Summary:
- Four unifying principles form the basis of biology.
- The cell theory states that all living things are made up of cells, and living cells always come from other living cells.
- The gene theory is the idea that the characteristics of living organisms are controlled by genes, which are passed from parents to their offspring.
- The homeostasis theory is about maintaining a stable internal environment or keeping things constant.
- The evolution theory explains how modern living things have descended from ancient life forms that no longer exist on Earth.