To illustrate this point, Kenny compares what has happened to
life expectancy in Britain and India. The average age span in
both countries was 24 years in the 14th century, but Britain
then began a gradual rise, and by 1931 its life expectancy was
60.8 years, compared to just 26.8 for its colony. Since then,
though, the numbers have begun to converge — by 1999, Indians
lived on average to 63, while Brits nudged upward to 77. One of
the main reasons for the gap-closing is the fall of infant
mortality. In 1900 Britain, the infant survival rate was 846 per
1,000 births, compared to 655 in India. Today, 992 British
infants out of every 1,000 survive, compared to 920 Indians.
Kenny notes: “Broadly, the results suggest that it takes one-
tenth the income to achieve the same life expectancy in 1999 as
it took in 1870. Why does it take so much less money to get
these results than it used to? Consider the virtuous circle of
agricultural improvements, such as the way discovering how to
properly use inorganic fertilizers