Unrelated languages worldwide use almost the same word for 'mother'

From English 'mama' to Mandarin 'māma' to Swahili 'mama', languages with no historical connection converge on strikingly similar sounds for 'mother' and 'father'. A linguist argued these aren't inherited from a common ancestor language at all — they're simply the easiest sounds for a nursing infant to produce, which parents worldwide then adopt as the child's first words for them.

— Roman Jakobson, Why 'Mama' and 'Papa'? — In Perspectives in Psychological Theory, 1960