Malthus's population predictions.

Malthus, at least in his first edition, predicted continuing famines in Europe; a prediction which has proven false.
Elwell states that Malthus made no specific prediction regarding the future; and that what some interpret as prediction merely constituted Malthus's illustration of the power of geometric (or exponential) population growth compared to the arithmetic growth of food production. Rather than predicting the future, the Essay offers an evolutionary social theory. Eight major points regarding evolution appear in the 1798 Essay:
subsistence severely limits population-level
when the means of subsistence increases, population increases
population-pressures stimulate increases in productivity
increases in productivity stimulate further population-growth
since this productivity can never keep up with the potential of population growth for long, population requires strong checks to keep it in line with carrying-capacity
individual cost/benefit decisions regarding sex, work, and children determine the expansion or contraction of population and production
checks will come into operation as population exceeds subsistence-level
the nature of these checks will have significant effect on the rest of the sociocultural system — Malthus points specifically to misery, vice, and poverty
This theory of Malthus has had great influence on evolutionary theory, both in biology (as acknowledged by Darwin and Wallace) and in the social sciences (compare Herbert Spencer). Malthus's population theory has also profoundly affected the modern day ecological-evolutionary social theory of Gerhard Lenski and Marvin Harris. He can thus be regarded as a key contributing element of the canon of socioeconomic theory.