A man walks down the street and sees an attractive female he’d like to meet. Through which social strategies can he signal to the female his viability as a possible mate? Do his clothes suggest he is affluent or has the ability to attain valuable resources? Does his skin, full head of dark hair, and muscle tone suggest that he would be a good long-term partner or a short-term romance? Furthermore, should the woman also be attracted, how will she reciprocate her viability as potential mate? How will her desired reproductive strategy influence her decision to choose if the man is an acceptable partner?
According to Darwinian evolution, all paths lead to procreation and the survival of the species. Evolutionary psychology is the development of cognitive processes that lead to behaviors and motivations promoting procreation and survival. Improving motivation in the workplace is a matter of tapping into ancestral motivators by examining possible procreational drives. This article proposes a framework that takes an evolutionary psychological approach to personality and motivation. Through this framework, personality traits and behavior can be examined under different environments, traced back to procreational strategies, and solutions developed to increase motivation in the workplace.
Historical Context of Development
Rooted in the theory of evolution by natural selection (Darwin, 1891), evolutionary psychology takes a similar approach in viewing human motivations and behaviors as adaptive solutions to ancestral problems of survival and reproduction (Buss, 1991, 1995). In this way, evolutionary psychology offers a theory of personality established from a scientifically accepted one known to guide all human life (Buss, 1991). Most personality theories attempt to explain observed phenomena in human behavior. Some focus on childhood traumas and others on environmental and social influences. Evolutionary psychology takes the position that all behavior is dependent upon psychological mechanisms that formed through evolutionary processes, implying that all theories of psychology are inherently evolutionary psychological theories (Buss, 1995). Rather than competing against other psychological theories, evolutionary psychology offers a comprehensive metatheory that bridges many other disciplines together.
Four main theorists are credited with building the foundations of evolutionary psychology: Trivers, Williams, Symons, and Buss (Buss, 1989). As will be discussed in more detail below, each contributor developed theories critically important to understanding the evolutionary processes of adaptive mechanisms. For instance, Trivers’ (1971) theory of reciprocal altruism is crucial in discerning the influences the social environment has upon evolution. In fact, it would be difficult to conceive of evolutionary psychology without having a strong knowledge base of parental investment and sexual selection (Trivers, 1972), jealousy and sexual variety (Symons, 1981), updated views of evolution (Williams, 1972), and the differences between females and males in mate preferences (Buss, 1989).
Being born from other scientific disciplines, evolutionary psychology follows in the same methods used by other psychologists, including experimental methods, questionnaires, data in the public domain, and observational methods (Buss, 1995). More modern evolutionary psychologists, such as Cosmides and Tooby (2013), have focused heavily upon scientific methods to better investigate human behavior “to approach the study of the mind like an engineer” (p. 204). Under this approach, researchers are examining more specific phenomena of human behavior, attempting to understand the evolutionary adaptations, and what the modern manifestations might be. For instance, Cosmides’ (1989) study on social exchange theorizes that humans have developed a detection procedure for cheaters, or those who acquire resources through others without reciprocating. Although a cheater-detection mechanism may have developed as an adaptational solution, it clearly has an impact on our behavior in the modern era, as do most, if not all, evolutionary psychological adaptations.
Evolutionary Psychology Characteristics and Key Concepts
If the tenets of evolutionary psychology are to be accepted, then it is assumed our ancestors resolved problems related to environmental fitness. Those traits that hold some evolutionary benefit to survival and reproduction remain present in our psychological foundations. Therefore, those who failed to solve their environmental problems are not our ancestors, as all current humans are products of evolutionary success (Buss, 1991). Darwinian evolution is not separate from evolutionary psychology, as the same factors responsible for physical evolution are likewise the causes of evolved psychological mechanisms (Buss, 1995). These mechanisms evolved to solve problems related to individual survival and reproduction that are experienced throughout various environments. As humans are intensely social animals, the largest contextual inputs of these evolved psychological mechanisms are social interactions (Buss, 1991).
When discussing evolution, many assume “selection,” as in natural selection, involves conscious decisions by the person, or a sort of guiding hand by environmental forces. According to evolutionary psychology, this “fitness striver” approach adds an element that humans are predisposed to maximizing their environmental fitness and pursuing activities or mates that increase an individual’s fitness (Tooby & Cosmides, 1990). Conversely, evolutionary psychologists propose a “mechanism activator” approach that has humans exercising different adaptation mechanisms based upon their environmental and social contexts. This is to say, what works in one environment may not work in another. Again, this does not imply a conscious decision, but instead a triggering of an adaptation mechanism used to solve an individual problem of survival or reproduction.
If adaptation mechanisms are responsible for survival and reproduction strategies, then what are some of these mechanisms and how do they influence motivation and behavior? Furthermore, if survival is viewed as a necessary component to reproduction, then an argument could be made that all aspects of evolutionary psychology pertain to reproduction in one way or another. To better understand this aspect, it may be beneficial to give a non-human example that more drastically demonstrates similar mechanisms in humans.
The peacock is famous for its beautiful and majestic tail feathers. However, with it comes numerous drawbacks. One is that it is metabolically costly to produce and maintain (Li, Kenrick, Griskevicius, & Neuberg, 2012). Another is that the peacock’s tail is quite noticeable to predators looking for a meal. So, what is the evolutionary benefit to such a grandiose display that seems to harm individual survival? According to costly signaling theory, a subcomponent of evolutionary psychology, individuals send signals to potential mates, friends, or group members about their qualities (Buss, 2009). Because costly signals are expensive and only those with sufficient resources can display them, they are usually honest signals (Zahavi, 2008). In the case of the peacock, it would be difficult to fake being healthy by displaying a full and colorful tail. A healthy tail on full display is a signal to peahens that he is healthy, has access to needed resources, and is capable of avoiding predators – all qualities a peahen might seek in a mate. Applying this theory to human reproductive motivations, prospective mates do not display (signal) the traits they do not possess in abundance. A small and frail male would unlikely show signs of strength and aggression because others would out display him. Therefore, when choosing a reproductive strategy, both males and females signal the qualities that demonstrate their best characteristics as mates.
This leads into long-term vs. short-term mating strategies. Different environments, social contexts, and individual personality differences (natural variations) play roles in reproductive strategies. Following costly signaling theory, some males might put forth huge shares of resources and effort into multiple mates, choosing short-term reproductive strategies, and refraining from allocating resources to parenting (Buss, 2009). Contrarily, other males choose long-term strategies that put forth effort into attracting a single mate and then expending a majority of resources on parenting. An illustration of this might entail two males looking for a mate, one who uses a vast majority of his effort to look as affluent as possible to attract a short-term mate, and the other who shows signs of generosity, altruism, and agreeableness used to attract a long-term mate. Both strategies have benefits and drawbacks, but they also reveal what type of parental investment might be put forth (Buss, 2009).
