^^^ That's a good point. For folks interested in the details Google "Endocrine disruptors". The theory is that various man-made chemicals of a certain sort act as hormones ( = endocrine system) in animals (different chemicals act differently on different animals). Some of the chemicals are decomposition products of other chemicals and are thus, difficult to track through the ecosystem. Proof is extremely difficult (as is usually the case for all things ecological) but correlations are compelling. For example, I know of several developmental deformities in herps that were initially believed thought due to chemicals but later, turned out to be pathogenic microorganisms. Others are most probably due to man-made chemicals. Proof of causality in vitro is essentially following Koch's principal and not too difficult but IN THE NATURAL ENVIRONMENT is elusive.