Chapter 22: Descent with Modification. Theory of Evolution Change through time – Descent with...
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Transcript of Chapter 22: Descent with Modification. Theory of Evolution Change through time – Descent with...
Chapter 22: Descent with Modification
Theory of Evolution• Change through time
– Descent with modification– Genetic changes of a population through time
• Explains Biodiversity– Variety of life forms, with adaptations to specific
environments– Form=Function
• Explains relationship between living organisms– How organisms are related by descent from
common ancestors
Theory of Evolution• Pattern of Evolution
– Observations from natural world– Collected from variety of fields
• Biology, geology, physics, chemistry
• Process of Evolution– Mechanisms causing change
• Unifying theory of biology– Explains and connects observations from natural
world
Types of Evolution• Microevolution= change in the gene pool of a
population over many generations• 4 Methods of Microevolution
– Mutations• May be deleterious or neutral
– Natural Selection• Process in which individuals with favorable inherited traits
are more likely to survive and reproduce
– Genetic Drift= chance events cause genetic changes from one population to the next
– Gene Flow= individuals or gametes move to a different population
Natural Selection and Mutation
Classification of Species• Before 1700s, major belief was organisms did not
change through time but were “perfect” and “permanent”– Greek philosopher Aristotle= arranged species on a
scala naturae• Simple to complex• Viewed species as fixed, non-changing
• 1700s: Carolus Linnaeus= founder of taxonomy– Branch of biology concerned with classifying
organisms– Developed the binomial format for naming species
• Homo sapiens
Classification of Species
• In the mid-1700s, studies of fossils found evidence of life-forms different from those currently living
• Early 1800s, French naturalist Jean Baptiste Lamarck explained the differences in fossil records by proposing organisms evolved through time
Fossil Record• Primarily based on imprints or remains
left in sedimentary rock– Relative ages of fossils can be
determined based on their position in rock layers
– Radiometric dating allows for more precise aging of fossils
– Whole organisms can also be preserved in mediums preventing decomposition
• Insects in resin• Wooly mammoth frozen in ice
• Documents change of organisms through time
• Documents large number of extinct species
Classification of Species
• Lamarck proposed:– Organisms could change its traits by using or not
using certain body parts– These changes could be passed
to offspring • Not supported by genetics
Charles Darwin
• Born in 1809• Life-long naturalist• After college, joined the crew of the
HMS Beagle to explore and map parts of the South American coastline– Collected specimens of South
American plants and animals
HMS Beagle in port
TheGalápagosIslands
NORTHAMERICA
ATLANTICOCEAN
Chile
SOUTHAMERICA
AFRICA
EUROPEGreatBritain
Equator
PACIFICOCEAN
Malay Archipelago
AUSTRALIA
Tasmania
NewZealand
Brazil
Argentina
Cape Horn
An
des
Mtn
s.
