Evolution of lactase persistence: an example of human niche construction

Niche construction is the process by which organisms construct important components of their local environment in ways that introduce novel selection pressures. Lactase persistence is one of the clearest examples of niche construction in humans. Lactase is the enzyme responsible for the digestion of the milk sugar lactose and its production decreases after the weaning phase in most mammals, including most humans. Some humans, however, continue to produce lactase throughout adulthood, a trait known as lactase persistence. In European populations, a single mutation (−13910*T) explains the distribution of the phenotype, whereas several mutations are associated with it in Africa and the Middle East. Current estimates for the age of lactase persistence-associated alleles bracket those for the origins of animal domestication and the culturally transmitted practice of dairying. We report new data on the distribution of −13910*T and summarize genetic studies on the diversity of lactase persistence worldwide. We review relevant archaeological data and describe three simulation studies that have shed light on the evolution of this trait in Europe. These studies illustrate how genetic and archaeological information can be integrated to bring new insights to the origins and spread of lactase persistence. Finally, we discuss possible improvements to these models.

Values in middle childhood: Social and genetic contributions

Theories of value development often identify adolescence as the period for value formation, and cultural and familial factors as the sources for value priorities. However, recent research suggests that value priorities can be observed as early as in middle childhood, and several studies, including one on preadolescents (Knafo & Spinath, 2011), have suggested a genetic contribution to individual differences in values. In the current study, 174 pairs of monozygotic and dizygotic 7-year old Israeli twins completed the Picture-Based Value Survey for Children (PBVS–C; Döring et al., 2010). We replicated basic patterns of relations between value priorities and variables of socialisation – gender, religiosity, and socioeconomic status– that have been found in studies with adults. Most important, values of Self-transcendence, Self-enhancement, and Conservation, were found to be significantly affected by genetic factors (29%, 47% and 31% respectively), as well as non-shared environment (71%, 53% and 69% respectively). Openness to change values, in contrast, were found to be unaffected by genetic factors at this age and were influenced by shared (19%) and non-shared (81%) environment. These findings support the recent view that values are formed at earlier ages than had been assumed previously, and they further our understanding of the genetic and environmental factors involved in value formation at young ages.