Chapter 22: Descent with Modification (A Darwinian View of Life)
Darwin Introduces a Revolutionary Theory
Evolution is defined as a change in the genetic make up of a population that enhance organisms' ability to survive and reproduce . It is also the change in allelic frequencies in a population.
Natural Selection: a population can change over generations if individuals that possesses certain heritable traits leave more offspring than other individuals. It only involves heritable traits.
Evolutionary Adaption: an accumulation of inherited characteristics that enhance organisms ability to survive and reproduce in specific environments
Section 22.1: The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species
Many scientists in the 1700s believed that organisms experienced adaptations to their environments and believed that a Creator had designed each species for a specific purpose. On of these scientists was Carolus Linnaeus who founded taxonomy. Taxonomy is a branch of biology that focuses on the naming and classification of organisms. Linnaeus used a binomial system to categorize and name organisms. Organisms are classified by their genus and species.
To understand how animals have evolved over time paleontologists study fossils. Fossils are the remains or impressions of plans or animals in sedimentary rock. The study of fossils gives us a glimpse of organisms that populated the Earth at the time a certain layer of sedimentary rock formed. Georges Cuvier, the scientist who developed paleontology opposed the idea of gradual evolution and instead advocated catastrophism. Catastrophism is the theory that each layer of sedimentary rock represents a catastrophe that wiped out most of the species living at that time.
In contrast to catastrophism other scientists accepted the theory of gradualism-- the idea that profound change can take place through the cumulative effect of slow, continuous processes. Another scientist Charles Leyell took the theory of gradualism and formed it into a theory known as uniformitarianism. Uniformitarianism states that the same geological processes that occurred in history are operating at the same rate today and have not changed over the course of history.
Jean Baptiste Lamark published a theory of evolution that was commonly accepted before Charles Darwin's theory of natural selection. Lamark's theory consisted of two principles. The first principle was use and duse or the idea that parts of the body that are extensively used become larger and stronger while others deteriorate. The second principle is inheritance of acquired characteristics. This means that an organisms could pass modifications from use and duse to its offspring.
Section 22.2: In The Origin of Species, Darwin proposed that species change through natural selection
Charles Darwin's voyage on the HMS Beagle was the impetus for the development of his theory of evolution. He spend most of his time during this voyage on the shore collecting and observing thousands of South American animals and plants. This expedition sparked Darwin's interest in the geographic distribution of species. When the Beagle stopped at the Galapagos islands Darwin was fascinated by the unique birds and other species and how some species lived on 2 or 3 islands while others lived on one. Below is a picture of a blue footed booby and a frigate.
Within a decade of its publication Dariwn's book on his theory of natural selection had convinced most biologists that biological discovery was the result of evolution. Darwin had developed two main ideas: evolution explains life's diversity and that natural selection is a cause of adaptive evolution. In the beginning of his book The Origin of Species, Darwin referred to evolution as descent with modification--the idea that all living organisms are related by descent by a common unknown ancestor in the past.
Darwin's Theories:
1) Natural selection is the result of reproductive success as a result of "survival of the fittest"
2) The process of natural selection happens through the interactions between organisms and their environment that causes variations in the genotype of that population
3) Natural Selection = an organisms' adaption to its environment
Darwin derived a piece of his theory from the process of selective breeding of domesticated plants and animals. The process of breeding animals or plants to possess desired traits is called artificial selection. As a result of this humans have been able to bred animals or plants that bair little resemblance to their wild ancestors.
Multiple Choice Questions:
1) ____ stated that species evolved after a catastrophe when the species before it was mostly destroyed.
a. catastrophism
b. catabolism
c. gradualism
d. dissent with modification
2) True or False, Lamark's theory was never accepted by biologists before Charles Darwin's theory of evolution.
3) ___ is a geological theory that states that profound changes in the earth's features happen during slow, continuous processes.
a. uniformitarianism
b. gradualism
c. evolutionary adaption
d. paleontology
Answers: 1) A 2) False 3) A
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