Download AP Biology Chapter 22 Descent with Modification: A Darwinian View

AP Biology
Chapter 22 Descent with Modification: A Darwinian View of Life
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Evolution – change over time
Descent with Modification is the idea that living species are descendants of ancestral species that were
different from the present-day ones
HISTORICAL BACKGROUND FOR BASIS OF DARWIN’S IDEAS
Linnaeus –developed the two part binomial naming system; nested system groups organisms by increasingly
general categories (classification)
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Fossils – remains or traces of organisms from the past
Strata – superimposed layers of rock formed when new layers of sediment cover older ones and compress
them
Paleontology – study of fossils
Cuvier – noted fossils in different layers of rock were different than those today and each other; also species
appeared and disappeared in layers (fossils, extinction)
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Catastrophism – principle that events in the past occurred suddenly and were caused by mechanisms
different from those operating in the present
Hutton – proposed Earth’s geologic features could be explained by gradual mechanisms still operating (gradual
geologic change)
Lyell- proposed the same geologic processes are operating today as in the past (modern geology)
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Uniformitarianism – mechanisms of change are constant over time
Lamarck – evolutionary change explains patterns in fossils; proposed incorrect mechanism for how evolution
occurs – use & disuse and inheritance of acquired characteristics (species can change)
Malthus – much human suffering is consequence of human population’s potential to increase faster than
limitations of food and resources allow – can be applied to all populations (population limits)
Wallace – also developed a natural selection theory, gave paper to Darwin to review, (evolution, natural
selection)
DARWIN’S STUDIES
Darwin observed the animals of South America and the Galapagos Islands. Most notably he looked at beak
variation in finches
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Adaptations – characteristics of organisms that enhance their survival and reproduction in specific
environments
Natural selection – process in which individuals with certain inherited traits leave more offspring than
individuals with other traits
Darwin’s book On the Origin of Species was published in 1859. Outlined two main ideas:
1- descent with modification explains life’s unity and diversity
2- natural selection brings about the match between organisms and their environment
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Artificial selection – process in which humans have modified other species over many generations by
selecting and breeding individuals that possess desired traits
Darwin made these observations:
1- members of a population often vary greatly in their traits
2- all species are capable of producing more offspring than their environment can support and because of
lack of food or other resources, many of these offspring do not survive
With these observations, Darwin inferred the following:
1- individuals whose inherited traits give them a higher probability of surviving and reproducing in a given
environment tend to leave more offspring than other individuals
2- unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits
in the population over generations.
NATURAL SELECTION
Natural selection is a process in which individuals that have certain heritable characteristics survive and
reproduce at a higher rate than other individuals (increased fitness increased survival increased
reproduction)
Natural selection can, over time increase the match between organisms and their environment (those best
suited to environment survive)
In an environment changes, or if individuals move to a new environment, natural selection may result in
adaptation to these new conditions, sometimes giving rise to new species in the process (fitness in an
environment can change due to changes in environment)
SUPPORT FOR THEORY OF EVOLUTION
Observations & Studies – scientists have run many experiments and studies using artificial selection
techniques
Fossil Record – shows past organisms differed from present day organisms; shows extinctions, formations
of new species and new groups; radioactive dating can determine age of fossils to make the record
Anatomy – structures can show descent with modification
a. Homology – similar characteristics in related species resulting from common ancestry
b. Homologous structures – structures in different species that are similar because of common
ancestry (Ex. forelimbs of mammals, embryonic structures)
c. Vestigial structures – remnants of features that served important functions in the organism’s
ancestors; reduced in size and function (Ex. pelvis and leg bones in snakes)
Molecular – similarities in DNA sequence and genes observed show common ancestry
a. Evolutionary tree – diagram that reflects evolutionary relationships among groups of organisms
b. Convergent evolution – distantly related organisms coming to resemble each other through
independent evolution of similar features in different lineages features develop because of
similar environments
c. Analogous – similarities in organisms because of convergent evolution, not because of descent from
a common ancestor
Geographic – evidence collected by comparing fossil locations and organisms in different parts of the world
a. Biogeography – geographic distribution of species
b. Continental drift – slow movement of Earth’s continents over time
c. Pangaea – single large continent of all the landmasses on Earth that existed 250 million years ago;
began drifting 200 million years ago
d. Endemic – species confined to a specific, relatively small geographic area such as an island; these
species are found nowhere else in the world