How biology constrains, shapes, and facilitates human potential has always been contested territory, and nowhere has this debate been more contested than in discussions of human 'nature'. While the term 'human nature' may seem like an antiquated throwback to the days of vital essences and lumeniferious aether, I have been continually surprised to see individuals citing the modern denial of our 'nature' as the root cause of many societal ills. What's the basis of such concerns, and why do so many people put so much importance on a seemingly ill defined abstraction such as human 'nature'? I believe the importance given to human nature in our public discourse in part reflects the way that researchers approach how evolutionary processes influence our everyday lives. At our “core” are we just objectified manifestations of selective forces that acted on generations of humanity before us, or is each individual a novel synthesis of past evolutionary factors and here-and-now factors. The science that has attempted to answer these questions has changed significantly over the years, from sociobiology, to human ethology, to human behavioral ecology and evolutionary psychology. According to evolutionary psychology our everyday lives are shaped to varying degrees by a series of evolved psychological and cognitive programs/modules. It is hypothesized that these programs subtly shape nearly every aspect of our lives, from our mate choices, to the products we buy, to the political ideologies we adopt. Furthermore, these programs have such a large influence on us because they represent adaptations that have been instantiated in our biology by generations of natural selection. Despite being in the business of studying adaptations, defenders of evolutionary psychology rightly go to great lengths to resist claims that they are pan-adaptationists by proposing that psychological processes can be organized into three bins: adaptations, byproducts, and noise. A main assumptions is that one can differentiate psychological adaptations from byproducts or noise by documenting that specific traits have prespecified purpose and universality. This assumption provides the foundation for most hypotheses in modern evolutionary psychology. I argue that not only are such strong demarcations between adaptations, byproducts, and noise unnecessary for evolutionary processes, but that common approaches to estimate such demarcations are unavailable to evolutionary psychologists, and students of human behavior more broadly. Linking adaptations with shared functionality and universality has it’s roots in early ethology. One of the major advances that ethology introduced to the study of behavior was the ability to view behavior from an evolutionary lens. Much like a taxonomist could reconstruct the evolutionary relationships between species by comparing their morphologies, ethologists showed that one could do the same by comparing the behavior across different species. This approach was exemplified by Konrad Lorenz in his excellent book "Comparative Studies on the Behaviour of Anatinae” that built upon his advisors Oskar Heinroth’s studies of the evolution of behavioral displays in ducks and geese. Nonetheless, the early ethologists also appreciated the variability of animal behavior, and tended to only apply evolutionary analysis only to behaviors that met a certain criterion, they had to be universal, or develop predictably across all members of a species or population, and they had to have a purpose, they allowed the organisms to correctly respond to environmental challenges they had not yet experienced. These behaviors, called modal or fixed action patterns, were treated as the products of discrete developmental programs that assured that specific behaviors developed independent of specific experiences. Thus, as a healthy member of species X you would display functional behavior Y in response to some stimuli independent of your specific experiences with your environment. Until Lehrman's critique the main way that ethologists identified modal action patterns was to raise an individual in deprived settings to show that some behavioral traits and abilities were still predictably expressed. Once modal action patterns were identified comparisons between species could be made to investigate their evolutionary history. Much of the discussion around evolutionary psychology rests on its treatment of specific psychological and cognitive tendencies as equivalent to modal action patterns. Adaptive psychological and cognitive processes must be universal and purposeful, as stated by Dr. Al-Shawaf this means that "psychology and behavior predict universality at the level of the information-processing structure of the neurocognitive mechanisms that produce behavior”. This universality suggests that these psychological abilities arise independent of an individual’s specific experiences, and represent an environment than an individual has not yet, or may never, encounter (often proposed as the environment of evolutionary adaptedness). This requires that development is teleological, that it's directed towards specific outcomes through the utilization of developmental programs that unfold specific functional traits at the right time during ontogney. In response to similar claims made by ethologists many American comparative psychologists, such as T.C. Schneirla, Daniel Lehrman, Frank Beach and especially Zing-Yang Kuo, questioned the independence and preparedness of modal action patterns. In particular, research done by these comparative psychologists showed how behavior that seemed prepared for future environments were often developmental variations of prior functional behaviors utilized in novel ontogenetic contexts. For example, walking and gait in hatchling chickens were developmental reorganizations of similar leg movements made pre-natally to stimulate respiration and proper positioning in the egg. In particular they showed that even in isolation studies, specific experiences between an organism and its environment were essential factors in shaping the emergence of modal action patterns over development. Since then experiments have consistently demonstrated that the development of modal action patterns is dependent on a network of interacting developmental resources extending both outside and inside organisms. Therefore, the information “for” modal action patterns was not latent within the organism or its genes, but constructed via contingent relationships within and between an organism and its environment (Fig 1.). As stated by Oyama (1988) "the informational function of any developmental interactant is dependent on the rest of the system. This means that what counts as information is itself contingent and relational, not that information “is” the developmental system.” Thus, if latent developmental programs