The brain constantly evolves
Individuals are constantly experiencing various situations that create different neural connections within the brain. Hence, the physical structure of the brain may alter because of new connections between neurons, which also bring about different emotions. By the way, this physical change or growth can be measured by MRI scans.
No matter what we do, neurons get always stimulated and the brain improves. But depending on what we do, some neurons get stimulated even more intense which results in the strengthening of them and in the weakening of the others. The effect of stimulating and forming neurons is called neuroplasticity and as I mentioned before, it is caused by repetition, learning or damage.
If, for instance, someone practices very hard to become an engineer, the brain will create stronger connections between neurons and the two brain hemispheres, with the purpose to increase the capability to cope with mathematical tasks. The good thing about that, our brains possess this ability throughout our whole life. Consequently, virtually any talent or intelligence can be created by training and practice. As you may assume, rationality and emotionality can be strengthened because it does work the same way.