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Between 300,000 and 30,000 years ago, Africa experienced intense, local environmental variation.
In a compelling example of how environmental change can drive evolutionary development, two researchers, Masaaki Inaba and Eizo Akiyama, of the University of Tsukuba, Japan, have used computer simulations grounded in evolutionary game theory to demonstrate how intensified environmental variability in Africa during the Middle Stone Age may have promoted the evolution of cooperative behaviour and enhanced cognitive abilities in archaic hominins.
Fundamental to this research is the scientific consensus that Darwinian evolution is the only credible framework for explaining the patterns observed in the fossil record and the genomic evidence for natural selection.
The study also directly challenges a common creationist misrepresentation: that Richard Dawkins’ metaphor of the “selfish gene” implies that evolution inherently favours selfishness and therefore cannot account for altruism or cooperation. This flawed interpretation ignores the fact that evolutionary processes often favour cooperative strategies—especially in complex, fluctuating environments—without invoking supernatural causes.
Severe environmental change can fragment populations into small, isolated groups, where genetic drift plays a significant role in evolution. In such settings, beneficial mutations can rapidly drift to fixation, potentially giving the group a competitive advantage over neighbouring populations when contact is re-established. This process can produce a pattern in the fossil record that resembles 'punctuated equilibrium', with the apparent 'sudden' appearance of a major innovation.
Can you provide an account of the environment variability that would have influence human evolution in Africa in the Middle Stone Age, please. Environmental variability (EV) during the Middle Stone Age (MSA) in Africa — approximately 300,000 to 30,000 years ago — was a critical driver of human evolution. It influenced not just biological traits, but also behaviour, cognition, and social organisation, particularly the development of cooperation. Here's an account of the kinds of environmental fluctuations and their likely evolutionary consequences:The researchers have published their findings in PLOS Complex Systems (open access). Their work is also summarised in a University of Tsukuba research news item:
- Climatic Oscillations:
During the MSA, Africa experienced dramatic climatic variability on both short and long timescales. These included:Such shifts fragmented habitats and created resource unpredictability.
- Glacial–interglacial cycles: Driven by Earth's orbital changes (Milankovitch cycles), these cycles affected monsoonal patterns and vegetation cover.
- Arid–humid pulses: Alternating periods of intense drought and wetter conditions transformed landscapes rapidly. For example, the Sahara periodically changed from lush grassland ("Green Sahara") to hyper-arid desert.
- Rapid shifts: Abrupt climate events, such as Heinrich and Dansgaard–Oeschger events, would have caused rapid environmental transitions, forcing populations to adapt or migrate.
- Habitat Mosaic and Resource Distribution:
EV led to a mosaic of ecological niches - including coastal, savannah, montane, and forest environments. In such settings:
- Populations were often isolated, promoting genetic and cultural divergence.
- Resource distribution was patchy and unpredictable, favouring mobile, flexible groups that could cooperate to exploit scattered or short-lived opportunities (e.g., seasonal shellfish, game migrations, or plant tubers).
- Access to water and food during dry periods required group coordination, especially in arid or semi-arid zones like eastern and southern Africa.
- Evolutionary Pressures on Cooperation:
Environmental instability would have promoted cooperation in several key ways:
- Shared risk: Cooperation reduced individual risk during unpredictable times. Shared food caches, collective childcare, and hunting parties became advantageous.
- Knowledge pooling: In fluctuating environments, pooled ecological knowledge—of where to find water, edible plants, or shelter—was vital.
- Social learning and culture: Variability may have driven cumulative culture, where innovations (e.g. hafted tools, symbolic artefacts) were preserved and refined within cooperative groups.
- Social cohesion and alliance building: Maintaining intergroup ties would allow fission–fusion dynamics, reducing conflict and facilitating resource access over larger territories.
- Archaeological Correlates of Cooperative Behaviour:
There’s evidence from several MSA sites suggesting that humans were increasingly engaging in cooperative and symbolic behaviour during periods of environmental stress:
- Blombos Cave (South Africa): Artefacts such as ochre engraving and shell beads (ca. 100,000–70,000 years ago) suggest symbolic communication and possibly group identity.
- Pinnacle Point (South Africa): Use of marine resources like shellfish (from ca. 160,000 years ago) implies planning and coordination in intertidal foraging.
