[mehphp]

> It is not like water flowing in a direction guided by the terrain.

I understand it doesn’t seem intuitive at first, but evolution is actually quite similar to that.

> Trees produce thorns to keep away animals.

It's not that trees consciously produce thorns to keep animals away. Rather, trees with thorns (due to random mutations) are more likely to survive because they are less likely to be disturbed by animals. Over time, those trees are more likely to reproduce and pass on those traits.

Just like water flows down the path of least resistance, evolution naturally selects for traits that improve survival. The "selecting" we are referring to is used in the same sense that water "selects" which route it takes. It doesn't actually select anything, it's just following the laws of physics.