What’s Happened to Humans Over the Past 10,000 Years? 

How changing our environments may have changed us.

I started this project by asking how humans may have changed over the past 10,000 years, but satisfying answers proved elusive. Partly because, to know how we changed, we would have to know who we were before to compare with who we are now. The former seems unknowable, and the latter might be hard to pin down. After multiple essays, discussions with podcast guests, and a lot of thought, I’m not sure we can quantify who we are well enough to capture the complexities of our feelings, beliefs, and everyday attitudes to make this comparison. Because I can’t reconstruct who we were, or even who we are, with meaningful accuracy,I’ll instead examine what may have changed. More specifically, I’m interested in whether humans may have changed our environments and, if so, altered the conditions that change us. 

The Current Paradigm and Baseline Assumptions

While my initial investigation didn’t answer the original question, it led me to other people asking similar questions, and a body of work emerged. A meaningful story describing our transition from 10,000 years ago to the present, though quite dynamic, offers a useful template. No historical record is entirely accurate, and this story simplifies what really happened, but I think it is robust enough to serve as a baseline for asking new questions.

Here’s a summary of what I’ve learned so far. As we emerged from the Pleistocene, human social groups became less nomadic and more agrarian, surrounded by blossoming resource wealth. We started cultivating crops instead of gathering food, and learned to manage surplus food stores. Less movement allowed stability, and people could build structures meant to last. Stable resources and infrastructure supported population growth and larger village size. Often, the stories end here with population growth cited as the main driver of change. 

A more complete story suggests that this seemingly simple transition toward more sessile and agrarian living conditions may have required similar advances in social regulation. Where within-group behavior regulation was straightforward in smaller villages, larger populations required a new approach. Family dynamics, cultural norms, societal rules, and laws likely grew from the need to govern social interactions, including behavior. Human social groups became more complex, emerging as systems with many interacting parts, including ourselves and each other. Eventually, our ability to create things and materials led to industrial and technological revolutions, modern conveniences, and perhaps even our dependence on these modern systems.

Using this baseline, I will speculate about what else may have changed as humans evolved over the past 10,000 years, focusing on social group dynamics. To do so, I make several assumptions about the system, or systems, governing changes that may have occurred. First, life perpetuates in changing environments according to an integration of elements including DNA, sexual reproduction, variation in individual characteristics, and natural selection of these characteristics that lead to adaptation over the long term. 

Second, within this system, individuals die, but a lineage can perpetuate life indefinitely by adapting to future environmental changes. Fitness results when natural selection shows preference for a certain trait, combination of traits, or emergent property, and individuals with those characteristics experience a greater capacity to survive and reproduce.  I call this capacity to respond to change optionality, whereby variation in a species’ characteristics improves the likelihood that at least one of those characteristics will be considered fit in changing future environments. 

Third, increased optionality maximizes the potential for life to respond in dynamic environments.  More response options mean individuals or groups are less vulnerable to unforeseen environmental changes, and thus have a higher capacity for stability through time. Now let’s see what follows from these baseline assumptions.

What May Have Changed?

With these assumptions in place, I’ll examine how environment, ecology, behavior, and selection could have changed. I’ll begin with a linear analysis of each, and then consider what emerges when these elements interact.

Our environment changed

I define environment in an ecological sense, meaning the abiotic and biotic system components with which a species interacts. Perhaps my main assumption is that the human environment has changed in the past 10,000 years. Though we may not all agree about the precise pathways, what exactly transpired, or what the causal agents were, some potential changes are commonly referenced. First, as small villages became larger, we interacted with more people than we could have meaningful relationships with. Second, temporary settlements became more permanent, and the associated infrastructure changed. Last, social roles formerly assigned to individuals shifted to groups, and a division of labor related to these roles may have led to hierarchy.

Our ecology changed

Ecology captures how an organism interacts with the abiotic and biotic elements of the environment where it lives. When an environment changes, it follows that an organism’s ecology will respond. When a species’ ecology changes, it can modify the species itself. We can refer to the ecological characteristics as the niche, with each unique species occupying a unique niche. 

When a niche changes, the species must either maintain the adaptive relationships defining the niche by modifying the environment to counteract the changes, adjust and adapt to the new niche, or remain unchanged and risk extinction. While it’s impossible to know the myriad ways new habitats might have altered the human niche, or whether these changes were meaningful enough to induce species-level, long-term responses to our ecology, there was certainly interplay between emergent environmental features and how we interacted with the environment. I’m not suggesting we are becoming a new species, only that the interplay between behavior and group structure is critical to understanding human ecology. 

