The early mermaid's food source was mainly gathering and hunting. The collection objects can include slow-moving animals, such as oysters, mussels, snails and sea cucumbers, or plants, such as seaweed. The hunting targets are mainly various fishes, marine mammals, cephalopods and crustaceans. Some fishermen will go to the shore to catch some animals on the coast. Mermaids use dexterous hands to process and manufacture various tools in the ocean to catch various large animals. In this process, they found that some higher animals, such as dolphins, have social characteristics and can interact well with their peers. So they domesticated some small aggressive species to help them hunt, so there was a saying that "little dolphins are mermaid's best friends". Soon, some mermaids discovered the growth law of aquatic plants and shellfish, which consciously promoted the reproduction of these creatures in certain areas and eliminated natural enemies such as starfish. Over the long years, their directional selection has changed these species. These species are not competitive without the care of mermaids, but they can provide a lot of food under the care of mermaids. This is the mermaid's "agriculture". In order to protect herself and her labor from marine life, agricultural mermaids use corals, rocks, shells and other objects found in the sea to build buildings and plant anemones on them. You can live in it safely. The houses under the sea are connected together, forming an early village, which is the agricultural civilization of mermaid. These villages are built on tropical and temperate coasts. So "the coast is the cradle of mermaid civilization". Many mermaids like to keep a small octopus as a pet, because the small octopus is smart and independent, which can help mermaids catch many small creatures parasitic in the village.