Background

Every animal roaming earth today is in one way or the other successfully adapted to its particular evolutionary pressures. Among those animals are very close relatives of our own lineage (Homo): The other apes. But somehow the evolutionary path and the current behavioural patterns of Homo sapiens sapiens seem quite different even from our nearest living cousins. Analysis of mitochondrial DNA sequences in modern humans (in contrast to the other apes) indicate two drastic population expansions; one between 200,000 and 100,000 years ago and one approximately 50,000 years ago. Around the time of the second expansion, the first signs of a more complex and symbolic culture emerged in form of cave-art, body-decoration and burial rituals. Human culture is accelerating. A mere 25,000 years later, Homo sapiens sapiens is the only remaining species of the genus Homo and after another 25,000 years 6 billion of us populate every possible corner of the planet across a variety of habitats unmatched by any other primate species. So how were early Homo sapiens sapiens different, so that their population would explode while all other Homo species went extinct. How come that in contrast to our own species, all other ape species maintained a moderate population size, even prior to the destruction of their habitat by humans? The co-occurrence of the expansion in population and the increase in cultural complexity in our species gives rise to the speculation that some adaptation for culture and sociality shaped modern humans as we know them today. Underlying human social interactions is a conglomerate of cognitive abilities often summarized as social cognition. The aim of this project is to dissect some unique social cognitive features in Homo sapiens that might have caused their outstanding evolutionary history.

Methods

Cross-Species Comparison
To investigate abilities that are particular to humans and their evolutionary history, we need to isolate those that are unique to humans amongst their closest phylogenetic relatives, the other apes. In addition to serving as a background against which to compare human behaviour, the comparison within our phylogenetic family enables us to investigate the evolutionary trajectory of human sociality since the last common ancestor of all Hominoids.
Any cognitive ability, which is part of a shared repertoire between related species, is likely to be part of the evolutionary inheritance ever since their last common ancestor. The great apes are a close family of species with a common ancestor (Hominidae). Today 5 Hominid species are still in existence: Orangutans, Gorillas, Bonobos, Chimpanzees and Humans. If all these species share a particular cognitive preference or ability, it is most likely part of the evolutionary inheritance of the family at least ever since their last common ancestor, and therefore also an evolutionarily old, inherited cognitive default in humans. In this way, behavioral continuities across species are used to understand evolutionary past. Another ability might be present in Pan and Homo only. In that case, adding what we know about the timescale of phylogenetic diversions of the different ape genera (Figure 1), this ability would have been an evolutionary innovation, which occurred sometime since the last common ancestor of Homo, Pan and Gorilla (app. 10 million years ago). Yet another ability might for example only exist in Homo. This pattern would indicate an innovation sometime since roughly 5-6 million years ago, the time of the last common ancestor between Homo and Pan. In this example, Homo might have undergone special evolutionary adaptations, unique to its evolutionary past, and distinct from those of the other members of the family. In this project we will investigate which skills are unique to humans amongst the apes and attempt to reconstruct part of their evolutionary history.

Cross-Cultural Comparison
In addition to being unique amongst the apes, any property definitional of ‘being human’ is by necessity a human universal. However, what constitutes universality is not very well defined in the cognitive sciences, for the simple reason that many cognitive scientists at present tend to assume universality of their findings in the first place. This so called absolutist theoretical position attributes only small impact to culture but assumes that psychological phenomena are qualitatively the same across all cultures: happiness is happiness and jealousy is jealousy no matter where one observes them. In the early twentieth century, this was referred to as “the psychic unity of mankind”. Hence, in psychological research, universality is hardly ever considered an empirical question. In fact, many cognitive functions that have been put to the test turned out to vary across cultures: Visual illusions, colour categorization, eye-movements in scene-perception, temporal concepts numerical and spatial reasoning etc..
Considering universality of psychological phenomena makes important setting the appropriate level of analysis. In this project we are interested in human psychological universals on an inter-cultural level. This might include psychological phenomena that are universal across all individual humans, but it would also include phenomena, which are universal across group-averages, but vary across individuals. To answer the question of human universals in our project, we aim to compare social cognition across a selected set of diverse human cultural groups. We argue that any characteristic shared across cultures representing diverse modes of subsistence, ecological environments, and continents is a likely candidate for a human universal.