We are animals and hierarchy only becomes more important in large groups if merely for logistical purposes.

If we need 20 people to go pick the fruit today before it spoils, someone has to be responsible for, and capable of, getting 20 people to go do that. We can't just hope that 20 people feel like picking fruit today... And now you've got a management hierarchy... This issue only compounds the more specialized jobs you have and the more tightly they need to be coordinated.