Humans begin their existence as a single undifferentiated cell and proceed to become a highly complex and organized system consisting of specialized cells (liver, skin, brain, blood, etc.). This change BEST exemplifies the principle.

Orthogenetic

Explanation:

The Orthogenetic principle of development was put forward by Heinz Werner, in the year 1975.It is a biological principle of development. This principle of development states that all the aspects of the functioning of a living organism develop progressively from a less differentiated state to a more differentiated state. Besides differentiation, there is also hierarchic integration and articulation of functioning such as perception, cognition, etc. This leads to the development of more complex forms from a simple form.Therefore, a single undifferentiated cell giving rise to the complex organized system is an example of the orthogenetic principle.

We can use solar powered cars or ride bikes instead of cars that burn fossil fuels

We can plant more trees and plants.