Principles of Evolution (Chapters 22-25 in Campbell and Reese) 

The following is the first of our notes covering the principles of evolution.  Additional notes will follow. 

The modern theory of evolution explains the diversity of life from the perspective of science.  It provides a scientific explanation of how the multitude of species was created.  Advances in science, especially genetics, have strengthened this view of life in part by explaining the basis of variation and inheritance.  As you will see, variation and inheritance are both very important to the theory.  All aspects of modern biology are affected by the theory of evolution by means of natural selection.  It has been said that ‘nothing makes sense in biology except in light of the theory of evolution.’  Note the often used phrase, “The Darwinian Revolution”—a scientific revolution that has changed the focus of biology. 

Theories of Evolution 

I.  The Theory of Inheritance of Acquired Characteristics.  (1809) by  Jean-Baptiste Lamarck

Modifications acquired during one’s lifetime are inherited by the next generation, ex. giraffes acquired a long neck slowly over time as each generation of giraffe stretched its neck slightly longer in trying to reach leaves high in trees.  At fist glance this theory is deceptively close to Darwin’s theory (both include the concept that evolution produces life forms adapted to their environments) but the inheritance of acquired characteristics implies that the organism itself can control the direction of change.  Unfortunately, there have been no discoveries of any such mechanism of change. 

II.  The Theory of Evolution by means of Natural Selection 

A.  The founders:

Charles Darwin  (1809-1882)

English Scientist

Age 22 - HMS Beagle

Became ship's naturalist

5 year voyage 1831-1836

Alfred Wallace (1823-1913)

English Naturalist

1848-1852 Amazon R.

1854-1861 - Indonesia

 Both men were excellent observers and prolific collectors and both worked as taxonomists.

1858 - Wallace sends Darwin a letter, an essay in which he (Wallace) clearly communicates evolution by means of natural selection.  Darwin is known to have whined, "… all my originality [] will be smashed." (see p. 434)

1859 Darwin publishes On the Origin of Species by Means of Natural Selection 

B.  Seven Influential Factors for both Wallace and Darwin  

1).  Geology – study of the earth’s structure, origin, and history.  The book, Principles of Geology by Charles Lyell (1797-1875), includes the “theory of uniformity” or “uniformitarianism" - Geological processes have been uniform through time.  Geological changes of the past were caused by same, observable processes of today.  The process of change has been uniform through time.  Canyons and thick layers of sedimentary rock are the profound results of accumulated gradual change over vast stretches of time (gradualism, see p. 430).  The significance to biology is this, slight changes over a long time have large-scale impact and one can look at the present to see the processes of the past.  Three concepts from geology are important in shaping the theory of evolution by means of natural selection:

·        the earth must be very old [4.6 billion years]

·        one can look at the present to see processes of the past

·        slight changes over a long time have large-scale impact 

2).  Fossils - extinct forms similar yet distinct from extant forms.  Perhaps a history of change (evolution) connects the living with the extinct. 

3).  Island Life.  Isolated island populations differ slightly from nearby mainland populations.  e.g. Galapagos Islands (2 MYO, 600 mi. off W coast of S.A) the  birds, lizards, huge tortoises, similar to ‘nearby’ mainland species yet slightly different. 

Therefore there must have been Descent with modification (i.e., the island life evolved from mainland ancestors). 

4).  Overproduction of individuals - Thomas Malthus (British Economist) in his “Essay on the Principle of Populations”(1798) attempts to explain that much of human suffering, hunger, sickness, homelessness, and war are due to competition between an ever increasing number of individuals or groups of individuals for limited resources.  The number of individuals (population size) tends to increase exponentially.  This exponential capacity can’t be sustained (if it were, earth would be covered over many times with individual life forms).  Eventually, more individuals are born than can live to reproduce, leading to a struggle for existence.  Darwin and Wallace saw the concept relative to all species not just humans.  Only some individuals live to reproduce, many (in fact, most) will die before reaching reproductive age.  What determines, in nature [not human society] who lives and who dies?  An answer lies in part in variations among individuals. 

            [Social Darwinism is a distortion of the Theory of Evolution in the Darwinian sense, Social Darwinism was used by Hitler to justify the extirpation of Jews and his quest to destroy other countries; Antievolutionists use Social Darwinism as an attack on the Theory of Evolution.  Social Darwinism is the erroneous application of “survival of the fittest” to human societies.] 

5).  Individuals within a species vary extensively.  How does one know variations exist?  Taxonomy! A taxonomist observes and describes the variation within a species. You don’t have to be a taxonomist to know that individual people vary.  People vary not only in morphological traits such as hair texture and body shape but also in physiological traits as seen in the susceptibility of American Indians to European diseases [measles, mumps].  A knowledge of the variation in species of wild animal be they bird, beetle, or barracuda, requires the careful and detailed observation of many specimens.  Only a scrutinizing taxonomist, whether professional or amateur, sees the variation between individuals of wild species.  

6).  Many of the variations are inheritable and some variations may impart greater reproductive success, as in artificial selection below. 

7).  Artificial Selection – “selective breeding by humans of another species” (Harcourt Dictionary).  Variation among crops & livestock may be favored (selected) or disfavored (selected against), or neutral, i.e., neither favored nor disfavored, by man's control over which individuals are allowed to reproduce.  Man selects the best (according to his taste) and breeds these for future generations.  [see fig. 22.11, p. 436]