The principle of uniformitarianism states that

According to the law of Uniformitiarinism, all the earth dynamic geological process that is undergoing at present must have taken place in the past and with the same force and intensity. This law provides the geological events that have taken place in the past. The landforms that exist on earth now have formed from the continuous effects of geological processes. Some of the examples that follow uniformitarianism is rock cycle, water cycle, plate tectonic movements, and volcanic eruptions that are continuously taking place since the time of formation of the earth.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.