the degree of variation of life forms within a given
ecosystem, biome, or an entire planet. Biodiversity is a
measure of the health of ecosystems. Greater biodiversity
implies greater health. Biodiversity is in part a function
of climate. In terrestrial habitats, tropical regions are
typically rich whereas polar regions support fewer species.
Rapid environmental changes typically cause extinctions.
One estimate is that less than 1% of the species that have
existed on Earth are extant.
Since life began on Earth, five major mass extinctions
and several minor events have led to large and sudden drops
in biodiversity. The Phanerozoic eon (the last 540 million
years) marked a rapid growth in biodiversity via the
Cambrian explosion—a period during which nearly every phylum
of multicellular organisms first appeared. The next 400
million years included repeated, massive biodiversity losses
classified as mass extinction events. In the Carboniferous,
rainforest collapse led to a great loss of plant and animal
life. The Permian–Triassic extinction event, 251 million
years ago, was the worst; vertebrate recovery took 30
million years. The most recent, the Cretaceous–Tertiary
extinction event, occurred 65 million years ago, and has
often attracted more attention than others because it
resulted in the extinction of the non-avian dinosaurs.
The period since the emergence of humans has displayed an
ongoing biodiversity reduction and an accompanying loss of
genetic diversity. Named the Holocene extinction, the
reduction is caused primarily by human impacts, particularly
habitat destruction. Biodiversity's impact on human health
is a major international issue.
Distribution A conifer forest in the Swiss Alps (National
Selection bias amongst researchers may contribute to
biased empirical research for modern estimates of
biodiversity. In 1768 Rev. Gilbert White succinctly observed
of his Selborne, Hampshire "all nature is so full, that that
district produces the most variety which is the most
Biodiversity is not evenly distributed. Flora and fauna
diversity depends on climate, altitude, soils and the
presence of other species. Diversity consistently measures
higher in the tropics and in other localized regions such as
Cape Floristic Province and lower in polar regions
generally. In 2006 many species were formally classified as
rare or endangered or threatened; moreover, scientists have
estimated that millions more species are at risk which have
not been formally recognized. About 40 percent of the 40,177
species assessed using the IUCN Red List criteria are now
listed as threatened with extinction—a total of 16,119.
Even though terrestrial biodiversity declines from the
equator to the poles, this characteristic is unverified in
aquatic ecosystems, especially in marine ecosystems. In
addition, several assessments reveal tremendous diversity in
higher latitudes. Generally terrestrial
biodiversity is up to 25 times greater than ocean
A biodiversity hotspot is a region with a high level of
endemic species. Hotspots were first named in 1988 by Dr.
Norman Myers. Many hotspots have large nearby human
populations. Most hotspots are located in
the tropics and most of them are forests.
Brazil's Atlantic Forest is considered one such hotspot,
containing roughly 20,000 plant species, 1,350 vertebrates,
and millions of insects, about half of which occur nowhere
else. The island of Madagascar, particularly the unique
Madagascar dry deciduous forests and lowland rainforests,
possess a high ratio of endemism. Since the island separated
from mainland Africa 65 million years ago, many species and
ecosystems have evolved independently. Indonesia's 17,000
islands cover 735,355 square miles (1,904,560 km2) contain
10% of the world's flowering plants, 12% of mammals and 17%
of reptiles, amphibians and birds—along with nearly 240
million people. Many regions of high biodiversity and/or
endemism arise from specialized habitats which require
unusual adaptations, for example alpine environments in high
mountains, or Northern European peat bogs.
Biodiversity is the result of 3.5 billion years of
evolution. The origin of life has not been definitely
established by science, however some evidence suggests that
life may already have been well-established only a few
hundred million years after the formation of the Earth.
Until approximately 600 million years ago, all life
consisted of archaea, bacteria, protozoans and similar
The history of biodiversity during the Phanerozoic (the
last 540 million years), starts with rapid growth during the
Cambrian explosion—a period during which nearly every phylum
of multicellular organisms first appeared. Over the next 400
million years or so, invertebrate diversity showed little
overall trend, and vertebrate diversity shows an overall
exponential trend. This dramatic rise in diversity was
marked by periodic, massive losses of diversity classified
as mass extinction events. A significant loss occurred when
rainforests collapsed in the carboniferous. The worst was
the Permo-Triassic extinction, 251 million years ago.
Vertebrates took 30 million years to recover from this
The fossil record suggests that the last few million
years featured the greatest biodiversity in history.
However, not all scientists support this view, since there
is uncertainty as to how strongly the fossil record is
biased by the greater availability and preservation of
recent geologic sections. Some scientists believe that
corrected for sampling artifacts, modern biodiversity may
not be much different from biodiversity 300 million years
ago., whereas others consider the fossil record reasonably
reflective of the diversification of life. Estimates of the
present global macroscopic species diversity vary from 2
million to 100 million, with a best estimate of somewhere
near 13–14 million, the vast majority arthropods. Diversity
appears to increase continually in the absence of natural
Biodiversity supports ecosystem services including air
quality, climate (e.g., CO2 sequestration), water
purification, pollination, and prevention of erosion.
Since the stone age, species loss has accelerated above
the prior rate, driven by human activity. Estimates of
species loss are at a rate 100-10,000 times as fast as is
typical in the fossil record.
Non-material benefits include spiritual and aesthetic
values, knowledge systems and the value of education