Download Darwinian Evolution (Ch. 22)

AP BIOLOGY @ UHS
Darwinian Evolution (Ch. 22)
Historically Important Scientists and the History of Evolutionary Thought
Linnaeus, Carolus (1707-1778)
! Botanist, Taxonomist
! Founder of taxonomy (system of naming and classifying organisms) invented the system of Binomial Nomenclature
(eg. Ramphastos sulfuratus, the Keel-billed Toucan)
! Hierarchical system based on assessing similarities and differences in characteristics. [DKPCOGS]
! Believed in Creation & Fixity of Species
Cuvier, George (1769-1832)
! Vertebrate Zoologist, largely responsible for developing paleontology.
! First to use Comparative Anatomy to develop a system for classifying animals
! "only needed single bone to describe organism”
! staunch supporter of creation & fixity of species
! Explained how between layers strata unique fossils were found unlike those above and below.
! suggested that after each in a series of catastrophes, mass extinctions and repopulations made it appear that species
changes over time – Catastrophism. These were localized and the result of special creation.
! most crucial and longest-lasting contribution to biology was establishing extinction as a fact.
Lamarck, Jean Baptist de (1744-1829)
! Invertebrate Zoologist
! impressed by changes in species associated with geological strata
! Proposed an evolutionary theory:
Theory of Inheritance of Acquired Characteristics:
! more complex organisms are descended from less complex ones
! there is a built in drive to perfection
! Plants and animals adapt to the environment during there lifetimes; adaptations are passed to offspring.
(Inheritance of Acquired Characteristics)
e.g. Giraffes stretch for food ! Their necks elongate ! Longer necks are passed to offspring
! Use/Disuse: structures that are used extensively become larger/better and those that are not used become
smaller. This is inheritable.
! A change in the environment causes changes in the needs of organisms living in that
environment, which in turn causes changes in their behavior. Altered behavior leads
to greater or lesser use of a given structure or organ; use would cause the structure
to increase in size over several generations, whereas disuse would cause it to shrink
or even disappear
!
BUT we know there is no mechanism to permit this - cells that form gametes are separate from those in the rest of the
body
Lyell, Charles & Hutton, James
! Geologists (Lyell's book [Principle’s of Geology] described Hutton's ideas)
! Earth was dynamic, not static. Changes occur over vast amounts of time and the processes that are observed today are
the same processes that have always been on the earth.
Earth was subject to continuous cycles of erosion and uplift = Uniformitarianism Theory
! Erosion puts sediments into water sedimentary rock in which fossils are found.
! Uplifting of rocks forms land modern view is that such geological changes are periodic.
Darwin, Charles (1809-1882)
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1 of 6 children; mother (Susannah Wedgewood) died when
he was 8. Born the same day as Abraham Lincoln!
On November 11, 1838, Charles Darwin proposed to Emma
Wedgewood (his cousin), the daughter of Josiah Wedgewood
II (and granddaughter of Josiah Wedgewood who established
the famous pottery works); married on January 29, 1839.
Had 10 children, three died young.
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AP BIOLOGY @ UHS
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After his 1831-1836 voyage on HMS Beagle, Charles Darwin was chronically ill, having contracted
what was eventually termed Chagas Disease. April 19th, 1882 he had a fatal heart attack and died.
Buried in Westminster Abbey along with Newton, Lyell, and Faraday.
Darwin theories on evolution influenced by Lyell and Thomas Malthus (population explosions occur unless acted on by
limiting factors).
Published 19 books including, “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured
Races in the Struggle for Life”
DARWIN’S THEORY OF NATURAL SELECTION
Darwin’s theory of evolution through natural selection was written in an attempt to explain how adaptations can lead to a
change in a population over time. The population (group of interbreeding organisms of the same species in a geographic
area) is the smallest unit that can evolve over time. Evolution (change) is measured as a change in allele frequency within a
large population (next chapter). These changes would be the result of differential survival rates of members of the population
that are better adapted to their environment.
1.
In most species the number of individuals in a generation that survive and reproduce is relatively small.
! Without constraints, populations will grow exponentially, producing an ever more rapidly growing number of
organisms (Malthusian)
! Most population sizes are stable (exception: season changes) [stability]
2.
