Historic yield advances in the major crops have, to a large extent, been achieved by
selection for improved productivity of groups of plant individuals such as high-density
stands. Research suggests that such improved group productivity depends on “cooperative”
traits (eg, erect leaves, short stems) that—while beneficial to the group—decrease individual
fitness under competition. This poses a problem for some traditional breeding approaches,
especially when selection occurs at the level of individuals, because “selfish” traits will be …