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Galapagos Tortoise. (Photo by Rhenda Glasco)
EVOLUTION
Today is is generally accepted that species form through the process of evolution. Evolution was first formally
described by Charles Darwin and Alfred Henry Wallace in the late 1850s. Darwin's publication of The Origin of Species
shook the foundation of Christian doctrine: that all species were divinely created. The work was immediately condemned
by Catholics, Jews, and Protestants alike marking a rare consensus in a long bloody history of divisiveness.
The effort of these eminent naturalists and others, along with the bounty of hitherto unknown creatures found in
newly discovered lands undermined the belief in the literal Ark as presented by the Scripture. Such an ark, which
housed a pair of all species, was becoming quite crowded in the eighteenth century. Darwin and Wallace challenged
the existing view that a supreme being created each species for a specific habitat (which required no evidence),
and presented the concept of evolution by natural selection, for which they supplied evidence from their travels
in the tropics.
The theory of evolution through natural selection is relatively simple. Individuals within any population, whether
it be rhinoceros beetles, goanas, or barnacles, show variations in certain inheritable characteristics. These genetic
variations are often random or chance changes in the genetic makeup of an individual that occur during reproduction.
These differences in genetic characteristics mean some individuals are better suited to the conditions of their
environment and leave more offspring than those less fit. Over long periods of time, the genetic composition of
the population will change and the species essentially adapts (not consciously, but by "survival of the fittest")
to changes in their environment. When a population has undergone so much genetic change that it is no longer capable
of breeding with the original stock it is considered a new species.
In order for one species to become two or more species some form of geographic isolation is usually required (see
the elephant example under "Ice Ages/Glaciation). New species can also form through adaptive radiation which
occurs when a single species enters a habitat where niches remain unfilled. Gradually, those individuals with certain
characteristics, say a longer beak or stronger claws, will have the advantage over other individuals with different
traits. The individuals with these characteristics with thrive and produce more offspring and eventually fill the
open niche. The most famous example of adaptive radiation are Darwin's finches of the Galapagos Islands, but many
better examples exist like the lemurs of Madagascar (see chapter 4 under "Mammals") and the Honeycreepers
of Hawaii. Honeycreepers, a bird the size of finch, have radiated into many different niches on the Hawaiian islands
so that before human interference, some 30 species existed.
Convergent or parallel evolution is an interesting phenomenon whereby different species with different
ancestry evolve to occupy the same niche, usually on separate land masses. These phylogenetically different species
often develop very similar physical traits and behaviors, because those characteristics are superb for their niche.
Relatively new evidence suggests that evolution may not be the slow, continuous process, of Darwin's reasoning,
but a rather sporadic process that occurs in bursts of rapid change. This more chaotic view of evolution is encompassed
by the theory of punctuated equilibrium which proposes that most structural change occurs during the speciation
events, when a species originates and that very little further evolutionary change occurs thereafter. Therefore
we expect relatively rapid speciation after an extinction event or geographic isolation, but relatively little
or no evolution once the previously unoccupied niches are filled. Studies in the late 1990s uncovered a mechanism
in fruit flies that could help explain the rapid formation of new species in response to a changing environment.
So-called "Doomsday genes" may enable species that have existed with the same appearance and behavior
for thousands of years to undergo radical structural changes in mere generations in response to sudden environmental
changes.
"Rainforest" is used interchangeably with "rain forest" on this site. "Jungle" is generally not used.
Recent news
Beef consumption fuels rainforest destruction (02/16/2009)
Nearly 80 percent of deforestation in the Brazilian Amazon results from cattle ranching, according to a new report by Greenpeace. The finding confirms what Amazon researchers have long known – that Brazil's rise to become the world's largest exporter of beef has come at the expense of Earth's biggest rainforest.
How to save the Amazon rainforest (01/04/2009)
Environmentalists have long voiced concern over the vanishing Amazon rainforest, but they haven't been particularly effective at slowing forest loss. In fact, despite the hundreds of millions of dollars in donor funds that have flowed into the region since 2000 and the establishment of more than 100 million hectares of protected areas since 2002, average annual deforestation rates have increased since the 1990s, peaking at 73,785 square kilometers (28,488 square miles) of forest loss between 2002 and 2004. With land prices fast appreciating, cattle ranching and industrial soy farms expanding, and billions of dollars' worth of new infrastructure projects in the works, development pressure on the Amazon is expected to accelerate. Given these trends, it is apparent that conservation efforts alone will not determine the fate of the Amazon or other rainforests. Some argue that market measures, which value forests for the ecosystem services they provide as well as reward developers for environmental performance, will be the key to saving the Amazon from large-scale destruction. In the end it may be the very markets currently driving deforestation that save forests.
Amazon rainforest damage surges 67% in 2008 (12/20/2008)
The area of rainforest in the process of being deforested — razed but not yet cleared — surged in the Brazilian Amazon during 2008, according to new figures released by Brazil's National Institute for Space Research (INPE). The announcement comes shortly after the Brazilian government reported a 4 percent increase in forest clearing for the year. Using an advanced satellite system that tracks changes in vegetation cover INPE found that 24,932 square kilometers of Amazon forest was damaged between August 2007 and July 2008, an increase of 10,017 square kilometers -- 67 percent -- over the prior year.
Cutting deforestation can fight climate change, reduce poverty and conflict (09/24/2008)
Forest conservation can play a critical role in efforts to reduce greenhouse gas emissions and alleviate poverty, said a prominent group of politicians, development experts, and environmental NGOs meeting in New York City to discuss U.S. climate policy.
Future threats to the Amazon rainforest (07/31/2008)
Between June 2000 and June 2008, more than 150,000 square kilometers of rainforest were cleared in the Brazilian Amazon. While deforestation rates have slowed since 2004, forest loss is expected to continue for the foreseeable future. This is a look at past, current and potential future drivers of deforestation in the Brazilian Amazon.
