In other cases, the comparison shows significant discontinuity — the later population is genetically different from the earlier population in ways that are not easily explained by gradual drift or selection, suggesting that the later population arrived from elsewhere and partially or largely replaced the earlier one.

The patterns of turnover vary significantly across South America.

Some areas — particularly in Brazil, where the Lagoa Santa region is one focus of research — show evidence of continuity between early populations and later ones, with the genetics of ancient individuals from the early Holocene contributing to the ancestry of later populations from the same region.

Other areas show more evidence of turnover.

This spatial variability in population continuity has important implications for how Population Y should be interpreted.