Notes on the Web - Unit Six - Part 3
Natural Explanations for the Origin of Species

Bruce G. Stewart

General Objectives and Study Guide

Your objectives for these Notes on the Web and associated readings and exercises are:

• To explain how increased exploration and study of life throughout the world created logical and scientific doubt about the early literalist views of creation;
• To list and explain the significance of four areas of observation with respect to beliefs about species: mutants, domestication, metamorphosis, and vestigial organs;
• To summarize the main points of the first fully-formed theory of evolution proposed by Lamarck;
• To explain the reasons Lamarck's theory has been discarded;
• To describe the historical context of Charles Darwin's life and why he would have had to overcome bias against evolutionary thinking;
• To summarize the major influences, including observations from his travels, that affected Darwin's thinking about nature and that led him to discover the Theory of Evolution by Natural Selection and its main components.

Related Textbook Readings

• None for General Biology (BIO 1114) Class - Notes on the Web only
• For General Zoology (ZOO 1114) Class only:  Hickman, et al. (2006) Chapter 6 (in part)

A Brief Mention of the Ancient Greeks of the Few Centuries BC

Some early Greek scientists/philosophers were the first in recorded human history to propose natural explanations for the origin of life.  They were the first to drop the idea of supernatural intervention.  Anaximander, for example,  suggested that life arose from the sea, although he lacked any evidence for such a claim.  Aristotle and others  believed in spontaneous generation of living things from inanimate matter.  Although the Greeks searched for natural explanations for origin of life, their views are not believed by most historians to have been the germs of modern evolutionary thinking.

Development of Doubts about the Literal Accounts of Creation that were Held at the Time of the Renaissance

Evidences from geology, especially from studies by James Hutton and Charles Lyell, indicated that the Earth was much, much older than previously thought.   Lyell in his Principles of Geology was so bold as to suggest that the Earth could be over 100,000 years old rather than the few thousand years claimed by Ussher and others who held that view.  Natural explanations were proposed that could easily account for land forms through such things as erosion and weathering, deposition of sediments, volcanic eruptions, etc.

Explorations of the New World and other continents revealed a vast array of new forms of living things.  Two special problems could not be adequately explained by biblical literalists.  First, by the time of Linnaeus in the mid 1700's, the number of known species (15,000 including over 40 times the number of large animals known by Kircher) could not possibly have been accommodated in the biblical ark.  As Diamond (1985) stated it:

Sadly, creation scientists watched the overloaded ark sink under its own weight.

Second, the distribution of species could not be explained by the release of animals from a single location in the Old World, since unique species, families and orders of organisms often occur in specific geographic localities.

The Idea of Mutable Species was Explored

Erasmus Darwin and others of the late 1700's had begun to suggest that species might be capable of changing forms.  A formalization of these ideas was written by Erasmus Darwin (1794) in Zoonomia, or the Laws of Organic Life (as cited by Dillon 1974), years before Charles Darwin was even born.  Specifically, note the following quote from Erasmus Darwin (1794):

Would it be too bold to imagine that in the great length of time since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind, would it be to bold to imagine that all the warm-blooded animals have arisen from one living filament, which The Great Cause endued with animality, with the power of acquiring new parts, attended with new propensities, directed by irritations, sensations, volitions and associations; and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down those improvements by generation to its posterity, world without end!

Erasmus Darwin's evidences were compelling then, as they are today.   They included the following:

• mutant forms:  obvious evidence that offspring with altered structure can be produced
• domestic change:  obvious evidence that outer form can be changed over time
• metamorphosis:  obvious evidence that living beings can change drastically in form during a life span.  If this was possible, could it be possible for species to change over generations?
• vestigial (i.e. useless or almost non-functional) organs:  obvious evidence that organisms are not "perfect" creations. Could these be the remains of organs that formerly had a use in ancestors of a species?

A Fully-formed Theory of Evolution was Proposed

Jean Baptiste de Lamarck (1744-1829) was a pioneering French naturalist who developed the first complete theory of origin of species by evolution (who also, by the way, coined the term "biology"!)  He hypothesized that species changed over time through the inheritance of acquired characteristics and that change was inevitably in the direction of increased perfection or complexity.  Examples of how his theory was applied are as follows:

• giraffe illustration:  giraffes needing to reach higher into trees to reach food could stretch their necks ever so slightly (thus, improving themselves), and this new trait could be passed on to offspring
• snake illustration:  disuse of unneeded legs (for species invading thick vegetation) resulted in somewhat degenerated limbs and this trait could be passed on to offspring until after some generations, snakes had no legs

By this logic, a man who strengthens himself through weight-lifting would be able to pass this strength trait on to his children! Subsequent testing of Lamarck's theory of evolution through inheritance of acquired characteristics did not support the theory. (Note: This is the same discredited theory of evolution that Lysenko, the Russian politician of the 1930's chose to accept in spite of the lack of scientific support.)

