Wheat

Humans probably never selectively bred grasses to produce larger ears of seed. Instead it was the natural result of the intensive predation of grasses by both humans and other animals.

As grasses came under increasing predation, slow reproducing grasses began to be displaced by faster-reproducing grass. Such grasses put more energy into reproduction. By producing larger seeds, they gave their offspring a larger store of energy - to power rapid initial growth of the seedling plant, giving it a head start. At the same time, producing more seeds result in more seedlings. And coating the seeds in a tough outer case would increase their chances of surviving intact in the gut of a predator. Thus the grasses naturally evolved into progressively higher-yield wheat.

Probably, grass seeds did not initially need to be ground for the husk to be removed. This only became necessary when grasses had evolved such tough cases that most human teeth could not break them open. Those humans who had powerful enough jaws and teeth continued to eat the seeds. The rest either shifted to some other food source, or began to use stones to grind and smash open the seeds.

Conversely, if grasses ceased to be subject to intense predation, the advantages of fast reproduction vanished, and slower and slower reproducing grasses would gradually predominate.

The introduction of farms, on which these grasses were intensively cultivated, may well have ended the natural evolution of grasses towards higher yields - because on such farms, where all, or nearly all, the seeds were gathered, fast-reproducing grasses were no more successful in surviving than slower reproducers. But the human farmers probably kept the largest seeds, from plants with the largest ears, to sow the next year. In this way, they selected for the most productive plants. But the relative isolation of these plant crops meant that they did not cross-breed with other wild grasses to produce new variants. One single variety of grass would entirely predominate.

Intensive farming - growing thousands of plants in a small area - increased the number and reduced the time it took to gather what would have otherwise been a widely dispersed population of plants. Also, if other animals could be kept from consuming these crops, a greater proportion of them would be available for human consumption. With abundant fauna in the surrounding habitats, the threat from animals was probably considerable. Ditches, fences, and hedges probably served to keep out the larger grazing animals. Walls and moats may have kept out smaller ones like rats or mice. Nets may have been used to keep out birds. And of course a variety of predators would have been kept to ensure that where animals did get in, they were rapidly disposed of, before they could multiply and infest the crop. Only insects appear to have posed an almost insuperable threat.

Given such a need to defend against other grazing animals, the first farms may have been sited on islands in rivers. The river and its predators (such as crocodiles) not only supplied water to irrigate the plants as well as nutrient soils, but also provided a natural barrier to most animals. River deltas, in which such islands are abundant, may have provided the ideal location. And when farming extended to the river banks, artificial islands may have been created by digging waterways that served to both irrigate and defend.

On small ocean islands, it may have been possible for men to exterminate, probably over a long period, most animals that posed any threat to their crops. On these islands, with little influx of new immigrant grazing animals, fences and nets and guard predators would have become unnecessary.