The fact that living things change over a period of time is quite obvious. What early scientists tried to do was describe the process by which these changes took place.

Look around the classroom and you will see that we are all different in may ways. These differences in characteristics are called variations and they occur in all species of living thing.

Some variations may give one an advantage. For instance, tall basketball players have an advantage over shorter ones. In the natural world, the most important advantage is a survival advantage. What determins if a variation is helpful or harmful is whether or not it provides that survival advantage.

Those organisms that survive will be the ones reproducing. Their survival traits will become more common in the population, while the traits that did not lead to survival will die out.

Some of the variations within a species are caused by mutations - a change in the DNA of an organism.

• Most are minor.
   
• Some are harmful.
   
• Few are lethal.
   
• Very few are helpful.

Somatic mutations occur in regular body cells and cannot be passed to offspring.

Based on amount of DNA involved:

• Gene mutations involved only small amounts of DNA.
   
  • Point mutation
     
  • Frame-shift mutation
   
• Chromosome mutations involve large amounts of DNA.
   
  • Deletion mutation
     
  • Inversion mutation
     
  • Translocation
     
  • Nondisjunction

 
Extinction events:

Organisms do not become extinct - species become extinct.

Extinctions occur because of a change in the environment to which organisms are unable to adapt.

Dinosaurs are the famous extinction. Most believe a meteor caused their demise. Evidence suggests there have been at least 5 "mass extinctions" in Earth's past.

Extinction events are usually more gradual then meteors from the sky. Mankind has observed at least two species extinctions.

• The last dodo bird died in 1681.
• The last passenger pigeon died in 1914.

Creationism attributes the diversity of living things to a supernatural creator. This position requires "faith" - which by its very nature cannot be proven with an experiment. This makes Creationism "unscientific". Just because something is unscientifc doesn't necessarily mean it is not true, it only means that such studes are outside the realm of science.

Living things can be observed to change over a period of time. That can be tested and proven. Given enough time, can one species change so much that it becomes another species? THAT is the question.

You know more about DNA and chromosomes and how they relate to the characteristics of organisms than the BEST biologists at the turn of the 19^th century. Mendel wouldn't publish his work until 1865 and Walter Sutton's chromosome theory wouldn't be proposed until 1903.

Naturalists in 1800 were influenced by the following:

• Plato believed that organisms existed in an unchanging ideal form.
   
• Aristotle fet that organisms fit into an orderly "latter of nature", with primitive plants and animals at the bottom and humans at the top.
   
• Explorers were traveling to new lands and finding exotic animals that were similar to, but different from animals in other areas.
   
• Fossils were discovered, revealing organisms that existed in the past but did not exist in the present.

Jean-Baptiste Lamarck proposed that organisms changed when they needed to change.

He based his 1809 theory on two observations:

• Use and disuse - Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
   
• Inheritance of acquired traits - Individuals inherit the traits of their ancestors.

 
The Hardy-Weinberg Principle - 1908 - stated that a population will remain in genetic equilibrium if, and only if, all of these conditions are met:

• No mutations occur.
   
• Individuals neither enter nor leave the population through migration.
   
• The population is large.
   
• Individuals mate randomly.
   
• Natural selection does not occur.