Closely related to reproductive strategy is parental and kin investment. In humans, males tend to be less involved or invested in their offspring than females (Trivers, 1972). An obvious example of this is that human females must invest approximately nine months of gestation at a minimum. Males, on the other hand, do not need to provide any investment once copulation has occurred (a short-term strategy). Of course, the problem a female might have in selecting a mate is being able to tell whether he will provide food, security, resources, etc. after mating or whether he will continue on to his next mate. Because females have more at risk in selecting a poor choice of mate based on reproductive strategy, Trivers (1972) theorized that the sex more heavily invested in the offspring are the ones more selective or choosy in a partner. This prediction has been confirmed through many studies investigating female preferences for males demonstrating higher capacity for resource acquisition, increased status, and protection (Buss, 1989). It should be noted that for a variety of reasons, some people do not have offspring. Evolutionary psychology holds that the same investments made by parents are made by those investing in kin relationships (Buss, 1991, 1995; Cortina & Liotti, 2014). As evidence, Cosmides and Tooby (2013) discuss an evolved kin-detection system to prevent inbreeding and inspire kin-directed altruism.
Males, on the other hand, use signaling cues from females almost exclusively from appearance to determine the quality of a mate. Reproductive value is the expected future reproduction of a female (Buss, 1989). Therefore, the younger a female is, the more reproductive value she has. Fertility is the probability of current reproduction (Buss, 1989). This means that optimum fertility for most females is in their early 20s and decreases with age. Although there are cultural variations in both of these qualities, they are highly dependent upon age (Williams, 1977). This implies that age offers powerful cues to the reproductive value and fertility of females. Other cues of fertility include skin quality, muscle tone, lustrous hair, and a high-energy walk (Williams, 1977). While females are more selective in a mate, males are more attracted to youth and physical appearance due to their links to fertility and reproductive value (Buss, 1989).
Making evolutionary psychology even more comprehensive, all of the above individual features, and many more, take place under societal and environmental contexts. After all, our hunter-gatherer ancestors evolved in small cooperative groups that had to work together to solve common problems related to resource acquisition, defense, kin investment, and more. Stated more succinctly, cooperation leads to victory over less cooperative cultures, allowing the victors to remain alive for further reproduction (Cortina & Liotti, 2014). Taking these societal aspects a step further, emotions are thought to be socially derived signals used for solving adaptational problems. Buss (1991) discusses multiple studies investigating emotions, such as anger, anxiety, and panic, that are used to alert others interfering with reproductive strategies or to alert others of threats to status and group membership. Male jealousy is a prime example of a universally detected emotion among all cultures that signals to others a perceived threat to a valued relationship (Buss, 1995).
There exists much evidence for evolution through cooperative societies and reciprocal altruism, but cheater detection mechanisms offer some of the greatest evidence. Free riders, also known as cheaters, have motivational systems that avoid contributing to common goals, while benefitting from the combined efforts of others (Cosmides & Tooby, 2013). Humans have evolved sensitive systems used to detect those who violate social contracts of cooperation (Buss, 1995). This has been proposed as a contributory reason to our impeccable ability to recognize faces; there are great benefits to remembering who reciprocates altruism and collaboration, and who benefits from the contributions of others (Buss, 1995).
The brief background of evolutionary psychology presented here is highly lacking in the myriad of other research performed, phenomena discovered and analyzed, contributing theorists, interrelatedness of concepts, and much more. However, the key points of evolutionary psychology are discussed and exemplified to demonstrate their motivational impacts on humans in all life aspects. Individual variations in personality contribute to the reproductive strategy selected according to the person’s current environment. A change in social contexts and environment can influence behavior and lead to a change in different strategies, including reproductive strategy (Buss, 2009). Evolutionary psychology also provides researchers with a culturally-sensitive tool to further analyze human behavior and motivation, as evolutionary psychology specifically considers cultural and societal influences when investigating environmental factors contributing to human psychological development. Therefore, evolutionary psychology integrates well with all other psychological disciplines, offers a metatheoretical framework to analyze human psychological processes, and provides a comprehensive theory to bridge all aspects of human behavior and motivation.
Evaluating Evolutionary Psychology
To examine the comprehensiveness of evolutionary psychology theory, a different approach must be taken from that of evaluating other psychological theories of personality. Many competing theories of human personality development and behavior focus on biological, environmental, societal, and cultural influences, just to name a few. Evolutionary psychology theory, on the other hand, does not begin by asking how does personality develop and what are the contributing elements, but instead builds off the widely accepted and well-tested theory of evolution by natural selection. Buss (1995) discusses general evolutionary theory as one so well established, even though labeled a “theory,” it is assumed to be valid in its general principles. After all, if not valid, then the foundations of the field of biology fall apart. Therefore, working backwards using general evolutionary theory, we assume humans evolved to become our present-day selves, both physically and mentally. In this way, evolutionary psychology offers a personality theory rooted in processes known to guide all life (Buss, 1991); something every other theory of human behavior lacks.
If all behavior stems from evolving to solve problems regarding adaptations to the environment, then that suggests all personality theories are evolutionary psychological theories (Buss, 1995), whether competing theorists agree or not. Under this approach, evolutionary psychology is the only theory not attempting to ascertain how personality and behavior are created. Although the specific mechanisms for development may remain unknown, if we are to believe in general evolution theory, then we should accept that evolution is also responsible for personality and ensuing behavior. It seems this aspect alone makes evolutionary psychology a more valid theory than most others, if not all, due to its strong scientific foundation.
At the core of evolutionary psychology is how humans have evolved to overcome adaptive problems of individual survival and reproduction (Buss, 1991). Furthermore, anyone currently living had ancestors who successfully navigated these issues, so we should assume that their present physiological and psychological characteristics have utility in this regard. Buss (1991) details the two main variables influencing evolution as the physical environment and social environment. However, because overcoming reproductive challenges is an inherently social endeavor, social interactions are the most important contextual influence of personality. Buss (1991) lists eight socially-related reproductive problems: 1) successful intrasexual competition, 2) mate selection, 3) successful conception, 4) mate retention, 5) reciprocal dyadic alliance formation, 6) coalition-building and maintenance, 7) parental care and socialization, and 8) extra-parental kin investment. Successfully overcoming these eight classes of reproductive obstacles is where psychological processes evolved. In this view, every human behavior can be traced back to an evolutionary psychological solution.
