Human evolution theory utilizing concepts of neoteny & female sexual selection
An etiology of neuropsychological disorders such as autism and dyslexia, and the origin of left handedness.
"As compared with nonsmokers and exsmokers, smokers had substantially and significantly lower levels of all three major estrogens in the luteal phase of the menstrual cycle. ... In follicular specimens estrogen concentrations for smokers did not differ significantly from those of nonsmokers. However, in the luteal specimens current smokers had levels about one third below those of nonsmokers or exsmokers for all three estrogens. The differences were significant for each estrogen and for the total." (MacMahon, B., Trichopoulos, D., Cole, P. & Brown, J. (1982) Cigarette smoking and urinary estrogens. New England Journal of Medicine 307: pp. 1063)
"The most intriguing question raised by these data is whether reduced estrogen levels in smokers are responsible for a possible reduced risk of breast cancer. The epidemiologic evidence linking high estrogen levels to a high risk of breast cancer has accumulated rapidly in recent years (Numoff et al., 1981; MacMahon et al., in press; MacMahon et al., 1982 in press), and the possibility that a one-third reduction in luteal estrogen stimulus produces a 20 percent reduction in the risk of breast cancer is credible. ... An increased risk of osteoporosis or osteoporotic fractures has been reported among women who smoke. In view of the evidence that exogenous estrogens protect against such fractures, it is also possible that the mechanism whereby smoking increases the risk that they occur, if it does, is through a reduction in endogenous estrogens." (MacMahon, B., Trichopoulos, D., Cole, P. & Brown, J. (1982) Cigarette smoking and urinary estrogens. New England Journal of Medicine 307: pp. 1064)