Explain why different types of living organisms have a similar life form?

The similarity of life forms of different species of animals is due to similar living conditions. For example, a dolphin is a mammal and a shark is a fish, have a streamlined body, a strong tail bifurcated at the end, and a dorsal fin. Because they live in the same conditions – in the sea. Another reason for the similarity may be the need to protect against the same factors. For example, a cactus has thorns to retain water due to the heat. The spruce has thorns to retain water due to the cold.