CHARLES DARWIN AND THE THEORY OF EVOLUTION

Charles Darwin was not the first to consider the evolution of life. Many others had pondered the subject long before him. The C. Warren Irvin, Jr., Collection of Charles Darwin and Darwiniana has been formed to reflect Darwin's writings and interests and to place them in the context of the work of his immediate predecessors.

I. Early thoughts on the evolution of life:

A. Anaximander (Greek 611 BC) proposed the earth first existed in a fluid state, as it gradually dried, fishlike humans were formed. Later they developed to the point where they could live on land

B. Xenophanes (Greek 576 BC) studied under Anaximander. He was the first to recognize that fossils were the remains of ancient organisms

C. Empedocles (495 BC) believed all things were formed from the four classical elements, fire, water, earth and air. These were acted upon by the forces of love and hate

1. The interaction of the elements led first to plants, then a long series of trial and error events by which plants gave rise to animal life
2. The various animal parts arose in fortuitous combinations to produce the animals of the earth. The unworkable combinations ended in extinctions while the more viable types survived
3. He envisioned a type of natural selection which acted only on highly unnatural organisms

D. Gregory of Nyssa (331 AD) interpreted the scriptures in an evolutionary context. He believed that god created matter and endowed it with its fundamental properties. The world resulted from gradual development of matter according to its potential, rather than by a series of explicit acts of creation

E. St. Augustine (353 AD) extended this "potential" theory to animals. He believed that god would not have created such disagreeable things as mice and mosquitoes but that god might permit their creation by the action of natural laws

F. St. Thomas Aquinas (1225 AD) quoted St. Augustine and he argued against taking the bible literally. He referred to the six days in Genesis as being favored "by the superficial reading of Scripture"

G. Archbishop James Ussher (17th century) proclaimed that every species of organism had been created at 9:00 am on Sunday, Oct. 23, 4004 BC and that they had remained permanently unaltered since then

II. Eighteenth-Nineteenth Century Contributions - By the 18th century religious dogma had been challenged by many scientists. Astronomers argued that the earth was not the center of the universe. The geologist Hutton maintained that the earth was very ancient with "no vestige of a beginning - no prospect of an end"

A. Leclerc (Count Buffon) - argued that the presence of vestigial organs (useless organs) convinced him that animals must have changed since their creation

1. Wrote a 44-volume natural history of all known plants and animals
2. Provided evidence of descent with modification, and also speculated on various causative mechanisms
3. The following factors could influence evolutionary change: direct influences of the environment, migration, geographical isolation, overcrowding, and the struggle for existence. He assumed the inheritance of acquired characteristics
4. Buffon vacillated as to whether or not he believed in evolutionary descent, and professed to believe in special creation and the fixity of species

B. Erasmus Darwin (Charles Darwin's grandfather) - expressed the idea that all living things shared a common ancestry and that the reactions of plants and animals to their environment were responsible for adaptive modifications. These modifications were then inherited by their offspring. He suggested "millions of ages" might be required for the process

C. Cuvier - the first to use comparative anatomy to develop a system of classifying animals

1. Founded science of paleontology, the study of fossils, and suggested that a single fossil bone was all he needed to deduce the entire anatomy of an animal
2. Staunch advocate of special creation and fixity of species, which presented him with a serious problem when geological evidence of a particular region showed a succession of life forms in the earth's strata
3. To explain the fossil record, Cuvier proposed that a whole series of catastrophes (extinctions) and repopulations from other regions had occurred
4. Catastrophism = the term applied to Cuvier's explanation of fossil history, catastrophic extinctions occurred, after which repopulation of surviving species took place, giving an appearance of change through time

D. Lamarck - believed in evolution through the inheritance of acquired characteristics

1. Each species is created with a god-given drive toward perfection that, combined with environmental factors, impelled it along a relentless journey up the ladder of life
2. The production of new organs resulted from perceived needs
3. If an organ is used constantly it will tend to become highly developed, whereas disuse results in degeneration
4. Characteristics acquired over a life time were passed on to offspring
5. Experiments failed to uphold Lamarck's inheritance of acquired characters

E. Lyell - published Principles of Geology, which greatly influenced Charles Darwin in formulating his theory of evolution

Lyell maintained that the earth was hundreds of millions of years old and that the mountains, valleys, rivers and coastlines were not created by Noah's flood but by the ordinary action of rains, winds, earthquakes, volcanoes and other natural forces.

