Norway Rat

Norway rats demonstrate reciprocal food sharing that parallels vampire bat blood-sharing systems. Rats who receive food from partners later share food with those same partners, tracking specific individuals and their sharing history. This isn't automatic generosity—rats are more likely to share with individuals who have shared with them previously, punishing non-reciprocators with reduced food access.

Experimental evidence is robust. Researchers established rat pairs where one individual could share food with another. Partner A shared with partner B. Later, roles reversed—and B shared more with A than with a stranger who'd never helped. The rats remembered specific partners and their history, adjusting sharing behavior accordingly.

The memory window extends at least a week. Rats who received help days earlier still preferentially helped their benefactors. This extended memory enables cooperation across time gaps—you don't need to reciprocate immediately but must reciprocate eventually. The delay tolerance creates flexibility that strict same-day reciprocity wouldn't allow.

Food quality matters for reputation. Rats who share high-quality food receive better treatment than rats who share low-quality food. The system tracks not just whether you shared but how much value you provided. This creates incentives for genuine generosity rather than minimal compliance.

For organizations, Norway rats demonstrate that reciprocity tracking is cognitively accessible to non-primates. The fundamentals—remember who helped, help them back, punish defectors—don't require human-level intelligence. Simple systems can implement sophisticated cooperation.