exist for specific behaviors it is unclear how they could be instantiated without postulating some near supernatural force sitting outside both the organism and its environment and causally guiding and coordinating all the relationships within and between them. In response to these findings’ ethologists such as S.A. Barnett, Patrick Bateson and Johan Bolhuis began to question the assumption that modal action patterns occurred independent of specific experiences and proceeded to create a developmentally informed ethology without “instincts”. A uniting theme behind this new ethology/comparative psychology was that development was re-conceptualized as emerging prospectively. That is, all behavior arises from earlier conditions, but shows no direction towards later conditions. Development was freed from its teleological constraints. The behavior of any organism at any point in time reflected the current state of the organism and its relationship with its environment, and these antecedent states provided the foundation from which other consequential states can arise. There was no need for any program, guide, blueprint, invisible hand, vital essence or other abstraction to guide development to a final endpoint, as the lifecycle of organisms was simply a series of antecedent-consequent processes that reoccur anew within each individual. In contrast to this prospective view many behavioral researchers took a retrospective view that grounded developmental questions upon specific adaptive traits of interest. Here one looks back in time, starting with the trait under study and looks for potential developmental causes arising earlier in life. Such a teleological view often masks important developmental processes by selecting only those traits early in development that share some functional or perceptual similarity with the trait of interest (In contrast, the prospective developmental approach has continually shown the relevance of non-obvious and non-linear experiences in the development of modal action patterns). The fixivity of specific behaviors over ontogeny, or the seeming directionality of their development—which are a consequence of the retrospective perspective and not development per say—is often seen as evidence a developmental program, and used as a stand-in for past selection pressures. According to this view the development of adaptive traits don’t so much emerge as a consequence of previous states but unfolds according to an evolved program. Such developmental programs have often been used in evolutionary psychology as a way to assure that adaptive traits maintain their universality. This assumption has been sustained despite the lack of evidence that biological or psychological processes function like a program. In recent decades there has been a steady erosion of colloquial assumptions that genes function as developmental blueprints or programs, or that brains only act as computational programs that take in stimuli as input, process sensory information, and spit out behavior as outputs (This has its roots in Dewey’s classic 1896 critique of the reflex arc). This leaves one with the difficult question of where developmental programs are instantiated in the inherently interactive network of factors that define all psychological events. If one is unable to provide a testable and measurable substrate from which a program could be instantiated, it might be better to assume the more empirically supported observation that the universality of specific traits represents the shared antecedent-consequent interactions reconstructed across individual lifecycles. So what does this have to do with evolutionary psychology? Since phylogeny is just a reflection of recurrent and successful lifecycles, and those lifecycles consist of recurrent antecedent-consequent processes, there are opportunities for sudden, universal, and functional novel phenotypes to emerge via developmental reorganization. As stated by Lickliter 2014, "The novelty-generating aspects of development involved in such evolutionary change are the result of the developmental dynamics of living organisms, situated and competing in specific ecological contexts, and not simply the result of random genetic mutations". This process, called neophenogenesis, lays at the heart of the difficulties in demarcating where adaptive phenotypes begin and end. Many cases of neophenogenesis are considered noise, single individuals whom were shaped by incidental exposure to some experiences over development. Such events have now been widely observed, but “ noisy” responses can also cause animals to flexibly reorganize their developmental resources to solve the here-and-now challenges of everyday life. This has been seen in many studies of animal innovation. In many cases of animal innovation the behavior emerges and dies within a single individual, but it is increasingly shown that such innovations can spread to higher levels such as the group, population, and potentially the species. Thus identifying a shared functional behavior does not automatically mean that the behavior is the cumulative result of generations of selective pressure by default, as an increasing number of studies (especially in birds and mammals) have shown that novel, adaptive phenotypes can arise and spread quickly across a population. Large scale environmental changes can induce coordinated changes in developmental processes. Group and population level developmental accommodations have been seen in invasive species, ontogenetic responses anthropogenic changes, and responses to changes in social dynamics. Such examples highlight the ability reorganize developmental processes to coordinate changes across a whole group or population by exposing all individuals to novel shared experiences. Often these shared developmental accommodations can be directly functional, allowing individuals to survive and reproduce in the new novel environment. This has been observed in population scale shifts in migratory routes, mating patterns, and egg clutch size in European blackcaps exposed to sudden anthropogenic changes (Bearhop, S, et. al. 2005) and population level phenotypic divergence mediated by maternal effects in House finches moving into novel habitats (Badyaev, 2005). Another example of this can be seen in Terkel's studies of pine cone foraging in Israeli black rats. Throughout most of their range black rats do not consume pine nuts. However, a whole population of black rats learned to harvest pine nuts through developmental accommodations in a plantation of Jerusalem Pine in Israel (Fig 2). Here a single individual likely learned to open a pine cones themselves, and this spread throughout the population through the introduction of a new developmental resource, partially opened pine cones. Juveniles exposed to the partially opened pinecones left by adults