Development of the Theory of Evolution - Furman University

Development of the Theory of Evolution Textbook pages 1-3; 393-399. (But, your book has little historical background; lectures are important.) EVOLUTION = change in the characteristics of a group of related organisms over generations. Remember: A theory is not an untested

speculation. It is a broad explanatory framework that has been confirmed by repeated scientific testing. Charles R. Darwin 1809 1882 Theory of Evolution by

Natural Selection NOT the first to have ideas about evolution, but the first to develop those ideas fully and propose a workable explanation of what causes evolution.

Background - Taxonomy As more and more of the world was explored, thousands and thousands of new species were discovered. Classifying and cataloguing these species was a major focus of science. Carl Linnaeus (1707-1778) developed a system

of binomial nomenclature. Linnaeus also realized that nature was a hierarchy (kingdoms, classes, orders, families). Binomial Nomenclature

Every species has a 2-word name. 1st word is the Genus. 2nd word is the Specific epithet. Genus always capitalized; specific epithet never capitalized; both underlined or italicized Homo sapiens

Quercus phellos Background - Geology The earth is very ancient. Formation of sedimentary rocks (Now we can use radioisotope dating.) Two views on the formation of the earth:

Catastrophism (Cuvier, Agassiz) Uniformitarianism (Hutton, Lyell) Paleontology fossils! extinct forms that no longer exist modern forms not found in ancient rocks Pre-Darwinian Ideas on Evolution

Buffon (1707-1788) similarity of bone structure vestigial (useless) organs explained if all descended from common ancestor Lamarck (1744-1829) proposed a mechanism: Inheritance of Acquired Characteristics

as we shall see, it was incorrect, but was influential in its day. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life

Published in 1859 Title is NOT Origin of the Species The word species is used the plural sense Publication spurred by development of

similar theories by Alfred Russell Wallace Main components of The Origin of Species Evidence that evolution has occurred Mechanism that could cause evolution (mechanism = natural selection)

Evidence for evolution Fossil record (Chapter 20) Biogeography patterns of geographical distribution of living things on earth Structural and anatomical similarity Change in domesticated plants and animals Biogeography

patterns of geographical distribution of living things on earth One species is replace by another as you move from one location to another. The farther you move, the more unfamiliar the biota becomes. Patterns are especially clear on islands. Many animals and plants of the Galapagos are unique, endemic species. The most similar species are those of

South America, but they are not the same. Within the Galapagos, each island has its own unique species or subspecies of animals and plants. Again, islands that are close to each other tend to be similar. Biogeography reflects evolution The original colonists of the Galapagos were transported from South America, but

this is a rare occurrence, so they have been isolated for generations. Over those generations, they have changed (evolved) so that they are no longer the same as the original colonists. Similarity of structures Analogous structures similar because they serve a

common function. e.g. wings must be flat and positioned on either side of the body in order to allow flight. Homologous structures similarity that goes beyond function; may even go against function. e.g. bone structures similar in legs, wings, flippers, and even internal vestigial bones in legless animals

Homologous structures Homology arises from common ancestry. Analogous structures are similar because of function only, not because of common ancestry. Variation under domestication

Humans have caused new varieties of domesticated animals and plants to come into existence. This shows that species can change the mechanism may be due to which individuals within the species reproduce, and with whom.

Natural Selection: Supporting Observations

More are born than can survive (Malthus) Variation exists within populations Offspring resemble parents The characters which vary among members of a species may affect survival and reproductive success. Natural Selection

In a variable population, those heritable characteristics that increase survival and reproductive success of the organisms that possess them will be passed down to future generations more often than less beneficial traits. Thus, the population will change over time.

Variation within populations Darwin was the first to realize the true importance of variation in populations. Unlike Lamarck, Darwin did not propose that useful characteristics arise because they are needed. Instead, he realized that variation is just a natural fact of life; all species are variable. Natural selection works on this variability.

Beneficial traits become more common over time. If a population is not variable, it cannot evolve. Darwins weakness - Genetics Neither Darwin nor any of his contemporaries* really understood genetics. Why does variation exist? How is it inherited? A problem: If offspring are always intermediate

between their parents, why doesnt reproduction eventually blend away all variability? The answer would not be really known for 50 years. * One person who might have understood lived at this time as well, but nobody realized the importance of his findings Gregor Mendel, an Austrian monk.

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