The correct effect of the agricultural revolution in Middle America is A: people settle down into villages. The agricultural revolution led to the development of agriculture, which allowed people to produce food in a more stable and reliable manner. This shift enabled communities to settle in one place, leading to the establishment of villages and, eventually, more complex societies.
Options B and D are incorrect, as the agricultural revolution generally resulted in people reducing their reliance on hunting and gathering (not increasing it) and often led to an increase in population, not a decrease in childbirth rates. Option C is partially correct in that people began to stop hunting and gathering as they took up farming, but it does not capture the broader impact of settling down into villages.