were able to acquire the ability to open cones on their own over ontogeny thus constructing a shared functional developmental accommodation. Such developmental accommodations make it difficult with limited observations on a single population or species to assess if behavior reflects the refined product of generations of natural selection, or shared developmental accommodations meant to address here-and-now challenges. The whole dichotomy between an adaptation and a developmental accommodation becomes blurred, as all aspects of an organisms represent a synthesis between the past and present. This synthesis is necessary as all organisms must navigate an environment (either ecological or perceptual) that is a shifting mosaic of regularities and novelties. Even if one conceptualizes an evolved psychology as nothing more than a series of adaptive modules, the connections between the utilization of different modules and novel environment challenges would continually construct novel information processing networks that may bear little resemblance to their ancestral function. Fig 2. Likely a single innovation, a rat learning to open a pine cone quickly spread throughout a whole population of Israeli black rats. This novel developmental accommodation was sustained across the population as young individuals predictably encountered the half-opened pine cones from adults, thus recreating the acquired behavioral pattern anew during each lifecycle. Here lies the issue for evolutionary psychology. Their hypotheses relies on a demarcation between adaptation and byproduct through identifying universality and functionality of specific psychological abilities. A common response among evolutionary psychologists when faced with the emergence of functional neophenotypes is to claim these are simply the flexible outputs of the adaptive underlying cognitive-informational processing programs. However, this simply kicks the problem down the road by instantiating the program at a lower level of biological organization. Nonetheless, no level of biological organization is immune to developmental contingencies or accommodations. Studies across all levels of biological organization, from gene expression to social organization, have documented the routine occurrence of shared and functional developmental accommodations. It is therefore unclear that even if one could locate where a universal adaptive program is instantiated, that it would be immune to the effects of developmental accommodations. Another issue for evolutionary psychologists are developmental accommodations itself. Humans unlike most animals don’t have many (or any, depending on whom you ask) modal action patterns. However, the production of shared and functional developmental accommodations is what humans do, all the time, continually, on a scale and magnitude not seen before in any other species. Large scale changes in organismal-environment relationships that continually create novel brains, bodies, biologies and behaviors is part in parcel to human history. Human beings have are masters at manipulating the antecedent-consequent structure of developmental processes to directly create adaptive neophenotypes outside of, and in front of, selective forces. At no point in human history, be it the Pleistocene, the bronze age, the middle ages ,or the information age, can one stop, put a stake in the ground, and demarcate a line between conserved selective features and novel developmental accommodations. Humans are ultimate developmental niche constructors, we have the ability to plan, understand, and expand our potential by radically reorganizing our biology and behavior. Our potentials vasty outweighs the constraints of our ancestors. So what's the way forward? One way is to make evolutionary psychology truly evolutionary. A recent blog post by Kevin Bird discusses how evolutionary psychologists should apply techniques from evolutionary biology to identify where selection has, and is, acting. Nonetheless, without a detailed historical record or closely related comparison species it is woefully difficult with the current methodologies used in modern evolutionary psychology to identify phylogenetic history and selection. Another approach is to fully integrate the production of developmental accommodations into the study of evolutionary psychology. Baldwin (1896), Osborne (1986) and Loyd Morgan (1896) proposed testable hypotheses regarding how developmental accommodations and neophenotypes facilitate natural selection. Broadly, the continued production of functional neophenotypes is first maintained cross generations via recurrent developmental accommodations. Selection acts on these recurrent accommodations by selecting ontogenetic processes that more efficiently and predictably produce the trait under selection. This process may lower the energetic burden of producing complex traits over development, thus "freeing" the organisms to develop new accommodations in response to changing environments. This "assimilate-and-stretch" model outlined in Avital and Jablonka (2000) suggests that the continual production and assimilation of neophenotypes is a core component in the evolution of behavioral complexity, and continually blurs the line between adaptation and neophenotype. Niche construction theory proposes that organisms possess the ability to shape their own selective pressures through their influences on the external environment. Rather than just assimilating developmental accommodations in response to external pressures, the feedback between the emergence of neophenotypes and their corresponding changes in the environments creates novel selective landscapes. From the evolution of lactase persistence, to the emergence of agriculture, to the development of livestock domestication, and the continuing use of technology to drastically alter our psychologies and biologies there is little reason to doubt that niche construction has shaped the evolutionary trajectory of our species. Instead of attempting to identify signatures of past adaptions, evolutionary psychologists could be investigating at how novel interactions and feedback loops between human behavior and the environment could shape the continuing evolution of our psychological abilities. In conclusion, the fact that developmental accommodations can create widespread, novel, and functional phenotypes in front of selective pressures provides a large obstacle for our ability to understand the selective forces shaping human behavior. However, approaches emphasizing the role of developmental systems in evolution (as outlined by Johnston and Gottlieb (1990)) may inform a more robust and evolutionary approach to researching human behavior by focusing on which traits will lead us forward, rather than how the past constrains us.
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