Evo-devo, deep homology and FoxP2: implications for the evolution of speech and language

Abstract

The evolution of novel morphological features, such as feathers, involves the modification of developmental processes regulated by gene networks. The fact that genetic novelty operates within developmental constraints is the central tenet of the 'evo-devo' conceptual framework. It is supported by findings that certain molecular regulatory pathways act in a similar manner in the development of morphological adaptations, which are not directly related by common ancestry but evolved convergently. The Pax6 gene, important for vision in molluscs, insects and vertebrates, and Hox genes, important for tetrapod limbs and fish fins, exemplify this 'deep homology'. Recently, 'evo-devo' has expanded to the molecular analysis of behavioural traits, including social behaviour, learning and memory. Here, we apply this approach to the evolution of human language. Human speech is a form of auditory-guided, learned vocal motor behaviour that also evolved in certain species of birds, bats and ocean mammals. Genes relevant for language, including the transcription factor FOXP2, have been identified. We review evidence that FoxP2 and its regulatory gene network shapes neural plasticity in cortico-basal ganglia circuits underlying the sensory-guided motor learning in animal models. The emerging picture can help us understand how complex cognitive traits can 'descend with modification'.

Empirical approaches to the study of language evolution

“…Another nice example of deep homology is the importance of FoxP2 in vocal learning in humans and birds (Fitch, 2009b(Fitch, , 2011aScharff & Petri, 2011)-the same gene plays an important role in regulating vocal learning in these clades, but the ability itself was not present in the common ancestor of birds and mammals. Deep homology is important because there is increasing evidence that it is common and relevant in the evolution of cognition (Arendt, 2005;Parker et al, 2013;Salas, Broglio, & Rodríguez, 2003).…”

Insights into the Genetic Foundations of Human Communication

“…Similarly to children acquiring spoken language, juvenile zebra finches learn their vocalizations incrementally during a critical period by imitating an adult (Bolhuis et al 2010). The neural circuitry underlying vocal learning appears to be partly shared by humans and songbirds, despite these species being separated by large evolutionary distances, pointing to a deep homology (Fisher and Scharff 2009;Scharff and Petri 2011). Furthermore, the zebra finch genome has been sequenced, and sophisticated genetic experiments are possible in this species, such as the identification of neural molecules regulated by vocal behavior (Hilliard et al 2012), and the manipulation of the expression levels of genes of interest during the critical song-learning period (Haesler et al 2007).…”

A Molecular Genetic Perspective on Speech and Language

“…As with the mouse models, neural plasticity in striatal circuitry emerges as a common theme associated with this gene (Murugan et al, 2013;Schulz et al, 2010). There is insufficient space available in this chapter to give a full account of all the relevant songbird studies; for further information on this burgeoning area of work, the interested reader is referred to reviews by Bolhuis et al (2010), Petri (2011), andWohlgemuth et al (2014).…”