Travel Reference
In-Depth Information
The classification of life
We know so much more now. We know about evolution, and genetics, and
the double helix of life uniting all living organisms on this planet. Yet there
is speculation and mystery still about the categories into which we classify
life (the province the field of study known as taxonomy), their validity, and
the relationships among them (the province of systematics). We know that
life is organized into basic units, the species, and that species somehow come
into being, exist for a period of time, and then disappear through extinction.
Species were once recognizable only for their morphology and then, as life
scientists peered closer, through the recognition that species are entities that
can successfully interbreed. Finally, as technology advanced much further,
scientists delved into the very DNA of a species, to discover the nature of
the unique aspects of the genome that dictate the nature of all other charac-
teristics, be they physical or behavioral.
Defining species now dead is much harder. There is no DNA to play
with, no opportunity to observe breeding habits. Assigning
fossils
to species
groups is thus much more difficult than categorizing living creatures. Yet is it
done—with mistakes to be sure—but done nevertheless, probably with good
success. It is in the nature of
our
species to categorize things, to classify; and
fossils are no exception.
Many species still living have left no fossils; usually these are the crea-
tures with no skeletal or other hard parts that might readily fossilize. Con-
versely, many fossil species have no living relatives; such victims of extinc-
tion have left no kin, and these poor orphans are often left dangling in our
classification schemes. But a good many animals and plants on earth today
do
have a fossil record, and it is from these organisms that we can learn the
most about evolution.
No paleontologist is immune to the call of evolutionary study. Even we
stratigraphic paleontologists, who comb the rock record for adequate time
markers, quickly hear the siren song of evolutionary change as we dig fossils
from rocks. And the next natural step for any scientist is to write about it,
the evidence of evolution—to describe, to study it. That is what we do. It is
