Page 26 - Introduction to Paleobiology and The Fossil Record

PALEONTOLOGY AS A SCIENCE 13
debated whether there was a progression from
simple organisms in the most ancient rocks to
more complex forms later. The leading British
geologist, Charles Lyell (1797–1875), was an
antiprogressionist. He believed that the fossil
record showed no evidence of long-term, one-
way change, but rather cycles of change. He
would not have been surprised to fi nd evi-
dence of human fossils in the Silurian, or for
dinosaurs to come back at some time in the
future if the conditions were right.
Progressionism was linked to the idea of
evolution. The first serious considerations of
evolution took place in 18th century France,
in the work of naturalists such as the Comte
de Buffon (1707–1788) and Jean-Baptiste
Lamarck (1744–1829). Lamarck explained
the phenomenon of progressionism by a large-
scale evolutionary model termed the “Great
Chain of Being” or the Scala naturae. He
believed that all organisms, plants and
animals, living and extinct, were linked in
time by a unidirectional ladder leading from
simplest at the bottom to most complex at the
top, indeed, running from rocks to angels.
Lamarck argued that the Scala was more of
a moving escalator than a ladder; that in
time present-day apes would rise to become
humans, and that present-day humans
were destined to move up to the level of
angels.
Darwinian evolution
Charles Darwin (1809–1882) developed the
theory of evolution by natural selection in the
1830s by abandoning the usual belief that
species were fixed and unchanging. Darwin
realized that individuals within species showed
considerable variation, and that there was not
a fixed central “type” that represented the
essence of each species. He also emphasized
the idea of evolution by common descent,
namely that all species today had evolved
from other species in the past. The problem
he had to resolve was to explain how the
variation within species could be harnessed to
produce evolutionary change.
Darwin found the solution in a book
published in 1798 by Thomas Malthus
(1766–1834), who demonstrated that human
populations tend to increase more rapidly
than the supplies of food. Hence, only the
stronger can survive. Darwin realized that
such a principle applied to all animals, that
the surviving individuals would be those that
were best fitted to obtain food and to produce
healthy young, and that their particular adap-
tations would be inherited. This was Darwin’s
theory of evolution by natural selection, the
core of modern evolutionary thought.
The theory was published 21 years after
Darwin first formulated the idea, in his book
On the Origin of Species (1859). The delay
was a result of Darwin’s fear of offending
established opinion, and of his desire to bolster
his remarkable insight with so many support-
ing facts that no one could deny it. Indeed,
most scientists accepted the idea of evolution
by common descent in 1859, or soon after,
but very few accepted (or understood) natural
selection. It was only after the beginning of
modern genetics early in the 20th century, and
its amalgamation with “natural history”
(systematics, ecology, paleontology) in the
1930s and 1940s, in a movement termed the
“Modern synthesis”, that Darwinian evolu-
tion by natural selection became fully
established.
PALEONTOLOGY TODAY
Dinosaurs and fossil humans
Much of 19th century paleontology was dom-
inated by remarkable new discoveries. Collec-
tors fanned out all over the world, and
knowledge of ancient life on Earth increased
enormously. The public was keenly interested
then, as now, in spectacular new discoveries
of dinosaurs. The first isolated dinosaur
bones were described from England and
Germany in the 1820s and 1830s, and tenta-
tive reconstructions were made (Fig. 1.9).
However, it was only with the discovery of
complete skeletons in Europe and North
America in the 1870s that a true picture of
these astonishing beasts could be presented.
The fi rst specimen of Archaeopteryx, the
oldest bird, came to light in 1861: here was a
true “missing link”, predicted by Darwin only
2 years before.
Darwin hoped that paleontology would
provide key evidence for evolution; he
expected that, as more finds were made, the
fossils would line up in long sequences
showing the precise pattern of common
descent. Archaeopteryx was a spectacular