When considering evolutionary social problems, predictions might consist of mechanisms to detect cheaters – those who do not reciprocate after receiving a benefit from another person (Cosmides & Tooby, 1989) – or mechanisms for assessing status, position, and reputation (Buss, 1986). Not only has Cosmides (1989) presented evidence to support a cheater-detection heuristic, but a multitude of research has been performed empirically investigating numerous adaptations to solve ancestral environmental problems. A few of these include: fears of harmful elements, such as spiders, snakes, and darkness (Marks, 1987); male sexual jealousy in all cultures designed to increase paternity certainty (Daly & Wilson, 2014); and women of high reproductive value are more guarded and restrained than women of lower reproductive value (Dickemann, 1981).
If behaviors arise to solve reproductive problems, then adaptive solutions should include mechanisms and strategies for increasing reproductive opportunities, which is at the core of evolutionary psychology. This is precisely what is found across cultures. Wiggins (1991) discusses the two motivational components responsible for interpersonal behavior as power and intimacy. Similarly, Hogan (1983) states these top motivators as status and popularity. Employing these social hierarchical strategies are ways to increase the desirability, attraction, and reproductive efficacy of prospective mates, especially males. Each feature mentioned, as well as numerous others too lengthy to discuss, revolve around efforts to directly or indirectly increase reproductive chances (Buss, 1991).
Many sociobiologists believe in the same evolutionary processes that evolutionary psychologists use to explain human motivations and behavior, but differ in their views of how humans work to evolve (Buss, 1995). For instance, Alexander (1979) suggests that humans strive to maximize their environmental “fitness.” This position implies that humans have a genetic goal to reproduce as much as possible to pass along genes to the next generation, thus attempting to maximize “fitness.” However, Buss (1991) labels this as the sociobiological fallacy because it adds an element of assumption about the purpose of the evolved mechanisms responsible for behavior. Just because humans evolved to have a taste preferences for fatty foods (Buss, 1995), does not mean it was an end goal of human evolution, but instead fulfilled an evolutionary need that benefited survival and reproduction. The difference between the two theories is minor, but exemplifies the foundations of Darwinian evolution. Sociobiologists theorize that humans continuously strive to fit in their environments, whereas evolutionary psychologists believe evolution occurs through reproduction, and those who successfully reproduce are able to pass along their genes. Perhaps a simpler way of considering the differences between the two is that the sociobiologist’s view involves an active process of evolution, to constantly pursue ways to better fit in their environments. Contrarily, evolutionary psychologists take a passive view of evolution, that humans evolve through reproduction, and those who successfully reproduce are better adapted to their environments and able to pass along those genes that make them better adapted.
Another countertheory is the biosocial view, that biological differences between males and females interact with social and cultural influences (Wood & Eagly, 2002). The biosocial approach theorizes that there are no universal differences between the sexes, but that each quality is treated differently within various cultures and may have disparate outcomes. For instance, Eagly and Wood (1999) found considerable differences in desired mate values, such as earning capacity and cooking, between societies with men and women having similar roles and societies with less gender equality. Additionally, researchers Desteno, Bartlett, Braverman, and Salovey (2002) reanalyzed a study performed by Buss, Larsen, Westen, and Semmelroth (1992) that initially found jealousy to be a universal trait in males across all cultures. Desteno et al (2002) used a Likert-type scale to assess jealousy in males and females, rather than the forced-choice options provided by Buss et al. (1992), and found very contradictory results. The forced-choice model asking respondents to answer which would cause more distress, their mate having a sexual relationship with another person or forming a deep emotional bond with another person, revealed very different results from asking each respondent how much each factor would cause distress. Using the Likert-type scale on each choice, independently, nearly erased jealousy differences between the sexes.
At first glance, this counterevidence seems to provide large hurdles for evolutionary psychology to overcome. However, the theory of evolution itself requires variability among traits to work (Cortina & Liotti, 2014). This means that differences in mate values discovered by Eagly and Wood (1999), would be expected by evolutionary psychologists, when considering the social and cultural contexts of that society. After all, evolutionary psychology considers the biological mechanisms responsible for individual survival and reproduction (Buss, 1991). This suggests that the desired qualities in a mate are dependent upon the social contexts of the environment. For instance, Eagly and Wood (1999) give evidence of vast differences in earning capacity as an example that traits are not universal. This doesn’t seem to be a position that evolutionary psychologists would take as they generally accept that trait variations manifest differently under different social contexts. In an egalitarian society with sufficient resources, why would a male need to demonstrate his ability for earning capacity? This features would not seem to make him stand out from his reproductive competition, so it would be unlikely for him to choose this as his reproductive strategy. These results seem to reinforce evolutionary psychology more than disprove it.
Continuing on, male sexual jealousy has been found to be a universal trait across cultures (Buss et al., 1992). In fact, it is considered the leading cause of spousal homicide, independent of culture (Daly & Wilson, 2014). Although Desteno et al. (2002) make a good case for using a Likert scale instead of a forced-choice response in the methodology, it does not reveal which variable is worse to the respondent. If someone were to ask how distressful the death of a parent would be and then ask how distressful the death of a child would be, it would be conceivable that most respondents answer both are as bad as the scale allows. However, this does not answer which most people consider worse, which could be a very different answer. Therefore, it is understandable why people responded that spousal infidelity is as jealousy-inducing as that of a spouse forming an emotional bond with another. It does not mean that they are equal, just that when asked independently of each other, they are both seen as something incredibly negative. Yet, ranked against each other, one aspect can be viewed as more negative than the other, even with both topping out the Likert scale.
Modern Utility of Evolutionary Psychology
Evolutionary psychology, being one of the more recent theories of behavior and personality, is relevant in numerous scientific fields today, and seems to be gaining acceptance. Two of the most prominent names in evolutionary psychology, Cosmides and Tooby (2013) have concluded that evolutionary psychology can be utilized by any of the psychological sciences. Current research repeatedly demonstrates the wide range of topics investigated by evolutionary psychologists and its real-world practicality. After all, if the theory offers no feasible solutions to life problems, then it has little value. These current trends help establish the modern significance of evolutionary psychology, and why all aspects remain relevant.
Many people, when thinking of psychology, often consider the clinical side. Cortina and Liotti (2014) discuss an evolutionary perspective of posttraumatic stress disorder (PTSD) and how symptoms are extended exhibitions of fight, flight, or freeze responses. Additionally, the authors theorize that these symptoms prevent the afflicted from seeking help through their attachment systems in the aftermath of the trauma. This opens the door for therapeutic interventions by attempting to activate systems responsible for cooperation and social engagement (Tomasello, Carpenter, Call, Behne, & Moll, 2005). In other words, clinical therapy offered to those experiencing PTSD works to combat one adaptive mechanism, fight, flight, or freeze responses, by attempting to activate another adaptive mechanism, social exchange and engagement, to repair feelings of vulnerability, hopelessness, powerlessness, etc. The goal is to rebuild trust, communication, and attachment to others, even if only the therapists, to improve social engagement. Over time, isolation and mistrust begin to fade as the perpetual activation of the defense system responsible for the fight, flight, or freeze behaviors dissipates (Cortina & Liotti, 2014).
