Download Chapter 1 The Framework of Biology

Chapter 13 Life Evolves: Darwin & the Science of Evolution
CHAPTER OUTLINE
13.1 Evolution is the central idea in the study of biology.
Many fascinating examples exist of population's adaptations to their environment.
Adaptations can be observed from the molecular level to the ecosystem level. Evolution
is the change in allele frequencies of a population over many generations resulting in a
change in traits.
13.2 The intellectual climate of the 1800s set the stage for Charles Darwin's ideas
about evolution.
During the early 1800s, the scale naturae was accepted, a linear ranking of organisms
ending with humans as closest to God. Ideas from Malthus and Lyell were influential on
Charles Darwin as was his grandfather, Erasmus Darwin. Charles Darwin published his
ideas about natural selection in 1859, shortly after Alfred Russel Wallace proposed
similar ideas.
13.3 Darwin discovered the fundamental principles of evolution.
The Beagle voyage showed Darwin the true diversity of life.
Darwin's position as naturalist aboard the H.M.S. Beagle allowed him to see a diversity
of living organisms as well as regional similarities.
Darwin's study of fossils expanded his ideas about how species are related.
Darwin was able to observe many fossils from different ages, some very different from
modern animals, some similar.
Studies of geological formations showed Darwin that Earth changes over time.
Darwin studied Charles Lyell's Principles of Geology which proposed evidence that the
earth was older than previously thought and environments changed over time.
Five postulates summarize Darwin's ideas.
The five postulates are: life evolves, gradualism, multiplication of species, common
descent with modification, and natural selection.
Natural selection is the primary mechanism that drives the process of evolution.
Natural selection results from individuals well adapted to their environment producing
offspring. As natural selection proceeds, traits change in the population. In order for
natural selection to occur, there must be variation in alleles within a population and an
overproduction of offspring resulting in a struggle for existence. Environmental changes
drive natural selection.
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13.4 Scientific studies document many examples of natural selection.
Natural selection is seen in the fitness of species to their environment.
A population well adapted to its environment is fit; variation in alleles is still present in a
species that is fit.
Many studies trace natural selection in action.
Although many examples of natural selection occur over millions of years, some do occur
in shorter time spans such as the example of industrial melanism and the peppered moth.
Controlled experiments provide support for natural selection.
Studies of model organisms such as Drosophila melanogaster can be performed within
the controlled environment of the laboratory. Artificial selection affects the traits of a
population through selective breeding.
Three types of natural selection have been identified.
Directional selection, stabilizing selection and disruptive selection affect the allele
frequencies of populations in defined ways.
Sexual selection is a special case of natural selection.
Females choosing a mate apply sexual selection pressures which can change allele
frequencies in a population.
Other factors can change allele frequencies across generations.
Both genetic drift and the founder effect change a population's allele frequency.
13.5 Scientific evidence supports and expands upon Darwin's conclusions.
Research continues to support Darwin's ideas about natural selection.
Fossils show that life has changed over time.
Fossil evidence continues to be collected which supports the theory of evolution. The
example of horse evolution is presented.
The fossil record supports Darwin's idea of common descent.
The discovery of intermediate forms in the fossil record supports the idea that modern
forms have evolved from ancestral forms. The evolution of mammals and reptiles from a
reptile-like ancestor can be seen within the fossil record and includes pelycosaurs,
therapsids, and cynodonts.
Anatomical structures of living and extinct animals support the idea of common descent.
Study of anatomical structures among related organisms can reveal relationships.
Modern DNA studies support Darwin's principle that all life is related.
Most recently, evidence from DNA sequencing has revealed evolutionary relationships.
Scientists have found common proteins among organisms such as cytochrome c, a
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mitochondrial protein, containing variation in amino acid sequence. Differences indicate
length of time organisms have been evolving separately.
Evolutionary change can happen at different speeds.
As studies involving all types of evidence continue, scientists are seeing that evolution
occurs at different rates.
13.6 Arguments against evolution are not supported by scientific evidence.
Proposals of alternative explanations for the unity and diversity of life, such as Intelligent
Design, are not based on science, specifically, they are not testable or falsifiable.
13.7 How do you know? Are birds dinosaurs?
The example of Archaeopteryx is presented. Many scientists feel that birds are
representative of dinosaur descendants.
Now you can understand.
Antibiotic resistance is a modern example of natural selection.
What do you think?
A presentation of how humans may yet evolve should stimulate critical thinking.
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