Crops and weeds

An interesting article about weeds, how we've shaped them just as we've shaped the plants we consider crops, and what the effects of increased CO2 in the atmosphere may be on both of them.

This excerpt seems to support an earlier post I wrote about higher crop yields:

Coexistence with mankind has given rise to the sort of tough plants that flourish despite the worst we can do — hoeing, pulling, burning and, more recently, spraying the fields with herbicidal chemicals. Weeds have adapted to every means we used to exterminate them, even turning the treatments to their own advantage. Attacking a Canada thistle (actually of Eurasian origin and a regular entry in “worst weeds of North America” lists) with hoe or plow, for example, may destroy the plant’s aboveground growth but leaves the soil full of severed bits of fleshy root, each of which may sprout a new plant.

A result of this history is that crops and weeds embody diametrically opposed genetic strategies. Over the centuries, we have deliberately bred the genetic diversity out of our crop plants. Creating crop populations composed of clones or near clones was an essential step in achieving higher yields and the sort of uniform growth that makes large-scale, mechanized cultivation and harvesting possible. Because weed populations live as opportunists, however, they must include individuals with the ability to flourish in whatever type of habitat we make available. They also need diversity to cope with the wide range of punishments we inflict. A patch of Canada thistles, if it is to survive when the farmer switches from hoeing to herbicides, must include individuals that develop a resistance to the chemicals over time. Weed populations that lacked the necessary genetic diversity faded from our fields, lawns and waste places; historians of agriculture can cite many such casualties.