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EVOLUTION. Natural Selection. Mechanism for evolution Differential survival and reproduction of chance inherited variants, depending on environmental conditions. EVOLUTION by Natural Selection.

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natural selection
  • Mechanism for evolution
  • Differential survival and reproduction of chance inherited variants, depending on environmental conditions


Natural Selection


Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment


Where is the Proof?

evidence for evolution
Evidence for Evolution
  • What direct evidence supports this theory?
    • Changes in populations over time
      • Ex: peppered moth
evidence for evolution1
Evidence for Evolution
  • What direct evidence supports this theory?
    • Structural adaptations
      • Ex: mimicry; camouflage
evidence for evolution2
Evidence for Evolution
  • What direct evidence supports this theory?
    • Physiological changes
      • Ex: drug-resistant bacteria;
      • Ex: pesticide-resistant insects
e v i d e n c e
  • Biogeography
    • Study of the past and present geographical distribution of species
  • The Fossil Record
    • Succession of fossil forms is compatible with what is known from other types of evidence and the major branches of descent in the tree of life
  • Comparative Anatomy
  • Comparative Embryology
  • Molecular Biology
the fossil record
The Fossil Record
  • Remains of animals and plants found in sedimentary rock deposits give us an indisputable record of past changes through time. 
  • This evidence attests to the fact that there has been a tremendous variety of living things.
  •  Some extinct species had traits that were transitional between major groups of organisms. 

Their existence confirms that species are not fixed but can evolve into other species over time.

comparative anatomy
Comparative Anatomy
  • Homology- similarity in characteristics resulting from a shared ancestry
  • Homologous Structures- structures in different species that are similar because of common ancestry
  • Homologies and the tree of life are important in explaining ancestry.
  • Homologies shared by a greater number of species are likely to have evolved earlier on in history and are further down on the tree of life.
  • Homologies that have evolved more recently are seen on only small branches of the tree.
    • Example: tetrapods--the vertebrate branch consisting of birds, amphibians, mammals and reptiles.
      • They all have the same 5-digit limb structure which indicates these mammals all share a common ancestor.
  • Forelimbs of all mammals show the same arrangement of bones from shoulder to finger tip.
  • These occur even if the structure is used for a completely different function.
  • These anatomical differences would not have arisen in a new species if they did not share a common ancestor.

WING = flying

ARM = carrying

Front Leg = walking

Front Flipper = swimming


Radius & Ulna




a biogeographical example homologous vs analogous
ABiogeographicalExample: Homologous vs Analogous
  • Eutherians (placental) vs. Marsupials
  • Both of these are a type of flying squirrel, but are unrelated and distinctly different from one another.
      • Marsupials are born as embryos and develop in the mother’s pouch.
      • Eutherians develop completely within the uterus of the mother.
a biogeographical example homologous vs analogous1
ABiogeographical Example: Homologous vs Analogous
  • Although the two mammals look similar and occupy similar niches, the resemblance is not homologous--it’s analogous and the result of convergent evolution.
other similarities revealed
Other Similarities Revealed
  • Comparative embryology
    • Compares structures seen early on in development--pharyngeal pouches for example.
    • Ontogeny Recapitulates Phylogeny
  • Vestigial organs
    • Organs with little or no use remaining from ancestral lineages
      • Some snakes have vestiges of legs bones and a pelvis
      • Coccyx in humans (tail)
comparative embryology1
Comparative Embryology

Lizard Tortoise Pig Human

  • Molecular homologies exist as well--the genetic machinery of DNA and RNA also points to a common ancestor
    • the existence of Hox genes in development.
      • Genes and proteins with sequences of monomers that match indicate that the sequences must have been copied from a common ancestor
  • Explain, using examples, how the fossil record, comparative anatomy, and other evidence supports the theory of evolution.
    • At least one page, typed, double-spaced, & sources of info/pics cited.