Here's why:

* Natural Selection: This theory states that organisms with traits better suited to their environment are more likely to survive and reproduce, passing those advantageous traits on to their offspring.

* Biochemical Conditions: The environment includes biochemical factors such as:

* Availability of nutrients: Different organisms have different biochemical needs. The availability of specific nutrients can influence which organisms thrive.

* pH: The acidity or alkalinity of the environment can affect biochemical processes.

* Temperature: Enzymes, which drive essential biochemical reactions, have optimal temperature ranges. Extreme temperatures can disrupt these processes.

* Oxygen levels: Many organisms require oxygen for cellular respiration. Oxygen levels can vary significantly in different environments.

Example:

Consider the evolution of bacteria that can break down pollutants in soil. The presence of pollutants (a biochemical condition) provides a selective pressure. Bacteria with genes that allow them to metabolize these pollutants have an advantage, allowing them to survive and reproduce more effectively. Over time, the population of bacteria will evolve, becoming better adapted to the polluted environment.

In essence, biochemical conditions play a crucial role in shaping the selective pressures that drive evolution.