Pleiotropy and preadaptation in the evolution of human language capacity

Area of Science:

• Evolutionary Biology
• Genetics
• Linguistics
• Anthropology

Background:

• Human spoken language capacity is a genetic trait, but its content is culturally determined.
• Previous models indicated a high advantage threshold for the initial increase of communication.
• A gene-culture coevolutionary approach is needed to understand speech evolution.

Purpose of the Study:

• To model the hypothesis that speech evolved for communicating adaptive cultural traits.
• To investigate conditions that make the initial increase of communication less stringent.
• To explore scenarios for the early evolution of speech.

Main Methods:

• Gene-culture coevolutionary modeling.
• Analysis of two models: Model 1 (two adaptive traits) and Model 2 (memory capacity prerequisite).
• Examination of haploid sexual genetics and vertical transmission with stability analysis of equilibria.

Main Results:

• The invasion condition for communication increase becomes less stringent under proposed models.
• Model 1 shows that transmitting two adaptive traits eases the invasion condition.
• Model 2 demonstrates that an independent advantage from a prerequisite function (e.g., memory) also lowers the invasion threshold.

Conclusions:

• The evolution of speech may have been facilitated by the cultural transmission of adaptive traits.
• Less stringent conditions for speech evolution are plausible when considering multiple traits or associated cognitive benefits.
• These models offer a potential scenario for the initial stages of human speech evolution.