How did the Columbian exchange affect the world?

The Colombian exchange had both good and bad effects on
both sides of the Atlantic and other areas, primarily in the dispersion of useful plants
and animals but also the spread of harmful elements and
diseases.

Prior to the Colombian exchange, potatoes and
maize (corn) as well as turkeys were unknown outside the Americas. When introduced to
other parts of the world, they contributed to a substantially healthier diet. The end
result was a healthier population with more children surviving to adulthood, and
resulted in an explosion in the population. In the Americas, the introduction of hogs,
cattle, sheep, etc. were immensely beneficial to the Europeans who came there, but were
generally harmful to Indian settlements as they damaged or destroyed food crops. The
most important benefit to Indians was the introduction of the horse by the Spanish. It
soon became important in buffalo hunts on the plains. A less welcome arrival in the
Americas was the cockroach, which made itself at home and has
remained.

Sadly, diseases and other harmful elements were
part of the exchange. Thistles and other noxious plants were transported, probably
inadvertantly, from Europe to the Americas. Diseases such as small pox, measles and
mumps emaciated over 90% of the Indian population. In Europe, the introduction of
syphillis from the Americas (previously unknown in Europe but transported there by
conquistadores and others from the Americas) decimated that population. Human beings
were another sad element of the exchange, as slaves from Africa were introduced into the
Americas after attempts to enslave Indians proved
unproductive.

Charles C. Mann has an excellent new book,
1493 which provides elaborate detailed information on the Colombian
Exchange.