Natural Selection and Species Typical Behaviors - PowerPoint PPT Presentation


PPT – Natural Selection and Species Typical Behaviors PowerPoint presentation | free to view - id: 11842-ZWUzM


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

Natural Selection and Species Typical Behaviors


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

Number of Views:88
Avg rating:3.0/5.0
Slides: 32
Provided by: patric99


Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Natural Selection and Species Typical Behaviors

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

Homologous Structures
The Rise of Evolutionary Theory
  • Biologists also noted striking similarities
    during the embryonic development of different
  • 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

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.

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

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

Descent with Modification
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.

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

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.

  • 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
  • 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.

The Effect of Natural Selection
  • Natural selection is the differential
    reproduction of organisms as a function of
    heritable traits that influence adaptation to the
  • 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?

  • 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.

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

Modes of Selection
Where new alleles come from Genetic Mutation
  • A mutation is an error that occurs during DNA
  • 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

(No Transcript)
  • Mutation Rates

  • 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
  • Gene duplication followed by point mutation?

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.

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

The bottleneck effect
Population Mating Structure
  • One of the clearest examples of the psychological
    influences on allele frequency is mate
  • 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

Sexual Dimorphisms
  • Sexual Dimorphism Males and females of a species
    differ in their secondary sex characteristics
  • Sexual dimorphism is a product of sexual
  • 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.

(No Transcript)
(No Transcript)
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?

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