Along with hierarchies based on wealth and power, the development of agriculture was intertwined with a hierarchy based on gender. The system in which men have more power and access to resources than women and some men are dominant over other men is called patriarchy. Every society in the world that has left written records has been patriarchal, but patriarchy came before writing, and searching for its origins involves interpreting many different types of sources. Some scholars see the origins of gender inequality in the hominid past, noting that male chimpanzees form alliances to gain status against other males and engage in cooperative attacks on females, which might have also happened among early hominids. Other scholars see the origins in the Paleolithic, with the higher status of men in lineage groups.

Plow agriculture heightened patriarchy. Although farming with a hoe was often done by women, plow agriculture came to be a male task, perhaps because of men’s upper-body strength or because plow agriculture was more difficult to combine with care for infants and small children than was horticulture. The earliest depictions of plowing are on Mesopotamian cylinder seals, and they invariably show men with the cattle and plows. At the same time that cattle began to be raised for pulling plows and carts rather than for meat, sheep began to be raised primarily for wool. Spinning thread and weaving cloth became primarily women’s work; the earliest Egyptian hieroglyph for weaving is, in fact, a seated woman with a shuttle, and a Confucian moral saying from ancient China asserts that “men plow and women weave.” Spinning and weaving were generally done indoors and involved simpler and cheaper tools than plowing; they could also be taken up and put down easily, and so could be done at the same time as other tasks.

Though in some ways this arrangement seems complementary, with each sex doing some of the necessary labor, plow agriculture increased gender hierarchy. Men’s responsibility for plowing and other agricultural tasks took them outside the household more often than women’s duties did, enlarging their opportunities for leadership. This role may have led to their being favored as inheritors of family land and the right to farm communally held land, because when inheritance systems were established in later millennia, they often favored sons when handing down land. In some places inheritance was traced through the female line, but in such systems women themselves did not necessarily inherit goods or property; instead a man inherited from his mother’s brother rather than from his father. Accordingly, over generations, women’s independent access to resources decreased, and it became increasingly difficult for women to survive without male support.

As inherited wealth became more important, men wanted to make sure that their sons were theirs, so they restricted their wives’ movements and activities. This was especially the case among elite families. Among foragers and horticulturalists, women needed to be mobile for the group to survive; their labor outdoors was essential. Among agriculturalists, the labor of animals, slaves, and hired workers could substitute for that of women in families that could afford them. Thus in some Neolithic societies, there is evidence that women spent more and more of their time within the household, either indoors or behind walls and barriers that separated the domestic realm from the wider world. Social norms and ideals gradually reinforced this pattern, so that by the time written laws and other records emerged in the second millennium B.C.E., elite women were expected to work at tasks that would not take them beyond the household or away from male supervision. Non-elite women also tended to do work that could be done within or close by the household, such as cooking, cloth production, and the care of children, the elderly, and small animals. A special program set up under the third-century-B.C.E. Indian emperor Ashoka, for example, supported poor women by paying them to spin and weave in their own homes.

Social and gender hierarchies were enhanced over generations as wealth was passed down unequally, and they were also enhanced by rules and norms that shaped sexual relationships, particularly heterosexual ones. However their power originated, elites began to think of themselves as a group set apart from the rest by some element that made them distinctive — such as military prowess, natural superiority, or connections with a deity. They increasingly understood this distinctive quality to be hereditary and developed traditions — later codified as written laws — that stipulated which heterosexual relationships would pass this quality on, along with passing on wealth. Relationships between men and women from elite families were formalized as marriage, through which both status and wealth were generally passed down. Relationships between elite men and non-elite women generally did not function in this way, or did so to a lesser degree; the women were defined as concubines or mistresses, or simply as sexual outlets for powerful men. The 1780 B.C.E. Code of Hammurabi, for example, one of the world’s earliest law codes, sets out differences in inheritance for the sons a man had with his wife and those he had with a servant or slave, while not mentioning daughters at all:

If his wife bear sons to a man, [and] his maid-servant [has] also borne sons, [but] the father while still living . . . did not say to the sons of the maid-servant: “My sons,” and then the father dies, then the sons of the maid-servant shall not share with the sons of the wife, but the freedom of the maid and her sons shall be granted.2

Relations between an elite woman and a non-elite man generally brought shame and dishonor to the woman’s family and sometimes death to the man. (Early rules and laws about sex generally did not pay much attention to same-sex relations because these did not produce children that could threaten systems of inheritance.)

Thus, along with the distinctions among human groups that resulted from migration and were enhanced by endogamy, distinctions developed within groups that were reinforced by social endogamy, what we might think of as the selective breeding of people. Elite men tended to marry elite women, which in some cases resulted in actual physical differences over generations, as elites had more access to food and were able to become taller and stronger. By 1800 C.E., for example, men in the highest level of the English aristocracy were five inches taller than the average height of all English people.

No elite can be completely closed to newcomers, however, because the accidents of life and death, along with the genetic problems caused by repeated close intermarriage, make it difficult for any small group to survive over generations. Thus mechanisms were developed in many cultures to adopt boys into elite families, to legitimate the children of concubines and slave women, or to allow elite girls to marry men lower on the social hierarchy. All systems of inheritance also need some flexibility. The inheritance patterns in some cultures favored male heirs exclusively, but in others close relatives were favored over those more distant, even if this meant allowing daughters to inherit. The drive to keep wealth and property within a family or kin group often resulted in women inheriting, owning, and in some cases managing significant amounts of wealth, a pattern that continues today. Hierarchies of wealth and power thus intersected with hierarchies of gender in complex ways, and in many cultures age and marital status also played roles. In many European and African cultures, for example, widows were largely able to control their own property, while unmarried sons were often under their father’s control even if they were adults.