DDT DID thin eggshells. The problem was species used. It affected the eggs of raptors. The studies you cite showed that DDT did not cause eggshell thinning in chickens and Japanese quail and while the study was accurate, some of the conclusions drawn by the general public are not: first it was conducted on gallinaceous birds and second, DDT rather than DDE, a metabolite of DDT which has has been identified as the cause of egg-shell thinning was used.
Daniel W. Anderson (currently at Department of Wildlife, Fish, and Conservation Biology at the University of California-Davis), was one of the original researchers on eggshell thinning. He also agrees that the evidence shows that gallinaceous birds (poultry and fowls), herring gulls, and most passerine (perching) birds aren't as sensitive to DDE as raptors. But even though chickens and quail fed very high concentrations of DDE and an adequate amount of food experienced essentially no eggshell thinning or other reproductive problems, science shows pretty conclusively that it's another story for raptors.
The most persuasive study on this is: "DDE-induced Eggshell Thinning in the American kestrel: A Comparison of the Field Situation and Laboratory Results." published in the Journal of Applied Ecology by Jeffrey Lincer in 1975.
Here is an excerpt from that study:
Lincer noted that the "inverse correlation between DDE in North American raptor eggs and eggshell thickness is clear but does not prove a causal relationship since other chemicals or factors could be involved." So to find out what effect DDE might have, Lincer fed captive kestrels a DDE-laced diet and then compared their eggs with those taken from the nests of wild kestrels. Lincer found that dietary levels of three, six, and 10 parts per million (ppm) of DDE resulted in eggshells that were 14 percent, 17.4 percent, and 21.7 percent thinner respectively. "Despite the recent controversy, there can be little doubt now as to the causal relationship between the global contaminant DDE and the observed eggshell thinning and the consequent population declines in several birds of prey," concluded Lincer.
So, Rachel Carson was wrong in that it assumed all birds at risk but she was right to point out that so many of these pesticides that we took for granted - so much so we practically bathed in it and used it indiscrimminantly -have serious repercussions attached to them. No one thought about that before.
However, it is correct in that it put raptors at risk.
Now, I'll bring up something which you brought up in another debate when we discussed the birth control pill as an abortificant. You mentioned that is should be banned despite the fact it is one of the best and safest contraceptives for a woman to use. One of the reasons was if it were banned it would spur science to do research to find equally effective alternative methods. Now my question to you is - why not apply this same practicality to DDT? Shouldn't banning it have produced a flurry of science to create a better and safer pesticide?
The other hidden part of this problem - another unintended consequence to heavy pesticide use is resistance in insect populations. Would not DDT face that with continued heavy use rather than judicial use?
Unintended consequences are frequently an inability to see the whole picture - how so many things are really interconnected. In that - it has little to do with conservative or liberal except for one thing: Conservatives would rather wait and not induce change for fear of consequences and liberals would rather jump in and induce change in hopes of improving a problem.
