All living organisms depend upon their ability to perceive reality as accurately as possible in order to survive. Animals in the wild that misjudge or make an inaccurate assessment of their reality gets eaten. A monkey that perceives a log floating in the water instead of a crocodile gets eaten.
Every organism perceives reality through their senses, sometimes those senses makes errors. To be more specific, the brain interpreting the sense data coming from the sense organs can make errors. The goal therefore of organisms is to get rid of as much errors as in order to see reality as accurately as it can.
Over time organisms evolved strategies in order to compensate for these errors. Some animals developed speed, some strength, some poison, so it could still get away in case it makes an error.
One animal in particular developed a brain capable of reason and logic. This is what separates men from beasts.
So why reason and logic, abstract thinking? Why not just based everything on feelings? Listen to find out!