Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. BIOLOGY A GUIDE...

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.

BIOLOGYA GUIDE TO THE NATURAL WORLD

FOURTH EDITION

DAVID KROGH

An Introduction to Evolution:Charles Darwin, Evolutionary Thought,

and the Evidence of Evolution

Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.

16.1 Evolution and Its Core Principles


Common Descent with Modification

• Within the theory of evolution, a key principle is that of common descent with modification.

• This principle describes the process by which species of living things can undergo modification over time, with such change sometimes resulting in the formation of new, separate species.


Common Descent with Modification

• All species on Earth have descended from other species, and a single, common ancestor lies at the base of the evolutionary tree.


Natural Selection

• A second key principle in the theory of evolution concerns natural selection.

• Natural selection is a process in which the differential adaptation of individual organisms to their environment selects those traits that will be passed on with greater frequency from one generation to the next.


Importance of Evolution as a Concept

• The theory of evolution has an importance beyond the domain of biology. Through it, human beings have become aware that:

1. They are descended from other varieties of living things.

2. The organisms that populate the living world are not fixed entities, but instead are constantly undergoing modification.


16.2 Charles Darwin and the Theory of Evolution


Darwin and the Theory of Evolution

Figure 16.1



• Charles Darwin deserves primary credit for the theory of evolution.

• Darwin developed existing ideas about descent with modification while providing a large body of evidence in support of them.

• He was the first to perceive natural selection as the primary process that drives evolution.



• Darwin’s insights were inspired by the research he carried out during a five-year voyage he took around the world on the ship HMS Beagle, beginning in 1831.



Figure 16.2



Figure 16.3

NorthAmerica

SouthAmerica

Asia

Africa

Australia

equator

Europe

Dec. 1831-Oct. 1836

July 1834

Sept. 1835Galapagos Islands

Falkland IslandsMarch 1833March 1834

April 1832 Jan. 1836


16.3 Evolutionary Thinking before Darwin


Evolutionary Thinking Before Darwin

• Some of Darwin’s ideas can be traced to the work of Charles Lyell, who noted the dynamic geological nature of the Earth.



• Also important were Jean-Baptiste de Lamark and Georges Cuvier.

• Lamark noted the possibility of descent with modification.

• Cuvier noted the extinction of some species on Earth and the appearance of others within different time-frames.



Figure 16.5


16.4 Darwin’s Insights Following the Beagle’s Voyage


Darwin’s Insights

• Darwin understood descent with modification for several years before he comprehended that natural selection was the most important process driving it.

• It was his reading of a work by Malthus on limits to population growth that sparked his realization about natural selection.


16.5 Alfred Russel Wallace


Alfred Russell Wallace

• English naturalist Alfred Russel Wallace is the co-discoverer of natural selection as the principal process underlying evolution.


16.6 Descent with Modification Is Accepted


Descent with Modification is Accepted

• Descent with modification was accepted by most scientists not long after publication of Darwin’s On the Origin of Species by Means of Natural Selection in 1859.

• Scientists accepted it because it explained so many facets of the living world.



Figure 16.8



Figure 16.7



Figure 16.9

Pharyngeal slits exist in these five vertebrate animals . . .

sea lamprey pond turtle chicken domestic cat human being

pharyngeal slits

. . . evidence that all five evolved from a common ancestor


16.7 Darwin Doubted: The Controversy over Natural Selection


Controversy over Natural Selection

• The hypothesis that natural selection is the most important process underlying evolution was not generally accepted until the middle of the twentieth century.


Controversy over Natural Selection

• Its acceptance hinged on a modern synthesis in the theory of evolution that brought together lines of evidence from genetics, the fossil record, and the distribution of organisms throughout the world.


16.8 Opposition to the Theory of Evolution


Opposition to the Theory of Evolution

• Even today, the theory of evolution is regularly challenged as being unproven or simply wrong.


Opposition to the Theory of Evolution

• One factor leading to the appearance of a “scientific debate” over evolution is confusion about the meaning of the word theory.

• Though the average person may equate “theory” with speculation, in science a theory is a general set of principles supported by a lot of evidence that explains some aspect of the natural world.


16.9 The Evidence for Evolution


The Evidence for Evolution

• Six lines of evidence are consistent with the theory of evolution.


1. Radiometric Dating

• First, radiometric dating has confirmed the immense age of the Earth—an age that is consistent with the long periods of time scientists believe it has taken species to evolve.


2. Fossils

• Second, around the globe, fossils from the same evolutionary periods are consistently found together in geologic strata.


2. Fossils

• Moreover, there is excellent agreement between the relative ages assigned to fossils by evolutionary theory and the absolute ages assigned to them by radiometric dating.


2. Fossils

Figure 16.10


3. Comparative Morphology and Embryology

• Third, the theory of evolution explains the common occurrence of homologous physical structures in different organisms.


3. Comparative Morphology and Embryology

Figure 16.11

gorillacatwhale bat


4. Evidence from Biogeography

• Fourth, island biogeography—the geographic distribution of species on Earth’s islands—is explained by the theory of evolution.


4. Evidence from Biogeography

Figure 16.13


5. Evidence from Gene Modification

• Fifth, variations found in the DNA sequences of various organisms are consistent with evolutionary theory.


5. Evidence from Gene Modification

Figure 16.14

Large number of base differences between humans and yeast

Small number of base differences between humans and pigs

Number of DNA nucleotide base differences in the cytochrome c oxidase gene

66

36

31

20

17

13

human pig duck snake tuna moth yeast


6. Experimental Evidence

• And sixth, experimental demonstrations of evolution have been carried out in the laboratory and in nature.


Principles of Evolution

PLAYPLAY Animation 16.1: Principles of Evolution

Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings. BIOLOGY A GUIDE...

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