ABSTRACT
The recipe for a cake requires several ingredients to be combined in a particular order and cooked for a specified time and temperature. The RS theory suggests that the recipe for human handedness also requires ingredients to be combined in sequence and developed through certain environmental and cultural influences. The chief ingredients are represented in Figure 16.1, from the top down, as follows: (1) accidental buffeting during early growth, (2) a single gene that gives directional bias but may be absent, or present in single or double dose, (3) genetic expressivity, or extent of shift, that varies with factors influencing rate of growth including sex and twinning, and (4) sociocultural influences on the use of the left-hand that affect thresholds for the expression of sinistral tendencies. No other theory has proposed exactly the same ingredients and developmental processes as the RS theory. Some theories, however, share certain features. This chapter reviews other theories with the aim of acknowledging similarities but also pinpointing critical differences. A schematic representation of the right shift theory. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203759646/2b9e7cbc-ac77-4d09-a72b-49cc9e71f90a/content/fig16_01_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
