Introduction

In the early stages of human brain evolution, anticipating future events and learning from memories of the past were both essential to survival. As the brains of our primate ancestors navigated complex environments and encountered various selection pressures, several brain regions evolved to improve upon these cognitive abilities (Allen & Fortin, 2013, Teffer & Semendeferi, 2012). One such region, the prefrontal cortex (PFC), is associated with planning complex behavior and making decisions (Yang & Raine, 2009). Interestingly, the complexity of the microstructure and neural organization in the human PFC has significantly surpassed that of our closest primate relatives (Teffer & Semendeferi, 2012). While this structural and computational advantage in the PFC is important for personality, critical thinking, and moral behavior (Anderdon et al., 1999), it is also linked to excessive rumination, or self-directed thoughts about the past and future (Whitmer, 2009, Cooney et al., 2010). Furthermore, the PFC is one of many regions implicated in the regulation of psychological stress (Dedovic et al., 2009). While this is only one area in which humans have increased complexity relative to other animals, it provides an example of the dual nature of evolutionary effects. That is, increased cognitive processing capabilities arise along with increased potential for malfunction of those capabilities. Accordingly, it has been suggested that neural reorganizations through evolution may have predisposed modern humans to various mental disorders (Teffer & Semendeferi, 2012). In short, we evolved the ability to think, but along with these changes to brain structure came the potential for rumination, worry, and stress. Although humans born more than a century ago knew nothing about brain structure, they have known for millennia that deliberately resting from preoccupation with the past and the future and focusing on the present moment has tangible benefits.