Animal: DEVELOPMENT OF EVOLUTIONARY THEORY
Table of Contents
Pre-Renissance Thought | The Age of the Earth
| Evolutionary Thought During the 1770's
Evolution by Natural Selection | Natural Selection and Genetics |
Pre-Renissance Thought
Roman philosopher Lucretius (99-55 B.C.) coined the concept that all
living things were related and that they had changed over time. The
classical science of their time was observational rather than experimental. Another
ancient Greek philosopher,
his concept of the advancement of living things from inanimate matter
to plants, then animals and finally man. This concept of man as the
"crown of creation" still plagues modern evolutionary biologists
(See Gould, S.J., Wonderful Life, 1989, for a more
detailed discussion).
"scientists" were constrained by the prevailing thought patterns
of the Middle Ages -- the inerrancy of the biblical book of Genesis
and the special creation of the world in a literal six days of the 24-hour
variety. Archbishop James Ussher of Ireland, in the mid 1600's, calculated
the age of the earth based on the geneologies from Adam and Eve listed
in the biblical book of Genesis, working backward from the crucificxion.
According to Ussher's calculations, the earth was formed on October
22, 4004 B.C. These calculations were part of Ussher's History of the World, and the chronology
he developed was taken as factual, even being printed in the front pages
of bibles. Ussher's ideas were readily accepted, in part because they
posed no threat to the social order of the times; comfortable ideas
that would not upset the linked applecarts of church and state.
had for some time doubted the "truth" of a 5,000 year old
earth. Leonardo da Vinci
of the Last Supper, and the Mona Lisa, architect and engineer) calculated
the sedimentation rates in the Po River of Italy, and concluded it took
200,000 years to form some nearby rock deposits. Galileo, convicted
heretic for his contention that the earth was not the center of the
Universe, studied
inanimate artifacts. James Hutton, regarded as the Father of modern
Geology, developed (in 1795) the Theory of
work, certain geological processes operated in the past in much the
same fashion as they do today, with minor exceptions of rates, etc.
Thus many geological structures and processes cannot be explained if
the earth is only 5000 years old. British geologist Charles Lyell refined
Hutton's ideas during the 1800s to include slow change over long periods
of time; his book Principles of Geology had profound effects
on Charles Darwin and Alfred Wallace.
The Age of the Earth
over 4.5 billion years old. The Earth is thought older than 4.5 billion
years, with the oldest known rocks being 3.96 billion years old. Geologic
time divides into eons, eroas, and smaller units. An overview of geologic
time may be obtained at
The geologic time scale. Image is from
Evolutionary Thought During the 1700s
of learned men), attempted to pigeon-hole all known species of his time
(1753) into immutable categories. Many of these categories are still
used in biology, although the underlying thought concept is now
was based on the premise that the
to a higher category.
that species could change, in a forty-four volume natural history of
all (then) known plants and animals. This was a major break from earlier
concepts that species were created by a perfect creator and therefore
could not change because they were perfect, etc. Buffon also provided
evidence of descent with modification and speculated on various causative
mechanisms. In his written work, Buffon mentioned several factors could
influence evolutionary change: influences of the environment, migration,
geographical isolation, overcrowding, and the struggle for existence.
However, Buffon vacillated as to whether or not he believed in evolutionary
descent, and professed to believe in special creation and the fixity
of species.
poet in the late 1700's, proposed that life had changed over time. His
writings on both botany and zoology contained many comments that suggested
the possibility of common descent based on changes undergone by animals
during development, artificial selection by humans, and the presence
of vestigial organs. However, this Darwin offered no mechanism to explain
evolutionary descent.
the first accurate geologic map of England. He also, from his extensive
travels, developed that Principle of Biological Succession. This idea
states that each period of earth history has its own unique assemblages
of fossils. In essence Smith fathered the science of stratigraphy, the
correlation of rock layers based on (among other things) their fossil
contents.
Gottlob Werner and Baron
as a result of some great catastrophe (such as Noah's flood). This view
was a comfortable one for the times and thus was widely accepted. Cuvier
eventually proposed that there had been several creations that occurred
after catastrophies.
Lamarck, in 1809, concluded that organisms of higher complexity had
evolved from preexisting, less complex organisms. He proposed the
Lamarckian view is that today's giraffe's have long necks because their
ancestors progressively gained longer necks due to stretching to reach
food higher and higher in trees. According to the 19th century of use
and disuse the stretching of necks resulted in their development, which
was somehow passed on to their progeny. Today we realize that only bacteria
are able to incorporate non-genetic (aka nonheritable) traits. Lamarck's
work was a theory that plainly stated that life had changed over time
and provided (albeit an erroneous) mechanism of change. Additional information
about the biological thoughts of Lamarck is available by clicking
supplanted Lamarckianism, sporadic efforts to revive it continued into
this century, most notably in the Soviet Union under the guidance of
Troffim Lysenko.
