Download Chapter 22 - Darwinian Evolution

CHAPTER 22
Descent with Modification:
A Darwinian View of Life
22.1 – The darwinian revolution challenged traditional
views of a young earth inhabited by unchanging
species
• Historical Setting – Earlier views
• 1) Scala naturae (Aristotle 384-322 BC)
• Life-forms could be arranged on a scale of increasing complexity
• 2) Old Testament
• Perfect species were individually created by God
• 3) Carolus Linnaeus (1707-1778)
• Grouped species into general categories based on the pattern of
their creation
• Taxonomy
• Naming and classification
• Binomial Nomenclature
• 2 part naming system that includes Genus species
HISTORICAL SETTING (CONTD.)
• 4) Georges Cuvier(1769-1832)
•
Opposed evolution
• Advocated catastrophism – the events in the past happened suddenly
and by different mechanisms then today
• 5) Charles Lyell (1797-1875)
• Uniformitarianism
• Earth’s processes have not changed – Earth must be OLD
• Darwin studied his work
• 6) Jean-Baptiste de Lamarck (1744-1829)
• Early evolution:
• 1) use and disuse
• 2) inheritance of acquired characteristics
22.2 – Descent with modification by natural selection explains the
adaptations of organisms and the unity & diversity of life
• Darwin’s voyage on the HMS BEAGLE from 1831-1836 was the time that he
developed his theory of evolution by natural selection
• Darwin’s idea focused on natural selection vs. Lamarck’s idea focused on
inheritance of acquired traits
• Natural selection describes how adaptations arise:
• Adaptation = characteristics that enhance organisms’ ability to survive &
reproduce in specific environments
• Example: desert foxes have big ears, arctic foxes have small ears
• Natural selection = process in which individuals that have heritable
characteristics survive & reproduce at a higher rate than others
individuals
• Over time, NS can increase the match between organisms &
environment
• NS may result in adaptations to new conditions, potentially giving rise to
new species
• Artificial selection
• The process by which species are modified by humans
• Example: selective breeding for milk or meat production, etc
• Individuals do not evolve. POPULATIONS evolve
• Origin of Species published in 1859
• Darwin developed two main ideas:
• Descent with modification explains life”s unity and diversity
• Natural selection is a cause of adaptive evolution
Tree of life
Branches represent
diversity
• Darwin describe four observations of nature and drew 2 conclusions from
these
• Observation #1: Members of a population often vary greatly in their traits
• Observation #2: Traits are inherited from parents to offspring
• Observation #3: All species are capable of producing more offspring than
the environment can support
• Observation #4: Due to lack of food or other resources, many of these
offspring do not survive
• Inference #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
• Inference #2: This unequal ability of individuals to survive and reproduce will
lead to the accumulation of favorable traits in the population over
generations
SUMMARY OF NATURAL SELECTION
• Individuals with certain heritable characteristics survive and reproduce at a
higher rate than other individuals
• Natural selection increases the adaptation of organisms to their environment
over time
• If an environment changes over time, natural selection may result in
adaptation to these new conditions and may give rise to new species
22.3 EVOLUTIONARY EVIDENCE
Evidence for
Evolution
Direct
Observations
The Fossil Record
Homology
Biogeography
DIRECT OBSERVATIONS
• 1) Intense predation of wild guppies results in more drably colored mates
• 2) Evolution of drug-resistant viruses and antibiotic-resistant bacteria
THE FOSSIL RECORD
• Traces of organisms from the past
• Commonly found in sedimentary rock
• Paleontology = the study of fossils
• Fossils show evolutionary changes that have occurred over time & the origin
of major new groups of organisms
HOMOLOGY & CONVERGENT EVOLUTION
• 1) Homology
• Characteristics in related species can have similarities even with
different functions
• 2) Homologous Structures
• Anatomical sign of evolution
• Examples – forelimbs of mammals that are now used for various
purposes
• Flying in bats
• Swimming in whales
• Once used for walking
• 3) Embryonic homologies
• Comparison of early stages of animal development reveals homologies
in embryos that are not present in adults
• All vertebrate embryos have a post-anal tail & pharyngeal pouches
• Vestigial organs
• Structures of marginal importance
• Remnants of structures that were useful in ancestors
• Remnants of pelvis & leg bones in snakes
• 5) Molecular homologies
• Shared characteristics on the molecular level
• All life forms use DNA & RNA
• 6) Convergent evolution
• Explains why distantly related species can resemble one another
• Has taken place when two organisms developed similarities as they
adapted to similar environmental challenges
• Known as analogous
• “Similar problem, similar solution”
HOMOLOGOUS = EVIDENCE OF RELATION
ANALOGOUS = SIMILAR FUNCTION & SOLUTION
BIOGEOGRAPHY
• The geographic distribution of species
• 1) species in a discrete geographic area tend to be more closely related to
each other
• South American desert animals are more closely related to local animals
in other habitats than they are to the desert animals of Asia
• 2) Continental drift
• The movement of the tectonic plates
• The break-up of Pangaea
• Explains the relation of species on different continents
• 3) Endemic species
• Found at a certain geographic location and nowhere else
• Marine iguanas are endemic to the Galapagos
• 4) Darwin’s theory of evolution through natural selection explains the
succession of forms in the fossil record
• Transitional fossils have been found that link ancient organisms to
modern ones
SUMMARY
• 1) Evolution is change in species over time
• 2) Heritable variations exist within a population
• 3) These variations can result in differential reproductive success
• 4) Over generations, this can result in changes in the genetic composition of
the population
• INDIVIDUALS DO NOT EVOLVE – POPULATIONS DO