While the two groups remain distinct from each other, repeated use of the highest-performing parent lines has steadily reduced genetic diversity within each group. That narrowing gene pool could make it harder for breeders to continue improving yields or adapt corn to future challenges. The biggest concern emerged in the intermediate-maturity stiff-stalk group, where researchers found little remaining genetic variation for grain yield. “Our study reminds us of the importance of protecting and broadening the genetic diversity available to breeders. By introducing new sources of genetic diversity, breeding programs can continue developing better maize hybrids for future generations.”