Because our social interactions are primarily responsible for our evolved adaptation mechanisms (Buss, 1991), it would seem that evolutionary psychology would be beneficial to social and political psychologies. A sociopolitical study performed by Petersen, Sznycer, Cosmides, and Tooby (2012) investigated the social emotions and public opinions of welfare recipients. By examining the social exchange contexts of evolutionary psychology and applying them to modern-day issues, researchers can better assess the causes motivating public opinions, and work to find solutions to mitigate their impacts. For instance, our evolved cheater detection system and emotional systems responsible for anger and compassion provide sound reasoning for the mixed public opinion of welfare recipients based on whether they seem lazy or victims of circumstance (Petersen et al., 2012).
Understanding behavior through cognitive processes has led to some fascinating discoveries, from how humans think and learn to how we process visual stimuli. Evolutionary psychology is in a unique position to assist the cognitive sciences by analyzing the evolutionary adaptations influencing cognitive processes. For instance, Cosmides and Tooby (2013) discuss how predictions made by evolutionary psychologists, based upon foraging and hunting differences between males and females, have been detected regarding spatial cognition and navigation. Besides spatial cognition, evolutionary psychology has added to the knowledge base of the cognitive sciences in cues responsible for visual attention, categorization of concepts, reasoning, learning, and emotions influencing motivation (Cosmides & Tooby, 2013). Each contribution began with an evolutionary approach, such as the mental tools needed for foraging vs. hunting, and then investigated the cognitive concept, spatial ability differences between males and females, under those considerations. There have been numerous studies performed using the evolutionary approach and data has continuously upheld many evolutionary psychological, as well as cognitive, theories.
Although much of the research performed in the field of evolutionary psychology has focused upon motivational factors present in social situations, little research could be found on how these motivations manifest and interact in the workplace. If this theory revolves around ancestral motivations present in all social situations, then surely it has some applicability in an organizational setting as well. This provides another way in which evolutionary psychology is highly relevant in a modern context. As organizations worldwide look to increase productivity, evolutionary psychologists would be wise to explore the prosocial motivations responsible for forming our ancestral past and how they can positively contribute to higher intrinsic motivations.
An important focus of organizational psychology concerns the factors contributing to employee motivation. This includes recognizing both positive and negative motivators, and working to improve upon employee performance through increasing positive influences and removing negative ones. Over the years, organizational psychologists have benefitted from various needs theories, such as Maslow’s (1954) hierarchy of needs theory that focuses on fulfilling basic external needs before higher level intrinsic needs, and Herzberg’s motivation-hygiene theory that discusses hygiene factors responsible for preventing decreased performance and motivation (growth) factors responsible for increasing performance (Herzberg, Mausner, & Snyderman, 1959), just to name two popularly used workplace theories. As organizations constantly strive to increase worker motivation and productivity, organizational psychologists continue to seek new methods and knowledge in the pursuit of worker empowerment and self-efficacy. Can evolutionary psychology provide any value to the workplace? If so, how can the motivators responsible for individual safety and reproduction be applied in an organizational setting?
Evolutionary Psychology and Motivation
If one was looking to discover the most influential motivational tool in existence, that person might start by examining the motivator responsible for current existence, meaning evolution. It seems that once life begins, it has a strong motivation to perpetuate its species. Therefore, if these same drives could be translated into the workplace, organizations could realize great improvements in employee morale and productivity stemming from higher motivation.
As Buss (1991) discusses, there are two types of evolutionary adaptive problems shared by all living organisms, those dealing with individual survival and those pertaining to reproduction. Furthermore, since reproduction is inherently social, resolving these problems of social adaptations are the very mechanisms of interest to evolutionary psychologists (Buss, 1991). If the goal of individual survival is to reproduce or kin investment, then one might claim all evolutionary roads lead to procreation.
Many evolutionary psychologists view personality traits as psychological mechanisms that have evolved to help overcome problems of survival and reproduction (Buss, 1991). Therefore, behavior is the product of an individual’s variations in personality traits interacting with social contexts and environmental factors. This would seem to indicate that the same motivations responsible for survival and reproduction are present in all social situations, and ensuing behavior is dependent on which adaption strategies are implemented based on individual personality traits. This knowledge could be very useful in an organizational setting where tapping into new motivational sources, or recognizing motivational hindrances, can provide immense benefits.
The five-factor model of personality (the Big 5) is widely accepted by most personality psychologists from the various theoretical disciplines. This is no different with evolutionary psychologists, who also find extraversion, agreeableness, conscientiousness, neuroticism, and openness to experience to be present in all human personalities (Buss, 1991). Buss (1991) discusses three possible reasons for these five dimensions being ubiquitous: 1) they represent individual differences in strategies to solve environmental problems; 2) they are merely “noise,” or random variations in the system; and 3) the five trait dimensions summarize the most common social features humans have used to adapt to their social environments. With this third possibility in mind, coupled with the fact that most workplaces are inherently social environments just as reproductive strategies are inherently social, and it becomes apparent that the same social strategies used to solve reproductive challenges may overlap with those used to solve workplace challenges.
Six Degrees of Procreation – a Motivational Framework
Already discussed is how all evolutionary roads lead to reproduction. This includes survival mechanisms if they are viewed as ways to stay alive so that reproduction is possible, or to remain alive for kin investment. Additionally, there is a somewhat popular theory that all people are separated from each other by six degrees – the six degrees of separation – meaning that it only takes six relationships to link two people together, no matter how distant (Sacks, 2015). In fact, this theory has become so prevalent that it spawned into a parody that Kevin Bacon is the acting center of the universe and all other actors are connected to him by six degrees (relationships) or less (Togher, 2012). It has been dubbed the Six Degrees of Kevin Bacon. If Kevin Bacon is the acting center of the universe, then procreation is the motivational center of evolution. Therefore, a new motivational framework is proposed for the workplace in which procreational strategies are compared to organizational environments to detect common factors responsible for human motivation.
