for National Geographic News
Such an arrangement is known to arise in some modern primate species when males mature later in life than females and become much larger than their mates.
In these cases a single dominant male mates with and protects a large harem of females.
The new find is based on analysis of fossils from the human relative Paranthropus robustus.
The primate species, which lived in Africa about 2 million to 1.2 million years ago, is closely related to early humans but is a dead-end branch of the family tree.
P. robustus is a descendant of Australopithecus afarensis, the species that also gave rise to the Homo genus that includes modern humans.
Charles Lockwood, an anthropologist at University College London, and colleagues looked at roughly three dozen fossil skulls and teeth from P. robustus.
Telltale traits of the fossils showed that male members of the species matured late in life.
This led Lockwood to theorize that P. robustus males competed for groups of mates much the way gorillas do today.
The findings appear this week in the journal Science.
Male gorillas and orangutans grow significantly in adulthood and tend to become dramatically larger than females of their species.
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