According to the professor, what was a possible result of the selective breeding of crop plants?

Listen to part of a lecture in a history class.
Professor: We’ve been exploring early civilizations, those that existed 7,000 to 8,000 years ago. And today I’d like to talk about the switch from foraging, or searching for whatever wild foods were available, to farming: intentionally cultivating crops.
    Now, the way that switch is frequently portrayed is that it was an improvement. The development of agriculture is usually portrayed as a good thing, but there are advantages to foraging. For one thing, it provides a better balance of nutrients and, in particular, more protein, at least compared to the diet of the early farmers. Foragers ended up eating a greater mix of foods, both plants and animals, but the early farmers—and to some extent this is still true today—the early farmers concentrated on just a few crops, like rice and wheat. There was less variety and therefore a smaller range of nutrients and a lot more carbohydrates, so the quality of the diet wasn’t as good, and we have evidence of this. Foragers were on average almost 15 centimeters taller than the early farmers. That’s a lot! ln Greece and Turkey, when comparing skeletons from forager communities to those of early farming communities, we see that height declined when farming was adopted, quite dramatically I might add.
    Furthermore, farming increased one’s vulnerability to starvation. It was riskier to live off cultivated crops than to live off the wild, partly because it meant relying plants. Farmers, even modern farmers, only cultivated about 20 different plants on average and even then they really focused on just three: wheat, rice, and maize. Modern foragers, on the other hand, depend on over 100 different plants, what with fruits, nuts, berries, roots, beans, and so on. So, if a few cultivated crops failed... if the rice crops failed, for example, the farmers were in trouble. Now, of course, wild plants could fail too, but foragers ate so many different plants, they always had something to eat. Domesticated plants also may be more prone to failure than wild plants. We need to keep in mind that agricultural crops are the result of selective breeding. Farmers chose certain seeds, ones that have the qualities they wanted, refining the crop each harvest. So if seeds from the plumpest potatoes or the whitest rice grains were chosen, the heartier strains, the ones that can resist insect attacks, or disease, or extremes of temperature, or moisture, for example, may be eliminated because the farmer hadn’t chosen seeds from plants with these characteristics.
    So how did the switch from foraging to agriculture happen? Well, no one’s really sure. Some speculate that during the final phase of the last ice age about 10,000 to 13,000 years ago, there was a shift in climate in a number of locations that led to the decrease of food you could forage for. The failure of wild harvests may have caused people in different parts of the world to plant some crops to make up for the shortage. There’s evidence that the practice of cultivation existed at that time. In China, for example, rice was cultivated as long as 10,000 years ago by people who were also still eating wild rice. By counting the proportions of wild rice and cultivated rice in plant fossil remains, archaeologists have determined that the switch to farming there was a slow one, taking about 4,000 years.
    So it didn’t happen overnight, and there’s evidence that other groups of people also cultivated some cereal crops, blending both foraging and farming for thousands of years. So putting people in little boxes and classifying them as either foragers or farmers, well, we don’t do that anymore. Of course there were advantages to farming. Agriculture provided a greater quantity of food, and when you have an increasing population, as was the case in ancient Southwestern Asia, that’s a definite advantage. Also, with irrigation, crops could be planted in what was until then useless land. Wheat and barley, for example, didn’t grow naturally on the land between the Tigris and Euphrates Rivers in ancient Mesopotamia, but once that land was irrigated, all of it could become cultivated and hectare for hectare farming yielded more food than foraging. Farmers needed 20 times less land, 100 times less if they irrigated to feed the same number of people as foragers needed.