  Emily Martin (2003) also points out that Thornhill and Palmer make problematic assumptions in their definition of ‘rape’. She argues that they falsely assume that rape is a static trait not only across cultures, but across species, that they fail to see that characterizing a behavior as rape requires a culturally specific notion of consent and that cultural meanings of rape have changed over time. (See the entry on  feminist perspectives on rape for a more detailed discussion of issues of consent. There remains an opportunity for feminist philosophy of biology concerning rape to be further integrated with feminist literature concerning rape.) Martin points out a second category of assumptions in Thornhill and Palmer's work regarding individualism, competition, and aggression, arising out of evolutionary theory itself. She points out the influence of Malthus' work on overpopulation and scarcity of resources and of Adam Smith's economics on Darwin's formulation of natural selection. She argues that evolutionary explanations tend to be based on notions of individual competition under conditions of scarcity, which are historically and culturally specific and need not hold. She writes, “As Thornhill and Palmer, as well as most who espouse the tenets of sociobiology, see the world, it is make up of highly individualized agents bent on maximizing their own advantage, defined as increasing their genetic stake in the next generation. Any means to that end, however ruthless, violent or aggressive, will be looked for and justified as necessary to increasing fitness, so defined” (375).