Evolution can be a very efficient mechanism over the long term in shaping the development of an organism so that it becomes more efficient in its environment.
Take the Crocodile for example. It is a supreme predator and wonderfully adapted to a "wait then pounce" method of hunting. While it has weak muscles to open its jaws it can bite down with incredible force and speed. It couples this with an ability to lunge forward in the blink of an eye.
Humans, who evolved in Africa are, like other African primates, generally wary and scared of the Crocodile. No doubt it feasted in the past on our distant kin and some echo of this lurks within us. Look at a crocodile and you can just tell - that this is a beast built for killing.
As it is for Crocodiles of course then so it is with human beings. Our evolutionary advantages include our ability to think in the abstract and language.
We can use our brains to think things to ourselves like "That beast with the large jaws full off teeth is dangerous. I will keep my distance"
We can communicate these thoughts to others and co-operate in surviving by saying things like "dont go near that crocodile because it is dangerous and might eat you."
Within any species though there are some individuals who are just better fitted at surviving than others. Most humans are intelligent but some humans are dumber than is typical for our species. Nature has its ways of tending to weed out such individuals - a process called natural selection.
It is rare to capture this process in action in our own species. This video though shows the process of natural selection at work in humans and how nature is ruthless at dealing with the less fit.