Cells vary in size and complexity. Tissues are organized into organs. All cells have a plasma membrane. All cells have a cell wall. All cells contain genetic information.
All cells can divide to produce other cells.
All cells have cytoplasm. The best adapted individuals tend to produce the most offspring. Any population has the potential to produce more offspring than the environment can support. After making his two key observations, Darwin arrived at an important conclusion. When organisms are challenged by the environment, the environment causes the species to evolve.