We already know some monkeys display above average intelligence. One way by which we can tell is their use of tools. Studies have shown that capuchin monkeys use boulders and logs as anvils upon which they can crush nuts.
Did you know that tufted capuchin monkeys (Cebus apella) rub their fur vigorously with substances such as leaves, fruit, or insects? Such substances are often insecticidal, antiseptic, or anti-inflammatory.
In Rhesus monkeys the optimal sexual strategy is different for Alpha males, other males and females. Alpha males want females to mate exclusively with them, whereas other males and females benefit from promiscuity.