This is an idea from the Roma physician, Galen. I'm now read a text book i brought before i as re-student of UiTM. The text book of "personality physiology".
In AD 170m wrote that personality character was influenced by biology. He tough that the amounts off four foluid present in the body determined personality.
1. an abundance of phlegm made a person passive, calm and thoughtful (plegmatic)
2. an abundance of blood made a person happy, outgoing and lively (sanguine)
3. too much yellow bite made a person unstable, aggresive and excitabke (choleric)
4. an abundance of black bile made a person unhappy, pessimistic and somber (melancholic)