Evolution

• Natural selection is the process by which certain traits become more or less common in a population over time due to their impact on reproductive success.
• • Genetic change over time. 
  • A change to the DNA over millions of years.
• There are 5 ways that evolution can happen:

  1. Natural Selection
  2. Gene Flow
  3. Mutation
  4. Non-Random Mating
  5. Genetic Drift
• Gene Flow: The movement of alleles into and out of populations.  It can increase or decrease the genetic diversity of a population.

  Ex: 

  The concept of gene flow is demonstrated when a bird is driven off from its flock, joins another flock, and reproduces.
• Mutations are RANDOM.  They do not happen as a result of NEED.  An organism cannot generate a mutation for a specific purpose.  If a member of a species is born with a beneficial mutation, that individual will be more likely to survive and pass on the mutation.
• • Non-random matingthe probability that two individuals in a population will mate is not the same for all possible pairs of individuals.

  Organisms choose their mate often based on desirable characteristics 
• Genetic Drift: Random process where an event that results in a small population can cause a change in the genetic diversity, just by chance.
• • Evolution is the change in a species over time.
  • More specifically, it is the change in inherited characteristics in a species over the course of generations
• • In order for a species to change over time, changes must occur in that species’ DNA to create new traits in offspring
  • What can change DNA?
  • Crossing over during meiosis
  • Recombination during fertilization
  • Mutations
• • If this DNA change creates a new trait in an offspring that is advantageous for survival, that offspring will have a much greater likelihood of reproducing and passing its genes on to future generations
  • Example: bacterial resistance to antibiotics
• Lamarck’s Theory of Acquired Characteristics

  • An organism can pass on characteristics that it acquired during its lifetime to its offspring
  • Proposed by Frenchman Jean-Baptiste Lamarck in the early 1800s
  • Two Parts:
  • Use and Disuseindividuals lose characteristics they do not require and develop characteristics that are useful
  • Inheritance of acquired traitsindividuals inherit the traits of their ancestors
• Who Was Charles Darwin?

  • Charles Darwin was an English scientist who proposed a theory to explain how organisms change over time
  • In 1831 he set sail on a five-year voyage throughout the world and visited several continents and many remote islands
  • During these visits he made many observations of the plants and animals that he encountered throughout the world
  • In 1859 he published his famous work “On the Origin of the Species” in which he proposed the Theory of Evolution
• Theory of Evolution

  • Darwin based his theory on two ideas:
  • Variations among individuals of a species
  • Natural Selection Nature selects any trait that increases an organism’s ability to survive and reproduce
• Natural Selection

  • The theory of evolution and natural selection are based on the following ideas:
  • Overproduction within a population
  • Competition within a species
  • Survival of the Fittest
• Overproduction

  • More offspring are born than can possibly survive to reproduce themselves
  • For example, if all the offspring of bacteria, insects, dandelions, rabbits, etc. survived, they would overrun the earth!
  • This DOES NOT happen!
• Competition

  • In our world there is a finite (limited supply) of resources
  • As a result, individuals within a particular species are constantly competing for resources such as food, water, shelter, and mates!
  • There is simply not enough to go around!
• Survival of the Fittest

  • The individuals who survive are those who are most adapted to exist in their environment
  • This is due to the possession of adaptations (differences in form) that maximize their fitness
• • Fitness is the ability for an individual to survive and reproduce in its specific environment
• Adaptation

  • A variation in a population that increases the chances of survival
  • According to Darwin’s theory, a changing environment will select certain traits and behaviors of organisms that allow them to survive and reproduce
  • Examples of physical adaptations: Mimicry and camouflage
• • Stabilizing Selection: Intermediate phenotype favored
• • Disruptive (Diversifying) Selection: 2 extreme phenotypes favored
• Evolutionary Models

  • Simple branching diagrams can be used to represent the evolutionary relationships among different species
  • These diagrams are called phylogenetic trees
• Geologic Record

  • Some evidence for evolution comes from fossils.  
  • Fossils are traces or remains of once-living organisms that have been preserved by natural processes
  • Fossils that have formed in different layers of rock show how species have evolved over time
• Geographic Distribution

  • Different species on different continents look and behave in similar manners
  • These species evolved into similar organisms because they were exposed to similar pressures of natural selection
• Homologous Body Structures

  • Structures of different organisms that are similar in form but may differ in function
  • They show that these organisms may have shared a common ancestor
• Analogous structures look similar on the outside. Same function BUT different structure & development on the inside. Different origin. No evolutionary relationship
• Vestigial Structures

  • A structure that no longer serves a purpose in an organism but is present because it once was useful in the organisms’ evolutionary past
  • Ex: Whales with tiny pelvic bones, species of snakes with tiny legs, birds that have wings but cannot fly (penguins, ostriches)
• Comparative Biochemistry

  • Comparing the molecular makeup of an organism such as proteins, enzymes, and other body chemicals
  • The greater the similarity, the more closely related the organisms are and the greater the likelihood they share a common ancestor
  • Ex: Every organism on this earth contains genetic material in the form of DNA or RNA
• Macroevolution

  Long time scale events 

  that creates or destroys 

  new SPECIES 
• Microevolution

  Short term time frame. Change within a species. DOES NOT CREATE A NEW SPECIES.
• Extinction

  • The disappearance of an entire species
  • It typically occurs when the environment changes
  • Sometimes, the environment changes so much that there are no longer any members of the species that are adapted to survive
  • Based on the fossil record, 99% of the species that have ever lived on Earth, are now extinct
  • Resurrecting the Extinct
• ADAPTIVE RADIATION

  Adaptive radiation is ...

  … the sudden appearance of many new species when organisms move into unoccupied habitats and niches. 
• Convergent Evolution

  The process by which different species evolve similar traits.

  • Closely related organisms share characteristics because of common descent.  
  • Distantly related organisms can come to resemble one another because of convergent evolution. 
• Convergent Evolution

  These organisms face similar environmental demands and will often develop similar structures to meet the demands of the environment.

  Convergent evolution creates Analogous Structures (wings)  
• Divergent Evolution

  In divergent evolution, closely related species become more and more dissimilar.

  The descendants of a single ancestor diversify into species that each fit different parts of the environment.
• Coevolution

  • The process by which two species evolve in response to changes in each other.

  In coevolution, an evolutionary change in one organism may also be followed by ...

  a corresponding change in another organism.
• Punctuated Equilibrium

  Darwin was convinced that evolution was a very slow process that occurred over a very long time.  In many cases, the fossil record confirms that some species did evolve very slowly over time.  

  This idea was known as gradualism. 
• Punctuated Equilibrium

  Most of the time, species are in a state of equilibrium, meaning they are not changing very much.  However, every now and then, something happens to upset this equilibrium.  When this equilibrium is upset, changes in organisms can occur rapidly.