What does it mean by cooperation is in our own self-interest? i need 4 sentences on it plz : (

Cooperation (sometimes written as co-operation) is the process of groups of organisms working or acting together for a common or mutual benefit, as opposed to working in competition for selfish benefit. Many animal and plant species cooperate both with other members of their own species and with members of other species (symbiosis or mutualism)

Many animal species cooperate with each other in mutual symbiosis. One example is the ocellaris clownfish, which dwells among the tentacles of Ritteri sea anemones. The anemones provide the clownfish with protection from their predators (which cannot tolerate the stings of the sea anemone's tentacles), while the fish defend the anemones against butterflyfish (which eat anemones)

Which one is the underlined word?