Our behavior changed

One way our ecology likely changed is that we became increasingly surrounded by, and likely influenced by, each other. As our social structures grew in size and complexity, how might this have affected human behavior and interactions? The dominant paradigm summarizing what we think we know about these changes suggests a shift from small, reciprocal villages to larger, more autonomous cities, and from self-policed behavior to rules and laws as regulatory mechanisms. As the landscape becomes more complex, it follows that our interactions and behaviors respond in kind. 

Most research I encountered suggests that small villages regulated within-group behavior by reciprocity or self-policing. This is thought to reduce conflict and maintain stability when group size is small enough to know everyone, but the system doesn’t scale. Increasing group size probably induces the need for new rules regulating behavior. In increasingly large populations, every individual cannot feasibly know everyone or participate in all activities. While all individuals would be required to follow the rules, responsibilities associated with rule-making were likely assigned to groups.

Additionally, population growth likely necessitated new rules and behaviors to regulate so many individuals, detect an ever-increasing array of deviance, and even assign consequences. I think more behavioral changes related to the rule systems themselves required even more new behaviors. Increased behavioral complexity of individuals and groups almost certainly differed between ancestral and modern social groups. 

Within-group selection changed

If growing population size led to group structures for rule creation, enforcement, and punishment, it likely changed our environment and interactions. Rules may act like selection forces, promoting desired behavior and punishing undesired acts. Individuals who ‘followed the rules’ would have higher fitness, expressed as easier access to resources and higher reproductive success, and thus were more likely to pass on genes that might be related to good behavior. Similarly, selection forces would act to decrease the potential for undesired behaviors in future generations.

If the rules work as intended and selection for obedience occurs, groups comprised of obedient individuals would become more numerous. This pattern, where the range of behaviors decreases over a series of generations because a single behavior type is favored over others, is a specific type of selection called directional selection. A directional response is great for maximizing fitness in the face of consistent selection pressures, and could enhance group stability.

Between-group selection changed

We don’t know much about how ancestral groups interacted, though some propose two basic options depending on whether we knew the other group. According to these interpretations, encounters with unknown groups would result in conflict, while more neutral or positive interactions likely evolved between groups that were familiar with or related to each other. Because we know so little, I will use this common explanation as a baseline and assume modern trends may follow a similar pattern. At the least, I think it’s safe to assume that group interactions affect our behavior and can influence future generations.

While traditional evolutionary theory focuses primarily on how natural selection influences the fitness of individual traits, recent research efforts support the idea that selection also operates at the group level. While we don’t necessarily understand how behavior is inherited, group selection is an increasingly documented concept that could be working here. To proceed, I assume groups can respond like individuals, where interactions between groups can act as selection pressures influencing group structure and behavior.

I think we can describe between-group interactions generally as being positive, negative, or neutral. As rules evolved to reduce negative interactions by regulating behavior, maybe group interactions address a similar problem. Negative interactions between individuals or groups are likely most concerning, as they can introduce instability and may be worthwhile to explore here.  I think negative between-group interactions are likely to affect a group’s environment and ecology, and extremely negative examples may even lead to group extinction. Strategies to maintain stability through a balance of selection and fitness are likely to be necessary to regulate both group and individual interactions. 

What Emerges in the Transition From Ancestral to Modern Societies

The above analysis is a linear way of looking at what changed over the past 10,000 years following a reasonable baseline. I’ve examined these changes as a sequence, but none of them actually happened in isolation. Humans were simultaneously changing their environments, responding to those changes, changing their social rules, responding to those rules, and encountering other groups and individuals doing the same things. Because the human environment changed during this time period, the relationships between humans and our environment – our niche – could also change. What new responses arise when within- and between-group dynamics interact?

What Emerges Within-Groups

At the individual level, a feedback loop emerges connecting societal rules with desired behavior. The loop begins with rules acting like selection forces by rewarding obedient individuals with better access to resources and a higher probability of surviving and reproducing. Assuming behavioral selection is heritable, then fitness could influence successive generations and increase the proportion of desired behaviors. More individuals with desired traits would further increase the potential for desired behavior by transmitting advantages to future generations. 

Directional selection of behavior continues, with rules influencing fitness and increasing the occurrence of favorable behavior, strengthening the loop. However, selection for obedience also means the number of possible behavioral options decreases. This reduced optionality, measured by the narrowed potential for behavioral strategies other than obedience, means the species has a similarly reduced potential to respond to environmental change and is likely more vulnerable. If the behavior loop leaves the group more vulnerable to change, the system may require adjustment or modification.

