Charles Darwin and Natural Selection by yaosaigeng


									Charles Darwin and
 Natural Selection
    Darwin journeyed on the
    HMS Beagle as a naturalist
•    5 year journey
•    studied and collected many biological specimens
•    on Galapagos Islands, off coast of Ecuador, observed
     animals such as finches, tortoises, and iguanas
•    Thirteen different but similar species of finches, each
     with a distinctive bill that is specialized for a particular
     food source.
•    Suggested that these birds migrated from Ecuador
      and changed after they arrived.
Darwin’s ideas were influenced by:

• Jean Baptiste
  Lamarck, who
  hypothesized that
  acquired traits
  were passed onto
•Charles Lyell, a geologist, who
suggested that the Earth was much
older than 6000 yrs
•Thomas Malthus, who wrote that
human populations grow much faster
than their food supply

•Alfred Wallace, who suggested
natural selection after studying wildlife
in the Malay Archipelago.
Darwin observed differences
  among island species.
Marine iguana
Land iguana
    Thirteen different but similar
  species of finches, each with a
distinctive bill that is specialized for
          a particular food.
Suggested that these birds migrated from South
   America and changed after they arrived
  Key insights led to Darwin’s idea for natural
• Darwin noticed a lot of variation in
  domesticated plants and animals.
• Artificial selection is the
  process by which humans
  select traits through
• Heritability is the ability of a trait to be passed
• There is a struggle for survival due to
  overpopulation and limited resources.
• Darwin proposed that adaptations arose over
  many generations.

• Natural selection is a mechanism by
  which individuals that have inherited
  beneficial adaptations produce more
  offspring on average than do other
 Principles of Natural Selection
1. Variation. What can cause variation in a
• Genetic differences and mutation
2. Overproduction. What are pros and cons
   of overproduction?
• Having many offspring increases the
   chance for survival, but also results in
   competition for resources.
3. Adaptation. What determines whether
   an adaptation is beneficial or not?
• A certain variation that allows an
   individual to survive better than other
   individuals it competes against.
4. Descent with Modification. How does
   natural selection change a population
   over time?
• Over time, more members of the species
   will have adaptations that are well suited
   for survival and reproduction in an
Elephants in Queen Elizabeth
National Park, Uganda, Africa
   Normally, nearly all African
elephants, male and female,
have tusks. In 1930, only one
percent of the elephant population
in Queen Elizabeth Park was
tuskless because of a rare
genetic mutation. Food was
plentiful, and by 1963 there were
3,500 elephants in the park.
   In the 1970’s, a civil war began in
Uganda. Much of the wildlife was killed for
food, and poachers killed elephants for
their ivory tusks. By 1992, the elephant
population had dropped to about 200. But
by 1998, the population had increased to
1,200. A survey revealed that as many as
30 percent of the adult elephants did not
have tusks. Ugandan wildlife officials also
noted a decline in poaching.
Natural selection acts on distributions of traits.
• A normal distribution graphs as a bell-shaped

• Populations have a
  normal distribution
  when they are not
  undergoing natural
• Microevolution is evolution within a
  – observable change in the allele frequencies
  – can result from natural selection
Directional selection – favors one
    of the extreme variations
• Woodpeckers with long beaks capture the
  most insects, as they can reach the
  insects deep in the tree trunk.
• Stabilizing selection –
  favors the average
• Small spiders have a hard time capturing
• Large spiders easily spotted by birds
• Medium sized spiders are best suited to
  survive in their environment, reproduce
  more often, leave more offspring.
Disruptive selection - favors both extremes
• On light colored rocks, the light limpets are
  camouflaged and survive the best
• On dark rocks, the dark limpets are most
• Tan (intermediate) limpets are visible on
  both the light rocks and dark rocks, and
  their numbers decline due to predation
       Evidence of Evolution
A. Fossils
Fossil links found between
• fish and amphibians
• reptiles and birds
• reptiles and mammals

