Averaged face of blue-eyed male subjects (left). Averaged face of brown-eyed male subjects (right). Czech population. (Kleisner et al., 2010) Karel Kleisner’s team is continuing its work on eye color, face shape, and perceived personality traits: We tested whether eye color influences perception of trustworthiness. Facial photographs of 40 female and 40 male students were... Read More

In 1972, the U.S. passed the Clean Water Act, despite a presidential veto by Richard Nixon. Did this act also end an era of unusually high estrogen levels in the environment? (cartoon source) There has been much concern over the presence of “environmental estrogens� in our drinking water and elsewhere in the environment. These are... Read More

What causes exclusive male homosexuality? This is the question I’ve addressed in the last few posts. The answer is still elusive although there seems to be consensus on some points. One such point is the relative importance of inborn causation versus environmental causation. In men, an exclusively homosexual orientation has a heritability of 30-45%. A... Read More

In a previous post, I suggested that something in the environment had begun to alter male sexual development in Western countries by the turn of the 20th century. Among a small minority of men, probably those already weakly predisposed to heterosexuality, the result was a shift to exclusive male homosexuality, i.e., development of a female-like... Read More

In my last post, I argued that large quantities of estrogen were flushed into lakes and rivers across North America and northern Europe between the introduction of modern sewer systems in the late 19th century and the shift to secondary and tertiary sewage treatment after the 1960s. By separating out solid fecal waste and rapidly... Read More

What is the main source of estrogen in the environment? Birth control pills? An industrial compound with estrogenic properties, like DDT, PCBs, and dioxins? No, it’s women’s urine. The stuff that gets flushed down toilets millions of times a day. There is also testosterone in wastewater but at much lower levels, being less water?soluble (Tabak... Read More

One point is often raised about male homosexuality: it has always been with us. True, but has it ever changed in its nature or prevalence? Well, more gays have been ‘coming out of the closet.’ People are practicing openly what used to be done in secret. But have there also been more fundamental changes? Such... Read More