The money quote:
The College is in a ferment over a topic close to my heart: the historicity of Adam and Eve. Even conservative Christians, it seems, have trouble believing that Adam and Eve were the literal ancestors of humanity. That historicity has become increasingly problematic since the appearance of new papers in population genetics, showing that over the last few hundred thousand years, the population of Homo sapiens could not have been smaller than about 12,250 (10,000 who remained in Africa and 2,250 who migrated out of Africa to populate the rest of the globe).
In other words, the human population never comprised only two people. And if Adam and Eve weren’t the literal ancestors of humanity, then a critical part of the Genesis story is wrong: the acquisition of Original Sin. And if there were no Original Sin accrued by a literal Adam and Eve, then all of us—their supposed descendants—aren’t sinful by birth, and Jesus’s return wasn’t necessary. LINK.