All creatures are selfish because the genes which comprise them are selfish. Ultimately all actions are designed to act in the interests of replicating their genes.
Sometimes selfish behavior can appear to be selfless. For example paying a debt to a friend may appear selfless, but in fact it is a self-interested act if not repaying the debt will damage the ability to trade with the friend in the future.
Morality can be regarded as just an intelligent form of selfishness.
Selfishness is not to be confused with envy.
See