The chapters in Part IV address the question of human uniqueness in brain organization and behavior. In Chapter 14, Todd Preuss focuses on molecular genetic differences between human brains and the brains of our closest relatives. Particular emphasis is given to the role of foxP2, which has, at times, been called the human language gene. Not surprisingly, the true story of foxP2 is more complex, because as Preuss puts it, “we are trying to relate a multifunctional gene to a complex, high-level phenotype.” To deal with this complexity, Preuss suggests that we need a better understanding not of single-gene variation, but of variation in many genes and, particularly, brain development. Preuss also notes that human brains mature more slowly than the brains of other species, which would explain why brain metabolic activity is surprisingly high and structural plasticity unusually protracted in humans. Particularly interesting is the observation that some patterns of gene expression in the prefrontal cortex of humans are seen only during development in other species. The mechanisms underlying this heterochrony as well as their functional sequelae remain unclear. However, childhood is well known to be more protracted in humans than in other apes.
Lizabeth Romanski reviews in Chapter 15 the anatomical and physiological organization of the ventrolateral prefrontal cortex (vlPFC) of macaque monkeys. This cortical region is of special interest because its homolog in humans includes several language-related areas (e.g., Broca’s area). In a key experiment, Romanski and her colleagues took movies of vocalizing monkeys, separated them into audio and visual streams, and