Secondary grain
As secondary crops are in the Botany those cereals originally as sometimes referred to, weeds in the (primary) cornfields flourished, but later were economically interesting for people. The term comes from Nikolai Iwanowitsch Wawilow (1887-1943), who dealt with the gene centers of useful plants , those areas in which the greatest genetic diversity of these plants can be detected and in which they were probably cultivated for the first time. Wawilow described a kind of mimicry that had been brought about by human agriculture in some field weeds. As a result of the activity of the arable farmers, certain weeds have been selected since the Neolithic period in such a way that they also developed certain properties of the originally cultivated cereals. Later, when the environmental conditions changed, these plants were able to replace the original types of grain.
One example of this is rye , which used to be a weed in wheat fields . Through the spread of arable farming in the Neolithic from the Fertile Crescent to Europe, it gained competitiveness in the cool, temperate latitudes compared to wheat and thus gained importance for human nutrition. Rye was consequently cultivated in its purest form and no longer viewed as a weed . Another secondary grain is oats . Climate changes do not always have to be the reason for the anthropogenic upgrading of weeds. So the socio-cultural change can cause a shift in interests and thus result in the cultivation of weeds.