Complex sentence: Male Barbary macaques interfere in conflicts and form coalitions with other males, usually with related males rather than with unrelated males, suggesting that they do so in order to indirectly increase their own fitness.
Split into simpler sentences: Male Barbary macaques interfere in conflicts and form coalitions with other males, usually with related males rather than with unrelated males. These relationships suggest that males do so in order to indirectly increase their own fitness.