the childbearing years. Other researchers have argued that the emotional pain may cause the women to focus on the social circumstances that enabled the rape with the aim to prevent future rapes. Other research has found that during the fertile phase of the menstrual cycle women perform fewer behaviors that may increase the risk of an assault. Studies have also found that sensitivity for potential coercive behaviors in males as well as handgrip strength (but only in a simulated coercive situation) increase during the fertile phase of the menstrual cycle. On the other hand, a 2003 study found that the frequency of pregnancy from rape is significantly higher than that of pregnancy in non-coercive intercourse, and advanced the hypothesis that male rapists disproportionately target women exhibiting biological indications of fertility. Naturalistic fallacy Thornhill and Palmer write that "Rape is viewed as a natural, biological phenomenon that is a product of the human evolutionary heritage". They further state that by categorizing a behavior as "natural" and "biological" they do not in any way mean to imply that the behavior is justified or even inevitable. "Biological" means "of or pertaining to life," so the word applies to every human feature and behavior. But to infer from that, as many critics assert that Thornhill and Palmer do, that what is biological is somehow right or good, would be to fall into the so-called appeal to nature. They make a comparison to "natural disasters as epidemics, floods and tornadoes". This shows that what can be found in nature is not always good and that measures should be and are taken against natural phenomena. They further argue that a good knowledge of the causes of rape, including evolutionary ones, are necessary in order to develop effective preventive measures. Evolutionary psychologists McKibbin et al. argue that the claim that evolutionary theories are justifying rape is a fallacy in the same way that it would be a fallacy to accuse scientists doing research on the causes of cancer that they are justifying cancer. Instead, they say that understanding the causes of rape may help create preventive measures. Wilson et al. (2003) argue that evolutionary psychologists like Thornhill and Palmer use the naturalistic fallacy inappropriately to forestall legitimate discussion about the ethical implications of their theory. According to Thornhill and Palmer, a naturalistic fallacy is to infer ethical conclusions (e.g., rape is good) from (true or false) statements