Exogenous Factors

Environmental Pollution Issues

GIRES is aware of the mounting evidence that unusual development of sex characteristics and in sex ratios at birth in the animal and human populations may be associated with environmental pollution. The scientific discussion of this issue continues. A recent article, It’s Time to Learn From Frogs, in the New York Times provides a helpful summary of the anxieties being expressed about this issue. Individual studies of the effects in the human population include one in Japan in 2001, Declining Minamata Male Birth Ratio Associated with Increased Male Fetal Death Due to Heavy Methylmercury Pollution, and another in Canada in 2005, Declining Sex Ratio in a First Nation Community.


DES, or diethylstilbestrol, is the most widely studied endocrine disruptor. Roughly 2.5 million boys were exposed to DES in utero between 1948 and 1971, most after 1953 when it was proven that it had no effect in preventing miscarriage. Research began in earnest after it was discovered in 1971 that eight young women who had been prenatally exposed to DES had developed a rare vaginal clear cell adenocarcinoma.

It has subsequently been proven by McLachlan that DES exposure in rodents causes sexual variation. While there have been anecdotal case reports in the medical literature regarding the psychosexual effects of DES exposure, beginning in 1959, and a study documenting homosexuality among exposed women, little attention has been paid to this issue. But this situation is changing.

For the first time, Swan (2005) reported that an endocrine disruptor, the class of organic compounds known as phthalates, can cause demasculinization in human males. This builds on decades of work in other animal populations, particularly rodents, with an early emphasis on DES as the endocrine disruptor.

A couple of recent papers on this topic may be found below.

Beyer Minot Presentation 2005 (DOC, 83KB)

Kerlin Paper 2004 (DOC, 106KB)