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By cross-breeding plants and animals, our Stone Age ancestors realised they could boost the amount of food they produced.

These changes are often quite small ones, which involve editing sections of the DNA into a form that, its advocates say, could be produced through natural means like traditional cross-breeding, only much faster.

Much as animal species can be bred for hardiness by selectively mating the strongest pairs, the scientists gather the handful of chestnut trees from each stand that show improved blight resistance over their predecessors, and use only those for cross-breeding.

Mr. Currie of South Carolina spent 10 years cross-breeding peppers to create the new strain after previously breaking the heat record with the Carolina Reaper.

For many years, farmers produced new varieties through traditional cross-breeding techniques.