Evolution by Natural Selection
the lack of a mechanism hampered the acceptance of the idea as did its
implications regarding the biblical views of creation. Charles Darwin
and Alfred Wallace both worked independently of each other, traveled
extensively, and eventually developed similar ideas about the change
in life over time as well as a mechanism for that change: natural selection.
Darwin, former divinity student, former medical student, secured (through
the intercession of his professor) an unpaid position as ship's naturalist
on the H.M.S. Beagle. The voyage would provide Darwin a unique opportunity
to study adaptation and gather a great deal of proof he would later
incorporate into the theory of evolution. Darwin spent much time ashore
collecting plant, animal and fossil specimens, as well as making extensive
geological observations. On his return to England in 1836, Darwin began
(with the assistance of numerous specialists) to catalog his collections
and ponder the seeming "fit" of organisms to their mode of
existence. He eventually settled on four main points of the theory.
- Adaptation: all organisms adapt to their environments.
- Variation: all organisms are variable in their
traits. - Over-reproduction: all organisms tend to reproduce
beyond their environment's capacity to support them (this is based on
the work of Thomas Malthus, who studied how populations of organisms tended to grow geometrically
until they encountered a limit on their population size). - Since not all organisms are equally well adapted
to their
environment, some will survive and reproduce better than others -- this
is known as natural selection
also referred to as "survival of the fittest". In reality this merely deals with the reproductive
success of the organisms, not solely their relative strength or speed.
Adaptations of various organisms to their environments:
Selection of a wild mustard to produce some
food crops. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates
(http://www.sinauer.com/) and WH Freeman (
used with permission.
years in South America, publishing salvaged notes in Travels on the Amazon and Rio Negro in 1853.
In 1854, Wallace left England to study the natural history of Indonesia,
where he contracted Malaria. During a fever Wallace managed to write
down his ideas on natural selection.
Alfred Russel Wallace, codeveloper of the theory
of evolution. The image is modified from
as-yet-unpublished theory of evolution and adaptation was precisely
detailed. Darwin and his colleagues arranged for Wallace's paper to
be read at the July 1, 1858 meeting of the Linnean Society, along with a letter on the
same subject by Darwin. (
Wallace's paper, published in 1858, was the first to define the role
of natural selection in species formation. Darwin rushed to finish his
major treatise,
which remains one of the most influential books ever written. To be
correct, we need to mention that both Darwin and Wallace developed the
theory, although Darwin's major work was not published until 1859. While
there have been some changes to the theory since 1859, most notably
the incorporation of genetics and DNA into what is termed the "Modern
Synthesis" during the 1940's, most scientists today accept evolution
as the guiding theory on which modern biology is based.
field observations of organisms and their environment led both Darwin
and Wallace to the role of natural selection in formation of species.
They also utilized the works of Charles Lyell (geology) and Thomas Malthus.
Malthus' ideas were first published in 1798, and noted that the human
population was capable of doubling every 25 years. Population would
soon outstrip the food supply, leading to starvation, famine and war,
which would reduce the population. Wallace and Darwin adapted Malthus'
ideas about how scarce resources could affect populations.
The Wallace-Darwin Theory
- Individuals in a population have variable levels
of agility, size, ability to obtain food, and different siccesses in
reproducting. - Left unchecked, populations tend to expand
exponentially, leading to a scarcity of resources. - In the struggle for existence, some individuals
are more successful than others, allowing them to survive and reproduce. - Those organisms best able to survive and reproduce
will leave more offspring than those unsuccessful individuals. - Over time there will be heritable changes in
into a new species similar to, but distinct from, its parent species.
Natural Selection and Genetics |
Top
inheritable traits (variations) passed on to the next generation? (Recall
that Gregor Mendel had yet to publish his ideas about
linked to evolution in neoDarwinism, also known as the Modern Synthesis.
Links
- Enter Evolution UCMP Berkeley presents a site detaining
the basics of Darwin and Wallace's idea. - Darwin's Origin of Species Available to cure all
insomniacs! - The Darwin-Wallace 1858 Evolution Paper Prepared
by James L. Reveal, Paul J. Bottino and Charles F. Delwiche (U. of Maryland).
An excellent site to discover the origins of one of biology's major
theories. - Geologic Timeline This site, developed by the Fossil
Company, offers an image map that can be used to access data about the
various units of geologic time. - Science and Creationism: A View from the National Academy of Sciences
The National Academy of Science weighs in on the still raging debate
between scientists and creationists. Nothing is more needed that scientific
literacy, or at least the ability to distinguish between science and
nonsense.
Email: nolvyhindarto@gmail.com
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