Chapter 18-Darwin and Evolution

18.1 History of the Theory of Evolution

• Charles Darwin sailed on the Beagle when he was 22 in 1831
• pre-Darwinian view
• Earth is young
• each species is specifically created
• adaption is the work of a creator
• observations substantiate the prevailing world view
• post-Darwinian view
• Earth is old
• species are related by descent
• adaptation is the interplay of random variations and environmental conditions
• observation and experimentation test hypotheses, including evolution
• evolution-species change with time
• descent with modification
• Carolus Linnaeus came up with binomial nomenclature, but believed each species was individually created and occupied a specific rung on the ladder of life, with humans at the top
• Georges-Louis Leclerc provided evidence of descent with descent with modification
• Erasmus Darwin suggested the possibility of common descent
• Georges Cuvier founded paleontology
• paleontology-the study of fossils
• catastrophism-Cuvier hypothesized that a series of local catastrophes occurred whenever a new stratum showed a new mix of fossils. After the catastrophe, the region was repopulated by surrounding species, and the result of all these catastrophes was the appearance of change with time. Others suggested that after there were worldwide catastrophes, and after each one, God created a new species.
• Jean-Baptiste de Lamarck was the first to believe evolution occurred, and concluded that more complex organisms descended from less complex organisms, but believed the increasing complexity was a resultant of an inherent desire for perfection in all species
• Lamarck supported inheritance of acquired characteristics-the environment can bring about inherited change (giraffes' necks stretched when they ate, and passed this on)

18.2 Darwin's Theory of Evolution

• James Hutton believed the earth was subject to slow but continuous cycles of erosion and uplift
• Charles Lyell proposed uniformitarianism-slow erosion changes occurred at a uniform rate
• biogeography-the study of geographic distribution of life-forms on Earth
• Darwin noticed how similar species replaced each other
• Darwin wondered if the types of tortoises was correlated with the types of island vegetation
• Darwin speculated if the different types of finches could have descended from a type of mainland finch
• natural selection-mechanism for evolutionary change
1. the members of a population have heritable variations
2. in a population, many more individuals are produced each generation than the environment can support
3. some individuals have adaptive characteristics that enable them to survive and reproduce better than do other individuals
4. an increasing proportion of individuals in succeeding generations have the adaptive characteristics
5. the result of natural selection is a population adapted to its local environment
• Darwin emphasized variations, and suspected they were completely random and essential to the natural selection process
• Thomas Malthus prophesized that death and famien were inevitable because the human population increased too quickly
• each generation has the same reproductive potential as the previous generation, so there is a constant struggle for existence and only certain members will survive and reproduce
• fitness-the reproductive success of an individual relative to the other members of a population
• artificial selection
• adaptation-a trait that helps an organism be more suited to its environment

18.3 Evidence for Evolution

• fossil record-history of life recorded by remains from the past
• fossils are at least 10,000 years old (pieces of bone, impressions of plants pressed into shale, insects trapped in tree resin)
• extinct-died out
• Darwin concluded there were no rabbits in South America because they had no means to get there
• physical factors determine where a population can spread
• homologous structures-structures that are anatomically similar because they are inherited from a common ancestor (e.g. vertebrate forelimbs)
• analogous structures-structures that serve similar functions but are not constructed similarly nor inherited (e.g. wings)
• vestigial structures-anatomical features that are fully developed in one group of organisms but are reduced and may have no function in similar groups (e.g. tailbone)
• vertebrate homology extends to their embryological development
• degree of similarity in DNA base sequences
• evolution is now considered a theory