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The
acceptance of biological
evolution is an essential part of the modern scientific explanation
of the natural world. Most scientists and major religions in the Western World have
long since incorporated it into their understanding of nature and humanity. However,
some churches still maintain that there was a special and independent creation of every species and that life forms do not change through time
from generation to generation. These "creationists" often share beliefs
about the Judeo-Christian Bible that were widely held, even by scientists, during the early
19th century and before.
The traditional
Judeo-Christian version of creationism was strongly reinforced by
James Ussher , a 17th century
Anglican archbishop of Armagh in Northern Ireland. By counting the generations of the Bible and adding
them to modern history, he fixed the date of creation at October 23, 4004 B.C.
During Ussher's lifetime, debate focused only on the details of his calculations rather
than on the approach. Dr. Charles Lightfoot of Cambridge
University in England had the last word. He proclaimed that the time of creation was 9:00 A.M. on October
23, 4004 B.C.
This belief
that the earth and life on it are only about 6000 years old fit neatly with the then
prevalent theory of the "Great Chain of Being." This held that God created
an infinite and continuous series of life forms, each one grading into the next, from
simplest to most complex, and that all organisms, including humans, were created in their
present form relatively recently and that they have remained unchanged since then.
Given these strongly held beliefs, it is not surprising that 17th and 18th century
European biology consisted mainly of the description of plants and animals as they are
with virtually no attempt to explain how they got to be that way.
The leading
biological scientist of the mid 18th century was the Swedish botanist Karl von Linné
(Carolus Linnaeus in Latin). His 180 books are
filled with precise descriptions of nature, but he did little analysis or interpretation.
This is to be expected since Linnaeus apparently believed that he was just
revealing the unchanging order of life created by God. The goal of documenting
change in nature would not have made sense to him. Late in his life, however, he was
troubled by the fact that plant hybrids could be created by cross pollination.
These were varieties that had not existed before. Linnaeus stopped short of concluding
that these plants had evolved.
Despite his
limiting research bias, Linnaeus was a first class scientist. His most important
contribution to science was his logical classification system for all living things
which he proposed in his book Systema Naturae, first published in
1735.
In this and subsequent works, he described plants and animals on the basis of physical appearance
and method of reproduction. He classified them
relative to each other according to the degree of their similarities. He
used a binomial nomenclature in naming them. That is to say, organisms were
given two Latin names--genus and species . Each genus could have many related species.
Each genus was also part of larger categories of living things. This
Linnaean system of classification is today the basis for naming and
describing organisms in all fields of biology.
The concept of genus and
species was actually developed in the late 1600's by John Ray, an English
naturalist and ordained minister. However, it was Linnaeus who used this system to name us
Homo
sapiens (literally, "wise men").
He also placed us in the order Primates
(a larger, more
inclusive category than our genus) along with all of
the apes, monkeys, and prosimians. This was very controversial at the time since it implied that people were part
of nature, along with other animals and plants. In addition, it meant
that we were biologically closer to the other primates than to all other
animals.
Late in the
18th century, a small number of European scientists began to quietly suggest that life
forms are not fixed. The wealthy French mathematician and naturalist, George Louis Leclerc, Comte
de
Buffon , actually said that living
things do change through time. He speculated that this was somehow a
result of influences from the environment or even chance. He believed
that the earth must be much older than 6000 years. In 1774, in fact,
he speculated that the earth must be at least 75,000 years old. He
also suggested that humans and apes are related. Buffon was careful to hide his radical views in a
limited edition 44
volume natural history book series called Histoire Naturelle
(1749-1804). By doing this, he avoided broad public
criticism.
Buffon was an early advocate of
the Linnaean classification system. He was also a quiet pioneer in asserting that
species can change over generations. However, he publicly rejected the idea that species could
evolve into other species. One of his most significant contributions to
the biological sciences was his insistence that natural phenomena must be
explained by natural laws rather than theological doctrine.
Another late 18th century closet-evolutionist was Erasmus Darwin , the grandfather of the well
known 19th century naturalist, Charles
Darwin. Erasmus was an English country physician, poet, and amateur scientist.