- Katanda (DRC): Barbed bone harpoons dating to around 90,000 years ago show technological sophistication likely requiring social learning.
Conclusion:
Environmental variability in MSA Africa played a key role in shaping human evolution by selecting for flexibility, social cohesion, and cooperation. Groups that could cooperate effectively were more likely to survive environmental shocks, spread innovations, and expand into new niches. These pressures laid the groundwork for the complex social structures and cultural behaviours that distinguish Homo sapiens.
Environmental Variability Promotes the Evolution of Cooperation Among Humans: A Simulation-Based Analysis
Researchers at University of Tsukuba have demonstrated that intensified environmental variability (EV) can promote the evolution of cooperation through simulation based on evolutionary game theory. This result offers a new perspective for the reinterpretation of the variability selection hypothesis (VSH), which attributes improvement in human cognitive abilities to severe EV in Africa during the Middle Stone Age (MSA), as further relevant to the explanation of the evolution of sociality.
Tsukuba, Japan—Previous scholars have widely proposed that the emergence of advanced cognitive abilities and sociality in humans originated in Africa during the MSA. However, the specific mechanisms and processes underlying this evolutionary transition lack clarification. While the VSH is considered a leading explanation for this mystery, it has traditionally focused on the evolution of individual cognitive abilities. The current study aims to expand its explanatory scope to include the evolution of sociality and examines the influence of EV on the evolution of cooperative behavior among humans using multiagent simulation models grounded in evolutionary game theory.
The researchers developed two simple models of EV, namely, a regional and a universal variability model. The analysis was focused on the influence of changes in environmental conditions on cooperation among geographically distant groups. The results reveal that regional variability poses new opportunities for cooperators in resource-poor areas, thereby promoting the evolution of cooperation. In contrast, the effect of universal variability was weak, which implies that EV contributes little to the evolution of cooperation without changes in interregional resource distribution.
These findings provide new perspectives for archeological inquiry into the origins and development of social behavior during the MSA in Africa. In addition, they offer potential insights into the mechanisms through which EVs and large-scale crises shape cooperative behavior in modern society.
Publication:
AbstractA brief AI overview of evolutionary game theory:
The evolutionary process that led to the emergence of modern human behaviors during the Middle Stone Age in Africa remains enigmatic. While various hypotheses have been proposed, we offer a new perspective that integrates the variability selection hypothesis (VSH) with the evolution of cooperation among human groups. The VSH suggests that human adaptability to fluctuating environments was a primary force driving the development of key evolutionary traits. However, the mechanisms by which environmental variability (EV) influenced human evolution, particularly the emergence of large-scale and complex cooperative behaviors, are not yet fully understood. To explore the connection between intensified EV and the evolution of intergroup cooperation, we analyzed three stochastic models of EV: (i) Regional Variability (RV), where resource-rich areas shift while overall resource levels remain stable; (ii) Universal Variability (UV), where overall resource levels fluctuate but resource-rich areas remain stable; and (iii) Combined Variability (CV), where both resource-rich areas shift and overall resource levels fluctuate. Our results show that RV strongly promotes cooperation, while UV has a comparatively weaker effect. Additionally, our findings indicate that the coevolution of cooperation and network structures is crucial for EVs to effectively promote cooperation. This study proposes a novel causal link between EV and the evolution of cooperation, potentially setting a new direction for theoretical and empirical research in this field.
Author summary
This study investigates how changing environmental conditions may have influenced the emergence of cooperative behaviors among early human groups during the Middle Stone Age in Africa, a pivotal period in human evolution. We present a novel approach to explaining the link between environmental changes and the evolution of cooperation by using models that simulate fluctuations in resource availability across various patterns. Our findings suggest that cooperation is more likely to emerge and sustain when resource distribution across regions varies over time, in contrast to cases where overall wealth changes but remains concentrated in fixed areas. Furthermore, our results indicate that the coevolution of cooperation and social structures is crucial in determining whether environmental changes foster cooperation, highlighting a dynamic interplay between environmental factors and social adaptability. We believe these findings contribute to broader discussions in anthropology, archaeology, and the study of complex systems, enriching our understanding of human nature and society.
Introduction.
