Chapter 19 - Darwin
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Darwin published Origin of Species in 1859 with two points
Species were not created in their present forms but had evolved from
Natural selection is the proposed mechanism for evolution.
A population of organisms can change over time as a result of individuals
with certain heritable traits leaving more offspring than other individuals.
Evolutionary change is based on the interactions between populations of
organisms and their environment.
Evolutionary adaptations are inherited characteristics that enhance an
organismís ability to survive and reproduce in a particular environment.
II. Western culture resisted evolutionary views of life
The Scale of Nature and Natural Theology
1. Many Greek philosophers
believed in gradual evolution of life.
Plato believed that evolution would be counterproductive because
organisms that were perfect for their environment could not live in an imperfect
Aristotle believed that all living forms could be arranged on a scale of
Judeo-Christian culture used the idea of natural theology that was
dedicated to discovering the Creatorís plan by studying nature.
They saw adaptations as evidence that the Creator had designed each for a
Carolus Linnaeus was the founder of taxonomy who sought to discover order
in the diversity of life. He developed a two-part system of naming organisms that is
still used today. His clustering of
species implied no evolutionary kinship.
Curvier, Fossils, and Catastrophism
Fossils are relics or impressions of organisms from the past used to help
lay the groundwork for Darwinís ideas.
Most fossils are found in sedimentary rock formed from sand and mud that
settle in marshes, lakes and seas. Newer layers compress the older layers into strata.
Fossils in the layers show a succession of organisms.
Paleontology was developed by Georges Cuvier to study fossils.
He documented the succession of the fossil record when he noted that each
stratum contained layers that had a unique group of characteristics.
He recognized that extinction was evident.
He began the idea of catastrophism speculating that each boundary between
strata corresponded in time to a catastrophe that had destroyed many species.
II. Theories of geological gradualism helped clear the path for
James Hutton proposed the idea of gradualism where various landforms
about due to a gradual change. Profound
changes are a cumulative product
of slow but continuous processes.
Charles Lyell incorporated Huttonís theory in a theory known as
uniformitarianism that says these processes have not changed throughout time.
Darwin learned from this that geological change results from a slow
continuous action and that these slow changes have a substantial impact on
Lamarck placed fossils in evolutionary context
Jean Baptist Lamarck compared current species to fossil forms and said
could see several lines of descent. He
felt that evolution was driven to
greater complexity. He incorporated
1. Use and disuse where
parts of the body that are used remain and
those that arenít are done away with.
The inheritance of acquired characteristics that said modifications
during a lifetime can be passed to offspring.
IV. The Darwinian Revolution
Field research helped Darwin frame his view of life
1. Darwin began his voyage
on the HMS Beagle in December 1831.
Mission was to chart the poorly known stretches of the South American
He observed thousands of specimens.
Noted various adaptations like plants were very different from those
found in Europe but also varied as to whether they were found in a tropical
climate versus a temperate climate.
He also noticed that may of the species that inhabited the Galapagos
Islands lived nowhere else. He
focused on the finches that were unique to individual islands.
Darwin focuses on Adaptation
Darwin perceived the origin of the species and adaptation to the
environment were very closely related to
A new species could arise from an ancestral form by the gradual
accumulation of adaptations to a different environment like a geographical
barrier that isolates two populations.
Over a long period of time, these two populations could become dissimilar
enough to appear as two separate species.
Darwinís ideas were reiterated by Alfred Wallace working in the East
Indies. The discovery of someone
else who believed Darwinís theories catapulted him to write Origin of
Origin of species developed two main points
1. Descent with Modification
Darwin believed that all organisms related through descent from some
unknown organism and as descendants of that organism moved into various habitats
the accumulated modifications that fit them into specific ways of life.
Natural selection is differential success in reproduction.
It occurs through an interaction between the environment and the
variability inherent among the individual organisms making up the population.
The product is the adaptation of populations to their environment.
Organisms must have the ability to overreproduce.
He also noticed that artificial selection was possible for domestication.
Subtleties of Natural Selection
The population is important for evolution.
Remember a population is a group of interbreeding
individuals belonging to a particular species and sharing a
common geographic area.
A population is the smallest unit that can evolve.
Natural selection involves interactions between individual organisms and
their environment but individual do not evolve.
Natural selection can only amplify or diminish heritable variations.
1. Peter and Rosemary Grant
studied the beaks of finches on Daphne Major
of the Galapagos Islands.
Noted that the depth of the beak changed with the seasons of wet and dry.
The wetter the season, the smaller the beak and the drier, the larger the
Reinforced the point that natural selection is situational.
V. Evidence of Evolution
Evidence of evolution pervades biology
The geographical distribution of species.
Many species are indigenous yet closely related to species on the
The Fossil Record
The succession of the fossil record is compatible with other known types
The oldest known fossils are prokaryotes.
Also see a chronological appearance of different classes of vertebrate
Fish to amphibians to reptiles to mammals to birds which is consistent
with the fossil record.
Evolutionary transitions should leave signs in the fossil record.
Descent with modification is evident in anatomical similarities between
species groups in the same taxonomic category.
There is some similarities between the forelimbs of humans, cats, whales,
bats, and other mammals although the appendages are very different in function.
Similarity in characteristics is called homology and the anatomical signs
of evolution are called homologous structures.
This shows the remodeling process from ancestral structures.
Some homologous structures are vestigial organs or structures that have
little or no use to the organism now but may have been important in ancestors.
Closely related organisms go through similar stages in their embryonic
All vertebrates go through a stage where they have gill pouches.
As development progresses, the various vertebrates diverge more and more
taking on more distinctive characteristics.
Often used to establish homology among structures.
The ontogeny or development of the individual is a replay of the
phylogeny or history of the species.
Genes and gene products are now studied to reveal similarities.
Molecular biology supports the idea that all forms of life are related to
Mutations have helped with the changes in the expression of genes to