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Evolutionary psychologists have developed several models to explain the apparent contradiction of suicide and evolutionary theory. Denys de Catanzaro has conducted a lot of research into this field. Others, such as Donald H. Rubinstein, and Anne Campbell have also done work in this field. The major difficulty for evolutionary psychologists is to explain why an organism would so deliberately harm its own potential reproductive capacity. Suicide seems to be perhaps the ultimate maladaptive trait, other than, perhaps, infanticide of one's own children.
De Catanzaro begins to explain suicide by saying that differential reproduction is in fact much more important to evolution than is "survival of the fittest". That is to say, that mere survival is not particularly important to passing on genes. Even if someone is short lived, but reproduces a lot, they are likely to have more descendants than someone who lives a long time but does not reproduce very much. The other factor in explaining from the evolutionary perspective is inclusive fitness. Since an individual will share many genes with their relatives, it is in their evolutionary interest to ensure their relatives' survival and reproduction. More of their genes will be present in subsequent generations.
De Catanzaro believes that a general theory of suicide can be formed based on a calculation of the "costs of an individual's immediate death to the propagation of his or her genes". He developed a very complex equation that takes the various factors of the subject's potential reproduction, such as dependency of children, remaining reproductive potential, dependence on kin, and others, into account and is able to predict the subject's risk for suicide. Current research has been conducted mostly in the United States, with a large portion of the sample being young, educated, and religious.
According to de Catanzaro's variables, those at greatest risk of suicide include the elderly, especially those who are a burden on their family, anyone who is ostracized by their kin, someone unable to provide for their kin, dependent on their reproductively capable kin, or anyone who has difficulty relating with the opposite sex. All of these conditions will lead to emotional and psychological conditions that will make suicide more likely. De Catanzaro cites studies that show that emotions have a physiological basis to show that the self destructive response may be a natural, evolved response to their situation to ensure the continued propagation of one's genes.
According to this theory, those mostly likely to kill themselves would be the elderly dependent on financially pressed children, or someone with little hope of reproducing who is also dependent of kin. Dr. de Catanzaro's theory can also be applied to general self preservation. It can be used to predict how likely a mother or father is to sacrifice herself or himself to save their children, or other situations of that sort. De Catanzaro takes pains to recognize that his formula is only a base on which to predict likelihood of suicide or self sacrifice. He freely acknowledges that suicide is partially a learned behaviour, as is evidenced by the phenomenon of groupings of suicides occurring in short periods of time. He believes that there are many cultural phenomena that will affect any given individual. De Catanzaro also places strong emphasis on the fact that modern expressions of suicide may sometimes be unpredictable because we are in a different environment from that which we evolved in. He believes that there are many more suicides today than there would be in our "natural" environment due to stress and our confrontation with many situations that we have not been selected to deal with.
Another approach explains the differences between the sexes. One theory argues that men die of suicide more often than women because they do not value their lives as much as women. Since men are not essential to the survival of their offspring, and their potential for reproduction is much more varied, men have evolved to be less fearful of taking risks than women have. If a woman under natural conditions were to die, her children would most likely die as well. Therefore women have evolved to be more fearful of death and physical risk than men, and are therefore less likely to die of suicide. Under this theory suicide is just an expression of males' general willingness to take risks. This may be disclaimed by the fact that while men are 400% more likely to successfully commit suicide, the WHO reports that women attempt suicide more often than men[How to reference and link to summary or text].