Deepening our understanding of the evolutionary origins of modern human behavior is essential for comprehending the nature of humanity and society. In anthropology and archaeology, “modern human behavior" refers to traits unique to or primarily associated with Homo sapiens, marked by abstract thinking, symbolic expression, complex planning, and ultrasociality. These behaviors include language, religion, mythology, art, music, entertainment, humor, altruism, long-distance trade, and the creation of intergroup networks. Numerous studies concur that these behavioral patterns emerged during the Middle Stone Age (MSA) in Africa[1–5]. While there is broad consensus on when and where these behaviors originated, the mechanisms driving their emergence remain enigmatic, despite various proposed theories.
For several years, hypotheses [6–17] attempting to explain the evolution of hominin behavior by focusing on environmental variability (EV) in Africa during the MSA have garnered significant attention. Among these, Potts’ variability selection hypothesis (VSH) [6,7] proposes that intensified environmental change favored “versatilists" who are those capable of rapid adaptation to new environments over “specialists", who adapt to specific environments, and or “generalists", who adapt across a range of environments. Here, EV encompasses changes in landscape dynamics (such as land-lake oscillations), climate (such as like arid-moist climate oscillations), variations in flora and fauna, ultimately leading to the unpredictability of resource availability. Initially, this hypothesis was supported by a temporal correlation between intensified environmental changes, the replacement of human species, and the increased complexity of cultural artifacts, such as stone tools and ornaments [17]. In addition, the cognitive buffer hypothesis (CBH) [18–20] provides a neuroscientific basis for VSH, and a mathematical model [21] demonstrates its theoretical feasibility. The CBH posits that larger brain sizes in animals, including humans, evolved as a buffer against environmental variability, enhancing survival through improved problem-solving and learning abilities. In contrast, several theories [22–24] propose that EV and behavioral diversity do not necessarily drive human encephalization. These theories emphasize the role of social contexts, as suggested by the social brain hypothesis (SBH) [17,25–31], and consider other factors focus such as dietary influences [32,33]. The SBH argues that human intellectual abilities evolved in response to the selection pressures of complex social environments, which required the effective management of social relationships within and between groups. Therefore, much remains unknown about the impact of EV on the evolution of cognitive and behavioral traits in hominins.
Our study suggests that VSH, typically explained through the CBH, may also be connected to the SBH, which is generally considered separate from both VSH and CBH. While complex social environments encompass various factors, what uniquely characterizes human societies is the extensive and sophisticated cooperation observed, including intergroup cooperation and trade, which contrasts with the intragroup cooperation common in many animal societies. These advanced social behaviors are central to modern human behavior, and understanding their origins requires focusing on social factors that extend beyond individual-level adaptations, such as those proposed in CBH. Specifically, we demonstrate that EV fosters intergroup cooperation, which may have contributed to the development of complex social structures.
There are several points of concern when using the term “group." First, groups within the complex social environment described by the SBH are nested in a series of fractal-structured networks [31,34,35]. As a result, when smaller groups ally and cooperate to form a larger group, whether this cooperation is viewed as intragroup cooperation within the larger group or intergroup cooperation among the smaller groups depends on the level of analysis. For simplicity, we assume a certain level of grouping and analyze their intergroup cooperation, though this could alternatively be seen as intragroup cooperation from the perspective of a higher-level group. Furthermore, while treating groups as units of adaptation is highly debated in evolutionary biology [36–38], our focus here is on cultural evolution rather than biological evolution. In this cultural context, we assume that a group has a degree of autonomy, treating individual relationships and nested group structures as a black box. Here, autonomy suggests that the basic behavioral patterns for a group regarding which groups it cooperates with or does not are influenced by intergroup interactions and evolve over time.
In the study of the evolution of cooperation, many studies have been conducted within the framework of evolutionary game theory [39–44], though most assume a stable environment. Only a limited number of studies consider environmental factors in the evolution of cooperation, and these, typically in biological or physical contexts, focus on aspects such as extrinsic population variability [45,46], variability in game structure [47,48], variability in the strength of selection [49], the impact of EV on learning strategies [50], and resource pressure [51]. However, these studies do not fully address our research objective of understanding how EVs influences the evolution of cooperation.
Our research thus investigates how the unpredictability of resource acquisition (EV) may drive the evolution of cooperation among geographically dispersed groups, with a focus on the origins of the social aspects that characterize modern human behavior.
