Intensification of agricultural production in general
is both a cause and a consequence of increasing wealth. Agriculture contributes to economic
development and, in turn, benefits from the higher demands for animal products,
which, with a few cultural exceptions, are associated with increasing wealth. This relationship
underpins the skill with which GDP per capita (in Purchasing Power Parity, PPP) can predict
the proportion of extensively raised chickens and pigs (Fig 2)