Calling this framework the Six Degrees of Procreation is only to highlight that all personality traits can be traced back to possible social motivations involved in psychological reproductive mechanisms. For instance, someone scoring high on the Big 5 trait agreeableness might demonstrate personality characteristics such as trust, cooperation, and being courteous (Barrick & Mount, 1991). What organizational factors might be interfering with characteristics of agreeableness? Or, what organizational or departmental changes can be made to act as a catalyst for someone with a high amount of agreeableness? Following are the six steps of the framework, the Six Degrees of Procreation:
Identify the individual or group motivational problem
Identify similar ancestral problems and adaptations (Buss, 1991)
Correlate the organizational personality factors with those of our hunter-gatherer ancestors (Buss, 1991)
Examine variations in personality traits that may correspond to reproductive strategies (Buss, 1991)
Implement a strategy for influencing the individual or group’s trait adaptations
Monitor and reassess the effectiveness of the highlighted trait and chosen strategy
All personality traits, according to evolutionary psychology, revolve around two factors: 1) how does it help an individual reproduce, and 2) how does it help increase social influence to gain greater resources used for reproduction. Hogan (1983) notes that reproductive resources are closely linked with hierarchical position in groups. Trivers (1971) discusses how groups have higher cooperation and reciprocal alliance formation than other mammals, demonstrating that humans have evolved to work in cooperative groups. These features give evidence that not only have humans evolved due to social influences, but that group motivations are beneficial to goal attainment for the group as well as the individual. In a cooperative society, in which humans evolved (Cortina & Liotti, 2014; Trivers, 1971), more resources for the group translates into more resources for everybody within the group, even if those at the top of the hierarchy possess more.
The vast majority of organizations could be described as groups of people working towards common goals. This definition is quite similar to our ancestral societies that formed our personality traits used to overcome problems of adaptation. Under this view, many of the motivations in life could be applied to organizations. For example, status striving, an evolutionary motivation related to reproduction (Buss, 1991), could be a parallel to employee goals of advancement and recognition (Emmons, 1997). The Six Degrees of Procreation follows numerous other motivational theories, besides evolutionary psychology, in linking life motivations to those in the workplace.
In her book, A Manager’s Guide to Motivating Employees, Anne Bruce (2011) tells an interesting story about a car wash that experiences a loss of business after new promotional flyers were printed on a lower quality paper than previously used. Her story goes on to describe how the lower quality flyers affected the employees’ view of the company, which decreased their morale, thus impacting performance. Then, customers began noticing the quality and service differences, so they took their business elsewhere. In the business world, factors as seemingly tiny as paper quality can lead to unforeseen consequences. How might the Six Degrees of Procreation help improve employee morale and motivation? Ideally, it would be nice to retrace the steps in the example, and going back to discover the paper quality as the initial problem. Although this is quite possible, many managers will find themselves in situations that have no clear way to go back to the root(s) of the problem. This is another benefit of the Six Degrees of Procreation – it is not necessary to look to the past (although it could be very beneficial), because evolution, and motivation, are about progressing into the future.
Following is a breakdown of the six steps in practice, using the car wash example above:
1. Identify the individual or group motivational problem. All employees at the car wash have shown signs of decreased morale, motivation, and productivity. This situation requires a group-wide intervention. The motivational problem at hand isn’t the flyers, per se, but a lack of pride in performance and group goals. Each employee is acting as an individual with self-interests that may be in opposition to the business’ goals.
2. Identify similar ancestral problems and adaptations. Numerous evolutionary theories discuss the importance of group living, cooperative societies, and common goals as key factors in our ancestral past (Cosmides, 1989; Tooby & Cosmides, 1989; Trivers, 1971). Cortina and Liotti (2014) mention how more cooperative cultures from our evolutionary past were more likely to prevail over less cooperative ones.
3. Correlate the organizational personality factors with those of our hunter-gatherer ancestors. This example focuses more on the whole team than any individual employees. However, the car wash, viewed as a small society of employees, previously displayed signs of high cooperation, unity, a shared vision, and high quality work. These are the same characteristics of successful hunter-gatherer societies. Now that the opposite characteristics are being demonstrated, how did our ancestors overcome (adapt to) these problems?
4. Examine variations in personality traits that may correspond to reproductive strategies. There are possibly more than the eight reproductive strategies (successful intrasexual competition, mate selection, successful conception, mate retention, reciprocal dyadic alliance formation, coalition-building and maintenance, parental care and socialization, and extra-parental kin investment) offered by Buss (1991), but these should be sufficient in most cases. The reproductive strategies offered by coalition-building and maintenance seem to be most applicable here. Because this example involves the whole car wash team, individual variations in personality traits are not as pertinent. However, should the intervention be ineffective on only a select few employees, then it may be useful to return to this step to take a closer examination at those employee personality traits who are not benefitting from the intervention.
5. Implement a strategy for influencing the individual or group’s trait adaptations. This step is dependent upon the managers, supervisors, executives, and more depending on the organizational culture, resources, goals, etc. The manager of the car wash might look at team-building exercises, such as friendly competitions, team outings, new team goals, or any other methods that have shown group benefits to motivation. For instance, Parker, Jimmieson, and Amiot (2010) found that workers who perceived higher autonomy in their jobs, showed greater engagement and dedication to their jobs. Perhaps an intervention here might include giving workers a change to correct their own morale issues. This might involve allowing them to assist in the creation of the car wash’s promotional material.
6. Monitor and reassess the effectiveness of the highlighted trait and chosen strategy. As with all interventions, they should be closely monitored for effectiveness. If the methods are not working as expected, new information presents differing circumstances, or the intervention is exacerbating the problem, then a monitoring program should reveal these problems. Then, a reassessment may provide additional evidence for a more effective intervention. Conversely, a monitoring program will also reveal how successful the intervention is.
Using the Six Degrees of Procreation framework on a group may be different than that of individuals. For instance, individuals have their own personality traits that will surely be different from other group members. Evolutionary psychologists suggest that these personality variations are the very mechanisms used for selecting a reproduction strategy based on social contexts (Buss, 2009). This means that personality assessment measures, such as the MMPI-2, are essential for determining individual personality traits. Someone scoring high in neuroticism might require a very different intervention from someone scoring high in openness to experience. Another benefit to using a personality assessment like the MMPI-2 is that they have been extensively tested for validity and reliability (Roper, Ben-Porath, & Butcher, 1995). Psychometrically sound tests will provide higher quality information for use on any intervention strategy.
Of course, interviews and other assessment methods should be used as needed to help build a more complete personality profile. But what if the intervention strategy does not result in the desired behaviors? During the reassessing process (step 6), it might be determined that other personality traits might be more impactful in the specific situation. Since the personality assessments have already been performed and other pertinent information gathered, the six steps can be revisited in view of the different dominant personality trait chosen. For instance, if high neuroticism was being investigated for ancestral reproductive strategies and it failed to make the desired behavioral change, then the individual’s profile might also show high openness to experience. Return to step 2, in this case, of the Six Degrees of Procreation and identify different adaptive problems and solutions related to reproductive styles with high openness to experience. It is important to remember that personality traits, according to evolutionary psychology, can shift as a function of life history (Buss, 1991). This could mean that a long-term employee has different motivations today than when she first started. In this event, an updated profile should be determined before proceeding with the framework.
