Every human alive shares one woman as a direct maternal-line ancestor
In 1987, geneticists compared mitochondrial DNA — passed only from mother to child — across 147 people from five populations worldwide. Every lineage traced back to one woman who lived in Africa roughly 150,000–200,000 years ago, nicknamed 'Mitochondrial Eve'. She wasn't the only woman alive then, just the only one whose unbroken maternal line survives in everyone living today.