He put forth three principles that constitute the theory of uniformitarianism:

1. natural laws are constant in space and time
2. scientists should attempt to explain events of the past through the same sorts of natural processes that we can observe directly today
3. most geological change occurs slowly and gradually, not through sudden catastrophic events

CHARLES DARWIN

I. Charles Darwin (1809-1882) 

A. Englishman who spent two years in medical school at Edinburgh and then trained as a clergyman at Cambridge for three years. He was mostly bored by his studies but while at college he became friends with some of the most respected scientists of the time

B. Through a college contact he accepted an unpaid post as naturalist aboard the HMS Beagle which sailed around the world for 5 years (1831-1836)

C. When Darwin left England he believed the church dogma of special creation as told in Genesis. However, his observations over five years led him to question it

D. Darwin took along Lyell's just published Principles of Geology which challenged belief that the earth was created by divine plan only 6,000 years ago. He was impressed by Lyell's emphasis on the great antiquity of the earth's rocks and he gradually began to think that the characteristics of organisms as well as the face of the earth could change over time

E. Darwin got off the ship wherever possible and he collected specimens and  took notes on virtually every fossil and living organism he encountered. These observations sowed the seeds of his theory of evolution

F. Darwin was amazed by the variety of organisms he encountered during his voyage. Everywhere he looked, he saw new and oddly shaped trees, exotically colored flowers and birds, and beetles and other insects

G. Darwin quickly realized that the diversity of living organisms was only part of the mystery of life. He found even greater numbers of fossil species. In Argentina, he discovered fossil armadillos, giant ground sloths, peculiar horses, and creatures that reminded him of the hippopotamus.

1. Darwin soon became convinced that living organisms (extant) were vastly outnumbered by extinct forms. He was convinced that extinction and the appearance of new species were real phenomena that had to be explained
2. Fossils of giant armadillos and sloths caused him to think that although they belonged to extinct forms, they were constructed on the same basic plan (ground plan) as the small extant species of the region
3. This started him thinking of a fossil sequence of animal species through the ages and the causes of extinction. He realized that living species have ancestors

H. Darwin also noted that organisms differed markedly from continent to continent and on opposite sides of natural barriers such as mountains, deserts, and large rivers

1. On traveling from north to south in South America he observed that one species was replaced by similar, but slightly different species. E.g. he noted the differences in ostriches from area to area. He couldn't imagine that god would create several minor versions of species separately, one for each locality.
2. He concluded that not only did species change through time, but also they changed with geographical distance.

I. Darwin wrote in his journal "it was evident that such facts could only be explained on the supposition that species gradually became modified; and the subject haunted me"

J. Darwin also witnessed the forces of geology in action: 

1. He saw the eruption of a volcano in Chile and later learned that another volcano 500 miles away had blown its top the same night
2. He also experienced an earthquake that lifted beds of marine mussels "still adhering to the rocks, ten feet above the high water mark"
3. He observed beds of fossil marine organisms thousands of feet above sea level and he began to understand how the Andes Mountains were formed by uplift. His belief in geological uniformitarianism was strengthened

K. Throughout his journey, Darwin marveled at the "perfection of structure" that made it possible for organisms to do whatever they needed to do to stay alive and produce offspring

1. He called this perfection of structure fitness, by which he meant the combination of all traits that help organisms survive and reproduce in their environment
2. Darwin also began to question what process had "fit" these organisms to their physical environments and to each other

II. Darwin's visit to the Galapagos Islands, a cluster of rugged volcanic islands only a few miles apart, 600 miles west of Ecuador had the most profound impact on his thinking

A. Darwin noted that these islands were inhabited by a surprising number of bizarre and often beautiful plant and animal species. He surmised correctly that many of these species were endemic (found nowhere else)

