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. A testable hypothesis is an answer to the general question which can be answered by doing an experiment. A statement of scientific fact. A question which arises from observations.