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Natural Selection and Species Typical Behaviors

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As knowledge of the world grew, biologists were struck by the ... Man has used this to selectively breed animals for desirable characteristics. e.g. Dog breeds ... – PowerPoint PPT presentation

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Title: Natural Selection and Species Typical Behaviors


1
Natural Selection and Species Typical Behaviors
2
Charles Darwin and Alfred Russell Wallace
3
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.

4
Homologous Structures
5
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

6
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.

7
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

8
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

9
Descent with Modification
10
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.

11
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.

12
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.

13
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.

14
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?

15
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.

16
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

17
Modes of Selection
18
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

19
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20
  • Mutation Rates

21
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?

22
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.

23
Genetic Drift
24
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.

25
The bottleneck effect
26
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

27
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.

28
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30
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?

31
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
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