Science 1101:Interdisciplinary Science: Basic Principles

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Science 1101Interdisciplinary Science Basic
Principles

• Lecture 11

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Evolution and Natural Selection

• Approximately 1.5 million living species
  described
  
• Likely at least 10 million species today
• May represent only 1 of species ever to have
  lived on earth
  
• 1 billion species presumed to have lived

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Reason for this diversity?

• Natural selection
• Physical environment acts on various
  characteristics of organisms (variation among
  individuals of some species)
  
• Sorts out harmful ones, leaving individuals
  with beneficial or neutral characteristics to
  produce next generation
  
• Keeps organisms well-suited for survival in their
  environment
  

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Natural selection drives evolution

• Development of various forms or species to best
  match the environment
  
• Can best take advantage of variations within that
  environment
  

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History of concept of evolution by natural
selection

• Lamarck - inheritance of acquired
  characteristics
  
• Darwin, Wallace - natural selection, but
  mechanism really unknown
  
• Mendel - genetic understanding of the acquisition
  of inherited traits
  

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Old Theories of Evolution

• Jean Baptiste Lamarck (early 1800s) proposed
• The inheritance of acquired characteristics
• He proposed that by using or not using its body
  parts, an individual tends to develop certain
  characteristics, which it passes on to its
  offspring.

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The Inheritance of Acquired Characteristics

• Example
• A giraffe acquired its long neck because its
  ancestor stretched higher and higher into the
  trees to reach leaves, and that the animals
  increasingly lengthened neck was passed on to its
  offspring.
• This idea was proven wrong, however, when it was
  discovered that traits were passed on to
  offspring due to genetics.

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Charles Darwin

• Influenced by Charles Lyell who published
  Principles of Geology.
  
• This publication led Darwin to realize that
  natural forces gradually change Earths surface
  and that the forces of the past are still
  operating in modern times.

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Charles Darwin

• Darwin set sail on the H.M.S. Beagle (1831-1836)
  to survey the south seas (mainly South America
  and the Galapagos Islands) to collect plants and
  animals.
• On the Galapagos Islands, Darwin observed species
  that lived no where else in the world.
  
• These observations led Darwin to write a book.

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Charles Darwin

• Wrote in 1859 On the Origin of Species by Means
  of Natural Selection
  
• Two main points
• 1. Species were not created in their present
  form, but evolved from ancestral species.
  
• 2. Proposed a mechanism for evolution
  NATURAL SELECTION
  

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Natural Selection

• Individuals with favorable traits are more likely
  to leave more offspring better suited for their
  environment.
  
• Also known as Differential Reproduction

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The peppered Moth

• Example The peppered Moth
• Pre 19th century- most of the peppered moths were
  light colored. A dark variety was also present.
  
• The lighter variety was more present because it
  could hide from predators by blending in with the
  light color on the trees.
  
• Mid 19th century the industrial revolution
  created lots of soot that covered the barks of
  the trees the darker variety could blend in with
  the new color and became the dominant variety.

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Artificial Selection

• The selective breeding of plants and animals by
  man.
  
• Primitive Ears of Corn Modern
  Domesticated Corn
  

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Darwin Descent with modificationvia natural
selection

• Genetic variation is the raw material of
  natural selection
  
• A trait or characteristic that is favored by the
  environment is more likely to be passed on to the
  next generation (inherited) whether it is long
  ears for a rabbit, a long neck for a giraffe, or
  flashy coloration for a guppy

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The normal distribution of ear lengths in a
population of rabbits (an example)
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The normal distribution of ear lengths in a
population of rabbits (an example)
No selection acting on ear length
Increased Predation
Number of Rabbits
Short Average Long Ear Length
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The normal distribution of ear lengths in a
population of rabbits (an example)
Number of Rabbits
Short Average Long

Ear Length
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Evidence of Evolution

• Biogeography
• Geographical distribution of species.
• 2. Fossil Record
• Fossils and the order in which they appear in
  layers of sedimentary rock (strongest evidence).

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Evidence of Evolution

• 3. Taxonomy
• Classification of life forms.
• 4. Homologous structures
• Structures that are similar because of common
  ancestry (comparative anatomy)

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Evidence of Evolution

• 5. Comparative embryology
• Study of structures that appear during embryonic
  development.
  
• 6. Molecular biology
• DNA and proteins (amino acids)

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Evolution by natural selection - established some
intriguing ideas

• 1) Individuals that form a population of a
  species are not identical
  
• 2) Some of the variation between individuals can
  be inherited
  

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Evolution by natural selection - established some
intriguing ideas

• 3) All populations are capable of exponential
  growth, but most individuals die before
  reproducing, and most others reproduce at less
  than their maximum rate
• 4) Different ancestors leave different numbers of
  descendents they do not all contribute equally
  to subsequent generations

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• Natural selection acts on the individual while
  evolution is a change of gene frequencies in a
  population.

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Evolution change through time
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Microevolution

• A change in a populations gene pool over several
  generations.
  
• Evolutionary changes in species over relatively
  brief periods of geological time.

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Five Mechanisms of Microevolution

• 1. Genetic drift
• Change in the gene pool of a small population
  due to chance.
  
• This happens in populations
• Two examples
• a. Bottleneck effect
• b. Founder effect

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Genetic drift

• A. Bottleneck Effect
• Genetic drift (reduction of alleles in a
  population) resulting from a disaster that
  drastically reduces population size.
  
• B. Founder Effect
• Genetic drift resulting from the colonization of
  a new location by a small number of individuals.
  
• Results in random change of the gene pool.

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Five Mechanisms of Microevolution

• 2. Gene Flow
• The gain or loss of genes from a population by
  the movement of individuals or gametes.
  
• e.g. Immigration or emigration.

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Five Mechanisms of Microevolution

• 3. Mutation
• Change in an organisms DNA that creates a new
  gene.
  
• 4. Non-random mating
• The selection of mates other than by chance.
• 5. Natural selection
• Differential reproduction.

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Speciation

• Speciation
• The evolution of new species
• There are two patterns of speciation we will
  discuss.
  
• Anagenesis
• Cladogenesis

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Anagenesis

• One species changes into another species over
  time
  
• Original species evolves out of existence and
  is replaced by new species
  
• Evolutionary extinction

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Cladogenesis

• One species gives rise to one or more additional
  species while still remaining
  
• Clade-set of species descended from a particular
  ancestral species

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Mutation, Evolution, and Speciation

• Mutations usually produced by mutagens (e.g.,
  Chemicals, viruses)
  
• 1 mutation per gene in every 100,000 sex cells
• Higher organisms have 10,000 genes
• 1 in 10 individuals has newly created mutation

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Mutation, Evolution, and Speciation

• 1 in 1000 mutations may be beneficial
• 1 in 10,000 individuals per generation has a
  useful mutation
  
• Most individuals have at least one mutant gene
  (original, or passed down from ancestors)
  

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Mutation, Evolution, and Speciation

• Estimate - 500 mutations are necessary to produce
  new species from existing one
  
• Rate of new mutations 1 million times greater
  than needed to account for known rate of evolution

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So.

• Mutations produce the variation, and natural
  selection acts upon the changes
  
• Add in nonrandom mating, changing environment
• End product EVOLUTION