Question: is there a scientific reason for why everyone has a different personality ?

Oli Wilson answered on 9 Nov 2017:

It seems like a person’s personality comes from their own biology as well as their environment. Some people are naturally more outgoing and risk-taking than others (something you can even see in some animals like fish!), others are more likely to stick to a task or look for a reward, and a lot of that variation is due to how they’re wired, biologically. But those natural characteristics can be affected by experiences – if someone who’s naturally a risk taker has a really bad experience it might make them more timid in the future. And our culture – what the people around us are like – must have a huge effect too.
So basically, everyone has different personalities because everyone’s biology is different, and because no two people have the same journeys through life 🙂