Humans change the environment in many
ways, both accidental and deliberate:
We put chemicals into the soil, water,
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
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