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EVOLUTION (Evidence (Patterns in the Fossil Record ((Transitional form -…

- - - - Transitional form - organisms that show the intermediate states between an ancestral form and that of its descendants
      - Discovered 2 years after Darwin published On The Origin of Species.
      - Relative dating - comparing fossils' ages by where there are found in the Earth (superposition)
      - Radioactive dating - radioactive elements in fossils or sediments surrounding fossils (ex: radioactive carbon to nitrogen in 60,000 years)
  - - - Homologous structures - similar structures in related organisms that are a result of common ancestry
      - Whales and hummingbirds both inherited their skeletons from a tetrapod ancestor.
      - Their bodies have been modified and parts have been lost through natural selection, resulting in adaptation to their respective lifestyles over millions of years.
      - Vestigial structures - little or no purpose to present organism, but provide evidence for common ancestry
  - - - Homologous structures observed during early embryological development
      - These homologous structures may not be visible in the fully developed organism.
      - For example, all of the organisms on the right begin early development with a tail and gill slits.
  - - - DNA sequences
      - Amino acid sequences
      - Chromosomes
      - Gene expression (which genes are turned on and off/the timing of when genes are turned on and off)
      - ....can all be compared to determine relatedness of organisms
      - For example, we can learn about the evolution of humans and our closest living relative, the chimpanzee, by comparing chromosomes.
      - Humans have 23 pairs of chromosomes, while chimpanzees have 24 pairs.
- - - - a change in a DNA sequence (usually occurring because of errors in replication or repair)
      - the ultimate source of genetic variation
      - random
      - can be beneficial, neutral, or harmful for the organism, but mutations do not "try" to supply what the organism "needs"
      - **The only mutations that matter to large-scale evolution are those that can be passed on to offspring (occur in reproductive cells like eggs and sperm and are called germ line mutations).
  - - - Gene Flow = Migration
      - movement of individuals, and their genetic material, from one population to another
      - Examples: pollen being blown to a new destination, people moving to new cities or countries
      - If gene versions are carried to a population where those gene
        versions previously did not exist, gene flow
        can be a very important source of genetic variation.
      - Sex can introduce new gene combinations into a population and is an important source of genetic variation.
  - - - Genetic drift affects the genetic makeup of the population but, unlike natural selection, through an entirely random process.
      - Does NOT work to produce adaptations
      - In each generation, some individuals leave behind a few more descendants than other individuals -- by chance!
  - - - Charles Darwin & Alfred Russel Wallace
      - Thomas Malthus published
        a book in 1797 called Essay on the Principle of Population
      - Struggle for existence
      - Darwin and Wallace both realized that if an animal has some trait that helps it to withstand the elements or to breed more
        successfully, it may leave more offspring behind than others. On average,
        the trait will become more common in the following generation, and the generation after that.
      - Individuals must compete.
      - On The Origin of Species - one of the most influential scientific books of all time