Talking about shrinking of your brain, there are many reasons like diet, climate, environment, diseases and so on. There is also another peculiar reason that is more often discussed among anthropologists and paleoanthropologists is the shift on depending of your way of survival with compare to you ancestors. Your brain is a complex nervous system and it carries various vital functions for your survival. However there used to be other vital functions of brain which are no longer required by you.
You are now dependent, if not fully but at large scale on technology. You do not require to know the location of where or when any kinds of edibles are found as because you are not the primary one to fetch your food. You do not require to have the minimum knowledge about the movement of Planets, Constellations, Polaris, Wind, River Flow and so on because you have the Global Navigation Satellite Systems.
Such and many more functions are no more stored in your memory or not required to store because of which there is decrease in size of the brain.
It might be painful to you but some experts related to this subject consider you are getting dumber.
Thank you for reading.
If you like reading more keep following.