Absolutely EVERYTHING is made up of atoms.  That includes living things.  The stuff on the Periodic table are the building blocks from which everything is made of. These building blocks come together to form molecules. The interaction between the building blocks or between the molecules or between the building blocks and the molecules, is called a chemical reaction.

The molecules then got together to form a cell.  The cell then started taking in other molecules in order to sustain the chemical reactions going on inside of it.  What goes on inside a cell is nothing more than a chemical reaction.

The cells then got together to form an organism.  The organism started taking in nutrients, which is nothing more than a bunch of molecules, in order to sustain the chemical reactions going on inside of it.  What goes on inside an organism is nothing more than a chemical reaction.  Every thought, every memory, every emotion, that pops into your head is nothing more than a chemical reaction.

Sentient life is thus nothing more than a set of self sustaining chemical reactions.

So when a scientist tells you that evolutionary traits that are beneficial to a species tends to become prevalent among that species, what he means is that a trait that is beneficial to a set of self sustaining chemical reactions tends to become prevalent among that set of self sustaining chemical reactions.  And being able to think is one of those traits.

In other words, a set of self sustaining chemical reactions evolved the ability to think purely by chance and it became prevalent because thinking helps the set of chemical reactions to sustain itself.  In fact, every set of self sustaining chemical reactions came into existance by pure chance.  Every step that gave rise to sentient life was due to pure chance.

Is this making any kind of sense to you yet?