Natural Selection and Species Typical Behaviors

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Natural Selection and Species Typical Behaviors
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Charles Darwin and Alfred Russell Wallace
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The Rise of Evolutionary Theory

• As knowledge of the world grew, biologists were
  struck by the huge variety of species.
• They also noticed that many of these species
  shared similar structural features Homologies.
• Unearthed fossils showed that creatures existed
  in the past that did not exist today.
• These extinct creatures shared homologous
  features with existing creatures suggesting that
  they were related.

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Homologous Structures
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The Rise of Evolutionary Theory

• Biologists also noted striking similarities
  during the embryonic development of different
  species.
• Human embryos have gill slits and tails
• Many species posses characteristics that seem to
  have a purpose
• The turtles shell
• The porcupines quills
• The skunks smell
• The beak size of different species of bird
• The giraffes long neck

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The Theory of Special Creation

• William Paley (1802) promoted the Theory of
  Special Creation with his watchmaker analogy.
• This argument is still made today as The Argument
  from Design.
• Does not explain adaptation, extinction,
  speciation, evidence from the fossil record and
  biogeographical evidence.

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Artificial Selection

• Individuals in a species differ in many
  measurable characteristics that are inherited.
• Man has used this to selectively breed animals
  for desirable characteristics.
• e.g. Dog breeds
• Size
• Temperament

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Charles Darwin

• Charles Darwin wanted to explain how organisms
  could change over time naturally evolution
• Thomas Malthus the struggle for existence
• Charles Darwin presented the fundamental
  principles of evolution by Natural Selection in
  his book, On the Origin of Species by Means of
  Natural Selection, in 1859.
• Darwin called evolution descent with
  modification

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Descent with Modification
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The Principles of Evolution

• Organisms produce an excess of offspring, many
  more than are required to replace the parents.
• The individuals within a population of organisms
  show a range of variability across numerous
  physiological and behavioral traits.
• Because of competition for limited resources,
  individuals that are better able to compete for
  resources will be more likely to reproduce.

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Darwin and Evolutionary Theory

• Because of the differential reproduction of
  individuals with certain characteristics, these
  characteristics will become more prevalent with
  each succeeding generation evolution
• Eventually, as a result of this Natural
  Selection, enough change may take place that
  populations may become reproductively isolated
  from other populations, hence the origin of a new
  species.

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The Modern Synthesis

• Darwin thought in terms of quantitative
  characteristics, characteristics that vary along
  a continuum.
• Blending
• Mendel discovered particulate gene inheritance.
• During the 1940s The Modern Synthesis combined
  Darwins theory of Natural Selection with what
  was known about the nature of inheritance.
• This gave rise to the study of Population
  Genetics and a new definition of evolution
• Change in traits within a population over time
  (evolution) is the result of change in the
  relative frequencies of the alleles that
  influence them.

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Terms

• A population is a localized group of individuals
  belonging to the same species.
• A species is a group of populations whose
  individuals have the potential to interbreed and
  produce fertile offspring.
• The total aggregate of genes in a population at
  any one time is called the populations gene
  pool.
• If all members of a population share the same
  single allele that gene is said to be fixed.
• If there are two or more alleles for a gene, each
  allele has a relative frequency.

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The Effect of Natural Selection

• Natural selection is the differential
  reproduction of organisms as a function of
  heritable traits that influence adaptation to the
  environment.
• That is, the environment places selective
  pressure upon an organism to adapt.
• An adaptation is an evolved solution to specific
  problems that contributes either directly or
  indirectly to successful reproduction.
• The fin of a fish
• The hoof of a horse
• The concept of space and time?

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Fitness

• Natural selection can be indexed by reproductive
  fitness. The measure of an individuals success in
  passing on genes through reproduction.
• Traits that increase fitness will be selected
  for, traits that decrease fitness will not.
• Inclusive fitness Selection favors
  characteristics that cause an organisms genes to
  be passed on, regardless of whether the organism
  passes them directly. genes eye view approach
• Traits that promote kin selection will be
  selected for.

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Three modes of Natural Selection

• Directional selection Fitness increases with a
  trait value.
• Beak size in Darwins finches when precipitation
  is low.
• Stabilizing selection Average trait values have
  the highest fitness and fitness decreases as the
  trait moves away from the average.
• Human birth weight
• Diversifying selection Phenotypes at the
  extremes are favored over average phenotypes.
• Often leads to new species

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Modes of Selection
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Where new alleles come from Genetic Mutation

• A mutation is an error that occurs during DNA
  replication.
• Most occur in somatic cells
• Only mutations that occur in germinal cells can
  be passed on to offspring
• New alleles originate only by mutation.
• New alleles that do not influence the fitness of
  the organism are called neutral mutations
• Many mutations result in loss of function
• PKU
• 2 1 reductase deficiency
• Cystic Fibrosis

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• Mutation Rates

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Mutations

• Most mutations are detrimental to the organism
  and thus, decrease fitness.
• Loss of function mutations
• Some mutations can increase fitness and are
  passed on to offspring.
• Example
• The genes for red and green cone pigment are
  located very close on the X chromosome in
  primates.
• Gene duplication followed by point mutation?

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Genetic Drift

• Genetic Drift the change in allele frequencies
  due to chance.
• Coin toss example
• The magnitude of the effect of genetic drift is
  due to the size of the population.
• Small population large effect
• Large population small effect
• In small populations, genetic drift can lead to
  the fixing of alleles.

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Genetic Drift
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Genetic Drift

• The bottleneck effect Disasters that reduce a
  population rapidly can affect the relative
  frequency of alleles and reduce genetic
  variability.
• Example The cheetah
• The founder effect Genetic drift is high
  whenever a small number of organisms colonize a
  new environment.

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The bottleneck effect
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Population Mating Structure

• One of the clearest examples of the psychological
  influences on allele frequency is mate
  preference.
• Mate preference occurs when members of one sex
  prefer to mate with individuals that have certain
  traits Sexual selection.
• Over time, sexual selection can have effects
  similar to Natural Selection.
• Traits that increase fitness are selected for

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Sexual Dimorphisms

• Sexual Dimorphism Males and females of a species
  differ in their secondary sex characteristics
• Sexual dimorphism is a product of sexual
  selection.
• Sexual dimorphisms result from
• Intrasexual selection Competition for mates
  between members of the same sex favors traits
  that improve competitive ability.
• Intersexual selection Choosiness on the part of
  one sex favors traits that are better at
  attracting that sex.

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Common Misperceptions

• Natural selection can fashion perfect organisms.
• Evolution builds upon existing structures which
  may not be optimal for their adapted usage.
• Knees and lower back of humans
• Adaptations are compromises
• Genetic drift does not choose most fit alleles
• New alleles do not rise on demand
• Question Why cant pigs fly?

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Common Misperceptions

• Evolution has a goal.
• Evolution is a process that occurs, but it is not
  goal oriented
• Evolution works for the good of the species
• Evolution acts to maximize DNA replication.
  There are many instances where this activity is
  actually harmful to the species in general.
• Natural selection explains everything.
• There are many characteristics that are not due
  to selective pressures, they are by-products