Often, the cause is difficult to determine because the parents may show no obvious adverse effects associated with exposure to hormone copycats, and the damage to the offspring may not reveal itself until maturity. The table on the next page shows the general trends during the last 50 years in uses of chlorinated organic chemicals and pesticides around the world. Note that peak use appears to have occurred in the 1960's and 1970's, when today's generation of young adults was being born to parents who were exposed as adolescents. The second table summarizes general trends of pollution-related declines and abnormalities in the wildlife kingdom. Many of these declines of bird, fish, reptile and mammal populations are correlated to exposures to pollutants capable of disrupting endocrine functions.
Chemicals frequently blamed include PCBs, DDT and dioxins.
Nevertheless, definitive links between specific chemicals and many wildlife maladies have not been proven because animals are exposed to so many chemicals. For example, alligators in Florida's Lake Apopka don't reproduce well. Males have abnormally small phalluses. Around the Great Lakes, bald eagle reproduction is low and an unusual number of baby eagles are born with crossed beaks. The parent eagles' diet of PCB-contaminated fish and birds appears to be the cause.