Question

how do we know evolution has occurred

Answer 1

the change in the biosphere by the plants and animals

Answer 2

Evolution occurs after several centuries. The fossils which are found in the lowest layer have simple body organization. The fossils which are found a little bit above have a bit complexed design than the fossil found in the lowest level and so on. The fossils which are found in the top layer have very complex body organization. Hence, we can see that at first, the organization of organisms was very simple but now their body organization is very complex. This is how we know that evolution has occurred.
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