Introduction: Evolution Natural Selection and Species

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IntroductionEvolution Natural Selection and
Species

• Professor Pamela L. Pannozzo
• Principles of Biology II BSC 1011

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Where Does Biological Diversity Come From?
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Pre-1850s Thoughts on the Origin of Life

• Earth believed to be only thousands of years old
• Different organisms and their structures were the
  results of the Creator
• Species were specially created and unchangeable
  over time

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A Journey Charles Darwin and the HMS Beagle

• 1831 - 22 year old Charles Darwin served as
  naturalist on a five-year mapping expedition
  around the world
• Studied and collected plants and animals
• Examined fossils
• Observed series of related but distinct forms of
  life

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Charles Darwins 5 Year Expedition
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Darwins Observations

• Earth of great geological change
• Earthquakes, volcanoes, ancient oceans
• Glyptodont fossils
• Geographical distribution of species
• Galapagos finches

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Other Influences on Darwins Thinking

• Thomas Malthus (1798) populations of plants and
  animals tend to increase exponentially resources
  are limited though reproductive rate is
  not?competition for survival
• Charles Lyell (1830) geological and fossil
  records suggest Earth is very old and species
  have changed over time
• Artificial Selection selective breeding of
  plants and animals to achieve certain desired
  characteristics in their offspring

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Darwins Postulates

• Individuals vary in their traits
• Traits are inherited
• There is competition for limited resources
• Only the most fit organisms are able to
  survive and reproduce

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Evolution

• The change in inherited characteristics of a
  population from generation to generation,
  eventually resulting in new species

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The Theory of Natural Selection

• On the Origin of Species, 1959
• Explanation for why and how evolution occurs
• Individuals with traits best suited to the local
  environment generally have more surviving
  offspring. This increases the representation of
  certain heritable variations in the next
  generations. This differential reproductive
  success is called natural selection.

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Traits are Inherited, Not Acquired
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Two Meanings of Evolution

• Macroevolution
• Origin of new species over vast periods of time
• Microevolution
• Genetic changes within a species over generations

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How Fast Does Evolution Occur?

• Organism-specific
• Bacteria vs. Mammals
• Punctuated Equilibruim
• Gradualism

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What is the Evidence for Evolution?

• Observed Changes in traits in rapidly reproducing
  organisms
• Aripo River system guppies (effects of predation
  and mate attraction)
• Pathogen bacteria and viruses 9effect of
  drug-resisitance)
• Fossils
• Molecular BiologyDNA, Proteins
• Anatomical Homologies

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Fossils

• Sedimentary rock burials
• Radioisotopic dating

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Fossils at different depths show successive
changes over time
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Fossil Evidence Shows Cetaceans Evolved from
Terrestrial Animals
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Molecular Biology

• Broad genomic differences
• Proteomic differences
• Individual gene sequences

Hemoglobin ß chain amino acids
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Anatomical Homologies

• Embryology
• All vertebrates share basic developmental
  instructions

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Anatomical Homologies

• Homologous structures
• Vertebrates share like skeletons, body plans,
  organs from same origin

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Convergent Evolution

• Analogous structures
• Unrelated organisms develop like adaptations due
  to similar environmental pressures

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Convergent Evolution
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How Do We Determine Species?
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The Biological Species Concept

• Species a group of organisms that can
  successfully interbreed in nature and produce
  fertile offspring
• Requires reproductive isolation
• What about?
• Dog wolf -gt wolf-hybrid (fertile)
• Horse donkey -gt mule (infertile)
• Tiger lion -gt liger (males infertile (?),
  females fertile, but health problems)
• Other definitions of species?
• Morphology, ecological niche, phylogeny

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Evolution Commonly Occurs On Islands
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Types of Reproductive Isolation

• Prezygotic barriers
• Habitat isolation (physical barriers)
• Temporal isolation
• Behavioral isolation
• Mechanical isolation
• Postzygotic barriers
• Reduced developmental viability in first
  generation
• Sterility of first generation
• Feeble or sterile second generation offspring

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Two Mechanisms of Speciation

• Allopatric speciation
• Geographic barrier separates gene pools, prevents
  interbreeding
• Sympatric speciation
• Less common
• No geographic barrier
• Chromomsomal mutations, genetic mutations
  enabling use of different resources, sexual
  selection