different environments) on the personality and behavior. And in this scenario, the DNA heritage had a higher impact on the development of Steve and Mona compared to the totally different environments.

Paper Title: Classical twin studies and beyond

What it really means: Twins can teach us a lot about how DNA vs Environment influence who we are.

Twins definition: Twins can be either monozygotic (MZ) also known as identical twins or dizygotic (DZ) known as fraternal twins. Easily, in the identical twins, one sperm cell fertilizes one egg, making 1 zygote which will divide to form two embryos.  In the fraternal twins, two eggs are fertilized by two separate sperm cells.

How & What can twin teach us about nature and nurture :  The story of Steve Jobs & Mona Simpson gave you a hint about what can we learn. Now imagine what can we learnf from, identical twins (Same DNA) that grew up apart (different shared environment) and lived specific unique experiences (unique environmental influences). Before going on with this I want to emphasize on two points :

  • No twins were separated on purpose to study nature vs nurture however many twin registers were made all over the world. Those registers, contains multiple hundreds of thousands of registered twins (grown up together or apart). Many studies have been made using these registers to understand, behavioral development, IQ, health, aging, food intake and many others parameters.
  • I want to emphasize on the differences between shared environment and unique environment. We grow up in a family, go or not to college, society dictates some rules to follow, this is considered as shared environment. Having a car accident, winning the lottery or meeting the one, those are considered as unique environmental factors.

What did we learn from twin studies : Cognitive and personality traits as well as health related traits were studied on a large population of identical and fraternal twins growing apart and non-growing apart. A small glimpse of what we learned is resumed in this Figure (Simplified figure from the paper).

For instance, thrill seeking is highly influenced by genetics (65%) and not at all by shared environment. Only unique environmental experiences influences this personality trait of about 35%. On the other hand, religion is solely influenced by the shared environment.  Which makes sense, as most of those who grow up in a certain religious family would tend to adopt similar beliefs.

To conclude, we are who we are due to a mixture between what we have in our genes, the surrounding environment and the decision and behavioral acts we take in the cursus of our existence. Knowing the influence of each part in our personality can help us finally understand ourselves and others better. Knowing better about our genes would help you meet yourself and not only.

You can also watch Professor McGue’s video for more information about twin studies.