What is evolutionary game theory? Evolutionary game theory is a framework that applies the principles of classical game theory—typically used to study strategic decision-making among rational agents—to the context of biological evolution. Instead of assuming conscious strategy, it models how behaviours or traits spread through populations over time via natural selection.So, in this scenario, intensified environmental variability created a range of conditions in which cooperative strategies emerged as the evolutionarily stable strategy. Cooperative behaviour became more likely in individuals with enhanced cognitive abilities and empathy—traits that favoured those who could anticipate the actions and needs of others. In small, fragmented populations, these traits could have led to rapid evolutionary change, enabling such groups to outcompete and ultimately replace populations lacking these advantages.
Core Concepts:
- Strategies as Traits:
In evolutionary game theory, a “strategy” refers to a behavioural trait or set of responses—like cooperation, defection, aggression, or altruism. These are usually genetically or culturally inherited.- Payoffs as Fitness:
The "payoff" of a strategy is interpreted in terms of biological fitness - the expected reproductive success of an individual using that strategy. Successful strategies increase in frequency over generations.- No Rational Agents:
Unlike classical game theory, players (organisms) are not assumed to make rational decisions. Instead, behaviours evolve through selection and replication.- Population Dynamics:
The theory studies how the frequency of different strategies changes over time in a population, often using mathematical models such as replicator dynamics.- Evolutionarily Stable Strategy (ESS):
A strategy is called an ESS if, once it is common in a population, it cannot be invaded by a rare mutant strategy because it yields a higher or equal fitness payoff.
Example Applications:
- Cooperation vs Defection (e.g., Prisoner’s Dilemma):
Models explain how cooperation can emerge even in situations where selfishness appears to be favoured.- Altruism and Kin Selection:
Game-theoretic models help describe how behaviours that reduce an individual’s fitness (like altruism) can evolve if they increase the fitness of related individuals (inclusive fitness).- Territoriality, Mating, and Signalling:
Strategies in animal behaviour—such as fighting for territory or choosing mates—are often modelled to determine which traits are stable over time.- Cultural Evolution:
Human social norms, language, and cooperation can be studied using evolutionary games, especially under variable environments and networked interactions.
In the Context of Human Evolution:
In the above study, evolutionary game theory is used in simulations to evaluate how environmental variability affects the success of cooperative vs selfish behaviours. The results support the idea that cooperation may be favoured in unpredictable environments—because pooling resources and information improves group survival—thereby shaping the evolution of human social and cognitive traits.
Example: The Hawk-Dove Game:
Scenario:
Two individuals compete over a shared resource (e.g. food, territory, or mates). They can adopt one of two strategies:
- Hawk – Always fights aggressively to win the resource.
- Dove – Displays or threatens but retreats if attacked.
The interaction has the following outcomes:
Hawk–Dove Game Payoff Matrix Player ↓ / Opponent → Hawk Dove Hawk 50% chance of winning (fight), but risk of injury (-C). Net payoff (V-C)/2 Wins the resource without a fight: payoff = V Dove Retreats, gets nothing: payoff = 0 Shares the resource: payoff = V/2
Where:
- V = Value of the resource
- C = Cost of fighting (C > V)
Payoff Matrix - Summary: Player ↓ / Opponent → Hawk Dove Hawk (V-C)/2 V Dove 0 V/2
This can be represented diagramatically:
Implications:
- If everyone plays Hawk, frequent injuries reduce fitness, so Doves may start to do better.
- If everyone plays Dove, Hawks exploit them easily.
- Mixed populations of Hawks and Doves often emerge, and their proportions reach a balance where neither strategy can outcompete the other. This is an evolutionarily stable strategy (ESS).
In Evolutionary Terms:
- Individuals don’t “choose” a strategy. Traits (e.g., aggressiveness vs passivity) are inherited.
- Over generations, natural selection favours the strategy with the higher average fitness payoff in the population.
- If the environment changes (e.g., resource scarcity or cost of injury increases), the balance of strategies may shift.
Human Relevance:
This kind of model can be extended to humans to explain behaviours like:
- Conflict resolution
- Sharing and cooperation
- Formation of alliances or dominance hierarchies
- Evolution of social norms (e.g. punishments for cheating)
In the context of the Middle Stone Age, cooperative strategies (like mutual aid or information sharing) could be seen as evolutionarily stable under certain environmental pressures—particularly when survival depends on social cohesion.
This interpretation aligns well with the known fossil record of human evolution in Africa, as well as with the evidence for major climatic and environmental changes during the Middle Stone Age.
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