Prenatal Androgen Effects as a Proximate Mechanism Underpinning Variation in Social Behavior Among Female Nonhuman Primates

While the role of ecological factors in shaping primate social systems has been a central focus for decades, less attention has been given to phylogenetic relationships and the potential role of underlying proximate mechanisms. This study aimed to investigate the relationship between one such proximate mechanism, prenatal androgen effects (PAEs), and aspects of social behavior in female nonhuman primates using the 2D:4D ratio as a proxy for PAEs and phylogenetically controlled methods. In general, female 2D:4D ratios were highest in monogamous species (low inferred PAEs) and lowest in polygynandrous and polygynous species (high inferred PAEs). 2D:4D ratios also varied with the form of polygyny/polygynandry, potentially with regard to the need for competitive over cooperative behaviors and the intensity of female reproductive competition. Species characterized by female dominance had lower 2D:4D ratios than species characterized by male dominance or codominance. There were no significant relationships between 2D:4D ratio and either degree of frugivory or group size. Relationships between 2D:4D ratios and the directional consistency index and 2D:4D ratios and rates of female–female agonism were also nonsignificant although sample sizes for both of these variables were small. Female social relationships are a manifestation of complex competitive and cooperative behaviors and the results suggest that PAEs may act as a proximate mechanism underlying the expression of certain aspects of behavior in female primates in ways that are adaptive to their social system.

Experimental evidence for yawn contagion in orangutans (Pongo pygmaeus)

Yawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood. Scholars have suggested a link between contagious yawning (CY) and sociality due to its appearance in mostly social species. Nevertheless, as findings are inconsistent, CY’s function and evolution remains heavily debated. One way to understand the evolution of CY is by studying it in hominids. Although CY has been found in chimpanzees and bonobos, but is absent in gorillas, data on orangutans are missing despite them being the least social hominid. Orangutans are thus interesting for understanding CY’s phylogeny. Here, we experimentally tested whether orangutans yawn contagiously in response to videos of conspecifics yawning. Furthermore, we investigated whether CY was affected by familiarity with the yawning individual (i.e. a familiar or unfamiliar conspecific and a 3D orangutan avatar). In 700 trials across 8 individuals, we found that orangutans are more likely to yawn in response to yawn videos compared to control videos of conspecifics, but not to yawn videos of the avatar. Interestingly, CY occurred regardless of whether a conspecific was familiar or unfamiliar. We conclude that CY was likely already present in the last common ancestor of humans and great apes, though more converging evidence is needed.

Grounded procedures: A proximate mechanism for the psychology of cleansing and other physical actions

Experimental work has revealed causal links between physical cleansing and various psychological variables. Empirically, how robust are they? Theoretically, how do they operate? Major prevailing accounts focus on morality or disgust, capturing a subset of cleansing effects, but cannot easily handle cleansing effects in non-moral, non-disgusting contexts. Building on grounded views on cognitive processes and known properties of mental procedures, we propose grounded procedures of separation as a proximate mechanism underlying cleansing effects. This account differs from prevailing accounts in terms of explanatory kind, interpretive parsimony, and predictive scope. Its unique and falsifiable predictions have received empirical support: Cleansing attenuates or eliminates otherwise observed influences of prior events (1) across domains and (2) across valences. (3) Cleansing manipulations produce stronger effects the more strongly they engage sensorimotor capacities. (4) Reversing the causal arrow, motivation for cleansing is triggered more readily by negative than positive entities. (5) Conceptually similar effects extend to other physical actions of separation. On the flipside, grounded procedures of connection are also observed. Together, separation and connection organize prior findings relevant to multiple perspectives (e.g., conceptual metaphor, sympathetic magic) and open up new questions. Their predictions are more generalizable than the specific mappings in conceptual metaphors, but more fine-grained than the broad assumptions of grounded cognition. This intermediate level of analysis sheds light on the interplay between mental and physical processes.

The role of inhibitory control in animacy effect: evidence from retrieval practice tasks

Animate stimuli are remembered better than inanimate stimuli. The proximate mechanism of this preferential retrieval of animate stimuli has not been clarified. The present study proposes an inhibitory control explanation for the advantage of the memory of animate stimuli. The retrieval practice paradigm is employed to examine the role of inhibitory control in animacy effect in two experiments. The results of Experiment 1 revealed a strong inhibitory effect on animate stimuli but was not reliable on inanimate stimuli, suggesting that animacy effect is not due to the insensitivity to the inhibitory control. The results of Experiment 2 show the absence of animacy effect when animacy is designed as a between-subject variable, suggesting that the memory of artifact may be influenced by the memory of animals. These findings are discussed using the inhibitory control account and suggest that the role of inhibitory control in animacy effect is to selectively inhibit the memory of other categories in order to facilitate the retrieval of animals, indicating that inhibitory control is, in part, responsible for the animacy effect.

Identity fusion and fitness interdependence

Fitness interdependence is the degree to which two or more organisms influence each other's success in replicating their genes. Identity fusion may be a proximate mechanism that aligns behavior with fitness interdependence. Although identity fusion may usually lead to behaviors that are fitness enhancing, in evolutionarily novel environments, it may be hijacked in ways that are highly detrimental to fitness.

Neurobiology of Reproduction in Molluscs

Ultimately, the outcome of successful reproduction—fertilization of eggs and production of surviving offspring—is relevant for how these processes evolve. However, a thorough understanding of the underlying, proximate mechanism is essential for interpreting evolutionary outcomes properly. Comparing neuroendocrine processes across different species, with different sexual systems, is one way of uncovering similarities and differences in regulation of their reproductive processes. Here, we provide an overview of the neuroendocrine control of reproductive processes in molluscs. In doing so, we also illustrate that it is relevant to consider the sexual system when addressing the neurobiology of reproduction. For example, our overview indicates that hermaphroditic molluscs seem to regulate their male and female reproduction via largely nonoverlapping neurobiological wiring and neuroendocrine substances, whereas this is not necessarily the case for separate-sexed molluscs. Clearly, this has implications for the available degrees of freedom within sexual systems in terms of evolutionary pathways.