Research natural selection.

The evolution of unicellular organisms is controlled by their environment.

But for us, multicellular organisms with blood, our body is the environment in which our cells live. The conditions of this environment change depending on our actions. Complex animals are too complex to rely on luck for their evolution.

Our mind decides which actions are necessary to survive in the environment. These actions create specific kind of stress in our body. This stress determines which cells get to live and to die.

Adult creatures can't be defined by a single DNA, we are a walking environment for many cells with unique DNA of their own. These cells evolve in accordance with our will. Not us.

In practice, everyone not defective will eat and reproduce. Some special outliers may appear and screw the balance, but they are very rare and aren't the main source of progress.