Variations among individuals of a population exist. Everyone is unique.
! Most/much variation is inheritable. (Some of observed variation is environmental, some is genetic)
! This came from observing animal breeding.
3.
Limited resources within an environment, and large numbers of individuals of any given species, leads to a
“struggle for existence”
! Certain variations within a population will enable members to survive longer, reproduce, and produce more
offspring (viable) [Natural Selection]
4.
Inherited favorable characteristics become more common from one generation to the next.
! Over time (key point), the accumulation of different characteristics can differentiate one group of organisms from
another.
! Members become isolated [geographically, behaviorally, temporally (time), reproductively, genetically]
! Through many generations of time, evolution is the result. (Darwin used "descent with modification")
EVIDENCES USED BY BIOLOGIST TO SUPPORT DARWINIAN EVOLUTION
BIOGEOGRAPHY.
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study of the distribution of organisms.
Related organisms are found living close to one another.
Island species are related to the species found on the nearest continent. They may be different from any other species
due to changes in the population as they are under different environmental pressures from mainland species. (eg.
Galapagos Is, Indonesian Islands)
THE FOSSIL RECORD.
!
provides evidence that the variety of species that has inhabited the earth has changed over time
What is a fossil ?
! remains of organisms that have been buried quickly so that decomposition has stopped or slowed
! usually found in sedimentary rock produced through the weathering of parent rock
! settles & is converted to rock
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AP BIOLOGY @ UHS
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Geological processes form layers of rock = strata
each stratum has its own type of fossils; vertebrate species have fish coming before amphibians, then reptiles
and then mammals and birds. Fossils at the lowest level are the oldest and get younger with each layer as you
move upward. Dating using strata called Relative Dating and uses the Principle of Superposition.
boundaries between layers show transitions -- many are mass extinctions - and form basis for dividing time.
Actual dates are estimated from the decay of radioactive isotopes and the measurement of half-life to determine
the Absolute Dating.
COMPARATIVE ANATOMY.
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Comparing structures of various organisms leads to system of classification that indicates evolutionary relationships.
Similar structures indicate that organisms may have descended from a common ancestor and that the structure has
changed due to specific environmental pressures that have been selected for.
Homologous Structures - those that have evolved from a common
original structure.
! Have the same structure but a different function.
! Evolution used one structure and modified it to fit a new
situation. (Common Ancestory).
Commonly used example: forelimb of human, bird, whale, dolphin,
bat, etc.
Analogous Structures - those that have evolved from different
original structures but function similarly.
! Have same function but different structure. The result of
unrelated groups adapting to a similar environment. (Different
Ancestory).
! Natural selection has taken similar environmental roles and modified them in a similar manner. This is called
Convergent Evolution.
Commonly used example: flying structures of insects and vertebrates; lungs of mammals and trachea of insects.
Vestigial Structures - those structures that functioned in an ancestral organisms, but that are reduced (in structure and
function) in the descendant.
! Serve little or no purpose in an extant (currently or actually existing) species but may have in an ancestor. Natural
selection (not Lamarkian Use and Disuse) has selected for organisms within the population that have reduced or absent
forms of the structure, it is metabolically efficient.
Commonly used examples: nictating membrane of eye, caudal vertebrae of coccyx, appendix of intestines, muscles that move
the ears, vestigial hind legs of whales and snakes
COMPARATIVE EMBRYOLOGY.
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Comparing the stages of development of various organisms allows scientists to view the origins of various structures and
the steps involved in morphogenesis (formation of shapes)
Comparing the general appearance of embryos from different species at various stages in development shows them to be
quite similar. Organisms share common homeoboxes (regulatory sequences in genes)
Certain embryonic structures are shared by all chordates, but show interesting structural and functional changes during
development.
!
e.g. notochord (develops into jointed vertebral column in higher vertebrates), gill slits (used for gas exchange in fishes, jaw
support and other functions in higher vertebrates), aortic arches (becomes heart)
MOLECULAR BIOLOGY.
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a comparison of DNA and amino acid sequences in proteins of various species
closely related species should have more similar DNA & more similar sequences in certain proteins (like cytochrome C;
electron carrier of ETC and hemoglobin molecules, Ubiquitin in proteosome function)
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