History of Evolution
It is hard to say
at what time before the nineteenth century that the idea of evolution in the
animal kingdom was first raised. Several Greek philosophers thought that the
living world was subject to transformations. Their conclusions were based on
philosophical ideas and speculations.
In 1801, the
French naturalist Lamarck became the first to introduce the concept of
evolution. He published his work in a book called Zoological Philosophy.
Cuvier, another French naturalist published History of Fossilized
Bones" in 1812, in which he compared present day animals with fossils
showing the existence of extinct species.
Charles Darwin
(1809-1882), British naturalist, laid the foundation of the evolutionary theory
with his concept of the development of all forms of life through the
slow-working process of natural selection. After graduating from Cambridge in
1831, the 22-year-old Darwin was taken aboard the English survey
ship H.M.S. Beagle.
He noted, for example, that certain fossils of supposedly
extinct species closely resembled living species in the same geographical area.
In the Galapagos Islands in Ecuador,
west of South America at the equator, he
studied some forms of life such as huge turtles and swimming lizards not found
anywhere else in the world. Darwin
saw that these animals were similar to more common forms. The similarities
convinced him that the Galapagos animals were related to more common turtles
and lizards. In Galapagos, Darwin
saw finches that shared so many features, but differed mainly in their beak
structures, eating habits, and their sizes. He thought they must have had a
common ancestor. Each of the 13 famous finches of Galapagos was identified as a
distinct species.
After returning
to England in 1836, Darwin began recording
his ideas about changeability of species in his Notebooks on the
Transmutation of Species. Darwin's
explanation for how organisms evolved was brought into sharp focus after he
read An Essay on the Principle of Population (1798), by the British
economist Thomas Robert Malthus, who explained how human populations remain in
balance. Malthus argued that any increase in the availability of food for basic
human survival could not match the large rate of population growth. The latter,
therefore, had to be checked by natural limitations such as famine and disease,
or by social actions such as war.
Malthus introduced the term "Natural
Selection" that Darwin
popularized. Darwin
immediately applied Malthus's argument to animals and plants, and by 1838 he
had arrived at a sketch of a theory of evolution through natural selection. For
the next two decades he worked on his theory and other natural history
projects.
Darwin's theory was first announced in
1858. In a paper presented at the same time by Alfred Russell Wallace, a young
naturalist had come independently to the theory of natural selection. Darwin's
complete theory
was published in 1859, in The Origin of Species. Often referred to as
the "book that shook the world," the book was sold out on the
first day of publication and subsequently went through six editions.
Darwin's theory of evolution by natural
selection is essentially that, because of the food-supply problem described by
Malthus, the young born to any species intensely compete for survival. Those
young that survive to produce the next generation tend to embody favorable
natural variations (however slight the advantage may be) and these variations
are passed on by heredity. Therefore, each generation will improve adaptively
over the preceding generations and this gradual and continuous process is the
source of the evolution of species. Natural selection is only part of Darwin's
conceptual
scheme; he also introduced the concept that all related organisms are descended
from common ancestors in his second book, Descent of Man (1871).
In The Origin
of Species, Darwin
did not offer solid evidences of human evolution, only suggesting in the
conclusion that in the future, "Much light will be thrown on the origin
of man and his history." In the same book, Darwin described serious challenges
to the
whole concept of natural selection in three chapters with the following titles:
·
Difficulties of the theory, chapter 6.
·
Miscellaneous objection to the theory of
natural selection, chapter 7.
·
On the imperfection of the geological
record, chapter 10.
In his second
book, Darwin
presented his guesswork about humans and apes. He believed that humans were the
products of biological evolution, and that they descended from primitive
ancestors. His hypothesis did not state that humans descended from any of the
great apes: orangutan, gibbon, chimpanzee, and gorilla. Both humans and apes
descended from some common primate ancestors that are now extinct.
The reaction to The
Origin of Species was immediate. Some biologists argued that Darwin could not
prove
his hypothesis. Others criticized Darwin's
concept of variation, arguing that he could not explain the origin of
variations. In fact, many scientists continued to express doubts for the
following 50 to 80 years. The most publicized attacks on Darwin's ideas,
however, came not from
scientists but from religious opponents. The thought that living things had
evolved by natural processes denied the special creation of humankind and
seemed to place humanity on a plane with animals; both of these ideas were
serious contradictions to orthodox theological opinion.