Whales from land mammals
 Fossil linking fish and amphibians
• 365 million years old
• arm bone with fish fin
• found in Pennsylvania
• thought to be from a
  lobed-finned fish
Archaeopteryx – links reptiles and
A fossil of Archaeopteryx was discovered at about the same time Darwin published On the Origin of
Species. This pigeon-size creature had a dinosaur like shape, complete with a long bony tail, heavy
jaws with serrated teeth, and three long fingers. It also had feathers like those of modern birds.
Hind leg bones in whales
An amphibious reptile
found in Texas, 2005
  Diarthognathus, an animal with
reptile and mammal characteristics
Early mammals may have looked
          like this
 of the
     B. Biological Molecules
• Differences in amino acid sequences
  and DNA are greater between species
  that are distantly related than between
  species that are closely related
• phylogenetic trees show how
  organisms are related through
        Homeobox genes
C. Homologous structures – similar
in structure, with different functions
      D. Vestigial Structures
• Structures that are reduced in size and
  either have no use or a less
  important use than they do in other,
  related organisms.
• Examples: wings on flightless birds,
  Human ear muscles, human wisdom teeth
  human appendix , hind leg bones in
The cassowary, a flightless bird
         with wings
Wisdom teeth in human
Human appendix
      E. Vertebrate Embryos
• Early in development, vertebrate embryos
  have similar characteristics such as a tail,
  buds that become limbs, and pharyngeal
  pouches that hold the gills of fish and
  Vertebrate embryos
       Examples of Evolution
A. Tuskless elephants becoming more common in
B. Antibiotic resistance in bacteria
    such as those that cause
   pneumonia and tuberculosis
C. Pesticide resistance in insects
               • Tobacco plants are sprayed
                 with pesticides
               • The pesticides kill many
                 insects, but not all.
               • Survivors lay eggs
               • Future generations are
      D. Industrial Melanism
• Example is the peppered moth.
• Explained by the concealment hypothesis.
• Peppered Moth Simulation
    E. Beaks of finches

• the changing of a species that results in its
  being better suited to its environment.

• Examples: camouflage, mimicry,
  echolocation, migration, dormancy
Mimicry: one species resembles
Snake mimicry: which is
Eastern Coral snake
Highly venomous

King snake
Echolocation in bats.
Dormancy: cacti embryos coming
       out of dormancy
        Patterns of Evolution
A. Divergence – Darwin’s finches.
   Dogs evolving from wolves. Can lead to
   formation of new species (speciation)
     B. Convergent evolution
• distantly related organisms evolve similar
• Example is seen in the streamlined, finned
  bodies of dolphins and sharks.
• The fins would be an example of
  analogous structures.
Five Evolutionary forces
1. Natural Selection: certain
   traits might be an
   advantage for survival
2. Mutation: creates new
   genetic variation
3. Sexual selection: certain
   traits may improve
   mating success; alleles
   for these traits increase
   in frequency
4. Gene flow: movement of individuals to
   or from a population (also known as
   migration). Immigrants add alleles,
   emigrants take alleles away.

Example: troops of baboons in eastern
   Africa. Females remain with the troop,
   but younger or less dominant males
   leave their birth troop, eventually joining
   another troop. This ensures gene flow.
5. Genetic drift: random change in allele
   frequency in a population. Causes a loss
   in diversity.

Example: In the 1800’s, northern elephant
   seals were overhunted. The population
   was reduced to about 20 individuals.
   Hunting has ended, and there are now
   about 100,000 seals. However, the
   population has little genetic variation.
Genetic drift
 the genetic contribution of an
individual to the next generation's
gene pool relative to the average
for the population, usually
measured by the number of
offspring that survive to
reproductive age
• a change in gene frequency in a population —
  such as all the individuals of one beetle species
  living on a particular mountaintop.
• generally refers to evolution above the
  species level
Evolution of whales from land-
     dwelling mammals
• transitional fossils between land mammals
  and whales
• vestigial structures such as pelvic and leg
  bones, and external ear muscles
• nostrils at end of snout in embryos;
  nostrils travel to top of head before birth
• DNA for milk protein very similar in hippos
  and whales

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