Who’s the daddy? Uncertainty pays off (Image: Papio Ursinus/NaturePL)

Sometimes it pays to give underlings a treat. Dominant male chacma baboons allow lower-ranking males to mate with their females as a way to protect the dominant male’s own offspring in their absence.

That’s the conclusion reached by Louise Barrett of the University of Lethbridge in Alberta, Canada, who studied 11 years of observations from a baboon troop in De Hoop Nature Reserve, South Africa.

Chacma baboons have a despotic social structure in which a single alpha male can almost completely monopolise mating opportunities by guarding females during their oestrus periods. Yet Barrett found that subordinate males in the De Hoop troop fathered 23 of 64 offspring during that time.


Closer analysis showed that this was not because the alpha male was too tired, too busy, or too inexperienced to guard the females. Instead, he appeared to be willingly ceding copulations to subordinate males

Spare dads

The alpha male’s apparent generosity may be a strategy for protecting his young after he is no longer around. When an alpha male dies or wanders off, new alpha males – usually from an outside group – move in, and tend to try to kill infants from the previous regime. Having “spare dads” in the troop may help ensure that these infants receive protection, says Barrett.

Sure enough, subordinate males who had fathered an offspring were more likely to stick with the troop – an average of 23 months, versus just five months for subordinates without offspring.

This may allow them to form closer social bonds with the females, which makes them more likely to protect females and infants. “If you’re a subordinate and you haven’t fathered an infant, you’re not likely to make those kinds of bonds with a female,” says Barrett.

The strategy appears to pay off: just one of five infanticides in the study troop occurred when subordinate fathers were present.

Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0913294107)