Conceptual challenges and directions for social neuroscience

Abstract

Social neuroscience has been enormously successful and is making major contributions to fields ranging from psychiatry to economics. Yet deep and interesting conceptual challenges abound. Is social information processing domain specific? Is it universal or susceptible to individual differences and effects of culture? Are there uniquely human social cognitive abilities? What is the "social brain," and how do we map social psychological processes onto it? Animal models together with fMRI and other cognitive neuroscience approaches in humans are providing an unprecedented level of detail and many surprising results. It may well be that social neuroscience in the near future will give us an entirely new view of who we are, how we evolved, and what might be in store for the future of our species.

Figure 1. Two Eusocial Species

Eusociality refers to the rigid and highly organized colonial behavior seen in some insect species, such as ants, termites, and bees. It involves overlapping generations, cooperative care of the young, and specialized castes, including allocation of reproduction. On the face of it, its evolution seems impossible, since an individual's advantage in passing on its genes should always trump its eusocial role as a nonreproductive caste. However, some insects with haplodiploidy (where the number of chromosome copies determines sex) feature the interesting phenomenon that an individual may be genetically more closely related to a sibling than to their offspring, raising the possibility that kin selection can drive the evolution of eusociality. However, even this does not seem enough, and group selection (i.e., at the level of the entire colony) appears to be necessary and may in fact be the key driving force for the emergence of eusociality (Wilson and Hölldobler, 2005). This requires several convergent criteria that favor cooperation and can be considered a highly advanced transition into a tightly colonial existence often called a “superorganism.” Evidently, it is very difficult for eusociality to arise, but once established it is extremely successful and stable. For instance, out of the over 2600 families of artho-pods, only 15 contain eusocial species. Ants and termites comprise only about 2% of insect species, yet they constitute over half of the globe's total insect biomass. In vertebrates, eusociality only exists in two species of mammals, both mole rats found in Africa. Intriguingly, some of the conditions for the evolution of eusociality and for the highly cooperative behaviors of eusocial species have been suggested to be present in humans as well, raising the possibility that group selection and a transition to a different form of collective existence may be at play in our species as well. (Left) The naked mole rat, Heterocephalus glaber, one of only two eusocial mammals. These rodents have social structures similar to those seen in bees and ants: a single breeding queen and division of sexual reproduction and labor among all the individuals within a subterranean hive. Naked mole rats cannot live for long left on their own and require the specialized cooperative behaviors of other members of their colony to thermoregulate, obtain food, and defend against potential predators. They are also fascinating because they have the longest lifespan of any rodent and a surprisingly large brain specialized for somatosensory and olfactory processing (image by Rochelle Buffenstein) (Jarvis and Sherman, 2002). (Right) Excavation of a leafcutter ant nest by Bert Hölldobbler and colleagues, showing the intricate way in which this “superorganism” has structured its environment. Photo by Wolfgang Thaler from Hölldobler and Wilson (2008).