Modern parents report feeling far more exhausted than their ancestors ever did, and scientists are trying to understand why. A German study of nearly 40,000 people found first-time mothers lose about one hour of sleep per night in the first three months after birth, while fathers lose roughly 20 minutes. Surprisingly, neither parent had fully recovered their pre-pregnancy sleep even after six years.

The gap between parents and non-parents is smaller than expected. Parents with children under six sleep around seven hours nightly—only 10-14 minutes less than non-parents. Yet hunter-gatherer societies like the Hadza in Tanzania show similar sleep durations but report much higher satisfaction. Anthropologist David Samson spent three months living with the Hadza and found they viewed separate infant sleep as "insane."

The key difference may lie in expectations. Our ancestors didn't pressure themselves to achieve consolidated, uninterrupted sleep—a concept that only emerged after the Industrial Revolution. Many cultures practice "breastsleeping," where mothers and infants sleep together and mothers remain semi-conscious during feeds. This might explain why our ancestors felt less fatigued despite similar sleep durations.