He believed that evolution has occurred in living things, including humans, but
he only had rather fuzzy ideas about what might be responsible for this
change. He wrote
of his ideas about evolution in poems and a relatively obscure two volume
scientific publication entitled Zoonomia; or,
the Laws of Organic Life (1794-1796).
In this latter work, he also suggested that the earth and life on it must
have been evolving for "millions of ages
before the commencement of the history of mankind."
The first
evolutionist who confidently and very publicly stated his ideas about the processes
leading to biological change was a French protégé of the Comte de Buffon.
He was Jean-Baptiste Chevalier de Lamarck . Unfortunately, his theory about these processes
was incorrect.
Lamarck
believed that microscopic organisms appear spontaneously from inanimate
materials and then transmute, or evolve, gradually and progressively into more complex forms through a
constant striving for perfection. The ultimate product of this
goal-oriented evolution was thought by Lamarck to be humans. He believed that evolution was mostly due
to the inheritance
of acquired characteristics as creatures adapted to their environments. That is, he believed that evolution
occurs when an
organism uses a body part in such a way that it is altered during its lifetime and this
change is then inherited by its offspring. For example, Lamarck thought that
giraffes evolved their long necks by each generation stretching further to get leaves in
trees and that this change in body shape was then inherited. Likewise,
he believed that wading birds, such as herons and egrets, evolved their long
legs by stretching them to remain dry. Lamarck
also believed that creatures could develop new organs or change the structure
and function of old ones as a result of their use or disuse.
Lamarck did not invent the idea of inheritance of
acquired characteristics but stated it clearly and publicly in an 1809
publication entitled Philosophie Zoologique.
It was
relatively easy
for the French scientist, George Cuvier , and other critics of Lamarck to
discredit his theory. If it was correct, the children of cowboys who have developed bowed legs as
a result of a lifetime of riding horses would be born with bowed legs as well.
That, of course, does not occur. Likewise, the children of professional
weight lifters are not born with enlarged muscles.
While
Lamarck's explanation of evolution was incorrect, it is unfair to label him a
bad scientist. In fact, he was at the cutting edge of biological
research for his time. He and George Cuvier were largely responsible for making
biology a distinct branch of science.
Despite his
criticism of Lamarck, Cuvier did not reject the idea that there had
been earlier life
forms. In fact, he was the first scientist to document extinctions of
ancient
animals and was an internationally respected expert on dinosaurs.
However, he rejected the idea that their existence implied that
evolution
had occurred--he dogmatically maintained the "fixity" of species.
Cuvier
advocated the theory of catastrophism ,
as did most other leading scientists of his day. This
held that there have been violent and sudden natural catastrophes such
as great floods and
the rapid formation of major mountain chains. Plants and animals
living in those
parts of the world where such events occurred were often killed off
according to Cuvier. Then new life forms moved in from other areas. As
a result, the fossil
record for a region shows abrupt changes in species. Cuvier's
explanation relied solely on scientific evidence rather than biblical
interpretation.
A careful
examination of European geological deposits in the early 19th century led the English
lawyer and geologist,
Charles Lyell , to
conclude that Cuvier's catastrophism theory was wrong. He believed that there
primarily have been slower, progressive changes. In his three volume
Principles of Geology (1830-1833), Lyell documented the fact that the
earth must be very old and that it has been subject to the same sort of natural processes
in the past that operate today in shaping the land. These forces include erosion,
earthquakes, glacial movements, volcanoes, and even the decomposition of
plants and animals.
Lyell
provided conclusive evidence for the theory of uniformitarianism , which had been developed originally by the late 18th
century Scottish geologist, James Hutton. This held that the natural forces now
changing the shape of the earth's surface have been operating in the past much the same
way. In other words, the present is the key to understanding the past.
This
revolutionary idea was instrumental in leading Charles Darwin to his understanding of
biological evolution in the 1830's. However, it was not until the late 19th century
that most educated people in the Western world finally rejected the theory of catastrophism in favor of uniformitarianism.
Today, we
know that our planet has been shaped by occasional catastrophic events, such as
bombardment of large meteors, in addition to the comparatively slower natural processes
suggested by uniformitarianism. All of these events have potentially affected the
rate and direction of biological evolution."
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