Selection would favor those who dispersed. The other advantage to living in groups is better detection of, and defense against, predators. Field studies suggest that this is more often a factor for terrestrial primates, which may be easier for predators to sneak up on, and which have fewer escape routes compared to arboreal primates. Since these early primates were arboreal, it is less likely that living in groups would have provided enough better defense against predators to outweigh the additional competition for food. The descendents of these insectivores in the lineage that led to humans evolved into larger-bodied frugivores.
Fruit is concentrated in large amounts in just certain trees at any given time .
These frugivores are more likely to have lived in medium or even large groups. Those who lived in such groups would benefit from improved access to food, since fruit is found in compact patches that the group could effectively keep outsiders away from, while the amount of fruit in a given tree is large enough that the competition from fellow group members would not seriously reduce the amount available to each individual. Fossils of these frugivores show considerable variation in adult size, which is thought to indicate a significant difference in size between smaller females and larger males. The fossils indicate a lot of sexual dimorphism. This fits well with the idea that these primates lived in medium or large groups.