Self-study Exercise. Think of ways you could design experiments and/or gather observations that would test predictions from Lamarck's theory. You will have the opportunity to ask questions in class and/or via threaded discussion on Internet.

Modern molecular genetics shows clearly that Lamarckian evolution is impossible.  DNA gene codes within the reproductive cells of an organism cannot be a altered with purpose to improve the organism.  The DNA in an individual is not changed toward improvement by the environment or by any particular "need" the organism may have.

First Fully Supported Theory of Evolution:  Evolution by Natural Selection

• Charles Darwin was born in 1809 in Wales and had a strong interest in the study of nature.
• At "college age" he was pressured by his father to train to be a medical doctor; however, Charles found medical school very unpleasant and dropped.
• His father suggested that a career as a parson (i.e. in religious work) would be honorable and would allow some free time to pursue his interest in nature (as was often typical in those days).
• He attended Christ's College at Cambridge and graduated with a B.A. at age 21 (in 1830).
• As a part of his general education, Darwin received much excellent training in astronomy (e.g. from Professor George Peacock), botany (e.g. from Professor John Henslow, and geology (e.g. from Professor Adam Sedgewick) as well as other important areas of education.
• Upon graduation, and with no other attractive prospects, he had the great opportunity (through the influence of his professors) to take a professional position on the HMS Beagle, and English sailing ship, for an exploratory and trade voyage around the world.  This voyage turned into a 5-year journey including extensive explorations of South America, the South Sea Islands, and other far away places.

Darwin served first on the HMS Beagle as a professional companion of Captain Fitzroy, then also as the ship Naturalist with the following primary responsibilities:

• To explore the new lands and discover facts about the natural history of the lands and the life that would be found there; this included extensive inland travels, collections of specimens (both living forms and fossils forms), and careful written accounting of observations
• To look for evidence of the biblical account of creation and the flood!  Captain Fitzroy was an avid biblical literalist, and Darwin's own background had likewise influenced him toward that point of view!

What Darwin saw, studied, and learned was to change his preconceived views and ultimately would result in the beginning of modern biology.  These are some highlights.

Prior to the voyage, Darwin was given a copy of the recently published Principles of Geology.  The geological evidence he saw throughout the voyage showed graphic evidence that supported Lyell's view of natural processes as the creator of land forms.  He saw the evidence for an old age of the earth, a critical point which allowed him to contemplate species processes in a totally different way than before.

Darwin discovered fossils of organisms of whole types that were unknown from South America, and many were of types (e.g. a type of horse, a hippopotamus-like species, etc.) whose closest living types were on other continents!  Why were these species there?  Why were they no longer present (extinct)?

The geographic distribution of living organisms was incredibly different than what Darwin expected if all species had scattered about the Earth from the ark.  Unique forms abounded, and they occurred in puzzling patterns that would latter give Darwin important clues to the origin of species.  Some of the most striking examples were in the Galapagos Islands (an archipelago about 600 miles west of Ecuador) where whole series of species were found there and no where else in the world.

• The Galapagos Tortoises
• The Galapagos Marine Iguanas
• The Galapagos Finches

Why would unique species of a group (such as the Galapagos Tortoises) be found on individual or small groups of islands, but not on others?  Then, why would the entire group of species be found on the Galapagos but not any where else in the world?  Darwin's biblical literalist training gave him reason to search for a literalist answer, but the evidences were simply inconsistent with the view he had been taught.

Darwin's Return to England in 1836, The Years of Study of the Evidence, and The Development of a General Theory to Explain the Evidence

Darwin and other researchers in England studied the great collection of specimens over the next two decades.  The patterns of geographic variation became more evidence upon detailed study.  The questions remained as to what would explain these distributions.  Another event helped Darwin formulate his answers.

Darwin read a famous book by Thomas Malthus in 1837, called An Essay on the Principle of Population.  This essay presented the mathematically-based evidence that human populations were increasing at a geometrical rate while resources were increasing at a much slower rate.   Malthus was afraid of the population disaster that this would produce (unfortunately, that time has come in many areas of the world).  As a result of reading this essay, Darwin was prompted to realize that animals in general have a great reproductive capacity to produce more individuals than can actually be supported by the resources available.  This was a critical realization.  Darwin's idea began to take greater and greater form over the ensuing years and in the 1858, he and Alfred Russell Wallace who independently developed the same idea presented separate essays to the Linnean Society of London in which they proposed natural selection as a mechanism by which evolutionary change could produce new species.

In 1859, armed with three decades of evidence and careful analysis, Darwin published On the Origin of Species by Means of Natural Selection (the original 1250 copies sold out in one day!).  This book changed the course of biological study from that day forward, and in it brought biology into a modern age in which fanciful, supernatural, mythological explanations were no longer needed to provide answers on the origin of species.  The following summary of the theory of natural selection is written in Darwin's own words:

As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected.  From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

Cited or Related Literature

(in prep)

© 2005, 2007 Bruce G. Stewart

To Natural Selection and the Concept of Fitness)

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