Additional Research Beneficial to the Framework
There are a few immediately recognizable ways to make the Six Degrees of Procreation framework more effective and easier for organizational psychologists to use. Many jobs descriptions entail what qualifications, including personality type, an ideal candidate should possess. For example, sales positions often ask for outgoing, sociable, and assertive applicants. Additional research might include a database of common personality traits that have been found, and then correlated, to be often represented in more conventional and commonplace occupations. Although this should not be used in hiring decision, as it could create unfair biases in hiring practices, it would provide a quick reference to check for mismatched personalities and jobs. Although an introvert might excel in a sales position, should performance or motivational issues arise, a quick reference guide might reveal that sales positions are highly social and introverts may be better suited for other jobs.
In a similar vein, future research might investigate any possible correlations between reproductive strategy and job strategy. Do those seeking a short-term reproductive strategy also frequently seek out new jobs? Do long-term strategies show any difference in worker motivations? Different reproductive strategies have varying pros and cons. Do some strategies have more positive features than negative when translating motivations from sexual strategies to workplace strategies? Here again, research correlating strategy types, if significant correlations exist, would be a beneficial tool for organizational psychologists trying to link ancestral motivations used to overcome problems of adaptation with those in the modern working world.
However, one of the biggest conceivable benefits to the proposed framework would be a database containing evolutionary adaptations that have already been researched. For instance, loss aversion has been repeatedly demonstrated across cultures. Loss aversion is a bias that causes people to weigh losses more strongly than equivalent gains (Kahneman & Tversky, 1979). An example of this is that people are more psychologically affected by a loss of $100 than they are by gaining $100 (Kahneman & Tversky, 1979). Vohs and Luce (2010) discuss that loss aversion is such a researched phenomenon that it is safe to say losses impact people twice as much as gains. This seems to suggest that our ancestors formed an evolutionary adaptation to hold onto their resources already procured (Li et al., 2012). After all, losing current resources could directly impact their survival.
In the car wash example used above, having a database containing researched evolutionary psychological phenomenon would have been tremendously helpful. First, this information could have been used in a proactive manner before the decision to change paper quality was even made. Organizational changes need to be examined for what could be perceived as losses that might impact motivation. The change in paper quality may have been perceived by the workers as a sign that the company’s performance was slacking – a perceived loss. Under this light, the decision might not have been made at all, or perhaps made with a different implementation that included better communication or worker input. Although this proactive approach was not taken, trying to find strategies that remedy the decrease in motivation would be made easier by a database containing these types of findings.
Effectiveness on Diverse Populations
Another major benefit to evolutionary psychology is its universal applicability regarding different cultures. Evolutionary psychology holds society, culture, and the local environment as the strongest factors influencing reproductive strategies (Buss, 1991). Therefore, to fully assess motivations and behavior, it is vitally important to know the social contexts that helped mold the individual’s personality. In fact, cultural aspects are so important, they account for not only social influences on behavior, but possibly biological ones as well. Since a good deal of material presented thus far has discussed the social relevance of evolutionary psychology, which is germane to all populations, this section will focus on biological differences discovered in different populations.
A fascinating study by Chen, Burton, Greenberger, and Dmitrieva (1999) found that the 7R allele of the DRD4 gene appears at vastly higher rates in America than Asia. This allele has been associated with extraversion and novelty seeking (Ebstein, 2006), and is thought to be beneficial to people migrating to new environments (Chen et al., 1999). This study demonstrates that there are biological regional differences in addition to cultural ones. It is quite conceivable that a gene likely to assist a nomadic lifestyle might also be responsible for influencing behavior.
A cross-cultural study performed by Low (1989) found that boys across cultures are raised to show greater aggression and self-reliance than girls, while girls across cultures are raised to show more obedience, restraint, and responsibility than boys. There may be a biological necessity or evolutionary reason for teaching boys and girls these qualities, respectively, or perhaps it is a purely universal trait irrespective of culture. However, this example highlights that culture cannot be separated and analyzed independently from psychological mechanisms (Tooby & Cosmides, 1989). In short, evolutionary psychology is a discipline dedicated to acknowledging the cultural aspects influencing personality, behavior, and motivation in any population.
Having universal cultural applicability, evolutionary psychology is in a prime position to assist with diverse populations. Therefore, the Six Degrees of Procreation offers a culturally relevant and sensitive tool that recommends the organizational psychologist take a close examination of the social contexts involved in the organization, the organization’s culture, the department’s culture, and the individual’s culture when working to find an intervention strategy. In other words, without accounting for cultural differences that might be influential in any motivational strategy, reproductive or organizational, the framework would be rendered ineffective. Therefore, the whole framework is contingent upon evolutionary differences related to social contexts.
Modern Applicability and Relevance
Buss (1995) discusses a fellow evolutionary psychologist who once concluded that the word “evolutionary” would eventually be omitted from evolutionary psychology because the entire field of psychology is inherently evolutionary. This same sentiment is expressed in Symons (1987) often repeated phrase, “we’re all Darwinians.” In the evolutionary psychologist’s view, all other psychological disciplines are contained within evolutionary psychology. Personality development, behavior, motivation, psychopathology, clinical interventions, and much more are all explored and theorized in this one metatheory of human psychological development. At the crux of evolutionary psychology is survival and reproduction. All motivations stem from there. Therefore, the short answer to why evolutionary psychology is applicable in solving organizational issues regarding motivation is because it expresses the foundations of all human motivations. What better way to approach motivation than through its evolutionary roots?
Rather than continuing to discuss the influence of social groups on evolutionary psychology and motivation, in addition to evolutionary psychology being an all-encompassing theory of human psychology, perhaps an example will help illustrate the modern utility of the theory. The earlier referenced study performed by Petersen et al. (2012) examined numerous factors regarding welfare recipients and corresponding public attitudes. One aspect the study investigated was the difference in public opinion between welfare recipients viewed as lazy and those viewed as misfortunate. Working from the evolutionary systems responsible for social exchange – intergroup cooperation, reciprocal altruism, cheater and free rider detection, emotional responses, etc. – the authors’ predictions aligned with expected results according to evolutionary psychology. Although the findings provide evidence for the theory’s efficacy, it is important to note other aspects revealed in this study, which may provide an even stronger case for its utility in the real-world. Here, the tenets of evolutionary psychology are used to assist in answering questions related to political science, how perceptions are influenced, emotional foundations of anger and compassion with respect to work, intragroup dynamics, and intergroup cooperation.
