Each layer of fossils represented the remains of organisms that had died in a local catastrophe such as a flood: gradualism the view that earth and its living systems changed slowly over its history (ex. Believed that simple organisms evolved into more complex ones, replacing the ones that weren"t as favourably suite for their environment. Microscopic organisms were replaced at the bottom by spontaneous generation (in which living organisms arise from nonliving material, such as dirt or dead organisms) Body parts grow in proportion to how much they are used. And unused structures get weaker and shrink: mechanism 2: the inheritance of acquired characteristics . Changes that an organism acquires during its lifetime are inherited by its offspring. As a slightly new acquired trait would gradually develop further as generations past: ex. They are descended from short-legged ancestors that stretched teir legs to stay dry while feeding in shallow water.