but it is the 10th edition from 1758
that founded the modern zoological
naming system. Two volumes of
Linnaeus’ work are devoted to
plants and animals, which he
divided into classes, orders, genera,
and species. The binomial system,
in which every species is given a
generic name followed by a specific
name, is still in use today. Linnaeus
also wrote a third volume on rocks,
minerals, and fossils.Species concepts
Building on Darwin’s theory of
evolution by means of natural
selection, German-American
evolutionary biologist Ernst Mayr
cemented the biological concept of
species in his Systematics and the
Origin of Species (1942). He argued
that a species is not just a group of
morphologically similar individuals,but a population that can breed
only among themselves. Mayr went
on to explain how if groups within
a species become isolated from the
rest of the population, they may
start to differ from the rest, and
over time, through genetic drift and
natural selection, may even evolve
into new species.
Modern technological advances,
including electron microscopy and
mitochondrial DNA analysis, have
revealed much information—some
of it surprising—about the number
of species and the relationships
between them. In 1966, striving to
reflect the intricacies of evolution,
German entomologist Willi Hennig
proposed a new taxonomic system
of clades—groups of organisms
based on a common ancestor. In
the 1970s, American biologist Carl
Woese classified all life into threenew domains. As of 2018, about
1.74 million extant plant and animal
species have been described, but
estimates of the total number range
from 2 million to 1 trillion.The threat to diversity
By the late 20th century, however,
alongside a growing knowledge
of the scale and critical role of
biodiversity—and of how evolution
can destroy species as well as
create them—American ecologist
E.O. Wilson and others made the
world aware that human activity
was responsible for causing a rapid
acceleration in the extinction rate.
Some have even warned that Earth
could be on the verge of a sixth
mass extinction. Many policies are
now being proposed to counter
this, including the protection
of biodiversity hotspots. ■ORDERING THE NATURAL WORLD
1977
Carl Woese
establishes a new, third
category of organisms—
the prokaryotes.1988
Norman Myers’s
“biodiversity hotspots”
concept identifies ten hotspots
where conservation efforts
should preserve rare species.81
1942
Ernst Mayr develops the
biological species concept,
which categorizes species
based on their ability to
breed with each other.1988
Edward O. Wilson coins
the term biodiversity
and later identifies the
key human threats
to biodiversity.2018
The IUCN Red List shows that
more than 26,000 species –
more than 27 percent of all
those assessed—are at
risk of extinction.US_080-081_Ch_3_Ordering_the_natural_world_Intro.indd 81 17/12/2018 14:33