Cape ofGood Hope
PACIFICOCEAN
Charles Darwin: Voyage of HMS Beagle
Figure 22.5c
TheGalápagosIslands
PACIFICOCEANPinta
MarchenaGenovesa
EquatorSantiago
DaphneIslands
Fernandina
Isabela SantaCruz
SantaFe San
Cristobal
EspañolaKilometers
0 20 40 Florenza
Pinzón
Charles Darwin
• During voyage, made 2 important observations:– Animals and plants had characteristics specific to
the environment they inhabited– Organisms on islands were similar but different
from organisms on mainland• Darwin perceived adaptation to the
environment and the origin of new species as closely related processes
Figure 22.6
(a) Cactus-eater (b) Insect-eater
(c) Seed-eater
Charles Darwin
Charles Darwin
• 1844: wrote an essay on natural selection as the mechanism of descent with modification– Did not introduce his theory publicly
• 1858: Received manuscript from Alfred Russell Wallace– Developed a theory of natural selection similar to
Darwin’s• Darwin quickly finished The Origin of Species
and published it the next year
Charles Darwin
• 1859: The Origin of Species was published• Provided evidence of “descent with
modification”– Current species came from a succession of ancestors– As descendants spread into new habitats,
modifications (adaptations) accumulated as a result of new environmental factors
– Resulted in new species and increased diversity
• Proposed mechanism for evolution– Natural selection
Charles Darwin
• In the Darwinian view, the history of life is like a tree with branches representing life’s diversity
• Darwin’s theory meshed well with the hierarchy of Linnaeus
Figure 22.8Hyracoidea(Hyraxes)
Sirenia(Manateesand relatives)
†Deinotherium
†Mammut
†Platybelodon
†Stegodon
†Mammuthus
Elephas maximus(Asia)
Loxodonta africana(Africa)
Loxodonta cyclotis(Africa)
†Moeritherium
†Barytherium
60
Millions of years ago
34 24 5.5 2104 0
Years ago
Artificial Selection
• Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits– Artificial selection
Figure 22.9
Brusselssprouts
Kale
Selection for leaves
Selection for axillary (side) buds
Selection for apical (tip) bud
Cabbage
Broccoli
KohlrabiWild mustard
Selection for stems
Selection for flowers and stems
Darwin drew two inferences from two observations
• Observation #1: Members of a population often vary in their inherited traits
• 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
Darwin drew two inferences from two observations
• Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce
• Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations
Natural Selection• Unequal reproduction is the
essential part of natural selection
• Individuals with characteristics allowing them to be better at…– getting food– escaping predators– tolerating environment– attracting mates – …will survive longer and
potentially produce more offspring with the adaptive characteristic
Natural Selection• Explains the match between organisms and
their environment…
3 Key Points to Evolution by Natural Selection
• Individuals do not evolve, populations evolve– Evolution occurs as adaptations accumulate in populations
over several generations• Natural selection only works on heritable traits with
variation in the population– Acquired traits are not passed to offspring
• Evolution is not working towards a specific goal or “perfect” organisms– Natural selection results from an organism interacting with
a specific environment– Characteristics favorable in one environment may not be
favorable in another
Natural Selection: Summary
• 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
Evidence of Natural Selection: Response to Introduced Plant Species
• Soapberry bugs use their mouthparts to feed on seeds within fruits
• Southern Florida: feed on balloon vine with large fruit– Longer beaks
• Central Florida: feed on goldenrain tree with small fruit– Shorter beaks
• Correlation between fruit size and beak size also observed in Louisiana, Oklahoma, and Australia
Soapberry bug with beak inserted in balloon vine fruit
Figure 22.13b
On native species, southern Florida
Museum-specimen average
On introduced species, central FloridaN
um
ber
of
ind
ivid
ual
s
10
8
6
4
2
0
10
8
6
4
2
0
Beak
Beak length (mm)
6 7 8 10 11
RESULTS
9
• In all locations, beak size has evolved in populations that feed on introduced plants– Fruits smaller or larger than native fruits
• Evolution by natural selection• In Florida, this evolution in beak size
occurred in less than 35 years
Evidence of Natural Selection: Response to Introduced Plant Species
Evidence of Natural Selection: Antibiotic resistant bacteria
• Staphylococcus aureus is commonly found on people– S. aureus became resistant to penicillin in 1945,
two years after it was first widely used• One strain, methicillin-resistant S. aureus
(MRSA) is a dangerous pathogen– S. aureus became resistant to methicillin in 1961,
two years after it was first widely used
Evidence of Natural Selection: Antibiotic resistant bacteria
