Natural Selection Image Map

Humans change the environment in many ways, both accidental and deliberate:

  • We put chemicals into the soil, water, and air 

  • We chop down jungles and forests

Likewise, humans move animals around and introduce them into niches they would not have encountered on their own. Ever since the intercontinental travel began by sea several hundred years ago, humans have been re-distributing plant and animal life.
  • Creatures stow away in cargo or on the vessels or vehicles. Rats and cockroaches, for example, have over-run the entire planet, thanks to easy access to these means of transportation..

  • Bacteria and virus move with the animals and people that move about. A disease that pops up anywhere in the world will eventually spread everywhere. Recent examples include AIDS and West Nile fever.

Deliberate introduction of species into new environments can lead to unintended consequences. Examples include:

  • House sparrows, introduced into U.S. in 1850, now number in the hundreds of millions and have crowded out many bird species.

  • Rabbits, introduced into Australia in 1859, thrived so well that they ate all the grass down to the roots and killed shrubs and bushes by eating all the bark. An estimated population of 750 million rabbits ate as much grass as would have been eaten by 100 million sheep. A viral disease that would kill rabbits was introduced around 1950. At first, 98% of rabbits were killed, but the survivors became resistant. Today, their descendants are only about 25% susceptible.

  • Sheep and cattle have displaced countless communities of plants and animals that could otherwise occupy the vast spaces that cattle and sheep require.

  • Agricultural crops (corn, wheat, etc.) destroy the niches that could support a wide range of native species. 

We are rapidly becoming one homogenous world. In the process, we must be careful about upsetting the balance of nature. In the book, Rogue Primate by John Livingston says that "Nature thrives on diversity and variety. Anything that tends to reduce the normal complexity of interrelationships is biologically destructive."





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