Preschool is an evolutionary novelty
Throughout most of human history, people lived in small foraging bands of around 25 individuals. In such small groups, children rarely had playmates of the same age. Socialization meant interacting with people of all ages, from infants to grandparents (Konner 2005). In modern foraging groups, children play in multi-age playgroups (Hewitt and Lamb 2005) and may be watched over by multiple caregivers, including older sisters and grandmothers (Hrdy 2005).
Even after the rise of agriculture, the “warehousing” of small children would have been rare. Like foraging groups, village-based communities are characterized by multi-aged playgroups and older sibling caregivers. Historically speaking, segregating children by age is a relatively new idea. It is favored in industrialized societies where people lack the support of extended families and parents work outside of the home.
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