Reproductive labor or work is often associated with care giving and domestic housework roles including cleaning, cooking, child care, and the unpaid domestic labor force. The term has taken on a role in feminist philosophy and discourse as a way of calling attention to how women in particular are assigned to the domestic sphere, where the labor is reproductive and thus uncompensated and unrecognized in a capitalist system. These theories have evolved as a parallel of histories focusing on the entrance of women into the labor force in the 1970s, providing an intersectionalist approach that recognizes that women have been a part of the labor force since before their incorporation into mainstream industry if reproductive labor is considered. Some Marxist anthropologists and economists such as George Caffentzis suggest that reproductive labor creates value in a similar way to the way in which productive labor creates value, by increasing the value of labor power. Economist Shirley P. Burggraf suggests additional value could be realized by replacing government support systems for the elderly (such as the US Social Security System) based on an individual's payroll tax contributions, with parental dividends proportional to the income of one's own children. Such a system could potentially achieve greater efficiency by introducing a return on investment for reproductive labor, thereby incentivizing the care and rearing of children. The division between productive and unproductive labor is stressed by some Marxist feminists including Margaret Benston and Peggy Morton. These theories specify that while productive labor results in goods or services that have monetary value in the capitalist system and are thus compensated by the producers in the form of a paid wage, reproductive labor is associated with the private sphere and involves anything that people have to do for themselves that is not for the purposes of receiving a wage (i.e. cleaning, cooking, having children).