The active role of humans in the long history of domestication has been stressed in the debate over genetic engineering. By the time the third stage began, human control over animals seemed paramount, although every step to increased productivity was accompanied by unforeseen consequences that had to be culled. Unconscious selection is more often used for the selective pressures brought to bear on animals and plants by placing them in a human modified environment and exposing them to particular systems of husbandry. Examination of the role of unintentional human-influenced selection in the domestication of cereals was extended to several other plant types in the 1980s. Synanthropic selection occurs where a species is attracted to the highly modified environment that surrounds humans. The wolf’s habit of traveling in a pack can be seen as a preadaptation for migration with a human group.