When Our Ancestors Stopped Being Bullies: The First Great Social Revolution of Early Humans
– by Michael McBride
Imagine a world where the biggest, strongest individual gets to eat first, mate first, and make decisions while everyone else cowers in submission. This was the reality for our ancient ancestors millions of years ago, just as it is for many animals today. It was a social life dominated by bullies—mostly male but also female—who used brute force to control resources and social order. Yet, somewhere along our evolutionary journey, we flipped the script entirely.
In my recent study published in Evolution and Human Behavior, I investigated this pivotal transition in human evolution—the shift from a dominance hierarchy in which bullies rule to a reversed dominance hierarchy in which bullies are suppressed by coalitions of cooperating individuals. This transformation didn’t just change how our ancestors organized themselves socially; it fundamentally shaped what it means to be human.
Dominance Hierarchy and its Reversal
To understand this transition, we need to look back roughly 6-7 million years ago to our last common ancestor with chimpanzees and bonobos. As other scholars have explained, these ancient ancestors lived in societies where physical dominance determined social rank. The strongest individuals controlled access to food, mates, and territory through intimidation and violence, while everyone else fell in line.
This pattern of social interactions, while brutal, had its evolutionary logic. Strong individuals passed on their genes more successfully, and clear hierarchies reduced constant fighting. At the same time, this social arrangement also hindered the successful emergence of life-improving developments. For example, dominance hierarchy hindered more advanced forms or social cooperation and collective problem-solving.
Yet, sometime between that ancient ancestor and the emergence of modern humans, our hominin ancestors reversed the dominance hierarchy. Instead of submitting to bullies, individuals actively suppressed them, and bullying declined.
How and when this transition happened is still a mystery because many factors worked against coalition formation among the earliest hominins. Early hominins had limited cognition and communication abilities, which restricted their capacity to plan and coordinate complex group actions against bullies. Challenging a bully also meant taking on the huge risk of extreme physical harm. It probably wasn’t worth it to try to suppress bullies.
The Model and Key Findings
To study this transition, I developed a formal mathematical and game-theoretical model that tracks the evolution of different behaviors in early hominin populations. In each period of the evolutionary game, actors in a large population are randomly matched into trios to interact in what I call the Bullying Game. The strongest actor of the three can undertake bulling or not. If bullying occurs, then a second actor can challenge the bully or let the bully go challenged. If there is a challenge, then the third actor either helps in the challenge or does not help; helping means forming a coalition with the second actor. The bully’s reproductive fitness is highest after unchallenged bullying, but is lowest after a challenging coalition. Conversely, the victims suffer fitness losses after bullying, but a coalitional challenge minimizes those losses.
When matched in the Bullying Game, each actor acts according to their behavioral type which is inherited from their parent. The model identifies several distinct behavioral types, ranging from pure bullies who never help others to cooperative challengers who challenge bullies and help others who challenge bullies. Evolutionary selection determines the distribution of behavioral types in the population such that parents with higher fitness reproduce children of their same type at higher rates.
The analysis reveals how the evolution of types in the population depends on both the initial distribution of types in the population and on several key parameters. For example, evolutionary selection favors bullies when there are relatively few challengers because bullying goes unchecked, and selection disfavors challenging when there are few helpers because a solitary challenge against a strong bully yields a large fitness loss to the challenger. At the same time, challenging and helping have relatively higher returns when the fitness costs of being bullied are large because there is less to lose and more to gain from the challenge.
A key insight from the analysis is that populations can still get “stuck” in dominance hierarchies unless some specific conditions are met. First, potential helpers must also suffer significant fitness losses when they witness bullying. If the cost of living in a society with unchecked bullies is high enough to motivate helping in a challenge, then helpers emerge and challenges become successful. Second, the cost of challenging a bully must be relatively low. Finally, there must be just the right amount of genetic drift, which is random changes in population composition that aren’t based on fitness advantages. If there is too little drift in a dominance hierarchy, then challengers are driven to extinction before helpers can gain a foothold and make challenging a viable strategy. If there is too much drift, then the drift prevents a full reversal of dominance hierarchy because the evolutionary system has too much randomness. I argue in the paper that this right kind of drift was likely present, thus making the transition possible when the other key conditions were present.
Another striking finding is that societies undergoing this transition must go through an extremely violent phase. As conditions for helping improve, the rate of helping increases, which in turn drives an increase in challenging. Then, violence replaces submission as the common response to bullying, and conflict peaks as bullies who continue their violent ways are actively suppressed by coalitions. Our hominin ancestors had to navigate this dangerous period just before the transition’s completion.
Timing the Transition
But when did this momentous change occur? As previous scholars have noted, Homo erectus (about 1.8 million years ago) undertook large-game hunting and was the first hominin to spread across continents. These activities are both unlikely in a dominance hierarchy because they required new forms of social cooperation. For example, large-game hunting likely required new forms of meat sharing and a suppression of bullying to make it worthwhile for group members to undertake the danger and risks associated with hunting large animals. So, the transition must have happened sometime between 7 to 2 million years ago.
Here, the model helps again. By interpreting how the key evolutionary developments among our hominin ancestors would affect coalition formation and bully suppression in the model, I narrow down the possible window of time for the transition. Consider these developments:
- Bipedalism: Walking on two legs enabled longer travel, opened new forms of hunting, and freed hands for weapons. These developments increased the returns from many activities, but also increased the stakes from bullying and challenging bullies.
- Tools: Wood and stone tools increased access to new food sources, thereby also raising the bullying stakes. Stone tools first emerged 3.3 million years ago, but wood tools likely predated them.
- Cognition: As our ancestors’ cognition improved, they became smarter about social dynamics, including the ability to recognize potential allies and coordinate group actions that would increase the chance of success against bullies,
- Weapons: When anyone can kill with a weapon, physical size becomes less important than intelligence and cooperation. The emergence of weapons could have even been the ultimate trigger of the transition by making challenging coalitions more effective, though my analysis reveals that a weapons-free transition was also possible.
I conclude that the most likely time frame for the reversal of dominance hierarchy is during the late Pliocene or early Pleistocene epoch (roughly 3.5 to 2 million years ago), when bipedalism, cognitive abilities, and tool use had meaningfully developed and the Homo genus first emerged. This timing places the transition right before or near the emergence of the genus Homo, but also well before other important developments in human social life such as the emergence of more advanced forms of morality.
The Ongoing Legacy
The reversal of dominance hierarchy represents a seminal step in our evolutionary journey toward unprecedented cooperation. This transition built upon earlier developments like bipedalism, basic tool use, and improved cognitive abilities that had already begun distinguishing our lineage from other great apes. As new cooperative opportunities emerged, the costs of dominance hierarchy increased, and the transition could begin. However, the reversal of dominance hierarchy also paved the way for other critical innovations that would further transform human society. For example, the suppression of reproductive bullying would make cooperative breeding a more viable reproductive strategy. Understanding how the reversal of dominance hierarchy is part of a larger evolutionary sequence helps illuminate how our ancestors gradually assembled the building blocks of modern human cooperation, with each development creating conditions that made the next breakthrough possible.
This ancient revolution in bully suppression also reminds us that cooperation isn’t weakness—it’s one of our species’ greatest strengths, forged in the crucible of evolutionary pressure and refined over millions of years of social innovation. The specific conditions required for this transition to succeed make it all the more remarkable that our ancestors managed to navigate this complex evolutionary challenge, ultimately giving rise to the uniquely cooperative yet competitive species we are today.
Read the original paper here: McBride, M. (2025). Early hominins and the reversal of dominance hierarchy. Evolution & Human Behavior, 46(3), 106688.
