Until modern times in Japan, for the same reasons as those of current developing countries (malnutrition, deficient knowledge of health and poverty, etc.), the probability of small babies surviving to adulthood was quite low.
近世までの日本は、現在の開発途上国と同様の状況（栄養不足・健康への知識不足・貧困など）が原因で乳幼児が成人するまでの生存率はきわめて低くかった。