• Methicillin= inhibits a protein used by bacteria in their cell walls– MRSA bacteria use a different protein in their cell
walls• When exposed to methicillin, MRSA strains are
more likely to survive and reproduce than nonresistant S. aureus strains– MRSA strains are now resistant to many antibiotics
Evidence of Natural Selection: Antibiotic resistant bacteria
Antibiotic Applied
Most bacteria killed,High resistance strains remain
Reproduction
Final population composed of high resistance strains
Evidence of Natural Selection: Antibiotic resistant bacteria
• Natural selection does not create new traits– Works on existing traits already present in the
population– Mutations are raw material for natural selection to
act on• Local environment determines which traits
will be selected for or selected against in any specific population
Evidence of Natural Selection: Comparative Anatomy
• Homology= similar characteristics resulting from a common ancestor
• Homologous structures= similar structure in features even if function is different
• Example: Vertebrate Forelimbs
Figure 22.15
Humerus
Radius
Ulna
Carpals
MetacarpalsPhalanges
Human Cat Whale Bat
Evidence of Natural Selection: Comparative Anatomy
• Comparative embryology reveals anatomical homologies not visible in adult organisms
Evidence of Natural Selection: Comparative Anatomy
• Vestigial structures= remnants of features with served important functions in the organism’s ancestors
Evidence of Natural Selection: Molecular Biology
• Homologies also occur at the molecular level – Genes shared among organisms inherited from a
common ancestor
Evidence of Natural Selection: Molecular Biology
• Evolutionary history contained in an organism’s DNA
• Closely related species will have more similarities in DNA than distantly related species
• Darwin proposed all life forms are related– Supported by molecular biology– All organisms use same genetic language- DNA and RNA– Same genetic code for nearly all organisms– Humans and bacteria share homologous genes
Evidence of Natural Selection: Evolutionary Trees
• Evolutionary trees= hypotheses about the relationships among different groups– Form nested patterns in evolutionary trees
• Made using different types of data– Anatomical similarities– DNA sequence data
Figure 22.17
Branch pointLungfishes
Amphibians
Mammals
Lizardsand snakes
Crocodiles
Ostriches
Hawks andother birds
Feathers
Amnion
Digit-bearinglimbs
Homologouscharacteristic
Tetrapo
ds
Am
nio
tes
Bird
s
1
2
3
4
5
6
Evidence of Natural Selection: Evolutionary Trees
• Convergent evolution= evolution of similar, or analogous, features in distantly related groups– Arise when groups
independently adapt to similar environments in similar ways
• Convergent evolution does not provide information about ancestry
Evidence of Natural Selection: Biogeography
• Biogeography= geographic distribution of species
• Island animals resemble species on closest mainland more than they resemble species on islands closer and farther away
• Explanation: Animals on islands migrated from mainland, natural selection changed animals over time into separate species– Galapagos Finches– Marsupials in Australia
Evidence of Natural Selection: Biogeography
• Alfred Russel Wallace (1823–1913) – Father of biogeography
• Best known as the co-discoverer of the principles of natural selection with Darwin
• Main contribution was the study of species distributions across large spatial scales
Evidence of Natural Selection: Biogeography
• Wallace (1860) observed that animals can vary considerably over very short distances– Could not be explained until continental drift was
proposed• Continental drift from movement of Earth’s plates
explains the distributions of some species• Type of macroevolution
Types of Evolution• Macroevolution= change in groups above the
level of species, often results in new taxonomic groups
• Methods of Macroevolution– Adaptive radiation= periods of change when many
new species originate from a common ancestor– Mass extinctions= large number of species go
extinct within a relatively short amount of time• 5 mass extinctions have occurred through geological time
with 50% or more species lost
– Plate tectonics and Continental drift= movement of Earth’s plates
Mass Extinction Event Mass Extinction Event
Evidence of Natural Selection: Biogeography
Evidence of Natural Selection: Biogeography
• Endemic species= species that are not found anywhere else in the world
• Islands have many endemic species– Closely related to species on the nearest mainland
or island• Darwin explained that species on islands gave
rise to new species as they adapted to new environments
Evolution is a Theory
• In science, theory accounts for many observations and data – Attempts to explain and connect a huge variety of
phenomena• Darwin’s theory of evolution by natural selection
– integrates diverse areas of biological study – stimulates many new research questions
• Ongoing research adds to our understanding of evolution