These findings can be added to the bulk of interdisciplinary contributions made by evolutionary psychology. Returning to the topic of motivation in the workplace, the above research provides evidence for other psychological theories of employee motivation, such as Adams’ (1965) equity theory, which states that workers will compare their inputs and outputs to that of other workers to detect fairness. Furthermore, these findings, coupled with that of other research, give credence to the demotivational aspects of free riders who are perceived to do less than their share (Delton, Cosmides, Guemo, Robertson, & Tooby, 2012). Additionally, much research on organizational psychology revolves around increasing intrinsic motivations in the workplace by creating more cohesive groups (teams) working towards common goals (Carr & Walton, 2014). This description sounds like the modern equivalent of our evolutionary motivations, and demonstrates that evolutionary psychology has practical real-world value in all psychological and scientific disciplines related to humans.
Counterevidence and Contradictory Theories
Much of the counterevidence and opposing theories has already been presented and discussed above to reinforce the validity and comprehensiveness of evolutionary theory. Despite biosocial and sociobiological theories having somewhat nuanced differences from those of evolutionary psychology, they are hardly contradictory. During the literature review, no directly opposing theories could be found. This seems to speak to the conclusion of Cosmides and Tooby (2013), that evolutionary psychology integrates well with all psychological disciplines.
However, should new evidence be presented that gender dysphoria has a biological nature, evolutionary psychologists may have to reanalyze how this development fits into the theory. A development as such would not necessarily harm the theory, but new understandings of evolution would seem to be warranted. Another issue presenting challenges to evolutionary psychology theory is that some phenomena remain unknown until they reveal themselves. Some behaviors are partially due to still undiscovered motivations. Had loss aversion not been noticed and studied, might theorists attribute the difference in emotion to something else? Perhaps a theory detailing how humans are naturally miserly or hoarders would have been erroneously presented. Something like this would by no means falsify evolutionary psychology, but it presents a challenge in the field, that many adaptive behaviors may still be unknown or misinterpreted. However, this seems to speak more to the youth of the field, rather than problems within it.
Recent evidence has suggested there may be a biological basis for gender (apart from biological sex), rather than a strictly social one, as previously thought (Saraswat, Weinand, & Safer, 2015). This evokes interesting questions regarding evolutionary psychology, with the first one being, what is the evolutionary function or adaptation mechanism responsible for gender differences, if different from sex differences? Until this first question is better known it may be difficult to answer the harder questions, such as how do gender differences influence behavior? Do gender differences impact reproductive strategies in the same way sex differences do? Do gender differences even employ different reproductive strategies? This relatively new vision of human sexuality brings with it a host of questions, many of which have not even been considered yet. This is an important scientific development that warrants much attention not only with evolutionary psychology, but all scientific disciplines dealing with humans.
Cortina and Liotti (2014) theorize that our current civilizations are antithetical to the small hunter-gatherer societies in which we evolved. The authors offer large hierarchical institutions as ways to regulate and control the increased populations, such as religious, judicial, policing, and military institutions. Additional research would be beneficial in understanding the consequences of diverting from our ancestral roots. Furthermore, are there ways that organizations can benefit from creating environments that exploit our small society upbringing? Possessing a better understanding of these motivations, both positive and negative, would add useful information to numerous scientific disciplines, as well as the majority of human motivational theories. Therefore, to strengthen the motivational framework offered by the Six Degrees of Procreation, evolutionary psychologists would need to correlate more ancestral psychological mechanisms responsible for reproduction strategies and survival with that of workplace motivations, which may also provide organizational psychologists with a potentially powerful new set of tools.
Evolutionary psychology has gained steam in recent decades and has provided numerous theories explaining human behavior, motivations, and predicted outcomes. However, as the field continues to grow, the utility of evolutionary psychology has had little practicality in employee motivations. This comprehensive theory, which has demonstrated its real-world efficacy, would add value to understanding workplace interactions, behaviors, and motivations. Examining factors responsible for motivation, both positive and negative, through a different theoretical lens can lead to new approaches, possibly increasing employee motivation. As the field continues to grow, it has the potential to add immeasurable value to numerous psychological disciplines, including motivational and behavioral influences of interest to organizational psychologists.
Adams, J. S. (1965). Inequity in social exchange. Advances in Experimental Social Psychology, 267-299. doi:10.1016/s0065-2601(08)60108-2
Alexander, R. D. (1979). Darwinism and human affairs. London: Pitman.
Barrick, M. R., & Mount, M. K. (1991). The Big Five personality dimensions and job performance: A meta-analysis. Personnel Psychology, 44(1), 1-26. doi:10.1111/j.1744-6570.1991.tb00688.x
Bruce, A. (2011). Manager's guide to motivating employees (2nd ed.). New York: McGraw-Hill.
Buss, D. M. (1986). Can Social Science Be Anchored in Evolutionary Biology? Four Problems and a Strategic Solution. Revue européenne des sciences sociales, (73). 41.
Buss, D. M. (1989). Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures. Behavioral and Brain Sciences, 12(1), 1-49. doi:10.1017/s0140525x00023992
Buss, D. (1991). Evolutionary personality psychology. Annual Review of Psychology, 42(1), 459-491. doi:10.1146/annurev.psych.42.1.459
Buss, D. M. (1995). Evolutionary psychology: A new paradigm for psychological science. Psychological Inquiry, 6(1), 1-30. doi:10.1207/s15327965pli0601_1
Buss, D. M. (2009). How can evolutionary psychology successfully explain personality and individual differences? Perspectives on Psychological Science, 4(4), 359-366. doi:10.1111/j.1745-6924.2009.01138.x
Buss, D. M., Larsen, R. J., Westen, D., & Semmelroth, J. (1992). Sex differences in jealousy: Evolution, physiology, and psychology. Psychological Science, 3(4), 251-255. doi:10.1111/j.1467-9280.1992.tb00038.x
Carr, P. B., & Walton, G. M. (2014). Cues of working together fuel intrinsic motivation. Journal of Experimental Social Psychology, 53, 169-184. doi:10.1016/j.jesp.2014.03.015
Chen, C., Burton, M., Greenberger, E., & Dmitrieva, J. (1999). Population migration and the variation of dopamine D4 receptor (DRD4) allele frequencies around the globe. Evolution and Human Behavior, 20(5), 309-324. doi:10.1016/s1090-5138(99)00015-x
Cortina, M., & Liotti, G. (2014). An evolutionary outlook on motivation: Implications for the clinical dialogue. Psychoanalytic Inquiry, 34(8), 864-899. doi:10.1080/07351690.2014.968060
Cosmides, L. (1989). The logic of social exchange: Has natural selection shaped how humans reason? Cognition, 31(3), 187-276. doi:10.1016/0010-0277(89)90023-1
Cosmides, L., & Tooby, J. (1989). Evolutionary psychology and the generation of culture, part II. Ethology and Sociobiology, 10(1-3), 51-97. doi:10.1016/0162-3095(89)90013-7
Cosmides, L., & Tooby, J. (2013). Evolutionary psychology: New perspectives on cognition and motivation. Annual Review of Psychology, 64(1), 201-229. doi:10.1146/annurev.psych.121208.131628
Daly, M., & Wilson, M. (2014). Homicide. New Brunswick, U.S.A.: Transaction.
