The term pair bonder means that a male and female stay together to raise their offspring. Maybe they stay together for life, or only for mating season. This arrangement differs from promiscuous animals, which do not share parenting duties, and copulate with multiple partners.
About 3% of mammals are pair bonders, or socially monogamous. Socially monogamous means they stay together, but may fool around on the side. No species of animal is sexually monogamous, although a pair within a species may stay sexually monogamous.
Humans are a pair-bonding species. We have the brain circuits to bond to a mate, or in non-scientific terms, fall in love. Promiscuous animals do not have pair-bonding circuitry. The mechanisms for pair-bonding involve the reward circuitry and dopamine. Bonding to another is the original addiction. Studies of pair bonders show two things:
- They are more susceptible to addictions.
- Addictions hijack the pair-bonding mechanisms, making it harder to stay bonded, or “in love”.