Greenery hypothesis: an evolutionary explanation for why presence/absence of green affects humans

A growing body of empirical evidence shows that experiences of nature
provide people with psychological benefits (improved cognitive function
and mental health). Although our knowledge of the proximate causes of such
positive psychological responses of humans to nature has improved, their
ultimate (evolutionary) drivers remain poorly understood. Here, we propose
a new evolutionary psychological hypothesis – the greenery hypothesis –
that integrates recent findings in evolutionary psychiatry with many
experimental results that cannot be explained by several
hypotheses/theories previously developed. Our proposed hypothesis states
that humans have adapted to periodic severe environmental changes (severe
drought and re-watering cycles) by establishing both negative and positive
psychological responses to the absence or presence of greenery within the
landscape as cues to optimize their own behavioral activity. We partially
tested several predictions generated from the greenery hypothesis using a
multi-country questionnaire survey of approximately 7,000 people, and
obtained some supporting evidence. The greenery hypothesis has the
potential to yield several insights into the fundamental understanding of
the psychological responses of humans to the natural world and it could
have important implications for a wide range of related fields,
psychiatry, urban planning, biodiversity conservation, and animal welfare.