Natural Selection Image Map

Unintended  Consequences of Conservation Efforts

DDT Example

Have you read the Rachel Carson story yet (see Story Time)?    Rachel Carson worked at a time when DDT was a common insecticide.  Everyone thought it was about the safest bug killer available, and it was used with apparent success for many years. But then people noticed that certain bird species populations were declining. Especially alarming was the U.S. national symbol, the bald eagle. Click here to read about the eagle recovery program. Closer study revealed that bald eagle eggs were cracking and preventing chicks from developing and hatching. Without reproduction, no species can survive. The cause was attributed to DDT, which causes thinning of egg shells. This was an unintended consequence of using the insecticide. And so DDT was banned from use in the U.S. and many countries of the world.

But now there is yet another unintended consequence.  Malaria in tropical countries is spreading rapidly. Malaria is caused by a blood parasite that is transmitted from one person to another by mosquito bites. Mosquitoes are developing resistance to the insecticides that we have used as substitutes for DDT. Mosquitoes  might also eventually develop resistance to DDT. The point is that we need a wide array of insecticides to keep one step ahead of resistance changes in mosquito populations. 

Aedes aegypti mosquito on human skin.

Mosquito populations are increasing, causing an increase in the spread of malaria. DDT was, and is, our cheapest insecticide, and Third World countries cannot control mosquito populations without cheap insecticides. But DDT is banned.  While we have probably saved some bird species, we have allowed human malaria to kill thousands more people around the world.  Click here for more.

Gasohol Example

Clearly, we must stop using so much fossil fuel, such as oil, which is used to make gasoline for our cars and trucks.  Fossil fuels, once burned, cannot be replaced. They are not renewable.  In a world that will someday run out of oil (estimates range from 20 to 100 years), we simply must find alternatives.  

Government programs help farmers find a new market for their corn: gasohol.

One bright idea is to add alcohol to gasoline to reduce the amount of fossil fuel needed for vehicles. Alcohol, made from fermenting grain, is renewable. Alcohol would also reduce tailpipe emissions that contribute greatly to our air pollution.  Moreover, a gasohol program would provide a new market for corn farmers. Congressmen from corn-growing states are trying to make laws requiring the use of gasohol. Good ecology, good economics, good politics. Right? Wrong!

A Cornell University researcher, David Pimentel, has found that it takes more energy to make alcohol than alcohol supplies for gasohol. It takes 70% more energy (which comes from fossil fuels) to produce alcohol than alcohol produces. Click here to see the data and calculations. A gallon of alcohol costs at the time of this writing $1.74 a gallon to produce. Gasoline costs $0.95 per gallon to produce. That is why fossil fuels are used to produce the heat needed to make alcohol. Notice that alcohol costs more than the fossil fuels.

Even cleaner air is open to debate. The Environmental Protection Agency suspects that alcohol production plants are polluting the air with carbon monoxide, methanol, and other chemicals.

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