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For many years, it was believed that Bread Wheat had evolved
from Spelt by mutations that changed the form of the ear.
Newer scientific research now suggests that it evolved
independently about 8,500 years ago but from the same two
ancestors, Cultivated Emmer and a Goat Grass. This created a free-threshing
hybrid that differed from Spelt by the ear being roughly square
in section, with more grains and a tougher rachis. The grain was
also enclosed by a softer shell that would break away easily when
threshed to release the grains. After further evolution, it became
the source of the hexaploid Bread
Wheat, Triticum aestivum.
Initially the farmers grew wheat from seed they had saved from
the harvest of the previous year. Over many years, this created
different "landraces", each being a selection of wheat
suited to the type of soil or area where it had developed. By
using selected landraces and hybridisation, wheat breeders have
created and developed many improved varieties of wheat. Selected
reduced-height genes have been introduced
into wheat varieties to produce plants that use photosynthesis
to increase the grain yield instead of the plants growing taller.
In Britain, this gave an increase in yield from about 500 kg/ha
in the 1300's, up to 1,000 kg/ha in the 1800's, 2,000 kg/ha
by 1914, and up to 8,000 kg/ha in 2000 using newer varieties.