The meaning of absence: the primate tree that did not make it into Darwin's The Descent of Man

This paper engages with a specific image: Darwin's tree of the primates. Although this diagram was sketched in ink on paper in 1868, it did not make it into the publication of The Descent of Man (1871). This may seem all the more in need of an explanation because, as Adrian Desmond and James Moore have shown, Darwin strongly relied on the notion of familial genealogy in the development of his theory of organismic evolution, or rather descent. However, Darwin expressed scepticism towards visualizations of phylogenies in correspondence with Ernst Haeckel and in fact also in Descent, considering such representations at once too speculative and too concrete. An abstraction such as a tree diagram left little room to ponder possibilities or demarcate hypotheses from evidence. I thus bring Darwin's primate tree into communication with his view on primate and human phylogeny as formulated in Descent, including his rejection of polygenism. I argue that considering the tree's inherent teleology, as well as its power to suggest species status of human populations and to reify ‘racial’ hierarchies, the absence of the diagram in The Descent of Man may be a significant statement.

The reversal of human phylogeny: Homo left Africa as erectus, came back as sapiens sapiens

Background The molecular out of Africa hypothesis, OOAH, has been considered as an established fact amid population geneticists for some 25–30 years despite the early concern with it among phylogeneticists with experience beyond that of Homo. The palaeontological support for the hypothesis is also questionable, a circumstance that in the light of expanding Eurasian palaeontological knowledge has become accentuated through the last decades. Results The direction of evolution in the phylogenetic tree of modern humans (Homo sapiens sapiens, Hss) was established inter alia by applying progressive phylogenetic analysis to an mtDNA sampling that included a Eurasian, Lund, and the African Mbuti, San and Yoruba. The examination identified the African populations as paraphyletic, thereby compromising the OOAH. The finding, which was consistent with the out of Eurasia hypothesis, OOEH, was corroborated by the mtDNA introgression from Hss into Hsnn (Neanderthals) that demonstrated the temporal and physical Eurasian coexistence of the two lineages. The results are consistent with the palaeontologically established presence of H. erectus in Eurasia, a Eurasian divergence between H. sapiens and H. antecessor ≈ 850,000 YBP, an Hs divergence between Hss and Hsn (Neanderthals + Denisovans) ≈ 800,000 YBP, an mtDNA introgression from Hss into Hsnn* ≈ 500,000 YBP and an Eurasian divergence among the ancestors of extant Hss ≈ 250,000 YBP at the exodus of Mbuti/San into Africa. Conclusions The present study showed that Eurasia was not the receiver but the donor in Hss evolution. The findings that Homo left Africa as erectus and returned as sapiens sapiens constitute a change in the understanding of Hs evolution to one that conforms to the extensive Eurasian record of Hs palaeontology and archaeology.

On the Uniqueness of Human Normative Attitudes

Humans are normative beings through and through. This capacity for normativity lies at the core of uniquely human forms of understanding and regulating socio-cultural group life. Plausibly, therefore, the hominin lineage evolved specialized social-cognitive, motivational, and affective abilities that helped create, transmit, preserve, and amend shared social practices. In turn, these shared normative attitudes and practices shaped subsequent human phylogeny, constituted new forms of group life, and hence structured human ontogeny, too. An essential aspect of human ontogeny is therefore its reciprocal nature regarding normativity. This chapter reviews recent evidence from developmental psychology suggesting that, from early on, human children take a normative attitude toward others’ conduct in social interactions, and thus a collectivistic and impersonal perspective on norms. The chapter discusses to what extent humans’ closest living primate relatives lack normative attitudes and therefore live in a non-normative socio-causal world structured by individual preferences, power relationships, and regularities.

A culture–behavior–brain-loop model of human development

Chapter 8 introduces a culture–behavior–brain (CBB)-loop model of human development based on cultural neuroscience findings, and proposes a new framework for understanding human development regarding both human phylogeny and lifespan ontogeny. This model posits that culture shapes the brain by contextualizing behavior, and the brain fits and modifies culture via behavioral influences. Genes provide a fundamental basis for and interact with the CBB loop at both individual and population levels. The CBB-loop model advances our understanding of the dynamic relationships between culture, behavior, and the brain. Future brain changes owing to cultural influences are discussed based on the CBB-loop model.