Everyone’s in your family tree
…Now go all the way back to early modern humans, 30,000 years ago when Earth’s population was very sparse. The number of your forebears is so vast as to be beyond my calculator’s ability to show it to me. Each of those ancient beings had to’ve been your grandparent an uncountable number of times over. We needn’t go anywhere near that far back to be certain of our relationship to Confucius, Alexander the great or King Tut. Every Viking woman and medieval African chieftain, every early Mongol mother and Australian bushman would turn up over and over in your family tree.
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The genetic implications are vast. We’re a single species with far less genetic diversity than we’d assumed. As the number of our progenitors fans outward into the past, and the actual population shrinks, we reach Africa some 4000 generations ago. The number of the first modern humans appears to have been only a few thousand.