Perhaps a real geneticist will chime in, but I seem to recall we can find more genetic diversity within a family of another species say chimps or dogs than we do across the entire human species. We thought our lack of diversity was due to some "bottleneck" event where the global human population dropped to around 10K. But then we sequenced neanderthal and had to re adjust that to many repeated bottle necks each decreasing the chance of being it being a correct hyposisis as just one bottleneck is unproven. A different explanation is there were no global bottlenecks just the multitude of day to day local choices we have been making for a long time. (don't date the people from the other side of the river... they wear funny hats)
From a CS perceptive I would describe it as too much DFS not enough BFS which matters because backtracking means we go extinct.