It seems plausible that rules and laws created to reduce within-group conflict and maintain social order would need reinforcement over time to reduce vulnerability. When the environment is stable, the system works as intended. But when environmental conditions change, whether related to rules or some other element, the reduced optionality resulting from directional selection may inhibit a beneficial response, and the system is vulnerable. Elements like rule-making, rule-enforcing, and behavior regulation become more necessary to reinforce the feedback loop, maintain stability, and reduce vulnerability. Perhaps our modern police forces are examples of reinforcement modifications.

What Emerges Between-Groups

If we characterize within-group dynamics using the feedback loop above, how might this influence how groups interact? General ecological patterns often translate across levels, despite complexity introduced at higher levels of organization. One pattern worth investigating is whether group-level fitness follows a feedback loop similar to within-group fitness, where groups seek to maintain environmental consistency and manage stability and vulnerability.

The comparison begins with the assumption that both modern between- and within-group interactions address problems associated with undesired or negative behaviors and interactions. These interactions can induce harm, make it difficult for individuals to meet their needs, and even influence evolutionary processes. While rules may reduce negative behavior within groups, I propose avoidance and defense as comparable strategies that potentially influence between-group interactions. Both avoidance and defense might work to either modify or maintain group dynamics and promote stability. 

Avoiding conflict altogether by relocating or retreating seems reasonable, but perhaps also challenging. Avoidance strategies would have to consider interaction probability, capacity to flee, or perhaps other strategies I’m not considering. Reducing the likelihood of interaction would require the group to be located far from other groups, or to be somehow undetectable by other groups. It seems easier to imagine that these types of strategies may have worked better in the ancestral world. Modern technologies like GPS make it seem unlikely that these strategies would work very well today.

Defense may be a more plausible strategy for enhancing group stability and reducing vulnerability between groups. Where rule-following stabilizes behavior within groups, defensive behaviors might similarly stabilize relationships between groups. Within groups, interactions that avoid or reduce the potential to alter within-group structures would be selected for, and it appears as though this may also occur between groups. Specifically, defensive strategies may reduce a group’s vulnerability to being changed by another group. A group capable of defending itself would likely have a stability advantage in being better able to maintain its resources and territory. 

Perhaps feedback loops similar to those proposed for within-group interactions may also influence between-group interactions. If so, groups with defensive infrastructure may become more successful because they are able to resist systemic changes and enhance stability. Like individuals exhibiting undesired behavior risking punishment, groups with poor capacity for defense risk being changed, overtaken, or defeated. Between-group feedback loops may promote strategies like defense to address stability and vulnerability. Modern militaries may be examples. 

Are Modern Systems Changing Us?

It seems both within-group and between-group dynamics may converge, to some degree, on similar evolutionary themes. Perhaps comparable strategies evolved at different levels of organization to solve similar problems stemming from negative interactions. Individuals who follow within-group rule hierarchies gain adaptive advantage, and groups featuring hierarchies associated with defensive strategies may also be selected for. If the changes I describe here are accurate, it could mean that one of the things that may have changed over the past 10,000 years is our capacity to not only influence our ecology but to control it.

What distinguishes modern humans from our ancestors is not simply our capacity to alter our ecology, but that we may have become dependent on the conditions we created. Human-designed behavioral systems seem to increase within-group fitness. However, directional selection promoting fitness reduces optionality. If environmental conditions change, behaviors may no longer be fit, and the system may lack the capacity to respond. Modern societies may have become obligated to the changes we induced. Now we either accept vulnerability or address it in other ways.

Obedience and defense may have become requirements to reduce negative interactions. Again, these solve short-term problems and increase fitness, but also reduce optionality and our capacity to respond to other environmental changes. Individuals and groups lacking a variety of responses to change become more vulnerable to future conditions. To simplify the theme, humans introduced strategies to solve problems. The systems worked, but we became more dependent on them and had to manage the challenging consequences that came along with them. Instead of changing the strategies themselves, we continued to modify the systems.

At the very least, what I propose here suggests that there are new questions to be explored. If both within- and between-group selection in modern human societies reduce optionality, what does that mean for individual humans? In creating structures to regulate behavior, have we obligated ourselves and our environments to the difficult challenge of maintaining stability in systems that change according to other rules? If the system increasingly rewards conformity to structures that maintain its own stability, what happens to the individual’s capacity to meet their own needs?

Which brings me back to a more focused version of my original question. What happened to individual humans over the past 10,000 years? Has increasing group size shifted the focus of selection to the group over the individual? Do individuals have the capacity to determine their own fate? Do we even occupy the same niche as our ancestors? In the face of a changing climate, resource availability, and reduced individual and group measures of fitness, what can we do inside modern systems to influence our future?