Darwin, C. (1891). On the origin of species by means of natural selection, or, The preservation of favoured races in the struggle for life. London: John Murray.
Delton, A. W., Cosmides, L., Guemo, M., Robertson, T. E., & Tooby, J. (2012). The psychosemantics of free riding: Dissecting the architecture of a moral concept. Journal of Personality and Social Psychology, 102(6), 1252-1270. doi:10.1037/a0027026
Desteno, D., Bartlett, M. Y., Braverman, J., & Salovey, P. (2002). Sex differences in jealousy: Evolutionary mechanism or artifact of measurement? Journal of Personality and Social Psychology, 83(5), 1103-1116. doi:10.1037//0022-35220.127.116.113
Dickemann, M. (1981). Paternal confidence and dowry competition: For scientific purposes. European Journal of Personality, 4, 77-88.
Eagly, A. H., & Wood, W. (1999). The origins of sex differences in human behavior: Evolved dispositions versus social roles. American Psychologist, 54(6), 408-423. doi:10.1037/0003-066x.54.6.408
Ebstein, R. P. (2006). The molecular genetic architecture of human personality: Beyond self-report questionnaires. Molecular Psychiatry, 11(5), 427-445. doi:10.1038/sj.mp.4001814
Emmons, R. A. (1997). Motives and life goals. Handbook of Personality Psychology, 485-512. doi:10.1016/b978-012134645-4/50021-4
Herzberg, F., Mausner, B., & Snyderman, B. B. (1959). The motivation to work. Whitehouse Station: John Wiley & Sons.
Hogan, R. (1983). A socioanalytic theory of personality. In Nebraska symposium on motivation. Lincoln: University of Nebraska Press.
Kahneman, D., & Tversky, A. (1979). Prospect theory: An analysis of decision under risk. Econometrica, 47(2), 263. doi:10.2307/1914185
Li, Y. J., Kenrick, D. T., Griskevicius, V., & Neuberg, S. L. (2012). Economic decision biases and fundamental motivations: How mating and self-protection alter loss aversion. Journal of Personality and Social Psychology, 102(3), 550-561. doi:10.1037/a0025844
Low, B. S. (1989). Cross-cultural patterns in the training of children: An evolutionary perspective. Journal of Comparative Psychology, 103(4), 311-319. doi:10.1037//0735-7036.103.4.311
Marks, I. M. (1987). Fears, phobias, and rituals. New York: Oxford University Press.
Maslow, A. H. (1954). Motivation and personality. New York: Harper & Row.
Parker, S. L., Jimmieson, N. L., & Amiot, C. E. (2010). Self-determination as a moderator of demands and control: Implications for employee strain and engagement. Journal of Vocational Behavior, 76(1), 52-67. doi:10.1016/j.jvb.2009.06.010
Petersen, M. B., Sznycer, D. , Cosmides, L. & Tooby, J. (2012), Who deserves help? Evolutionary psychology, social emotions, and public opinion about welfare. Political Psychology, 33, 395-418. doi:10.1111/j.1467-9221.2012.00883.x
Roper, B. L., Ben-Porath, Y. S., & Butcher, J. N. (1995). Comparability and validity of computerized adaptive testing with the MMPI-2. Journal of Personality Assessment, 65(2), 358-371. doi:10.1207/s15327752jpa6502_10
Sacks, M. (2015). Six degrees of separation theory. In F. Wherry & J. Schor (Eds.), The SAGE encyclopedia of economics and society, 4, 1482-1482. Thousand Oaks, CA: SAGE Publications Ltd. doi: 10.4135/9781452206905.n624
Saraswat, A., Weinand, J., & Safer, J. (2015). Evidence supporting the biologic nature of gender identity. Endocrine Practice, 21(2), 199-204. doi:10.4158/ep14351.ra
Symons, D. (1981). The evolution of human sexuality. Oxford: Oxford University Press.
Symons, D. (1987). If we're all Darwinians, what's the fuss about? In C. Crawford, M. Smith, & D. Krebs (Eds.), Sociobiology and psychology: Ideas, issues, and applications (pp. 121-146). Hillsdale, NJ: Ertbaum.
Tomasello, M., Carpenter, M., Call, J., Behne, T., & Moll, H. (2005). Understanding and sharing intentions: The origins of cultural cognition. Behavioral and Brain Sciences, 28(05). doi:10.1017/s0140525x05000129
Togher, L. (2012). Strategies to improve research outcomes in the field of acquired brain injury: The Kevin Bacon effect, networking and other stories. Brain Impairment, 13(02), 271-280. doi:10.1017/brimp.2012.22
Tooby, J., & Cosmides, L. (1989). Evolutionary psychology and the generation of culture, part I. Ethology and Sociobiology, 10(1-3), 29-49. doi:10.1016/0162-3095(89)90012-5
Tooby, J., & Cosmides, L. (1990). The past explains the present. Ethology and Sociobiology,11 (4-5), 375-424. doi:10.1016/0162-3095(90)90017-z
Trivers, R. L. (1971). The evolution of reciprocal altruism. The Quarterly Review of Biology, 46(1), 35-57. doi:10.1086/406755
Trivers, R. L. (1972) Parental investment and sexual selection. In: Sexual selection and the descent of man, ed. B. Campbell. Aldine.
Vohs, K. D., & Luce, M. F. (2010). Judgment and decision making. In R. F. Baumeister & E. J. Finkel (Eds.), Advanced social psychology: The state of the science (pp. 733–756). Oxford, England: Oxford University Press.
Wiggins, J. S. (1991). Agency and communion as conceptual coordinates for the understanding and measurement of interpersonal behavior. In D. Cicchetti, & W. M. Grove (Eds.), Thinking Clearly about Psychology: Essays in Honor of Paul E. Meehl (pp. 89-113). Minneapolis, MN: University of Minnesota Press.
Williams, G. C. (1972). Adaptation and natural selection; a critique of some current evolutionary thought. Princeton, NJ: Princeton University Press.
Williams, G. C. (1977). Sex and evolution. Princeton, NJ: Princeton University Press.
Wood, W., & Eagly, A.H. (2002). A cross‐cultural analysis of the behavior of women and men: Implications for the origins of sex differences. Psychological Bulletin, 128, 699–727.
Zahavi, A. (2008). The handicap principle and signalling in collaborative systems. Sociobiology of Communication, 1-10. doi:10.1093/acprof:oso/9780199216840.003.0001