B. Darwin wrote about the Galapagos Islands:

"Considering the small size of these islands we feel the more astonished at the number of their aboriginal beings, and their confined range. Seeing every height crowned with its crater, and the boundaries of most lava-streams still distinct, we are led to believe that within a period geologically recent the unbroken ocean was here spread out. Hence both in space and time, we seem to be brought somewhat near to that great fact-that mystery of mysteries-the first appearance of new beings on this earth"

C. Darwin noticed that although the tortoises were clearly different from island to island they not only all resembled each other but they also resembled those of the mainland. This was also true for a group of small birds now called Darwin's Finches

He reasoned that an ancestral stock had migrated to the islands where they underwent profound changes under the different conditions of the individual islands. Apparently a single ancestral group could give rise to several different varieties or species

III. Darwin develops his theory of evolution

A. When Darwin left England in 1831 he accepted the religious dogma of special creation. On his return to England in 1836 he was convinced of the idea of "descent with modification", i.e. all organisms, including humans, are modified descendents of previously existing forms of life

B. Darwin thoughts developed in two stages:

1. the realization that organisms are not fixed and unchangeable
2. to provide an explanation of the process of evolutionary change

C. Darwin spent the next 20 years formulating his theory while also working on a number of other scientific projects

D. Darwin became interested in the domestication of plants and animals and how breeders artificially select different varieties of dogs, horses, fowl and crop and ornamental plants from one species

1. The breeders had only vague notions as to the origin or inheritance of the variable traits
2. Darwin acknowledged the unlimited variability in organisms but was never able to explain satisfactorily how a variant trait was inherited
3. In 1837 Darwin wrote "how [artificial] selection could be applied to organisms in a state of nature remained a mystery to me.

E. In 1838 Darwin read "An essay on the principle of population, as it affects the future improvement of society" by a mathematician named Malthus. Malthus maintained that human population increases geometrically yet the means of sustenance increase arithmetically. He claimed that sometime in the future human population growth would exceed resources and there would be intense competition causing war, misery and famine

1. From this Darwin concluded that competition exists among all living things and a "struggle for existence" might be the means by which well adapted individuals survive and the ill adjusted are eliminated

2. Darwin realized that perpetual selection existed in nature in the form of natural selection. In contrast to artificial selection, the breeder is replaced by conditions in the environment that prevent the survival and reproduction of certain individuals. Natural selection occurs without a conscious plan or purpose.

F. In 1858, while Darwin was working on his manuscript outlining his theory of evolution, he received a manuscript for review by a young English naturalist named Wallace. The title was "On the tendencies of varieties to depart indefinitely from the original type". To Darwin's surprise Wallace had independently come up with the same theory of natural selection!

Wallace was a naturalist working mostly in the Malay Archipelago. He had also read Essay on the principle of population by Malthus and it came into his mind during a malarial fever.  He wrote..."suddenly there flashed upon me the idea of survival of the fittest"

G. Darwin wanted to let Wallace publish first but Lyell convinced him that they should jointly present their work. Papers by both Darwin and Wallace were read before the Linnaean Society of London on July 1, 1858

H. Darwin was urged to publish his full theory of evolution as soon as possible. "On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life" was published and sold out on Nov. 24, 1859

The complete text of Darwin's "Origin of Species" is available on the web here

I. Both Darwin and Wallace share credit for the theory of natural selection, however there is much more to the theory of evolution than this. Over more than 20 years Darwin amassed massive amounts of meticulously documented evidence to support his theory of "descent with modification" which can be summarized as follows:

1. all species reproduce in excess of the numbers that can survive
2. yet adult populations remain relatively constant
3. therefore there must be a severe struggle for survival
4. all species vary in many characteristics and some of the variants confer an advantage or disadvantage in the struggle for life
5. the result is a natural selection favoring survival and reproduction of the more advantageous variants and elimination of the less advantageous variants

J. Darwin's theory came under severe criticism from the church however it gained almost immediate acceptance by most scientists of the day