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Evolution

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Title: Evolution


1
Evolution
2
Evolution
  • Evolution a change in gene frequencies in
    populations over time
  • Evolution explains
  • origin of species,
  • diversity of organisms and their relationships,
  • similarities and differences among species,
  • adaptation to the environment

3
CHARLES DARWIN ANDTHE ORIGIN OF SPECIES
  • Charles Darwins On the Origin of Species by
    Means of Natural Selection was published in 1859
  • co-presented with Alfred Wallace
  • Darwins 2 main points
  • All organisms descended from ancestral species
  • Natural selection was the mechanism for change

4
Darwins Theory of Natural Selection
  • Darwin based his theory of natural selection on
    two key observations
  • Overproduction
  • All species tend to produce excessive numbers
  • This leads to a struggle for existence
  • Individual variation
  • Variation exists among individuals in a
    population
  • Much of this variation is heritable

5
Survival of the Fittest
  • Inference Natural Selection leads to
    differential reproductive success
  • Individuals best suited for the local environment
    leave more fertile offspring
  • Evolution is the accumulation of more favorable
    variants over time
  • Natural Selection operates at the level of the
    individual, NOT for the good of the species

6
Natural Selection in Action
  • Examples of natural selection include
  • Pesticide resistance in insects
  • The development of antibiotic-resistant bacteria
  • Kettlewells Peppered Moths

7
Kettlewells Peppered Moths
  • Kettlewell studied the peppered moth (Biston
    betularia) from insect collections in England.
  • Birds ate moths that were easiest to find.

Selection for Light colored moths in
non-polluted areas
Selection for Black moths in polluted areas
8
Three General Outcomes of Natural Selection
  • Directional Selection
  • Selects in favor of one or the other extreme
  • Diversifying Selection
  • Selects in favor of two extreme types
  • Stabilizing Selection
  • Selects in favor of intermediate type

1) Directional Selection
3) Stabilizing Selection
2) Diversifying Selection
Selects in favor of two extreme types
Selects in favor of intermediate type
Selects in favor of one or the other extreme
9
Patterns of Evolution
  • Convergent Evolution
  • evolutionary change in two or more unrelated
    organisms that results in the independent
    development of similar adaptations to similar
    environmental conditions
  • Example anteaters found in Australia, Africa,
    North and South America

10
Patterns of Evolution
  • Divergent Evolution
  • occurs when a single group of organisms splits
    into two or more groups and each group evolves in
    increasingly different directions
  • Example Darwins Galapagos Finches

Figure 1.13
11
EVIDENCE FOR EVOLUTION
  • Common ancestry and descent with modification are
    found by studying
  • The fossil record
  • organisms appear in a historical sequence
  • Biogeography
  • the geographic distribution of species
  • Comparative anatomy
  • comparison of structures in different species
  • Comparative embryology
  • comparison of structures that appear during
    development
  • Molecular biology
  • comparison of genes and proteins

(right) Comparative embryology of vertebrates
supports evolutionary theory
12
Homologous structures
  • Homologous (also called divergent) structures
    have a similar anatomy due to common ancestry
  • Same form (function may or may not be the same)
  • Ex forelimbs of vertebrates

Human write
Cat Walk
Whale Swim
Bat Fly
13
Analogous structures
  • analogous (also called "convergent") structures
    have evolved independently
  • Serve the same function in different species
  • Ex wings of butterfly and bird

Bird Fly
ButterflyFly
14
The Origin of Species
  • The biological species concept defines species as
    groups of interbreeding natural populations that
    are reproductively isolated from other such
    groups

(a) Similarity between different species
(b) Diversity within one species
Figure 14.4
15
Mechanisms of Speciation
  • The two modes of speciation are
  • Allopatric speciation
  • other country
  • Sympatric speciation
  • same country

(b) Sympatric speciation
  1. Allopatric speciation

Figure 14.8
16
Allopatric Speciation
  • Members of a population become physically
    separated
  • The separated populations diverge, through
    changes in mating tactics or use of their habitat
  • They become reproductively separated such that
    they cannot interbreed and exchange genes

17
Sympatric Speciation
  • a species splits into two due to reproductive
    isolation without any geographic separation
  • Reproductive isolation may be
  • Pre-zygotic
  • Post-zygotic

18
Pre-zygotic barriers
  • Pre-zygotic barriers impede mating between
    species or hinder fertilization of eggs
  • Temporal isolation
  • Habitat isolation
  • Mechanical isolation
  • Gametic isolation
  • Behavioral isolation

19
Post-zygotic barriers
  • Post-zygotic barriers are backup mechanisms that
    operate should interspecies mating actually occur
    and produce hybrid zygotes
  • Hybrid inviability
  • Hybrid sterility

Horse
Mule (hybrid)
Donkey
Figure 14.7
20
Study Objectives
  • Define evolution and describe Charles Darwins
    contribution to the current Theory of Evolution.
  • Define natural selection and describe how natural
    selection works to change a population.
  • Describe some examples of natural selection,
    including Kettlewells study with the black and
    peppered moths.
  • Contrast directional, diversifying, and
    stabilizing selection.
  • Define convergent evolution and divergent
    evolution and give an example of each.
  • Describe five main lines of evidence in support
    of evolution.
  • Contrast homologous and analogous structures.
  • Define species.
  • Define speciation and describe two mechanisms by
    which speciation can occur (allopatric,
    sympatric).
  • Distinguish between pre-zygotic and post-zygotic
    barriers and describe ways in which sympatric
    populations can be reproductively isolated.
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