Evolution

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Evolution

Evolution is the branch of science that explains gradual change over time. This refers to two subtopics; Geological Evolution which explains the changes in the Earth (Pangea), and Organic Evolution which explains the changes in living things.

A.  Fossil records provide scientists with evidence that evolution occurred. 

Relative Dating – is the process of determining the age of fossils from the depth in rock strata.  The oldest fossils are found at the bottom (Letter E) or lowest level while the fossils found in upper layers represent organisms that lived at a more recent time (Letter A).  Also the lower layers are organisms that are more simplistic the the upper strata layers.  Examples would include cell structure and organ systems efficiency.

Absolute Dating – is a more accurate way of dating because the half life of the radioactive element carbon-14 is used to determine the actual age of a fossil.

B.  Skeletal Evidence of Evolution
Comparative anatomy is the study of structures of plants and animals.  Scientists study structural similarities and differences to find common ancestors.  Any organs or structural parts that are believed to be evolutionarily linked are called homologous structures. In the diagram provided the human arm, whale flipper and bat wind all have similar bone structures.  This leads scientists to believe that there was a common ancestor linking these specials together.

C.  Vestigial Structures
When looking at structural similarities between organisms, vestigial structures are included among them.  Vestigial structures are developed organs or bones that an organism possesses, but does not use anymore.  For examples; the appendix for humans was once used to digest inorganic material, but we have since changed our diet needs.  Pelvis bones located in whales and leg bones in pythons are other examples.

D. Comparative Embryology
Comparative embryology is the comparison of organism in their embryonic development stages.  At the early stages of development, many vertebrate species show many similarities.  Here you can see body, head and tail structures all look similar.  Even though these three organisms will not look anything alike past the embryonic stages.

E.  Biochemistry Similarities
Biochemistry similarities of living organisms included DNA, hormoes, and enzymes it may produce.   The greater similarities of these characteristics between organisms leads individuals to believe that there is a greater evolutionary link between them.  In the diagram to the right, an amino acid sequence segment for hemoglobin is taken from five different organisms.  Humans, gorillas, and chimpanzees all have similar amino acids, while horses and zebra have similar strands.  This demonstrates how similar DNA strands can lead to similar amino acids strands for these organisms.

Example of Evolution

Animals and plants have evolved throughout millions of years on planet earth.  Horses and elephants have been commonly studied for their evolutionary changes.
With these pictures you can see how horses have changed over the last 50 million years.  Starting as a Eohippus, which was the size of a fox with four digit toes, through natural selection and the passing of traits that were more suitable to the environment horses became larger, faster, and their teeth became flatter.

History of Evolution

Theories of evolution are continuously changing.
Evolution is an attempt to explain the diversity of species and their variations for survival

  1.  Jean Baptiste Lamarck (1809)
    1. Use and Disuse
      1.   New Organs arise according to the needs of the organism. (Adaptations)
      2. The size of the organ is determined by the degree to which it is used.  If the organ is not used, it will disappear.
      3. Vestigial Structures: Appendix and Coccyx bone
    2. Transmission of Acquired Characteristics
      1.    Useful characteristics acquired by two parents during their lifetime can be transmitted to their offspring.  This results in a better adopted species.
        1. The Giraffe Theory:  According to Lamarck, as the supply of food near the ground decreased, giraffes had to stretch their necks in order to reach food.  By doing this their necks became longer and this acquired trait was passed on to their offspring.
  2. Weisman (1870’s)
    -He disproved Lamarck’s theory of inheritance of acquired characteristics.
    – He removed the tails of mice over many generations.
    -According to Lamarck, the mice should be born without tails, but instead, they did have tails.

3.  Charles Darwin (1831-1835)
–  His ship the H.M.S. Beagle, went to South America to study fauna (animals) and flora (plants).
–  On the Galapagos Islands, off the coast of South America.  He studied land tortoises versus sea tortoises and finches’ beaks.

Darwins’ Theory of Evolution was based on Variation and Natural Selection

  1. Overproduction or Overpopulation– Within a population, more offspring are born than can possibly survive
  2. Competition– (Struggle for Existence) Those organisms with favorable variations or adaptations would be able to survive and reproduce than those with unfavorable variations.  *He called this process Natural Selection because nature selects the survivors.
  3. Survival of the Fittest– Those species with the best adaptations will survive!
  4. Speciation– (Variations) Overtime, favorable adaptations survive in a species while unfavorable ones disappear.  The end result is a new species.
  5. Reproduction– Individuals that survived reproduced to transmit these variations to their offspring.

*The weakness in Darwin’s theory was that he could not explain variation because he did not know about mutations!

In 1901 a scientist named Hugo DeVries explained how inherited genetic mutaions caused variations.  Mutations that were favorable to the environment and species were passed on to the next generation by reproduction, slowly increasing the population of the mutated trait.

Geographic Isolation

Geographic isolation occurs when geographic barriers isolate groups of a species from each other.  Examples that might cause this include mountain ranges, bodies of water, or deserts.  In the case of the diagram on the left a hawks migrating pattern was changed cause groups to be isolated from each other.  After generations of this isolation, reproductive isolation occurs, limiting genetic traits that are passed on to the separated groups.

Adaptive Radiation

Adaptive Radiation is the process where a new species or organism evolves from a common ancestor.  What can cause this to occur is a niche, which is the role an organism plays in an environment.  Meaning its eating habits, where it lives, and reproduction abilities.  During Darwin’s time in South America, he studied various finche species and noticed the different beak characteristics they all had allowed them to have different niches from each other.  Between the combination of genetic traits or mutations, the finches obtained very different beak characteristics.  Whether eating large or small seeds, large or small insects or a combination of the two, more species were able to coexist in the same environment.