Historically, cooperation between unrelated individuals was assumed to be something rarely seen in non-human species. But research on cooperation between male chimps shows that blood ties are not necessary for two chimps to cooperate.
The research relied on a combination of observational and genetic data. Observers watched for evidence of cooperation between male chimps as they hunted, patrolled territory, and groomed each other. Then they performed DNA tests on the chimps’ feces to determine which chimps were related.