The exploration of space must count as one of humanity’s greatest, most
astonishing achievements. Spacecraft have landed on the moon and Mars
and have passed close by Jupiter and even Pluto. Yet even as we plumb the
secrets of our solar system, we remain surprisingly ignorant of what the ento-
mologist Howard Evans [15] called “life on a little known planet”—our own.
No one can tell you how many species are on Earth—even to the nearest mil-
lion! Some biologists have estimated that about 1.5 million species of eukaryotes
have been discovered and named, but even this is a rough estimate. Experts
on insects, mites, nematodes, fungi, and many other groups of organisms know
that a far greater number of species have yet to be described and named. The
best recent estimate of the number of existing species is about 5 million—with
a margin of error of 3 million [12a]. This doesn’t include prokaryotes—archaea
and bacteria. We know from DNA samples that there are thousands of distinct
and unnamed prokaryote genomes in any sample of soil or seawater, or for that
matter, on and within a human body. And even among animals, the number of
existing species is probably less than 1 percent of all the species that have ever
lived on Earth. The diversity of life is truly overwhelming.
What we do know about this diversity is that it is very unevenly distributed
among major groups (higher taxa). There are about 220 living species in the pine
family, but the orchid family has about 18,000 species and the sunflower family
about 23,000. Among the orders of insects, there are 500 known speciesA diverse collection of weevils, scarabs, long-horned and metallic wood-bor-
ers, and other beetles. Beetles are by far the largest order of insects, with more
than 350,000 described species, and untold numbers yet to be described or
discovered. What accounts for their amazing diversity?The Geography of Evolution
of Biological
Diversity
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